Series of medium-entropy or high-entropy oxides as well as preparation method and application thereof

Abstract

The invention discloses a series of medium-entropy or high-entropy oxides as well as a preparation method and application thereof, and belongs to the technical field of inorganic non-metallic materials. The medium-entropy or high-entropy oxide has a tetragonal tungsten bronze structure, a bimetallic oxide Ta8W9O47 composed of VB group elements and VIB group elements is used as a matrix, one or more elements of the same group and the same valence state are doped into lattice sites of the VB group elements or the VIB group elements, and the medium-entropy oxide (NbxTa1-x) 8W9O47 (0 < = xlt, 0 < = xl0, 0 < = xl0, 0 < = xl0, 0 < = xl0, 0 < = xl0, 0 < = xl0, 0 < = xl0, 0 < = xl0) is synthesized. 1) or a high entropy oxide (NbxTa (1-x) 8 (MoyW1-y) 9O47 (0 < = xlt; 1), (0 < = y < lt; 1); or a bimetallic oxide Nb14W3O44 composed of VB group elements and VIB group elements is used as a parent body, one or more elements with the same group and the same valence state are doped into crystal lattice sites of the VB group elements or the VIB group elements, and the medium-entropy oxide (Nb1-xTax) 14 (MoyW1-y) 3O44 (0 < = xlt; 1), (0 < = y < lt; 1); or a bimetallic oxide Nb12WO33 composed of VB group elements and VIB group elements is used as a parent body, one or more elements with the same group and the same valence state are doped into crystal lattice sites of the VB group elements or the VIB group elements, and the medium-entropy oxide (Nb1-xTax) 12 (MoyW1-y) O33 (0 < = xlt; 1), (0 < = y < lt; 1). In addition, after being sintered into ceramics, the prepared medium-entropy or high-entropy oxide shows certain thermal expansion and thermal conductivity.

Description

Technical Field

[0001] The present invention belongs to the technical field of inorganic non-metallic materials, and particularly relates to a series of medium-entropy or high-entropy oxides, their preparation methods and applications. Background Art

[0002] Disclosing the information of this background art section is only intended to enhance the overall understanding of the present invention, and is not necessarily regarded as an admission or an implication in any form that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] Oxides, as the most widely existing material form in nature, especially transition metal oxides, as a class of inorganic materials, have a long history in physics, materials science, chemistry, etc. Transition metal oxides, as a typical strongly correlated electron system, have complex inter-electron Coulomb interactions. The d-orbital electrons in transition metals allow the charge, orbit, lattice, and spin in the system to be highly free, making the design and synthesis of materials flexible and providing a rich carrier for the discovery and regulation of novel physical properties. From the perspective of the bonding between transition metals and oxygen, the strong correlation of d-orbital electrons brings extremely strong electron polarization, and this interaction includes Hund exchange interaction, Coulomb repulsion, crystal field effect, etc. Different interactions gather together, competing and intertwining with each other. After long-term development, people have discovered oxide materials with rich physical properties, including superconductors, semiconductor materials, dielectric materials, magnetic materials, optoelectronic materials, ferroelectric materials, negative thermal expansion materials, zero thermal expansion materials, etc., covering fields such as electronics, thermoelectronics, piezoelectricity, energy storage, catalysis, thermal barrier coatings, functional ceramics, etc. Due to their huge application value, oxide materials have become increasingly important.

[0004] According to the characteristics of metal element composition, metal oxides can be divided into single-metal component oxides and multi-metal component oxides. The physical properties of single-metal component oxides have been widely studied, while the research on multi-metal component and medium-entropy or high-entropy oxides is relatively less. The atomic occupancy of multi-metal component oxides includes two situations, atomic ordered occupancy and atomic mixed occupancy. In order to expand the performance and application fields of oxide materials, it is necessary to turn our attention to bimetallic component oxide materials.

[0005] Bimetallic component oxides usually consist of an octahedral structure formed by the coordination of metals and oxygen. In this structure, there is a repulsive interaction between the electrons in the d-orbital and the ligands. Therefore, the d electrons near the ligands have higher energy compared to the electrons far from the ligands, which leads to the splitting of the d-orbital, forming two groups of orbital populations with different energy states, namely the d xy 、d xz and d yz orbitals and the d z2 , d x 2 -y 2 Orbitals. In addition to having rich electron orbitals, the bimetallic component oxides also have rich edge and corner connection structures, and the flexibility of the framework structure gives them a large flexible space in the field of thermal expansion.

[0006] The thermal expansion phenomenon is caused by the anharmonic interaction between atoms. The average atomic spacing increases with the increase of temperature, and the volume increases, which is called positive thermal expansion. The average atomic spacing decreases with the increase of temperature, and the volume decreases, which is called negative thermal expansion. The average atomic spacing remains unchanged with the increase of temperature, and the volume remains unchanged, which is called zero thermal expansion.

[0007] At present, the exploration of new excellent negative thermal expansion materials or zero thermal expansion materials is mainly achieved through two ways. One is to compound positive thermal expansion materials with negative thermal expansion to adjust the thermal expansion coefficient. The other is to achieve regulation through element doping and solid solution.

[0008] Therefore, for the bimetallic component oxide materials, a new type of medium-entropy or high-entropy oxide is prepared by element doping, and further used as a new type of thermal expansion material to explore the thermal properties, which expands the properties and application fields of oxide materials and thermal expansion materials. Summary of the Invention

[0009] In order to solve the deficiencies of the prior art, the purpose of the present invention is to provide a series of medium-entropy or high-entropy oxides and their preparation methods and applications.

[0010] In order to achieve the above purpose, the technical solution of the present invention is as follows:

[0011] On the one hand, the present invention provides a series of medium-entropy or high-entropy oxides with a tetragonal tungsten bronze structure. The bimetallic oxide Ta 8 W 9 O 47 is used as the matrix, and one or more elements of the same group and the same valence state are incorporated into the lattice sites of the VB group or VIB group elements;

[0012] The molecular formula of the medium-entropy or high-entropy oxide is (M A ) 8 (M B ) 9 O 47 , where M A is the element Ta or a combination of Ta and Nb, and M B is the element W or a combination of W and Mo.

[0013] The molecular formula of the medium-entropy oxide is (Nb x Ta1-x ) 8 W 9 O 47 (0 ≤ x < 1) or Ta 8 (W 1-y Mo y ) 9 O 47 (0 ≤ y < 1); Preferably, the molecular formula of the medium-entropy oxide is (Nb 0.5 Ta 0.5 ) 8 W 9 O 47 or Ta 8 (W 0.5 Mo 0.5 ) 9 O 47 。

[0014] The molecular formula of the high-entropy oxide is (Nb x Ta 1-x ) 8 (Mo y W 1-y ) 9 O 47 (0 ≤ x < 1), (0 ≤ y < 1); Preferably, the molecular formula of the high-entropy oxide is (Nb 0.5 Ta 0.5 ) 8 (Mo 0.5 W 0.5 ) 9 O 47 。

[0015] Preferably, the medium-entropy or high-entropy oxide has stable unit cell structure parameters in the temperature range of 300K to 1673K.

[0016] On the one hand, the present invention provides a method for preparing the above medium-entropy or high-entropy oxide, comprising:

[0017] Weighing the precursors of the oxides containing VB group elements and the precursors of the oxides containing VIB group elements according to a molar ratio, wherein the VB group elements are selected from Nb and Ta, and the VIB group elements are selected from Mo and W;

[0018] Mixing the precursors evenly in proportion and grinding to form a powder;

[0019] Pressing the powder into a shape and then sintering it;

[0020] Cooling the sintered product and then grinding it again to obtain the medium-entropy or high-entropy oxide.

[0021] Further, the precursors of the oxides containing VB group elements and the precursors of the oxides containing VIB group elements are single-metal component oxides, and the purity of the single-metal component oxide powders is above 99.99%, and the particle size is 100-500 mesh, preferably 200 mesh.

[0022] Further, the molecular formula of the prepared medium-entropy or high-entropy oxide is (M A ) 8 (M B ) 9 O 47 , where M A is the element Ta or a proportional combination of Ta and Nb, M B is the element W or a proportional combination of W and Mo, and the method includes:

[0023] Weigh the precursors containing VB group elements and the precursors containing VIB group elements according to the required molar ratio, where:

[0024] When M A is Ta, weigh Ta 2 O 5 ;

[0025] When M A is a proportional combination of Ta and Nb, weigh Ta 2 O 5 and Nb 2 O 5 , preferably weigh Ta 2 O 5 and Nb 2 O 5 ;

[0026] When M B is W, weigh WO 3 ;

[0027] When M B is a proportional combination of W and Mo, weigh WO 3 and MoO 3 , preferably weigh WO 3 and MoO 3 ;

[0028] Mix the weighed precursors evenly and grind them into a powder;

[0029] Press the powder into a mold and then sinter it;

[0030] Cool the sintered product and then grind it again to obtain the medium-entropy or high-entropy oxide.

[0031] Further, the molecular formula of the medium-entropy oxide is (Nb0.5 Ta 0.5 ) 8 W 9 O 47 When it is WO, weigh Ta 2 O 5 and Nb 2 O 5 as the precursors of group VB elements, and weigh WO 3 as the precursors of group VIB elements; among them, Ta 2 O 5 , Nb 2 O 5 and WO 3 The stoichiometric ratio is 2:2:9.

[0032] Furthermore, the molecular formula of the high-entropy oxide is (Nb 0.5 Ta 0.5 ) 8 (Mo 0.5 W 0.5 ) 9 O 47 When it is, weigh Ta 2 O 5 and Nb 2 O 5 as the precursors of group VB elements, and weigh WO 3 and MoO 3 as the precursors of group VIB elements; among them, Ta 2 O 5 , Nb 2 O 5 , MoO 3 and WO 3 The stoichiometric ratio is 2:2:4.5:4.5.

[0033] Furthermore, the sintering process is one of vacuum solid-phase sintering, spark plasma sintering and hot pressing sintering.

[0034] Furthermore, the specific process of the vacuum solid-phase sintering is: after pressing the mixed powder into a tablet, place it in a quartz tube, evacuate and seal it, and then heat it up for vacuum solid-phase sintering.

[0035] Furthermore, during the vacuum solid-phase sintering, the sintering atmosphere is Ar atmosphere or air atmosphere; the sintering temperature is 900 - 1200 °C, preferably 1000 - 1100 °C; the heating rate is 1 - 3 °C / min; the sintering time is 20 - 24 h.

[0036] Among them, the parent Ta 8 W 9 O 47The preparation process is the same as above, Ta 2 O 5 and WO 3 have a stoichiometric ratio of 4:9.

[0037] On the one hand, the present invention provides a ceramic material prepared from the above-mentioned medium-entropy or high-entropy oxides;

[0038] The preparation method of the ceramic material includes:

[0039] Performing ball milling on the medium-entropy or high-entropy oxides to make a green body, followed by degreasing treatment, sintering, and cooling to obtain the product.

[0040] Further, during the ball milling treatment, the ball milling time is 6 - 24 h; the ball milling speed is 200 - 600 revolutions; the ball-to-material ratio for ball milling is (8 - 12):1, where the ratio of large balls:medium balls:small balls = (1 - 3):(5 - 7):(3 - 5).

[0041] Further, during the ball milling, an alcohol solvent is also added, and the alcohol solvent is polyvinyl alcohol (PVA). The concentration of the alcohol solvent PVA is 3 - 8%. It is preferably to mix a certain amount of 5% concentration PVA in the green body, and PVA volatilizes during the degreasing process at 700 °C, leaving some pores inside the ceramic.

[0042] Further, the green body is molded by die pressing under 5 - 10 Mpa, preferably 8 Mpa.

[0043] Further, after the ball milling treatment, a drying treatment is also performed. The drying temperature is 100 °C, and the drying time is 24 - 48 h.

[0044] Further, during the degreasing treatment, the temperature is 600 - 700 °C, the degreasing time is 2 - 4 h, and the heating rate is 1 - 3 °C / min.

[0045] Further, the sintering is carried out using a tube furnace. The sintering atmosphere is an Ar atmosphere or an air atmosphere; the sintering temperature of the ceramic is 1000 - 1100 °C, the heating rate is 1 - 3 °C / min, and the sintering time is 3 - 24 h. The sintering time can be adjusted according to the required ceramic morphology.

[0046] On the one hand, the present invention provides a series of medium-entropy or high-entropy oxides with a tungsten bronze structure. Using the bimetallic oxide Nb 14 W 3 O 44 as the matrix, one or more elements of the same group and the same valence state are incorporated into the lattice sites of the VB group or VIB group elements; the molecular formula of the medium-entropy oxide is (M A ) 14 (M B )3 O 44 , wherein M A is Ta or a combination of Ta and Nb, and M B is W or a combination of W and Mo.

[0047] The molecular formula of the medium-entropy oxide is (Nb 1-x Ta x ) 14 (Mo y W 1-y ) 3 O 44 (0 ≤ x < 1), (0 ≤ y < 1); preferably, the molecular formula of the medium-entropy oxide is (NbTa) 14 (MoW) 3 O 44 .

[0048] Preferably, the lattice structure parameters of the medium-entropy or high-entropy oxide are stable in the temperature range of 300K to 1673K.

