A method for preparing single-phase high entropy oxide powder based on molten salt method

Abstract

A method for preparing single-phase high-entropy oxide powder by molten salt method. In this invention, single-phase uniform (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 high-entropy oxide powder is successfully prepared by molten salt method at a relatively low temperature. By adjusting the molten salt components and heat treatment temperature, the phase composition, morphology and particle size of (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 high-entropy powder are controlled. The technical solution of this invention enriches the preparation process of high-entropy oxide powder materials. The obtained (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 high-entropy oxide powder has the advantages of high purity, good crystallinity, uniform distribution of each component element, and good particle dispersibility. Moreover, the technical solution of this invention has the characteristics of low synthesis temperature, short synthesis cycle and simple process.

Description

Technical Field

[0001] The invention relates to the technical field of ferroelectric high entropy ceramic materials, and in particular to a method for preparing single-phase high entropy oxide powder based on a molten salt method. Background Art

[0002] "High entropy" is a new material design concept. In recent years, it has gradually expanded from the field of high entropy alloys to the research of ceramic materials. High entropy materials are a new type of solid solution materials containing five or more elements. Due to their unique physical properties and high potential value, they have attracted the interest of many researchers. The earliest high entropy metal material studied was high entropy alloys. Due to their good mechanical properties, oxidation resistance and thermodynamic mechanical properties, high entropy materials gradually developed into high entropy ceramics. As a new ceramic material system that has gradually developed on the basis of high entropy alloys in recent years, high entropy ceramics have only been around for a few years, but their emergence has provided new concepts and routes for the development of non-metallic materials with excellent performance. In 2015, Rost et al. first reported (MgNiCoCuZn)O oxide high entropy ceramics, and different high entropy ceramic systems such as borides and nitrides have been reported one after another. As the entropy of these high entropy materials increases, the dipole moment, polarization strength and lattice thermal conductivity inside the material will decrease, causing changes in their macroscopic electrical properties. Among them, (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 ceramics, due to the disorder of microscopic components after high entropy treatment, have diffuse phase transition and frequency dispersion, and are typical relaxor ferroelectric materials. The high entropy configuration affects its internal crystal structure, thereby changing its physical properties and making it exhibit unique electrical properties.

[0003] The earliest high-entropy ceramics were prepared by solid-phase reaction method, that is, the raw materials were fully mixed and partially dissolved by ball milling, and then the mixed raw materials were fully calcined at high temperature to form a uniform and single high-entropy phase. Since high-entropy ceramics are a single-phase multi-component solid solution formed by 5 or more elements at the A or B position of the lattice. Researchers usually use nano-scale raw materials, pre-treat the raw materials by ball milling, or increase the heat treatment temperature and other means to increase the reaction driving force of the reactant ions during the heat treatment process to obtain a single-phase high-entropy solid solution. At the same time, in order to prevent the high-entropy phase formed during the cooling process from being dissolved, separated or precipitated as a second phase, people usually use rapid cooling methods such as quenching to prepare it. However, the solid-phase method for preparing high-entropy ceramics has a high reaction temperature, a long reaction time, difficulty in accurately controlling the product ratio, high energy consumption, and low efficiency, which makes the preparation process of high-entropy ceramic materials complex and costly.

[0004] Document "Dielectric properties and electrocaloric effect of high-entropy (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3ceramic" was synthesized by solid phase method with high configuration entropy single phase uniform (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 powder, but when the calcination temperature is lower than 900℃, an obvious second phase exists in the ceramic powder. Summary of the invention

[0005] In order to overcome the shortcomings of the above-mentioned prior art, the object of the present invention is to provide a method for preparing single-phase high entropy oxide powder based on a molten salt method, by adjusting the molten salt composition and the heat treatment temperature to control (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 high entropy oxide powder phase composition, morphology and particle size, in order to solve the technical problem that the solid phase method in the prior art is difficult to prepare single-phase high entropy oxide powder at a lower temperature, the technical scheme of the present invention enriches the preparation process of high entropy oxide powder materials, and the obtained (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 high entropy oxide powder has the advantages of high purity, good crystallinity, uniform distribution of various component elements, and good particle dispersibility. The technical solution of the present invention has the characteristics of low synthesis temperature, short synthesis cycle, and simple process.

[0006] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is:

[0007] A method for preparing single-phase high entropy oxide powder based on a molten salt method comprises the following steps:

[0008] Step 1: Weigh the raw materials and mix the molten salt

[0009] Using pure Na2CO3, Bi2O3, BaCO3, SrCO3, CaCO3 and TiO2 as raw materials, according to the chemical formula Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2) The molar ratio of Na, Bi, Ba, Sr, Ca and Ti elements in TiO3 is weighed; the corresponding masses of Na2CO3, Bi2O3, BaCO3, SrCO3, CaCO3 and TiO2 are weighed; molten salt is added to the weighed raw materials, and the mass ratio of the raw materials to the molten salt is 1:(1-4), to obtain an oxide mixture containing molten salt;

[0010] Step 2: Grind and dry

[0011] The oxide mixture containing molten salt obtained in step 1 is ground with ethanol as a liquid medium to obtain a uniformly mixed wet material; the wet material is dried at a drying temperature of 50-100° C. for a drying time of 4-10 hours to obtain a dried oxide mixture;

[0012] Step 3: Low temperature calcination

[0013] Calcine the oxide mixture dried in step 2, and cool it to room temperature in the furnace to obtain a cooled calcined product;

[0014] Step 4: Preparation (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 high entropy oxide powder

[0015] The cooled calcined product obtained in step 3 was repeatedly rinsed with deionized water and filtered. The Cl - until the washing liquid contains no Cl - ; will not contain Cl - The calcined product is dried at a temperature of 50-100° C. for 4-10 h, and the dried calcined product is ground for 5-20 min to obtain (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 high entropy oxide powder.

[0016] The molten salt added in step 1 is NaCl, KCl or NaCl-KCl.

[0017] The mass ratio of NaCl to KCl in the NaCl-KCl is 1:(1-2).

[0018] The grinding time in step 2 is 0.5-3h.

[0019] The particle size of the wet material after grinding in step 2 is 1-10 μm.

[0020] In step 3, the calcination temperature is 700-850° C., the holding time is 2-8 hours, the heating rate is 2-5° C. / min, and the atmosphere is air.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The present invention successfully prepared a single-phase high entropy oxide powder at a relatively low temperature (700°C) by a molten salt method. The synthesis temperature in the present invention is similar to that of the solid phase method (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 ) Compared with TiO3 high entropy powder, it reduces the reaction temperature of the high entropy oxide material preparation process by 200℃, saving costs and reducing energy consumption.

[0023] 2. The present invention adjusts the molten salt composition and determines that the molten salt medium is more suitable for preparing (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 ) TiO3 high entropy powder molten salt medium, compared with single salt, NaCl-KCl composite salt prepared (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )The TiO3 high entropy powder particles are evenly distributed and have a uniform particle size of about 0.5 μm.

[0024] In summary, the present invention successfully prepares a single-phase uniform (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 high entropy oxide powder, by adjusting the molten salt composition and heat treatment temperature to control (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )The phase composition, morphology and particle size of TiO3 high entropy powder have the advantages of high powder purity, uniform distribution of various component elements, low synthesis temperature, short preparation cycle and simple process. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is the XRD diagram of the present invention when the calcination temperature is 750°C, wherein: Figure 1(a) The molten salt used is KCl, Figure 1 (b) The molten salt used is NaCl-KCl, Figure 1 (c) The molten salt used is NaCl.

[0026] Figure 2 is a SEM image of the calcination temperature of the present invention at 750°C, wherein: Figure 2 (a) The molten salt used is KCl, Figure 2 (b) The molten salt used is NaCl-KCl, Figure 2 (c) The molten salt used is NaCl.