[0049] On the one hand, the present invention provides a method for preparing the above medium-entropy or high-entropy oxide, comprising:

[0050] Weighing the precursors of the oxides containing group VB elements and the precursors of the oxides containing group VIB elements according to a molar ratio, wherein the group VB elements are selected from Nb and Ta, and the group VIB elements are selected from Mo and W;

[0051] Mixing the precursors evenly in proportion and grinding them into a powder;

[0052] Pressing the powder into a shape and then sintering it;

[0053] Cooling the sintered product and then grinding it again to obtain the medium-entropy or high-entropy oxide.

[0054] Furthermore, the precursors of the oxides containing group VB elements and the precursors of the oxides containing group VIB elements are single-metal component oxides, and the purity of the single-metal component oxide powders is above 99.99%, and the particle size is 100 - 500 mesh, preferably 200 mesh.

[0055] Furthermore, the molecular formula of the prepared medium-entropy oxide is (M A ) 14 (M B ) 3 O 44 , wherein M A is Ta or a combination of Ta and Nb, and M B is W or a combination of W and Mo, and the method comprises:

[0056] Weigh the precursors containing Group VB elements and the precursors containing Group VIB elements according to the required molar ratio, where:

[0057] When M A is Ta, weigh Ta 2 O 5 ;

[0058] When M A is a proportional combination of Ta and Nb, weigh Ta 2 O 5 and Nb 2 O 5 , preferably with a molar ratio of 1:1;

[0059] When M B is W, weigh WO 3 ;

[0060] When M B is a proportional combination of W and Mo, weigh WO 3 and MoO 3 , preferably with a molar ratio of 1:1;

[0061] Mix the weighed precursors evenly and grind them into a powder;

[0062] Press the powder into a shape and then sinter it;

[0063] Cool the sintered product and then grind it again to obtain a medium-entropy oxide;

[0064] Furthermore, when the molecular formula of the medium-entropy oxide is (NbTa) 14 (MoW) 3 O 44 , weigh Ta 2 O 5 and Nb 2 O 5 as the precursors of Group VB elements in a molar ratio of 1:1, and weigh WO 3 and MoO 3 as the precursors of Group VIB elements in a molar ratio of 1:1; among them, the stoichiometric ratios of Ta 2 O 5 , Nb 2 O 5 , MoO 3 and WO 3 are 3.5:3.5:1.5:1.5.

[0065] Furthermore, the sintering process is one of vacuum solid-phase sintering, spark plasma sintering, and hot pressing sintering.

[0066] Further, the specific process of the vacuum solid-phase sintering is as follows: After pressing the mixed powder into a sheet, it is placed in a quartz tube, evacuated and then sealed, and then heated for vacuum solid-phase sintering.

[0067] Further, during the vacuum solid-phase sintering, the sintering atmosphere is an Ar atmosphere or an air atmosphere; the sintering temperature is 900-1200 °C, preferably 1000-1100 °C; the heating rate is 1-3 °C / min; the sintering time is 20-24 h.

[0068] On the one hand, the present invention provides a ceramic material prepared from the above-mentioned medium-entropy or high-entropy oxide;

[0069] The preparation method of the ceramic material includes:

[0070] Performing ball milling on the medium-entropy or high-entropy oxide to make a green body, performing degreasing treatment, sintering, and cooling to obtain the ceramic material.

[0071] Further, during the ball milling, the ball milling time is 6-24 h; the ball milling speed is 200-600 revolutions; the ball-to-material ratio of the ball milling is (8-12):1, wherein the large balls: medium balls: small balls = (1-3):(5-7):(3-5).

[0072] Further, for the ball milling, an alcohol solvent is also added, and the alcohol solvent is polyvinyl alcohol (PVA). The concentration of the alcohol solvent PVA is 3-8%. It is preferably to mix a certain amount of 5% concentration PVA in the green body, and PVA volatilizes during the degreasing process at 700 °C, leaving some pores inside the ceramic.

[0073] Further, the green body is prepared by molding under a pressure of 5-10 Mpa, preferably 8 Mpa.

[0074] Further, after the ball milling treatment, a drying treatment is also performed, the drying temperature is 100 °C, and the drying time is 24-48 h.

[0075] Further, during the degreasing treatment, the temperature is 600-700 °C, the degreasing time is 2-4 h, and the heating rate is 1-3 °C / min.

[0076] Further, the sintering is carried out by tube furnace sintering, and the sintering atmosphere is an Ar atmosphere or an air atmosphere; the sintering temperature of the ceramic is 1000-1100 °C, the heating rate is 1-3 °C / min, and the sintering time is 3-24 h. The sintering time can be adjusted according to the required ceramic morphology.

[0077] On the one hand, the present invention provides a series of medium-entropy or high-entropy oxides with a tungsten bronze structure, which are composed of bimetallic oxides Nb of VB group and VIB group elements 12 WO 33is the matrix, and one or more elements of the same group and the same valence state are incorporated into the lattice sites of elements of Group VB or Group VIB; the molecular formula of the medium-entropy oxide is (M A ) 12 (M B )O 33 , where M A is Ta or a combination of Ta and Nb, and M B is W or a combination of W and Mo.

[0078] The molecular formula of the medium-entropy oxide is (Nb 1-x Ta x ) 12 (Mo y W 1-y )O 33 (0 ≤ x < 1), (0 ≤ y < 1); preferably, the molecular formula of the medium-entropy oxide is (NbTa) 12 (MoW)O 33 .

[0079] Preferably, the crystal cell structure parameters of the medium-entropy or high-entropy oxide are stable in the temperature range of 300K to 1673K.

[0080] On the one hand, the present invention provides a method for preparing the above medium-entropy or high-entropy oxide, including:

[0081] Weighing the precursors of the oxides of Group VB elements and the precursors of the oxides of Group VIB elements according to the molar ratio, where the Group VB elements are selected from Nb and Ta, and the Group VIB elements are selected from Mo and W;

[0082] Mixing the precursors evenly in proportion and grinding to form a powder;

[0083] Pressing the powder into a mold and then sintering;

[0084] Cooling the sintered product and then grinding again to obtain the medium-entropy or high-entropy oxide.

[0085] Furthermore, the precursors of the oxides of Group VB elements and the precursors of the oxides of Group VIB elements are single-metal component oxides, and the purity of the single-metal component oxide powders is above 99.99%, the particle size is 100 - 500 mesh, preferably 200 mesh.

[0086] The molecular formula of the prepared medium-entropy oxide is (M A ) 12 (M B )O 33 , where M A is Ta or a combination of Ta and Nb, and M Bis W or a combination of W and Mo, and the method includes:

[0087] Weigh the precursors containing Group VB elements and the precursors containing Group VIB elements according to the required molar ratio, where:

[0088] When M A is Ta, weigh Ta 2 O 5 ;

[0089] When M A is a proportional combination of Ta and Nb, weigh Ta 2 O 5 and Nb 2 O 5 , preferably with a molar ratio of 1:1;

[0090] When M B is W, weigh WO 3 ;

[0091] When M B is a proportional combination of W and Mo, weigh WO 3 and MoO 3 , preferably with a molar ratio of 1:1;

[0092] Mix the weighed precursors evenly and grind them into a powder;

[0093] Press the powder into a shape and then sinter it;

[0094] Cool the sintered product and then grind it again to obtain the medium-entropy oxide.

[0095] Furthermore, when the molecular formula of the medium-entropy oxide is (NbTa) 12 (MoW)O 33 , weigh Ta 2 O 5 and Nb 2 O 5 as the precursors of Group VB elements, and weigh WO 3 and MoO 3 as the precursors of Group VIB elements. Among them, the stoichiometric ratios of Ta 2 O 5 , Nb 2 O 5 , MoO 3 and WO 3 are 3:3:0.5:0.5.

[0096] Furthermore, the sintering process is one of vacuum solid-phase sintering, spark plasma sintering, and hot pressing sintering.

[0097] Further, the specific process of the vacuum solid-phase sintering is as follows: after pressing the mixed powder into a tablet, place it in a quartz tube, evacuate and then seal it, and then heat it up for vacuum solid-phase sintering.

[0098] Further, during the vacuum solid-phase sintering, the sintering atmosphere is an Ar atmosphere or an air atmosphere; the sintering temperature is 900-1200 °C, preferably 1000-1100 °C; the heating rate is 1-3 °C / min; the sintering time is 20-24 h.

[0099] As a specific embodiment, the preparation method of the medium-entropy or high-entropy oxide is as follows: weigh high-purity single-metal oxide powders according to the stoichiometric ratio and carefully grind them in a mortar; then cold-press the uniformly mixed sample using a tablet press, place the sample in a quartz tube, evacuate and seal the quartz tube with a hydrogen-oxygen flame; then sinter the sample, naturally cool it to room temperature in a muffle furnace, and then take out the sample and carefully grind it to obtain a pure-phase powder of the novel medium-entropy or high-entropy oxide.

[0100] On the one hand, the present invention provides a ceramic material prepared from the above-mentioned medium-entropy or high-entropy oxide;

[0101] The preparation method of the ceramic material includes:

[0102] Perform ball milling on the medium-entropy or high-entropy oxide to make a green body, perform degreasing treatment, sinter, and cool to obtain it.

[0103] Further, during the ball milling treatment, the ball milling time is 6-24 h; the ball milling speed is 200-600 revolutions; the ball-to-material ratio of the ball milling is (8-12):1, where the large balls: medium balls: small balls = (1-3):(5-7):(3-5).

[0104] Further, the ball milling also includes adding an alcohol solvent, and the alcohol solvent is polyvinyl alcohol (PVA). The concentration of the alcohol solvent PVA is 3-8%. It is preferably to mix a certain amount of 5% concentration PVA in the green body, and PVA volatilizes during the degreasing process at 700 °C and leaves some pores inside the ceramic.

[0105] Further, the green body is molded by die pressing at 5-10 Mpa, preferably 8 Mpa.

[0106] Further, after the ball milling treatment, a drying treatment is also performed, the drying temperature is 100 °C, and the drying time is 24-48 h.

[0107] Further, during the degreasing treatment, the temperature is 600-700 °C, the degreasing time is 2-4 h, and the heating rate is 1-3 °C / min.

[0108] Further, the sintering is carried out in a tube furnace, and the sintering atmosphere is an Ar atmosphere or an air atmosphere; the temperature for ceramic sintering is 1000-1100 °C, the heating rate is 1-3 °C / min, and the sintering time is 3-24 h. The sintering time can be adjusted according to the required ceramic morphology.

[0109] On the one hand, the present invention provides the application of the above-mentioned ceramic materials in precision instruments, aerospace, and energy storage.

[0110] One or some of the above technical solutions have the following advantages or beneficial effects:

[0111] 1. In the tungsten bronze-type (TTB) bimetallic component oxides composed of VB-VIB group elements in the present invention, the structure is formed by connecting octahedrons and tetrahedrons through a common vertex. At the same time, there are partial oxygen vacancies inside the crystal. For the first time, element doping and the introduction of oxygen vacancies are used to regulate and control the composition and structure to prepare single-phase medium-entropy or high-entropy oxides. The element doping is to dope elements of the same main group and the same valence state at the VB or VIB group element positions according to the average atomic volume theory.

[0112] 2. The present invention uses the bimetallic oxide Ta 8 W 9 O 47 with a tetragonal tungsten bronze structure composed of VB-VIB group elements as the matrix, and regulates and controls its structure and physical properties through element doping. Nb is doped at the Ta position to prepare a new type of single-phase medium-entropy oxide (Nb 0.5 Ta 0.5 ) 8 W 9 O 47 . Nb is doped at the Ta position and Mo is doped at the W position to prepare a high-entropy oxide (Nb 0.5 Ta 0.5 ) 8 (Mo 0.5 W 0.5 ) 9 O 47 . Among them,

[0113] (1) Medium-entropy or high-entropy is achieved through element doping at the metal atom sites, and new types of single-phase (Nb 0.5 Ta 0.5 ) 8 W 9 O 47 and (Nb 0.5 Ta 0.5 ) 8 (Mo 0.5 W 0.5 ) 9 O 47Through structural analysis, it is found that it has a distorted wolframite structure of the orthorhombic system. The ultraviolet-visible diffuse reflectance spectrum shows that the band gaps are all around 2.7 eV, belonging to wide-bandgap semiconductor oxides.

[0114] (2) Through variable-temperature X-ray diffraction, its thermal expansion properties are found. The c-axis has negative thermal expansion, while the a-axis and b-axis have positive thermal expansion. Overall, low thermal expansion is achieved in the wide temperature range of 300 K - 1673 K. (Nb 0.5 Ta 0.5 ) 8 W 9 O 47 's linear thermal expansion coefficient is close to that of Ta 8 W 9 O 47 . The thermal expansion coefficients α a , α b , α v first decrease and then increase with the increase of temperature. α c first increases slightly and then decreases with the increase of temperature. Among them, at 300 K, α a = 2.281 μK -1 , α b = 3.047 μK -1 , α c = -1.627 μK -1 , α V = 3.84 μK -1 , α L = 1.28 μK -1 ; at 1673 K, α a = 4.988 μK -1 , α b = 3.003 μK -1 , α c = -3.006 μK -1 , α v = 5.17 μK -1 , α L = 1.72 μK -1 . They all belong to low-thermal-expansion oxides, but after solid solution, the structural rigidity of (Nb 0.5 Ta 0.5 ) 8 W 9 O 47 is strengthened, and the absolute values of the linear thermal expansion coefficients in the three directions are smaller than those of Ta 8 W 9 O 47 . The structure changes less with temperature. (Nb 0.5 Ta 0.5 ) 8 (Mo 0.5 W 0.5 ) 9 O47 The coefficient of thermal expansion is α at 300K a = 2.026 μK -1 , α b = 2.297 μK -1 , α c = -1.552 μK -1 , α V = 3.60 μK -1 , α L = 1.20 μK -1 , at 1673K, α a = 2.021 μK -1 , α b = 2.290 μK -1 , α c = 1.052 μK -1 , α V = 3.59 μK -1 , α L = 1.20 μK -1 . By fitting and calculating the coefficients of thermal expansion in each temperature range from 300K to 1673K, it can be obtained that (NbTa) 8 (MoW) 9 O 47 is a low thermal expansion oxide in the temperature range of 300K to 1673K. It can be seen that as the entropy after solid solution increases, the structure of the oxide becomes more stable, and the change with temperature is smaller compared to the parent structure.

[0115] 3. The present invention uses the tungsten bronze (TTB)-type bimetallic component oxide Nb 14 W 3 O 44 as the parent body, and prepares the single-phase (NbTa) 14 (MoW) 3 O 44 medium-entropy oxide of the four-metal component. Specifically, by regulating its composition and structure, according to the average atomic volume theory, Ta element of the same main group and valence state is doped at the Nb atom site, and Mo element of the same main group and valence state is doped at the W atom position, and a new type of (NbTa) 14 (MoW) 3 O 44 medium-entropy oxide is prepared by solid-phase sintering.

[0116] Among them,

[0117] (1) By doping elements at the metal atom sites, a new type of single-phase (NbTa) 14 (MoW) 3 O 44. Through structural analysis, it is found that it is a distorted wolframite structure of orthorhombic system in a broad sense. Thermal analysis shows that this series of materials has good thermal stability in the measured temperature range (<1100 °C), and the band gap measured by ultraviolet spectroscopy is between 2.16 and 2.73 eV, both greater than 2 eV, belonging to wide-bandgap semiconductor oxides.

[0118] (2) The (NbTa) sintered in Ar atmosphere and air atmosphere 14 (MoW) 3 O 44 Thermal conductivity was measured, and it was concluded that oxygen supplementation did not have an absolutely beneficial effect on thermal conductivity. Instead, it was more related to the crystal structure and element mixed occupancy of the material itself.

[0119] (3) Through variable-temperature X-ray diffraction, its thermal expansion properties were found. The a-axis and b-axis show positive thermal expansion, and the lattice parameter c first decreases and then increases. Overall, low thermal expansion is achieved in the wide temperature range of 300 K - 1673 K. The lattice parameters a and b change from to c changes from to V changes from to According to the thermal expansion coefficient calculation formula and polynomial fitting, the thermal expansion coefficients α a 、α b 、α V first decrease and then increase with the increase of temperature, and α c first increases, then decreases and then continues to increase with the increase of temperature. Among them, at 300 K, α a = 2.306 μK -1 ,α b = -2.306 μK -1 ,α c = -1.573 μK -1 ,α V = 3.30 μK -1 ,α L = 1.10 μK -1 ; at 1073 K, α a = 2.35042 K -1 ,α b = 2.350 μK -1 ,α c = -0.388 μK -1 ,α V = 4.65 μK -1 ,α L = 1.55 μK -1 .; at 1273 K, α a = 3.560 μK-1 , α b = 3.560 μK -1 , α c = -0.320 μK -1 , α v = 7.91 μK -1 , α L = 2.63 μK -1 ; At 1673 K, α a = 7.442 μK -1 , α b = 7.442 μK -1 , α c = 2.489 μK -1 , α V = 17.97 μK -1 , α L = 5.99 μK -1 . Then (NbTa) 14 (MoW) 3 O 33 is a low thermal expansion oxide in the temperature range of 300 K - 1273 K.

[0120] 4. The present invention uses a bimetallic component oxide Nb 12 WO 33 with a tungsten bronze (TTB) structure composed of VB - VIB group elements as the matrix, and prepares a single - phase (NbTa) 12 (MoW)O 33 medium - entropy oxide of four - metal components. Specifically, by regulating its composition and structure, according to the average atomic volume theory, Ta element of the same main group and the same valence state is doped at the Nb atom site, and Mo element of the same main group and the same valence state is doped at the W atom position, and a new type of (NbTa) 12 (MoW)O 33 medium - entropy oxide is prepared by solid - phase sintering. Among them,

[0121] (1) A new type of single - phase (NbTa) 12 (MoW)O 33 is prepared by doping elements at the metal atom sites. Through structure analysis, it is found that it is a distorted stolzite structure in the orthorhombic system in a broad sense. Thermal analysis shows that this series of materials has good thermal stability in the measured temperature range (<1100 °C), and the band gap measured by ultraviolet spectroscopy is between 2.71 - 2.93 eV, belonging to wide - band - gap semiconductor oxides.

[0122] (2) (NbTa) 12 (MoW)O 33Thermal conductivity, and it is concluded that sintering in Ar atmosphere can introduce oxygen vacancies, thereby enhancing lattice disorder, increasing the number of phonon scatterings and phonon scattering, and reducing the thermal conductivity. Element doping and regulation also have a reducing effect on the thermal conductivity.

[0123] (3) Through variable-temperature X-ray diffraction, its thermal expansion properties were found. The a-axis and c-axis have positive thermal expansion, and the b-axis has negative thermal expansion. Overall, low thermal expansion is achieved in the wide temperature range of 300 K - 1673 K. From 300 K to 1673 K, the lattice parameter a changes from to b changes from to c changes from to V changes from to According to the thermal expansion coefficient calculation formula and polynomial fitting, the thermal expansion coefficients α a , α c , α V first decrease and then increase with the increase of temperature, and α b first increases and then decreases with the increase of temperature. Among them, when the sample is at 300 K, α a = 1.746 μK -1 , α b = -0.724 μK -1 , α c = 1.340 μK -1 , α V = 4.82 μK -1 , α L = 1.61 μK -1 ; at 1073 K, α a = 2.326 μK -1 , α b = -0.056 μK -1 , α c = 1.983 μK -1 , α V = 5.35 μK -1 , α L = 1.78 μK -1 ; at 1273 K, α α = 2.736 μK -1 , α b = -0.051 μK -1 , α c = 2.390 μK -1 , α v = 6.74 μK -1 , α L = 2.25 μK -1; At 1673 K, α a = 3.829 μK -1 , α b = -0.248 μK -1 , α c = 3.410 μK -1 , α v = 11.07 μK -1 , α L = 3.69 μK -1 . Then NbTa 12 MoWO 33 is a low thermal expansion oxide in the temperature range of 300 K - 1273 K.

[0124] 5. After sintering the prepared medium - entropy or high - entropy oxides into ceramics, they exhibit certain thermal expansion and thermal conductivity properties, showing great potential in application fields such as precision instruments, aerospace, and energy storage.

[0125] 6. The preparation method of the compound provided by the present invention is simple, has a short reaction cycle, low cost, and can obtain high - purity products. BRIEF DESCRIPTION OF THE DRAWINGS

[0126] The specification drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0127] Figure 1 is the structure diagram of Ta 8 W 9 O 47 in Example 1 of the present invention; wherein, (a) is the side view on the ab plane; (b) is the 3D view;

[0128] Figure 2 is the graph of the temperature - dependent XRD unit - cell parameters of Ta 8 W 9 O 47 in Example 1 of the present invention; wherein, (a) is the variation trend of the unit - cell parameter a; (b) is the variation trend of the unit - cell parameter b; (c) is the variation trend of the unit - cell parameter c, and (d) is the variation trend of the unit - cell volume V;

[0129] Figure 3 is the XRD pattern of the room - temperature powder prepared in Example 1 and Example 3 of the present invention; wherein, a is the XRD pattern of the room - temperature powder of (Nb 0.5 Ta 0.5 ) 8 W 9 O 47 prepared in Example 1; b is the XRD pattern of the room - temperature powder of (Nb 0.5 Ta0.5 ) 8 (Mo 0.5 W 0.5 ) 9 O 47 XRD pattern of the room-temperature powder;

[0130] Figure 4 For the (Nb 0.5 Ta 0.5 ) 8 W 9 O 47 prepared in Example 1 of the present invention, the microscopic morphology and element analysis diagram; wherein, (a) is the electron microscopic morphology diagram of (Nb 0.5 Ta 0.5 ) 8 W 9 O 47 ; (b) is the EDS energy spectrum of (Nb 0.5 Ta 0.5 ) 8 W 9 O 47 and the atomic percentages of each element;

[0131] Figure 5 For the (Nb 0.5 Ta 0.5 ) 8 W 9 O 47 prepared in Example 1 of the present invention, the energy spectrum analysis; wherein, (a) is the high-angle annular dark field (HAADF) image of the analysis area, and (b)-(e) are the high-angle annular dark field (HAADF) images of Nb, Ta, O, and W elements respectively;

[0132] Figure 6 For the (Nb 0.5 Ta 0.5 ) 8 (Mo 0.5 W 0.5 ) 9 O 47 prepared in Example 3 of the present invention, the microscopic morphology and element analysis diagram; wherein, (a) is the electron microscopic morphology diagram of (Nb 0.5 Ta 0.5 ) 8 (Mo 0.5 W 0.5 ) 9 O 47 ; (b) is the electron microscopic morphology diagram of (Nb 0.5 Ta 0.5 ) 8 (Mo 0.5 W 0.5 ) 9 O 47EDS energy spectrum and atomic percentages of each element;

[0133] Figure 7 For the (Nb 0.5 Ta 0.5 ) 8 (Mo 0.5 W 0.5 ) 9 O 47 energy spectrum analysis; wherein, (a) is the high-angle annular dark field (HAADF) image of the analysis area, and (b)-(f) are the high-angle annular dark field (HAADF) images of Nb, Ta, Mo, W, and O elements respectively;

[0134] Figure 8 For the (Nb 0.5 Ta 0.5 ) 8 W 9 O 47 comparison diagrams of ceramic morphologies under a scanning electron microscope (SEM) in two different sintering atmospheres; wherein, (a-c) are in an Ar atmosphere; (d-f) are in an air atmosphere;

[0135] Figure 9 For the (Nb 0.5 Ta 0.5 ) 8 (Mo 0.5 W 0.5 ) 9 O 47 comparison diagrams of ceramic morphologies under a scanning electron microscope (SEM) in two different sintering atmospheres; wherein, (a-c) are in an Ar atmosphere; (d-f) are in an air atmosphere;

[0136] Figure 10 For the (Nb 0.5 Ta 0.5 ) 8 W 9 O 47 graph of the change of the variable-temperature XRD unit cell parameters with temperature; wherein, (a) is the change trend of the unit cell parameter a; (b) is the change trend of the unit cell parameter b; (c) is the change trend of the unit cell parameter c, and (d) is the change trend of the unit cell volume V;

[0137] Figure 11 For the (Nb 0.5 Ta 0.5 ) 8 (Mo 0.5 W 0.5 ) 9 O 47The temperature-variable XRD cell parameter vs. temperature graph; among them, (a) is the variation trend of cell parameter a; (b) is the variation trend of cell parameter b; (c) is the variation trend of cell parameter c, and (d) is the variation trend of cell volume V;

[0138] Figure 12 For the (Nb 0.5 Ta 0.5 ) 8 W 9 O 47 prepared in Example 2 of the present invention, the ultraviolet-visible diffuse reflectance spectroscopy analysis curve graph; among them, (a) is the ultraviolet-visible diffuse reflectance absorption spectrum of (Nb 0.5 Ta 0.5 ) 8 W 9 O 47 prepared in an Ar atmosphere; (b) is the band gap obtained by the Taucolot method; (c) is the ultraviolet-visible diffuse reflectance absorption spectrum of (Nb 0.5 Ta 0.5 ) 8 W 9 O 47 prepared in an air atmosphere; (d) is the band gap obtained by the Taucolot method;

[0139] Figure 13 For the (Nb 0.5 Ta 0.5 ) 8 (Mo 0.5 W 0.5 ) 9 O 47 prepared in Example 4 of the present invention, the ultraviolet-visible diffuse reflectance spectroscopy analysis curve graph; among them, (a) is the ultraviolet-visible diffuse reflectance absorption spectrum of (Nb 0.5 Ta 0.5 ) 8 (Mo 0.5 W 0.5 ) 9 O 47 prepared in an Ar atmosphere; (b) is the band gap obtained by the Taucolot method; (c) is the ultraviolet-visible diffuse reflectance absorption spectrum of (Nb 0.5 Ta 0.5 ) 8 (Mo 0.5 W 0.5 ) 9 O 47 prepared in an air atmosphere, and (d) is the band gap obtained by the Taucolot method;

[0140] Figure 14 For Ta 8 W 9 O47 , (Nb 0.5 Ta 0.5 ) 8 W 9 O 47 , (Nb 0.5 Ta 0.5 ) 8 (Mo 0.5 W 0.5 ) 9 O 47 Thermal conductivity of ceramics prepared by sintering in Ar atmosphere and air atmosphere;

[0141] Figure 15 Side view of Nb 14 W 3 O 44 in the ab plane for Example 5 of the present invention;

[0142] Figure 16 (NbTa) 14 (MoW) 3 O 44 Powder room temperature X-ray diffraction (XRD) pattern of;

[0143] Figure 17 (NbTa) 14 (MoW) 3 O 44 Microscopic morphology and elemental analysis diagram of; wherein, (a) is (NbTa) 14 (MoW) 3 O 44 Electron microscopic morphology diagram of; (b) is (NbTa) 14 (MoW) 3 O 44 EDS energy spectrum and atomic percentage of each element;

[0144] Figure 18 (NbTa) 14 (MoW) 3 O 44 Energy spectrum analysis of; wherein, (a) is a high-angle annular dark field (HAADF) image of the analysis area, and (b)-(f) are high-angle annular dark field (HAADF) images of Nb, Ta, Mo, W, and O elements respectively;

[0145] Figure 19 (NbTa) 14 (MoW) 3 O 44Comparison diagrams of ceramic morphologies under scanning electron microscopy (SEM) in two different sintering atmospheres; among them, (a-c) are in Ar atmosphere; (d-f) are in air atmosphere;

[0146] Figure 20 (NbTa) of Example 6 of the present invention 14 (MoW) 3 O 44 Graph of the change of the unit cell parameters of (NbTa)(MoW)O with temperature in variable-temperature XRD; among them, (a) change trend of unit cell parameter a; (b) change trend of unit cell parameter b; (c) change trend of unit cell parameter c, (d) change trend of unit cell volume V;

[0147] Figure 21 (NbTa) of Example 6 of the present invention 14 (MoW) 3 O 44 TG-DSC curve of (NbTa)(MoW)O

[0148] Figure 22 (NbTa) of Example 6 of the present invention 14 (MoW) 3 O 44 Ultraviolet-visible diffuse reflectance spectroscopy curve of (NbTa)(MoW)O; among them, (a) ultraviolet-visible diffuse reflectance absorption spectrum of (NbTa)(MoW)O prepared in Ar atmosphere 14 (MoW) 3 O 44 ; (b) band gap obtained by Taucolot method; (c) ultraviolet-visible diffuse reflectance absorption spectrum of (NbTa)(MoW)O prepared in air atmosphere 14 (MoW) 3 O 44 ; (d) band gap obtained by Taucolot method

[0149] Figure 23 (NbTa) of Example 6 of the present invention 14 (MoW) 3 O 44 Thermal conductivity of ceramics sintered and prepared in Ar atmosphere and air atmosphere

[0150] Figure 24 Structure diagram of NbWO of Example 7 of the present invention; among them, (a) 3D view; (b) side view on the ac plane 12 WO 33 ; (a) 3D view; (b) side view on the ac plane

[0151] Figure 25 (NbTa) of Example 7 of the present invention 12 (MoW)O 33 Powder room-temperature X-ray diffraction (XRD) pattern of (NbTa)(MoW)O

[0152] Figure 26 Microscopic morphology and elemental analysis diagram of (NbTa) in Example 7 of the present invention 12 (MoW)O 33 ; among them, (a) is the electron microscopic morphology diagram of (NbTa) 12 (MoW)O 33 ; (b) is the EDS energy spectrum of (NbTa) 12 (MoW)O 33 and the atomic percentages of each element;

[0153] Figure 27 Microscopic morphology and elemental analysis diagram of (NbTa) in Example 7 of the present invention 12 (MoW)O 33 Energy spectrum analysis; among them, (a) is the high-angle annular dark field (HAADF) image of the analysis area, and (b)-(f) are the annular dark field (HAADF) images of Nb, Ta, Mo, W, and O elements;

[0154] Figure 28 Comparison diagram of ceramic morphology of (NbTa) in Example 8 of the present invention under two different sintering atmospheres by scanning electron microscope (SEM); among them, (a-c) are in Ar atmosphere; (d-f) are in air atmosphere; 12 (MoW)O 33 ; among them, (a) is the electron microscopic morphology diagram of (NbTa)

[0155] Figure 29 Microscopic morphology and elemental analysis diagram of (NbTa) in Example 8 of the present invention 12 (MoW)O 33 Variation diagram of temperature-dependent XRD unit cell parameters with temperature; among them, (a) is the variation trend of unit cell parameter a; (b) is the variation trend of unit cell parameter b; (c) is the variation trend of unit cell parameter c, and (d) is the variation trend of unit cell volume V;

[0156] Figure 30 Microscopic morphology and elemental analysis diagram of (NbTa) in Example 8 of the present invention 12 (MoW)O 33 TG-DSC curve;

[0157] Figure 31 Microscopic morphology and elemental analysis diagram of (NbTa) in Example 8 of the present invention 12 (MoW)O 33 Ultraviolet-visible diffuse reflectance spectroscopy analysis curve diagram; among them, (a) is the ultraviolet-visible diffuse reflectance absorption spectrum of (NbTa) prepared in Ar atmosphere 12 (MoW)O 33 ; (b) is the band gap obtained by using the Taucolot method; (c) is the ultraviolet-visible diffuse reflectance absorption spectrum of (NbTa) prepared in air atmosphere 12 (MoW)O 33Ultraviolet-visible diffuse reflectance absorption spectrum; (d) Band gap obtained by the Taucolot method;

[0158] Figure 32 (NbTa) of Example 8 of the present invention 12 (MoW)O 33 Thermal conductivity of ceramics prepared by sintering in Ar atmosphere and air atmosphere. Detailed implementation manners

[0159] It should be noted that the following detailed description is exemplary and is intended to provide further illustration of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0160] Currently, the exploration of new excellent negative thermal expansion materials or zero thermal expansion materials is mainly achieved through two approaches. One is to compound positive thermal expansion materials with negative thermal expansion to adjust the thermal expansion coefficient. The other is to achieve regulation through doping and solid solution of elements. The present invention mainly dopes elements in bimetallic component oxides (Ta 8 W 9 O 47 , Nb 14 W 3 O 44 type and Nb 12 WO 33 ) composed of VB-VIB group elements to achieve entropy regulation, so as to prepare medium-entropy or high-entropy materials, and then explore the influence of solid solution effect on the physical properties in terms of thermal expansion. Medium-entropy or high-entropy materials show excellent physical properties and good application prospects in various fields. It is challenging to discover low-thermal expansion materials with a wide temperature range and good thermal stability through the entropy stabilization effect, which is also the key content of the present invention.

[0161] In K x WO 3 with a tetragonal TTB structure, W and O form octahedral coordination and are connected to each other through shared vertices to form a five-membered ring, and the center of the pentagon is occupied by the K element. By expanding the unit cell in the b direction three times and replacing the K element with the Nb element, the crystal structure of Nb 18 W 16 O 93 will be obtained. The two main metal atom positions in this structure are the octahedral center and the center of the five-membered ring, and the occupation ratios of the two metal elements are relatively complex. And the tetragonal TTB-type Ta 8 W 9 O 47 structure is the same as that of Nb 18 W 16 O 93Highly similar, also having a similar five-membered ring structure, this way of connecting vertices makes it have good structural rigidity. As the temperature rises, the bond angles and atomic distances change, resulting in thermal expansion behavior.

[0162] The present invention combines the average atomic volume theory, using Ta 8 W 9 O 47 as the matrix, doping Nb with an atomic radius close to that of Ta at the Ta position, and for the first time synthesizing a single-phase (Nb 0.5 Ta 0.5 ) 8 W 9 O 47 medium-entropy oxide with a negative thermal expansion along the c-axis and positive thermal expansions along the a-axis and b-axis, ultimately achieving low thermal expansion behavior. Ta 8 W 9 O 47 and (Nb 0.5 Ta 0.5 ) 8 W 9 O 47 are used for comparison to explore the effects of solid solution on thermal conductivity and thermal expansion performance; Ta with the same main group and valence state as the doped Nb atom and Mo with the same main group and valence state as the doped W atom are doped at the W atom position. A new type of (Nb 0.5 Ta 0.5 ) 8 (Mo 0.5 W 0.5 ) 9 O 47 high-entropy oxide is prepared by solid-phase sintering, and then whether the ceramic materials prepared after high-entropyization have more excellent thermal properties, including low thermal expansion performance and thermal conductivity performance in a wider temperature range, is studied. Similarly, taking Nb 14 W 3 O 44 as the matrix, single-phase (NbTa) 14 (MoW) 3 O 44 four-metal component medium-entropy oxide is prepared by metal doping and introducing oxygen vacancies; taking Nb 12 WO 33 as the matrix, single-phase (NbTa) 12 (MoW)O 33 four-metal component medium-entropy oxide is prepared by metal doping and introducing oxygen vacancies.

[0163] Unless otherwise specified, the raw materials in the examples of the present invention are all purchased through commercial channels.

[0164] Experimental raw materials: niobium oxide powder (Nb 2 O5 , 99.9%), tantalum oxide powder (Ta 2 O 5 , 99.9%), tungsten oxide powder (WO 3 , 99.9%) molybdenum oxide powder (MoO 3 , 99.9%).

[0165] X-ray diffractometer, model D8-ADVANCE, manufacturer BRUKER (Germany), test conditions: The diffractometer uses Cu-Kα target radiation, the tube voltage and tube accelerating current are 40 kV and 40 mA respectively, continuous ten scans are used, and the scan step size and scan speed are 0.02° and 2° / min respectively.

[0166] In-situ XRD model is PANalytical X'Pert Pro MPD, Holland. The variable temperature stage accessory model is Anton Paar HTK-16, Austria, test conditions: temperature 300 K–1673 K, heating rate: 5 °C / min, XRD scan range is 5°-95°, and all XRD tests are carried out in a nitrogen atmosphere. The Rietveld refinement of the diffraction pattern is performed using Fullprof software to obtain the unit cell parameters of the samples at different temperatures.

[0167] Equipped with an energy dispersive spectrometer EDS model is Oxford X-MaxN, UK, and the SEM of the field emission scanning electron microscope is model FEI-Nova 450, USA.

[0168] Laser flash thermal conductivity meter, model LFA 427, manufacturer NETZSCH NANOSTAR (Germany), test conditions: temperature range from 300 K to 725 K.

[0169] Shimadzu 3600 type UV-vis NIR is tested in the range of 200 - 800 nm, and the band gap of the material is calculated by the Taucplot method proposed by Tacu et al.

[0170] High-resolution transmission electron microscope (HRTEM, JEM-2100F, JEOL, JPN) collects high-resolution images, selected area electron diffraction patterns, and elemental composition in the microstructure at 200 keV.

[0171] High-entropy materials are a new type of multi-principal element materials composed of multiple elements in equiatomic ratio (or near equimolar ratio). These materials were initially defined as being composed of 5 or more elements in equiatomic ratio or near equiatomic ratio, with high-entropy effect, slow diffusion effect, and lattice distortion effect.

[0172] The first generation of high-entropy alloys: composed of 5 or more alloying elements, the composition element content ratio is equiatomic ratio, and the phase structure is a single-phase complex alloy.

[0173] Second-generation high-entropy alloy: An alloy composed of four or more alloying elements, with the composition ratio of the constituent elements being non-equiatomic, and the phase structure being a complex solid-solution alloy with a two-phase or multi-phase structure.

[0174] High-entropy ceramic: Sometimes also referred to as a high-entropy compound, it refers to a single-phase ceramic containing at least four types of cations or anions. The concept of high-entropy ceramics inherits from the field of high-entropy alloys.

[0175] In the present invention, if the metal elements of (Nb 0.5 Ta 0.5 ) 8 (Mo 0.5 W 0.5 ) 9 O 47 are near-equiatomic and it is a single-phase ceramic with four types of cations or anions, then it is a high-entropy ceramic material. However, the atomic ratios of the metal elements of (Nb 0.5 Ta 0.5 ) 8 W 9 O 47 , (NbTa) 14 (MoW) 3 O 44 and (NbTa) 12 (MoW)O 33 differ greatly, so they cannot be strictly defined as high-entropy materials. Therefore, (Nb 0.5 Ta 0.5 ) 8 W 9 O 47 , (NbTa) 14 (MoW) 3 O 44 and (NbTa) 12 (MoW)O 33 are defined as medium-entropy materials in the present invention.

[0176] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in conjunction with specific embodiments.

[0177] Example 1

[0178] This example provides a method for preparing a novel medium-entropy oxide (Nb 8 W 9 O 47 ) by using Ta 0.5 Ta 0.5 ) 8 W 9 O 47。

[0179] Ta powder with a purity of 99.9% 2 O 5 powder, WO powder with a purity of 99.9% 3 Nb powder with a purity of 99.9% 2 O 5 powder, according to the stoichiometric ratio of Ta 2 O 5 :Nb 2 O 5 :WO 3 =2:2:9 for weighing, and carefully grinding in a mortar; then cold-pressing the uniformly mixed sample using a tablet press, placing the sample in a quartz tube, evacuating and sealing the quartz tube with a hydrogen-oxygen flame; then sintering the sample, with an Ar atmosphere, heating from room temperature to 1000 °C in 360 min, holding for 24 h, and then naturally cooling to room temperature in a muffle furnace, and then taking out the sample and carefully grinding to obtain Ta 8 W 9 O 47 -type (Nb 0.5 Ta 0.5 ) 8 W 9 O 47 phase powder.

[0180] At the same time, powder samples for solid-phase sintering in an air atmosphere were also prepared for comparison. Except for the different atmosphere, other conditions were the same as those for vacuum solid-phase sintering.

[0181] Take the above-prepared (Nb 0.5 Ta 0.5 ) 8 W 9 O 47 sample, and collect its X-ray diffraction pattern using an X-ray powder diffractometer, as shown in Figure 3 a. Perform refinement on the room-temperature XRD of (Nb 0.5 Ta 0.5 ) 8 W 9 O 47 . The structural model used for refinement is an orthorhombic structure. At room temperature, the diffraction peaks of the refinement results of (Nb 0.5 Ta 0.5 ) 8 W 9 O 47 have no obvious impurity peaks. The reliability factors R p =7.09% and R wp =9.22% obtained from the refinement results are within a reasonable range, indicating that the synthesized phase has high purity and the refinement results are reliable.

[0182] Take the above-prepared (Nb0.5 Ta 0.5 ) 8 W 9 O 47 For the powder sample, scanning electron microscopy was used to perform morphological characterization and EDS elemental analysis on it. As Figure 4 shown, the surface of the microscopic grains is smooth, with a size of approximately 500 nm, presenting a smooth flake structure. By performing EDS point scanning on a single grain, it was found that the atomic percentage of Ta element is 28.3%, and that of Nb element is 19.3%, which is close to an equal ratio. The total content of Ta and Nb is 47.6%, which is close to an equal ratio with the W element content of 52.4%. Moreover, the elemental ratio of Nb and Ta to the W element is 0.908, which is close to the designed ratio of 0.89. This indicates the successful synthesis of the target product. As Figure 5 shown by the elemental surface scanning analysis, the distributions of Ta, Nb, W, and O elements in a single grain are uniform, indicating the successful synthesis of the target product.

[0183] Among them, the matrix Ta 8 W 9 O 47 was also provided in this example. Its preparation process is the same as above. Weighing was carried out according to the stoichiometric ratio of Ta 2 O 5 :WO 3 = 4:9. The structural diagram of Ta 8 W 9 O 47 is as Figure 1 shown.

[0184] Figure 2 This is the graph of the temperature-dependent XRD unit cell parameters of Ta 8 W 9 O 47 in Example 1 of the present invention; among them, (a) shows the change trend of the unit cell parameter a; (b) shows the change trend of the unit cell parameter b; (c) shows the change trend of the unit cell parameter c, and (d) shows the change trend of the unit cell volume V. As Figure 2 can be seen: as the temperature increases, the unit cell parameters a and b of Ta 8 W 9 O 47 are almost linearly positively correlated with the temperature, while c is linearly negatively correlated. The unit cell volume V shows a gradually increasing trend, with a relatively gentle increase in the range of 700K - 1300K and larger increases at both ends. The unit cell parameters a and b increase from to at 1673K. The unit cell parameter c decreases from at 300K to at 1673K. The unit cell volume V expands from at 300K to

[0185] The coefficient of thermal expansion α is calculated by the thermal expansion calculation formula and polynomial fitting in the temperature range of 300K to 1673K a 、α b 、α c 、α V first decreases and then increases with the increase of temperature, where α a = 3.331(1) μK -1 ,α b = 3.331(1) μK -1 ,α c = -0.759(3) μK -1 ,α V = 6.62(1) μK -1 ,α L = 2.21(1) μK -1 At 1673K, α a = 4.231(1) μK -1 ,α b = 4.231(1) μK -1 ,α c = -3.726(3) μK -1 ,α V = 5.91(1) μK -1 ,α L = 1.97(1) μK -1 。By calculating the coefficient of thermal expansion at each temperature point from 300K to 1673K, it can be concluded that it is a low thermal expansion oxide in the temperature range of 300K to 1673K.

[0186] Example 2

[0187] In this example, a new medium entropy oxide (Nb 8 W 9 O 47 ) prepared with Ta 0.5 Ta 0.5 ) 8 W 9 O 47 in Example 1 as the matrix was further sintered to prepare a ceramic material to explore its thermal properties.

[0188] Take the (Nb 0.5 Ta 0.5 ) 8 W 9 O 47The powder material is wet ball-milled using a planetary ball mill with a ball-to-material ratio of 10:1, large balls:medium balls:small balls = 2:6:4, and ball-milled for 6 h at a rotational speed of 400. The slurry obtained from ball milling is placed in a drying oven at 100 °C for 24 h of drying to obtain a powder raw material with a smaller particle size. The powder is mixed with 5% concentration of PVA for ceramic preparation. The powder obtained from vacuum solid-phase sintering is transferred to an agate mortar for grinding. During the grinding process, 5% concentration of PVA is added. After grinding evenly, the sample is loaded into a 12.8 mm tablet press mold for tableting. Under a pressure of 8 MPa and holding for 2 min, a cylindrical green body with a diameter of 12.8 mm and a height of about 1.5 mm is finally pressed. The green body is placed in a clean alumina high-temperature boat with a layer of alumina powder at the bottom, and then the boat is placed in an Ar atmosphere sintering tube furnace and held at 700 °C for 2 h for degassing. The degassed sample is re-loaded in a clean alumina boat and sintered at a rate of 3 K / min from room temperature to the sintering temperature in an Ar atmosphere and an air atmosphere respectively, and naturally cooled to room temperature after holding for 3 h to obtain a pure ceramic bulk sample.

[0189] The SEM images of the ceramic bulk materials prepared in this example at different magnifications are as Figure 8 shown. It can be clearly observed from the figure that the sample is not dense and there are many pores in the middle. It is related to the ceramic preparation method. The green body density obtained by pressing with a powder press is limited, and a certain amount of 5% concentration of PVA is mixed in the green body. During the degassing process at 700 °C, some pores are left in the ceramic due to the volatilization of PVA. After high-temperature sintering at 1100 °C, the uniformly crushed grains after ball milling grow again, and the rough surface becomes smooth. The specimen is composed of uniform grains of 500 nm–2 μm, and there are pores less than 250 nm between the grains. The grain size of the ceramic sintered in the air atmosphere is larger than that of the ceramic sintered in the Ar atmosphere. The surface of a single grain of the ceramic sintered in both atmospheres is very smooth, and the agglomerated small-sized grains combine together to form large grains at 1100 °C. Comparing the surface morphology of the ceramics, the surface morphology of the ceramic sintered in the Ar atmosphere is flatter, the ceramic surface morphology is denser, the single grains and pores of the ceramic sintered in the air atmosphere are larger, and the density is lower. It shows that (Nb 0.5 Ta 0.5 ) 8 W 9 O 47 In the presence of oxygen, oxygen vacancies are replenished, and the grain growth rate is relatively faster and the porosity is larger.

[0190] The materials prepared in Example 2 under different temperature conditions are analyzed by X-ray diffraction, and the relationship between the temperature and the unit cell parameters obtained by analysis is as Figure 10As shown, the results show that: the lattice parameters a, b, and c of the prepared material show regular changes with the increase in temperature. Moreover, the lattice parameters a and b almost show a linear upward trend, the lattice parameter c shows a linear decreasing trend, and the lattice volume V shows a linear upward trend. The lattice parameter a increases from at 300 K to at 1673 K. b increases from at 300 K to at 1673 K. c decreases from 3.9119(2) at 300 K to at 1673 K. The lattice volume V increases from at 300 K to at 1673 K.

[0191] According to the calculation formula of the thermal expansion coefficient and polynomial fitting, the thermal expansion coefficients α a , α b , α V first decrease and then increase with the increase in temperature, and α c first increases slightly and then decreases with the increase in temperature. Among them, at 300 K, α a = 2.281(2) μK -1 , α b = 3.047(3) μK -1 , α c = -1.627(3) μK -1 , α V = 3.84(1) μK -1 , α L = 1.28(1)1 μK -1 At 1673 K, α a = 4.988(1) μK -1 , α b = 3.003(2) μK -1 , α c = -3.006(3) μK -1 , α V = 5.17(2) μK -1 , α L = 1.72(2) μK -1 . By calculating the thermal expansion coefficients at each temperature point from 300 K to 1673 K, it can be concluded that it is a low thermal expansion oxide in the temperature range of 300 K to 1673 K. (Nb 0.5 Ta 0.5 ) 8 W 9 O 47 and Ta 8 W 9 O47 Belonging to low thermal expansion oxides, but after solid solution, (Nb 0.5 Ta 0.5 ) 8 W 9 O 47 strengthens the structural rigidity, and the absolute values of the linear thermal expansion coefficients in three directions are smaller than those of Ta 8 W 9 O 47 , and the structure changes less with temperature.

[0192] After solid solution, (Nb 0.5 Ta 0.5 ) 8 W 9 O 47 strengthens the structural rigidity, and the absolute values of the linear thermal expansion coefficients in three directions are smaller than those of Ta 8 W 9 O 47 , and the structure changes less with temperature.

[0193] The absorption spectra of the powder samples prepared by sintering in Ar atmosphere and in air atmosphere in Example 2 at different incident wavelengths were measured using ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS) as Figure 12 shown. The powder samples tested were powder samples formed by crushing ceramics. The Taucplot method was used to obtain the band gap E g of the oxide. According to the formula (αhv) 1 / n = B(hv - E g ), where α represents the absorption coefficient, h represents Planck's constant, ν represents the incident light frequency, B is a proportionality constant, and E g is the band gap of the semiconductor. For an indirect band gap semiconductor, n = 2. The band gap E g of the material prepared by solid-phase sintering in Ar atmosphere in Example 2 was measured to be 2.63 eV, and the band gap E g of the material prepared by solid-phase sintering in air atmosphere in Example 2 was 2.8 eV, belonging to wide-band gap semiconductor oxides. It was found that a decrease in the oxygen vacancy content would lead to a slight increase in the band gap.

[0194] The thermal diffusivity D of the ceramic material prepared in Example 2 was measured using a laser flash thermal conductivity meter from Netzsch, Germany. The thermal conductivity κ was calculated through κ tot = D×ρ×C p . The density ρ of the sample was measured by the Archimedes drainage method, and the specific heat C p was calculated through the Dulong-Petit formula. The relationship between the thermal conductivity and temperature is as Figure 14 shown. The thermal conductivity κ Ar of the material obtained in Example 2 was 0.963 W·m -1 ·K-1 @ 300 K, κO 2 = 1.281 W·m -1 ·K -1 @ 300 K. The thermal conductivity of the material prepared in the air atmosphere in Example 2 is higher than that of the sample sintered in the Ar atmosphere, indicating that the atmosphere sintering will cause significant differences in the thermal conductivity. The oxygen vacancies existing in the sample sintered in the Ar atmosphere are beneficial to reducing the thermal conductivity. The Ar atmosphere sintering can introduce a large number of highly disordered oxygen vacancies into the oxide, greatly increasing the number of phonon scatterings and phonon scattering, thus decreasing the thermal conductivity.

[0195] In summary, high-purity (Nb 0.5 Ta 0.5 ) 8 W 9 O 47 phase can be prepared by the method described in this example.

[0196] Example 3

[0197] This example provides a preparation method of a novel high-entropy oxide (Nb 8 W 9 O 47 ) by element doping and the introduction of oxygen vacancies using Ta 0.5 Ta 0.5 ) 8 (Mo 0.5 W 0.5 ) 9 O 47 as the matrix.

[0198] Ta 2 O 5 powder with a purity of 99.9%, WO 3 powder with a purity of 99.9%, Nb 2 O 5 powder with a purity of 99.9%, and MoO 3 powder with a purity of 99.9% are weighed according to the stoichiometric ratio of Ta 2 O 5 :Nb 2 O 5 :MoO 3 :WO 3 = 2:2:4.5:4.5, and carefully ground in a mortar; then the uniformly mixed sample is cold-pressed into shape using a tablet press, placed in a quartz tube, evacuated, and the quartz tube is sealed with a hydrogen-oxygen flame; then the sample is sintered, heated from room temperature to 1000 °C in 360 min, held for 24 h, naturally cooled to room temperature in a muffle furnace, and then the sample is taken out and carefully ground to obtain Ta 8 W 9 O 47type of high-entropy oxide (Nb 0.5 Ta 0.5 ) 8 (Mo 0.5 W 0.5 ) 9 O 47 phase powder.

[0199] At the same time, a powder sample prepared by solid-phase sintering in an air atmosphere was also prepared for comparison. Except for the different atmospheres, other conditions were the same as those for vacuum solid-phase sintering.

[0200] Take the above-prepared (Nb 0.5 Ta 0.5 ) 8 (Mo 0.5 W 0.5 ) 9 O 47 sample, and use an X-ray powder diffractometer to collect its X-ray diffraction pattern, as shown in Figure 3 b. Refine the room-temperature XRD of (Nb 0.5 Ta 0.5 ) 8 (Mo 0.5 W 0.5 ) 9 O 47 The refined structure model for the room-temperature XRD is an orthorhombic structure. At room temperature, the diffraction peaks of the refined (Nb 0.5 Ta 0.5 ) 8 (Mo 0.5 W 0.5 ) 9 O 47 XRD have no obvious miscellaneous peaks, and the unit cell parameters are The parameter factors R p 、R wp values obtained from the refinement results are all within a reasonable range, and the refinement results are reliable. Compared with the unit cell parameters of (Nb 0.5 Ta 0.5 ) 8 W 9 O 47 which are the unit cell parameters a, b, c, and V all increase to a certain extent, which is consistent with the increase in doping elements and the increase in the comprehensive atomic radius.

[0201] Take the above-prepared (Nb 0.5 Ta 0.5 ) 8 (Mo 0.5 W 0.5 ) 9 O 47The sample was characterized by scanning electron microscopy for its morphology and EDS elemental analysis. As Figure 6 shown, the microscopic grains are micron-sized smooth rod-like structures. EDS point scanning of a single grain found that Ta, Nb, Mo, and W are close to an equimolar ratio. The total content of Ta and Nb elements is 46.2%, and the total content of Mo and W elements is 53.9%. The ratio of the two is 0.857, which is extremely close to the designed ratio of 8:9 = 0.89, indicating the successful synthesis of (Nb 0.5 Ta 0.5 ) 8 (Mo 0.5 W 0.5 ) 9 O 47 high-entropy oxide. As Figure 7 shown by the elemental mapping analysis, the distribution of Ta, Nb, Mo, W, and O elements in a single grain is uniform, indicating the successful synthesis of (Nb 0.5 Ta 0.5 )8(Mo 0.5 W 0.5 ) 9 O 47 high-entropy oxide.

[0202] Example 4

[0203] In this example, a new high-entropy oxide (Nb 8 W 9 O 47 ) prepared using the matrix of Example 3 with Ta 0.5 Ta 0.5 ) 8 (Mo 0.5 W 0.5 ) 9 O 47 was further sintered to prepare a ceramic material, and its thermal properties were investigated.

[0204] Taking the (Nb 0.5 Ta 0.5 ) 8 (Mo 0.5 W 0.5 ) 9 O 47The materials were wet-milled using a planetary ball mill with a ball-to-material ratio of 10:1, large balls:medium balls:small balls = 2:6:4, and milled for 6 h at a rotation speed of 400. The slurry obtained by ball milling was placed in a drying oven at 100 °C for 24 h of drying to obtain a powder raw material with a smaller particle size. The powders were mixed with 5% concentration of PVA for ceramic preparation. The powders obtained by vacuum solid-phase sintering were transferred to an agate mortar for grinding, and 5% concentration of PVA was added during the grinding process. After uniform grinding, the sample was loaded into a 12.8 mm tablet die for tablet pressing. Under a pressure of 8 MPa and holding for 2 min, a cylindrical green body with a diameter of 12.8 mm and a height of about 1.5 mm was finally pressed. The green body was placed in a clean alumina high-temperature boat with a layer of alumina powder at the bottom, and then the boat was placed in an Ar atmosphere sintering tube furnace and held at 700 °C for 2 h for degassing. The degassed samples were re-loaded into a clean alumina boat and sintered at a rate of 3 K / min from room temperature to the sintering temperature in an Ar atmosphere and an air atmosphere respectively, and naturally cooled to room temperature after holding for 3 h to obtain pure ceramic bulk samples.

[0205] The SEM images of the ceramic bulk materials prepared in this example at different magnifications are as Figure 9 shown. (Nb 0.5 Ta 0.5 ) 8 (Mo 0.5 W 0.5 ) 9 O 47 The ceramic samples are not dense and there are many pores in the middle. After high-temperature sintering at 1100 °C, the uniformly broken grains after ball milling grow again, and the rough surface becomes smooth. The specimen is composed of uniform grains about 500 nm in size, and there are pores less than 500 nm between the grains. The particle sizes of the ceramics sintered in the two atmospheres are close, the grain surfaces are very smooth, and the aggregated small-sized grains combine together to form large grains at a high temperature of 1000 °C. Comparing the surface morphologies of the ceramics, the surface morphology of the ceramics sintered in an Ar atmosphere is flatter, the ceramic surface morphology is denser, the individual grains and pores of the ceramics sintered in an air atmosphere are larger, and the density is lower. However, there are large rod-like particles on the surfaces of the ceramics sintered in the two atmospheres.

[0206] The relationship between the temperature and the unit cell parameters of the materials prepared in Example 4 under different temperature conditions analyzed by X-ray diffraction analysis is as Figure 11 shown. It can be seen that with the increase of temperature, the unit cell parameters a and b show a gradually increasing trend, the unit cell parameter c shows a decreasing trend as a whole, and there is an increasing trend at high temperatures. The unit cell volume V shows an increasing trend. The unit cell parameter a increases from at 300 K to at 1673 K, and b increases from at 300 K to As Figure 11 (a) and 11(b) show that both the a-axis and the b-axis increase nearly linearly with the increase of temperature, while c decreases from at 300K to As Figure 11 (c) shows, the change of the c-axis does not show good regularity. Instead, it changes with a very low slope before 973K, and there is a jump at 973K, and then it fluctuates around 3.927. Generally speaking, the change of the c-axis is very small, almost zero change. Therefore, the change trend of the unit cell volume is consistent with that of the a-axis and the b-axis. The unit cell volume V increases from at 300K to As Figure 11 (d) shows.

[0207] According to the calculation formula of the thermal expansion coefficient and linear fitting, the thermal expansion coefficients in the temperature range from 300K to 1673K are calculated. α a , α b , α V then decrease continuously with the increase of temperature. α c first increases slightly, then decreases and then continues to increase with the increase of temperature. Among them, for the sample, α a = 2.026(1) μK -1 , α b = 2.297(2) μK -1 ,

[0208] α c = -1.552(2) μK -1 , α V = 3.60(4) μK -1 , α L = 1.20(1) μK -1 . At 1673K, α a = 2.021(2) μK -1 , α b = 2.290(1) μK -1 , α c = 1.052(2) μK -1 , α V = 3.59(5) μK -1 , α L = 1.20(5) μK -1 . Through fitting calculation of the thermal expansion coefficients in each temperature segment from 300K to 1673K, it can be obtained that (NbTa) 8 (MoW) 9 O 47It is a near-zero thermal expansion oxide in the temperature range of 300K to 1673K. It can be seen that with the increase of entropy after solid solution, the structure of the oxide becomes more stable, and the change with temperature is smaller than that of the parent structure.

[0209] The absorption spectra of the powder samples prepared by sintering in Ar atmosphere and atmospheric atmosphere in Example 4 at different incident wavelengths were measured using ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS) as Figure 13 shown. The band gap E of the oxide was obtained using the Taucplot method. g , according to the formula (αhv) 1 / n = B(hv - E g ), where α represents the absorption coefficient, h represents Planck's constant, ν represents the incident light frequency, B is a proportionality constant, and E g is the band gap of the semiconductor. For an indirect band gap semiconductor, n = 2. The band gap E g of the material prepared by solid-phase sintering in Ar atmosphere in Example 3 was measured to be 2.67 eV, and the band gap E g of the material prepared by solid-phase sintering in atmospheric atmosphere was 2.79 eV. It belongs to a wide-band gap semiconductor oxide. It was found that a decrease in the oxygen vacancy content would lead to a slight increase in the band gap.

[0210] The thermal diffusivity D of the material prepared in Example 4 was measured using a laser flash thermal conductivity meter. The thermal conductivity was calculated by κ tot = D × ρ × C p . The density ρ of the sample was measured by the Archimedes drainage method, and the specific heat C p was calculated by the Dulong-Petit formula. The relationship between the thermal conductivity and temperature is as Figure 14 shown. The thermal conductivity κ Ar of the material obtained in Example 4 was 1.137 W·m -1 ·K -1 @300K, and κO 2 = 0.715 W·m -1 ·K -1 @300K. Comparing the thermal conductivities of the Ta 8 W 9 O 47 parent and the ceramic materials sintered in different atmospheres in Examples 2 and 4, it was found that the amplitude of the change in the thermal conductivity of the ceramic sample sintered in Ar atmosphere with temperature was smaller than that of the sample sintered in atmospheric atmosphere. For the ceramics prepared in atmospheric atmosphere, the thermal conductivity of the sample decreased with the increase of entropy, while for the ceramics prepared in Ar atmosphere, the thermal conductivity of the sample increased with the increase of entropy. The minimum value of the thermal conductivity was for the sample prepared in atmospheric atmosphere in Example 4, (Nb 0.5 Ta 0.5 ) 8 (Mo 0.5 W 0.5 )9 O 47 , κO 2 = 0.52 W·m -1 ·K -1 @ 723 K. The high-entropy structure design can introduce a large number of highly disordered oxygen vacancies. Due to the high-entropy stabilization effect, the doped multi-component cations greatly increase the number of phonon scatterings and phonon scattering, significantly improving the thermal conductivity and potentially obtaining higher temperature phase stability and lower thermal conductivity.

[0211] In summary, through the method described in this embodiment, high-purity (Nb 0.5 Ta 0.5 )( 8 (Mo 0.5 W 0.5 ) 9 O 47 phase can be prepared.

[0212] Example 5

[0213] This example provides a method for preparing a novel medium-entropy oxide (NbTa) 14 W 3 O 44 as the matrix by introducing element doping and oxygen vacancies. 14 (MoW) 3 O 44 .

[0214] Ta 2 O 5 powder with a purity of 99.9%, WO 3 powder with a purity of 99.9%, Nb 2 O 5 powder with a purity of 99.9%, and MoO 3 powder with a purity of 99.9% are weighed according to the stoichiometric ratio of Ta 2 O 5 :Nb 2 O 5 :MoO 3 :WO 3 = 3.5:3.5:1.5:1.5, and carefully ground in a mortar; then the uniformly mixed sample is cold-pressed into shape using a tablet press, placed in a quartz tube, evacuated, and the quartz tube is sealed with a hydrogen-oxygen flame; then the sample is sintered, heated from room temperature to 1000 °C in 360 min, held for 24 h, naturally cooled to room temperature in a muffle furnace, and then the sample is taken out and carefully ground to obtain the medium-entropy oxide (NbTa) 14 W 3 O 44 type (NbTa) 14 (MoW) 3 O44 Phase powder.

[0215] At the same time, a powder sample prepared by solid-phase sintering in an air atmosphere was also prepared for comparison. Except for the different atmosphere, other conditions were the same as those of vacuum solid-phase sintering.

[0216] Among them, Nb 14 W 3 O 44 The side view on the ab plane is as Figure 15 shown. The present invention is based on the structure of Nb 14 W 3 O 44 as shown in Figure 15 shown. Nb 14 W 3 O 44 is composed of Nb-O 6 octahedrons and W-O 4 tetrahedrons. Green represents Nb atoms, purple represents W atoms, and red represents oxygen atoms. The octahedrons and tetrahedrons are connected by sharing vertices. At the same time, there are some oxygen vacancies inside the crystal. According to the average atomic volume theory, Ta elements of the same main group and the same valence state are doped at the Nb atom position, and Mo elements of the same main group and the same valence state are doped at the W atom position. A new type of (NbTa) 14 (MoW) 3 O 44 medium entropy oxide is prepared by solid-phase sintering.

[0217] Take the above-mentioned (NbTa) 14 (MoW) 3 O 44 powder sample prepared in vacuum, and use an X-ray powder diffractometer to collect its X-ray diffraction (XRD) pattern, as Figure 16 shown. At room temperature, the diffraction peaks of the refined result of (NbTa) 14 (MoW) 3 O 44 have no obvious miscellaneous peaks. The reliability factor obtained from the refined result, among which (NbTa) 14 (MoW) 3 O 44 The reliability factor is within a reasonable range. It can be seen from the XRD pattern that the fitting results of most diffraction peaks are good and there are no impurity diffraction peaks, indicating that the synthesized phase has high purity.

[0218] Take the above-mentioned (NbTa) 14 (MoW) 3 O 44 powder sample prepared by vacuum solid-phase sintering, and use a scanning electron microscope to perform morphological characterization and EDS elemental analysis on it, as Figure 17 shown. Among them, (NbTa)14 (MoW) 3 O 44 The microscopic grains show a rock salt structure with a size of approximately 1 μm. EDS point scanning of individual grains reveals that the Ta and Nb ratios are close to being in equal proportion, and the atomic percentage of the Mo element is nearly twice that of the W element. This may be related to the solid solubility limits of each element. In the Nb 14 W 3 O 44 type of medium-entropy oxide crystal structure, there are some oxygen vacancies inherently, and the mixed occupancy of elements at the metal atom positions will also lead to deviations in element ratios. Figure 18 The Mapping diagram shows that the distributions of Nb, Ta, Mo, W, and O elements in individual grains are uniform, indicating the successful synthesis of Nb 14 W 3 O 44 type of medium-entropy oxide.

[0219] Example 6

[0220] In this example, a new medium-entropy oxide (NbTa) 14 W 3 O 44 prepared using the matrix in Example 5 was further sintered to prepare a ceramic material, and its thermal properties were explored. 14 (MoW) 3 O 44 44

[0221] Take the (NbTa) 14 (MoW) 3 O 44 powder material prepared under vacuum above, and use a planetary ball mill for ball milling. The ball-to-material ratio is 10:1, and the ratio of large balls: medium balls: small balls = 2:6:4. Ball mill at 400 revolutions per minute for 6 hours. Put the slurry obtained from ball milling into a drying oven at 100 °C for 24 hours to obtain a powder raw material with a smaller particle size. Mix the powder with 5% concentration of PVA for ceramic preparation. Transfer the powder obtained by vacuum solid-phase sintering to an agate mortar for grinding. During the grinding process, add 5% concentration of PVA. After grinding evenly, load the sample into a 12.8 mm tablet mold for tablet pressing. Press at 8 MPa pressure and hold for 2 minutes to finally form a cylindrical green body with a diameter of 12.8 mm and a height of about 1.5 mm. Place the green body in a clean alumina high-temperature boat with a layer of alumina powder at the bottom, and then put the boat into an Ar atmosphere sintering tube furnace and hold at 700 °C for 2 hours for degassing. Re-load the degassed sample with a clean alumina boat, and perform ceramic sintering in an Ar atmosphere and an air atmosphere environment at a rate of 3 °C / min from room temperature to 1100 °C sintering temperature. After holding for 3 hours, naturally cool to room temperature to obtain a pure ceramic bulk sample.

[0222] SEM images of the ceramic bulk materials prepared by the present invention at different magnifications are as follows Figure 19 shown. It can be clearly observed from the figure that the ceramic samples are not dense and there are many pores in the middle. After high-temperature sintering at 1100 °C, the uniformly crushed grains after ball milling grow again, and the rough surface becomes smooth, presenting a smooth salt rock structure. (NbTa) 14 (MoW) 3 O 44 The ceramic specimens are composed of uniform particles with a size of 500 nm - 1 μm. There are pores between the particles, and the voids around the particles are separated due to the shrinkage of the particles, reducing the apparent density of the ceramic bulk and the hardness of the specimens. Figure 19 (a) and 19(d) show that the particle size of the ceramic sintered in an O 2 atmosphere is larger than that of the ceramic sintered in an Ar atmosphere, and the surface of a single grain will be smoother. Comparing Figure 19 (c) and 19(f) of the ceramic surface morphology, the spacing of the voids on the surface of the ceramic sintered in an Ar atmosphere is smaller, indicating that (NbTa) 14 (MoW) 3 O 44 in the presence of oxygen, the grain growth rate is faster, the density decreases, and the hardness decreases.

[0223] X-ray diffraction was used to analyze the (NbTa) prepared by the present invention under different temperature conditions 14 (MoW) 3 O 44 ceramic materials. The relationship between temperature and lattice parameters obtained by analysis is as follows Figure 20 shown. The results show that the lattice parameters a, b, and c of the prepared materials change regularly with the increase of temperature. It can be seen that with the increase of temperature, the lattice parameters a and b show a gradually increasing trend, that is, the whole lattice expands in the a and b directions, the lattice parameter c first decreases and then increases, and the unit cell volume V finally shows an increasing trend. From 300 K to 1673 K, the lattice parameters a and b change from to c changes from to V changes from to

[0224] According to the calculation formula of the thermal expansion coefficient and polynomial fitting, the thermal expansion coefficients α a 、α b 、α V first decrease and then increase with the increase of temperature, and α c first increases, then decreases, and then continues to increase with the increase of temperature. Among them, the sample has α a = 2.306 μK -1 ,αb = -2.306 μK -1 , α c = -1.573 μK -1 , α v = 3.30 μK -1 , α L = 1.10 μK -1 ; At 1073 K, α a = 2.35042 K -1 , α b = 2.350 μK -1 , α c = -0.388 μK -1 , α V = 4.65 μK -1 , α L = 1.55 μK -1 .; At 1273 K, α a = 3.560 μK -1 , α b = 3.560 μK -1 , α c = -0.320 μK -1 , α V = 7.91 μK -1 , α L = 2.63 μK -1 ; At 1673 K, α a = 7.442 μK -1 , α b = 7.442 μK -1 , α c = 2.489 μK -1 , α V = 17.97 μK -1 , α L = 5.99 μK -1 . By fitting and calculating the thermal expansion coefficients in each temperature range from 300 K to 1673 K, it can be obtained that (NbTa) 14 (MoW) 3 O 44 belongs to low thermal expansion oxides in the temperature range of 300 K - 1273 K.

[0225] For (NbTa) 14 (MoW) 3 O 44 perform TG - DSC thermal analysis. As Figure 21 shown, the upper curve shows that (NbTa) 14 (MoW) 3 O 44The weight of the sample decreased slightly after 1000 °C, indicating a slight volatilization after 1000 °C. However, there were no obvious endothermic or exothermic peaks in the following DSC curve, indicating that no phase change occurred within the entire temperature measurement range.

[0226] The absorption spectra of the powder samples prepared by sintering in Ar atmosphere and in air atmosphere in the present invention at different incident wavelengths were measured using ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS) as Figure 22 shown. The Taucplot method was used to obtain the band gap E g of the oxide. According to the formula (αhv) 1 / n = B(hv - E g ), where α represents the absorption coefficient, h represents Planck's constant, ν represents the incident light frequency, B is a proportionality constant, and E g is the band gap of the semiconductor. For indirect band gap semiconductors, n = 2. The band gap Eg of (NbTa) 14 (MoW) 3 O 44 prepared by solid-phase sintering in Ar atmosphere was measured to be Eg = 2.16 eV, and the band gap Eg of (NbTa) 2 (MoW) 14 (MoW) 3 O 44 prepared by solid-phase sintering in O

[0227] The thermal diffusivity D of the materials prepared in the present invention was measured using a laser flash thermal conductivity meter. The thermal conductivity κ tot was calculated by κ p = D × ρ × C p . The density ρ of the sample was measured by the Archimedes drainage method, and the specific heat C Figure 23 was calculated by the Dulong-Petit formula. The relationship between the thermal conductivity and temperature is as 14 (MoW) 3 O 44 of the ceramic materials sintered in different atmospheres was investigated. It was found that the number of oxygen vacancies decreased during sintering in air atmosphere, and it was found that the thermal conductivity of all samples decreased with increasing temperature. The κAr of the (NbTa) 14 (MoW) 3 O 44 sample was 1.24 W·m -1 ·K -1 @300 K, and κO 2 = 1.15 W·m -1 ·K -1 @300 K. The (NbTa) 14 (MoW) 3 O44 The thermal conductivity is higher than that of sintering in an air atmosphere. It is found that oxygen supplementation does not have an absolutely beneficial effect on the thermal conductivity. Instead, it is more related to the crystal structure and element mixed occupancy of the material itself.

[0228] Example 7

[0229] This example provides a method for preparing a novel medium-entropy oxide (NbTa) 12 WO 33 using Nb as the matrix and realizing it through element doping and the introduction of oxygen vacancies. 12 (MoW)O 33 .

[0230] Ta powder with a purity of 99.9% 2 O 5 powder, WO powder with a purity of 99.9% 3 Nb powder with a purity of 99.9% 2 O 5 powder, MoO powder with a purity of 99.9% 3 are weighed according to the stoichiometric ratio of Ta 2 O 5 :Nb 2 O 5 :MoO 3 :WO 3 = 3:3:0.5:0.5, and carefully ground in a mortar; then the uniformly mixed sample is cold-pressed into a shape using a tablet press, placed in a quartz tube, evacuated, and the quartz tube is sealed with a hydrogen-oxygen flame; then the sample is sintered, heated from room temperature to 1000 °C in 360 min, held for 24 h, naturally cooled to room temperature in a muffle furnace, and then the sample is taken out and carefully ground to obtain the medium-entropy oxide (NbTa) 12 WO 33 -type 12 (MoW)O 33 phase powder.

[0231] At the same time, a powder sample for solid-phase sintering in an air atmosphere was also prepared for comparison. Except for the different atmosphere, other conditions were the same as those for vacuum solid-phase sintering.

[0232] Among them, the structure diagram of Nb 12 WO 33 is as shown in Figure 24 , where (a) is the 3D view; (b) is the side view on the ac plane. Based on the structure of Nb 12 WO 33 as shown in Figure 24 , Nb 12 WO 33 consists of Nb-O 6 distorted octahedra and W-O4 It is composed of tetrahedrons and shows an ordered structure when viewed from a 3D perspective. According to the average atomic volume theory, Ta elements of the same main group and the same valence state are doped with Nb atoms, and Mo elements of the same main group and the same valence state are doped at the W atom position. A new type of (NbTa) 12 (MoW)O 33 medium-entropy oxide is prepared by solid-phase sintering.

[0233] Take the (NbTa) 12 (MoW)O 33 powder sample prepared in vacuum above. Use an X-ray powder diffractometer to collect its X-ray diffraction (XRD) pattern, as Figure 25 shown. At room temperature, the refined diffraction peaks of (NbTa) 12 (MoW)O 33 have no obvious miscellaneous peaks. The reliability factor obtained from the refined results, among which the reliability factor of (NbTa) 12 (MoW)O 33 is within a reasonable range. It can be seen from the XRD pattern that most of the diffraction peak fitting results are good and there are no impurity diffraction peaks, indicating a high phase purity of the synthesized material.

[0234] Take the (NbTa) 12 (MoW)O 33 powder sample prepared by vacuum solid-phase sintering above. Use a scanning electron microscope to perform morphological characterization and EDS elemental analysis on it, as Figure 26 shown. Among them, (NbTa) 12 (MoW)O 33 shows that the microscopic grains are of a rock salt structure with a size of about 1 μm. Perform an EDS point scan on a single grain and find that the ratio of Ta and Nb elements is close to an equal ratio, and the ratio of Mo and W elements is also close to an equal ratio. Figure 27 Mapping surface scan shows that in (NbTa) 12 (MoW)O 33 a single grain, the distribution of Nb, Ta, Mo, W, and O elements is uniform, indicating the successful synthesis of the Nb 12 WO 33 type medium-entropy oxide (NbTa) 12 (MoW)O 33 .

[0235] Example 8

[0236] In this example, the new type of medium-entropy oxide (NbTa) 12 WO 33 prepared using the matrix in Example 7 is further sintered to prepare a ceramic material, and its thermal properties are explored. 12 (MoW)O 33

[0237] Take the (NbTa) obtained by the above vacuum preparation 12 (MoW)O 33 The powder material is ball-milled using a planetary ball mill with a ball-to-material ratio of 10:1, large balls: medium balls: small balls = 2:6:4, and ball-milled for 6 h at a speed of 400 rpm. The slurry obtained by ball milling is placed in a drying oven at 100 °C for 24 h of drying to obtain a powder raw material with a smaller particle size. The powder is mixed with 5% concentration of PVA for ceramic preparation. The powder obtained by vacuum solid-phase sintering is transferred to an agate mortar for grinding. During the grinding process, 5% concentration of PVA is added. After uniform grinding, the sample is loaded into a 12.8 mm tablet mold for tablet pressing. At a pressure of 8 MPa and holding for 2 min, a cylindrical green body with a diameter of 12.8 mm and a height of about 1.5 mm is finally pressed. The green body is placed in a clean alumina high-temperature boat with a layer of alumina powder at the bottom, and then the boat is placed in an Ar atmosphere sintering tube furnace and held at 700 °C for 2 h for degassing. The degassed sample is reloaded into a clean alumina boat and sintered at a rate of 3 °C / min from room temperature to 1100 °C sintering temperature in an Ar atmosphere and an air atmosphere environment respectively. After holding for 3 h, it is naturally cooled to room temperature to obtain a pure ceramic bulk sample.

[0238] The SEM images of the ceramic bulk material prepared by the present invention at different magnifications are as Figure 28 shown. It can be clearly observed from the figure that the ceramic sample is not dense and there are many pores in the middle. After high-temperature sintering at 1100 °C, the uniformly broken grains after ball milling grow again, and the rough surface becomes smooth, presenting a smooth salt rock structure. (NbTa) 14 (MoW) 3 O 44 The ceramic specimen is composed of uniform particles of 500 nm–1 μm, and there are pores less than 200 nm between the particles. O 2 The particle size of the ceramic sintered in the O atmosphere is larger than that of the ceramic sintered in the Ar atmosphere, and the surface of a single grain will be smoother. Comparing Figure 28 (c) and 28(f) ceramic surface morphologies, O 2 the surface void spacing of the ceramic sintered in the O atmosphere is smaller, indicating that (NbTa) 12 (MoW)O 33 in the presence of oxygen, the grain growth rate is faster and the porosity decreases.

[0239] The (NbTa) prepared by the present invention under different temperature conditions is analyzed by X-ray diffraction 12 (MoW)O 33 ceramic material, and the relationship between temperature and lattice parameter obtained by analysis is as Figure 29As shown, the results show that the lattice parameters a, b, and c of the prepared material change regularly with the increase in temperature. It can be seen that with the increase in temperature, the lattice parameters a and c show a gradually increasing trend, while b shows a gradually decreasing trend, that is, the whole lattice expands in the a and c directions and contracts in the b direction, and the unit cell volume V finally shows an increasing trend. From 300K to 1673K, the lattice parameter a changes from to b changes from to c changes from to V changes from to According to the calculation formula of the thermal expansion coefficient and polynomial fitting, the thermal expansion coefficients α a , α c , and α V first decrease and then increase with the increase in temperature, and α b first increases and then decreases with the increase in temperature. Among them, when the sample is at 300K, α a = 1.746 μK -1 , α b = -0.724 μK -1 , α c = 1.340 μK -1 , α V = 4.82 μK -1 , α L = 1.61 μK -1 ; at 1073K, α a = 2.326 μK -1 , α b = -0.056 μK -1 , α c = 1.983 μK -1 , α V = 5.35 μK -1 , α L = 1.78 μK -1 ; at 1273K, α a = 2.736 μK -1 , α b = -0.051 μK -1 , α c = 2.390 μK -1 , α V = 6.74 μK -1 , α L = 2.25 μK -1 ; at 1673K, α a = 3.829 μK -1 , α b = -0.248 μK-1 , α c = 3.410 μK -1 , α V = 11.07 μK -1 , α L = 3.69 μK -1 . By fitting and calculating the thermal expansion coefficients in each temperature range from 300 K to 1673 K, it can be obtained that (NbTa) 12 (MoW)O 33 belongs to low thermal expansion oxides in the temperature range of 300 K - 1273 K.

[0240] For (NbTa) 12 (MoW)O 33 TG-DSC thermal analysis was carried out. As Figure 30 shown, from the TG curve on the upper side, it was found that the weight of the (NbTa) 12 (MoW)O 33 sample basically did not change, and there was no step-like mutation, indicating that (NbTa) 12 (MoW)O 33 has no water absorption and good thermal stability. From the DSC curve on the lower side, it can be seen that there is no endothermic peak or exothermic peak during the heating stage from 25 - 1100 °C, indicating that (NbTa) 12 (MoW)O 33 has good thermal stability at 1100 °C.

[0241] The absorption spectra of the powder samples prepared by sintering in Ar atmosphere and in air atmosphere in the present invention at different incident wavelengths were measured using ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS) as Figure 31 shown. The Taucplot method was used to obtain the band gap E g of the oxide. According to the formula (αhv) 1 / n = B(hv - E g ), where α represents the absorption coefficient, h represents Planck's constant, ν represents the incident light frequency, B is a proportionality constant, and E g is the band gap of the semiconductor. For indirect band gap semiconductors, n = 2. The band gap Eg = 2.71 eV of (NbTa) 12 (MoW)O 33 prepared by solid-phase sintering in Ar atmosphere was measured, and the band gap Eg = 2.93 eV of (NbTa) 2 prepared by solid-phase sintering in O 12 (MoW)O 33 atmosphere was measured. It shows the characteristics of wide band gap semiconductors and belongs to wide band gap semiconductor oxide materials.

[0242] The thermal diffusivity D of the material prepared by the present invention was measured using a laser flash thermal conductivity meter, and the thermal conductivity κ was calculated by tot κ = D × ρ × C p . The density ρ of the sample was measured by the Archimedes drainage method, and the specific heat C was calculated by p the Dulong-Petit formula. The relationship between the thermal conductivity and temperature is as shown in Figure 32 . The thermal transport properties of (NbTa) 12 (MoW)O 33 ceramic materials sintered in different atmospheres were studied. It was found that the number of oxygen vacancies decreased during sintering in air, and the thermal conductivity of all samples decreased with increasing temperature. The thermal conductivity of the (NbTa) 12 (MoW)O 33 sample κAr = 1.06 W·m -1 ·K -1 @ 300 K, κO 2 = 1.39 W·m -1 ·K -1 @ 300 K. The thermal conductivity of (NbTa) 12 (MoW)O 33 prepared in air is higher than that sintered in Ar atmosphere. The high-entropy structure design can introduce a large number of highly disordered oxygen vacancies. The initial raw material synthesis method is vacuum solid-phase sintering, and the raw materials themselves contain oxygen vacancies. However, the results show that oxygen supplementation does not have an absolutely beneficial effect on the thermal conductivity. More importantly, it is related to the crystal structure and element mixing position of the material itself.

[0243] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A series of medium or high entropy oxides, characterized in that: Ta8W9O is a bimetallic oxide composed of VB and VIB group elements and has a tetragonal tungsten bronze structure. 47 It is a matrix whose lattice sites of group VB or group VIB elements are doped with one or more elements of the same group and of the same valence; The molecular expression of the medium-entropy or high-entropy oxide is (M A )8(M B )9O 47 , where M A is element Ta or a combination of Ta and Nb, M B It is the element W or a combination of W and Mo.

2. A series of medium or high entropy oxides according to claim 1, characterized in that: The molecular expression of the intermediate entropy oxide is (Nb x Ta 1-x )8W9O 47 (0≤x<1) or Ta8(W 1-y Mo y )9O 47 (0≤y<1); The molecular expression of the high entropy oxide is (Nb x Ta 1-x )8(Mo y W 1-y )9O 47 (0≤x<1),(0≤y<1); Preferably, the medium-entropy or high-entropy oxide has a stable unit cell structure within a temperature range of 300K to 1673K.

3. A series of medium or high entropy oxides, characterized in that: With tungsten bronze structure, bimetallic oxide Nb composed of VB group and VIB group elements 14 W3O 44 The matrix is ​​a lattice site of a VB group or VIB group element doped with one or more elements of the same group and the same valence state; the molecular expression of the medium entropy oxide is (M A ) 14 (M B )3O 44 , where M A is Ta or a combination of Ta and Nb, M B It is W or a combination of W and Mo.

4. A series of medium or high entropy oxides according to claim 3, characterized in that: The molecular expression of the intermediate entropy oxide is (Nb 1-x Ta x ) 14 (Mo y W 1-y )3O 44 (0≤x<1),(0≤y<1); Preferably, the medium-entropy or high-entropy oxide has a stable unit cell structure within a temperature range of 300K to 1673K.

5. A series of medium or high entropy oxides, characterized in that: With tungsten bronze structure, bimetallic oxide Nb composed of VB group and VIB group elements 12 WO 33 The matrix is ​​a lattice site of a VB group or VIB group element doped with one or more elements of the same group and the same valence state; the molecular expression of the medium entropy oxide is (M A ) 12 (M B ) 33 , where M A is Ta or a combination of Ta and Nb, M B It is W or a combination of W and Mo.

6. A series of medium or high entropy oxides according to claim 5, characterized in that The molecular expression of the intermediate entropy oxide is (Nb 1-x Ta x ) 12 (Mo y W 1-y ) 33 (0≤x<1),(0≤y<1); Preferably, the medium-entropy or high-entropy oxide has a stable unit cell structure within a temperature range of 300K to 1673K.

7. The method for preparing a series of medium-entropy or high-entropy oxides according to any one of claims 1 to 6, characterized in that: include: Weighing a precursor of an oxide of a VB group element and a precursor of an oxide of a VIB group element according to a molar ratio, wherein the VB group element is selected from Nb and Ta, and the VIB group element is selected from Mo and W; The precursors are mixed uniformly according to a certain proportion and ground into powder; Pressing the powder into a shape and then sintering it; The sintered product is cooled and then ground again to obtain medium-entropy or high-entropy oxides.

8. The preparation method according to claim 7, characterized in that: The molecular formula of the prepared medium-entropy or high-entropy oxide is (M A )8(M B )9O 47 , where M A It is element Ta or Ta and Nb in proportion, M B The element is W or a combination of W and Mo in proportion, and the method comprises: The precursor containing the VB group element and the precursor containing the VIB group element are weighed according to the desired molar ratio, wherein: When M A When it is Ta, weigh Ta2O5; When M A When Ta and Nb are combined in proportion, Ta2O5 and Nb2O5 are weighed, preferably in a molar ratio of 1:1; When M B When it is W, weigh WO3; When M B When W and Mo are combined in proportion, WO3 and MoO3 are weighed, preferably in a molar ratio of 1:1; The weighed precursors are mixed evenly and ground into powder; Pressing the powder into a shape and then sintering it; The sintered product is cooled and then ground again to obtain medium-entropy or high-entropy oxides; Or, the molecular expression of the prepared medium entropy oxide is (M A ) 14 (M B )3O 44 , where M A is Ta or a combination of Ta and Nb, M B is W or a combination of W and Mo, and the method comprises: The precursor containing the VB group element and the precursor containing the VIB group element are weighed according to the desired molar ratio, wherein: When M A When it is Ta, weigh Ta2O5; When M A When Ta and Nb are combined in proportion, Ta2O5 and Nb2O5 are weighed, preferably in a molar ratio of 1:1; When M B When it is W, weigh WO3; When M B When W and Mo are combined in proportion, WO3 and MoO3 are weighed, preferably in a molar ratio of 1:1; The weighed precursors are mixed evenly and ground into powder; Pressing the powder into a shape and then sintering it; The sintered product is cooled and then ground again to obtain a medium entropy oxide; Or, the molecular expression of the prepared medium entropy oxide is (M A ) 12 (M B ) 33 , where M A is Ta or a combination of Ta and Nb, M B is W or a combination of W and Mo, and the method comprises: The precursor containing the VB group element and the precursor containing the VIB group element are weighed according to the desired molar ratio, wherein: When M A When it is Ta, weigh Ta2O5; When M A When Ta and Nb are combined in proportion, Ta2O5 and Nb2O5 are weighed, preferably in a molar ratio of 1:1; When M B When it is W, weigh WO3; When M B When W and Mo are combined in proportion, WO3 and MoO3 are weighed, preferably in a molar ratio of 1:1; The weighed precursors are mixed evenly and ground into powder; Pressing the powder into a shape and then sintering it; The sintered product is cooled and then ground again to obtain a medium entropy oxide; Preferably, the molecular formula of the intermediate entropy oxide is (Nb 0.5 Ta 0.5 )8W9O 47 When the stoichiometric ratio of Ta2O5, Nb2O5 and WO3 is 2:2:9, Ta2O5 and Nb2O5 are weighed as precursors of the VB group elements in a molar ratio of 1:1, and WO3 is weighed as a precursor of the VIB group elements. Preferably, the molecular formula of the high entropy oxide is (Nb 0.5 Ta 0.5 )8(Mo 0.5 W 0.5 )9O 47 When, Ta2O5 and Nb2O5 are weighed in a 1:1 molar ratio as precursors of VB group elements, and WO3 and MoO3 are weighed in a 1:1 molar ratio as precursors of VIB group elements; wherein the stoichiometric ratio of Ta2O5, Nb2O5, MoO3 and WO3 is 2:2:4.5:4.5; Preferably, the molecular formula of the intermediate entropy oxide is (NbTa) 14 (MoW)3O 44 When the stoichiometric ratio of Ta2O5, Nb2O5, MoO3 and WO3 is 3.5:3.5:1.5:1.5, Ta2O5 and Nb2O5 are weighed as precursors of the VB group elements in a molar ratio of 1:1, and WO3 and MoO3 are weighed as precursors of the VIB group elements in a molar ratio of 1:

1. Preferably, the molecular formula of the intermediate entropy oxide is (NbTa) 12 (MoW)O 33 When, Ta2O5 and Nb2O5 are weighed in a 1:1 molar ratio as precursors of VB group elements, and WO3 and MoO3 are weighed in a 1:1 molar ratio as precursors of VIB group elements; wherein the stoichiometric ratio of Ta2O5, Nb2O5, MoO3 and WO3 is 3:3:0.5:0.5; Preferably, the sintering process is one of vacuum solid phase sintering, spark plasma sintering and hot pressing sintering; Preferably, the specific process of vacuum solid phase sintering is: the mixed powder is pressed into tablets and placed in a quartz tube, which is sealed after vacuuming, and then heated for vacuum solid phase sintering; Preferably, during the vacuum solid phase sintering, the sintering atmosphere is Ar atmosphere or air atmosphere; the sintering temperature is 900-1200° C., preferably 1000-1100° C.; the heating rate is 1-3° C. / min; and the sintering time is 20-24 h.

9. A ceramic material, characterized in that: Prepared from a series of medium-entropy or high-entropy oxides as described in any one of claims 1 to 6; Preferably, the method for preparing the ceramic material comprises: The medium-entropy or high-entropy oxide is subjected to ball milling to be made into a green embryo, which is then subjected to plastic removal, sintered, and cooled to obtain the green embryo; Preferably, during the ball milling treatment, the ball milling time is 6 to 24 hours; the ball milling speed is 200-600 revolutions; the ball-to-material ratio of the ball milling is (8-12):1; Preferably, the ball milling treatment is followed by a drying treatment, wherein the drying temperature is 100° C. and the drying time is 24 to 48 hours; Preferably, during the plastic removal treatment, the temperature is 600-700°C, the plastic removal time is 2-4h, and the heating rate is 1-3°C / min; Preferably, during the sintering, the sintering atmosphere is Ar atmosphere or air atmosphere; the ceramic sintering temperature is 1000-1100° C., the heating rate is 1-3° C. / min, and the sintering time is 3-24 h.

10. Application of the ceramic material according to claim 9 in precision instruments, aerospace, and energy storage.

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