[0027] Figure 3 is a particle size distribution diagram of the present invention at a calcination temperature of 750°C, wherein: Figure 3 (a) The molten salt used is KCl, Figure 3 (b) The molten salt used is NaCl-KCl, Figure 3 (c) The molten salt used is NaCl.

[0028] Figure 4 is the XRD diagram of the molten salt type of NaCl-KCl of the present invention, wherein, Figure 4 (a) Temperature is 600°C, Figure 4 (b) Temperature is 700°C, Figure 4 (c) Temperature is 750°C, Figure 4 (d) Temperature is 800°C, Figure 4 (e) The temperature is 850°C.

[0029] Figure 5 This is a TEM image of the molten salt type of NaCl-KCl at a calcination temperature of 700°C of the present invention.

[0030] Figure 6 This is the SAED diagram of the molten salt type of NaCl-KCl at a calcination temperature of 700° C. in the present invention.

[0031] Figure 7 This is an MTEM image of the molten salt type of NaCl-KCl at a calcination temperature of 700°C of the present invention. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0033] A method for preparing single-phase high entropy oxide powder based on a molten salt method comprises the following steps:

[0034] The main raw materials used in the experiment are analytical grade Na2CO3 (purity 99.0%, Sinopharm Group), Bi2O3 (purity 99.0%, Sinopharm Group), BaCO3 (purity 99.0%, Sinopharm Group), SrCO3 (purity 99.0%, Sinopharm Group), CaCO3 (purity 99.0%, Sinopharm Group), TiO2 (purity 99.0%, Sinopharm Group), NaCl (purity 99.8%, Sinopharm Group), KCl (purity 99.5%, Sinopharm Group), and the liquid medium is deionized water or ethanol (chemically pure, Sinopharm Group).

[0035] Step 1: Weigh the raw materials and mix the molten salt

[0036] Using pure Na2CO3, Bi2O3, BaCO3, SrCO3, CaCO3 and TiO2 as raw materials, according to the chemical formula (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 ) The molar ratio of Na, Bi, Ba, Sr, Ca and Ti elements in TiO3 is as follows: weigh the corresponding masses of Na2CO3, Bi2O3, BaCO3, SrCO3, CaCO3 and TiO2, and the molar ratio is Na2CO3:Bi2O3:BaCO3:SrCO3:CaCO3:TiO2=1:1:2:2:2:10; add molten salt to the weighed raw materials, the mass ratio of the raw materials to the molten salt is 1:(1-4), the molten salt is NaCl, KCl or NaCl-KCl, wherein the mass ratio of NaCl to KCl of the composite salt NaCl-KCl is 1:(1-2), and obtain an oxide mixture containing molten salt;

[0037] Step 2: Grind and dry

[0038] The oxide mixture containing molten salt obtained in step 1 is placed in a mortar and ground with ethanol as the liquid medium for 0.5-3 hours to obtain a uniformly mixed wet material, and the particle size of the particles in the wet material is tested by a laser particle size analyzer to be 1-10 μm; the wet material is placed in an oven for drying at a drying temperature of 50-100° C. for 4-10 hours to obtain a dried oxide mixture;

[0039] Step 3: Low temperature calcination

[0040] The oxide mixture dried in step 2 is placed in an alumina crucible, and then placed in a muffle furnace for calcination at a temperature of 700-850° C., a holding time of 2-8 hours, a heating rate of 2-5° C. / min, and an air atmosphere, and then cooled to room temperature in the furnace to obtain a cooled calcined product;

[0041] Step 4: Preparation (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 high entropy oxide powder

[0042] The cooled calcined product obtained in step 3 was repeatedly rinsed with deionized water and filtered. The Cl - until the washing liquid contains no Cl - The concentration of silver nitrate is 1-2 mol / L, the content of silver nitrate is 3-5 drops, and the filtrate does not change color within 5-30 minutes, which proves that the filtrate does not contain Cl - ; will not contain Cl - The calcined product is washed once with ethanol, filtered, and then placed in an oven for drying at a temperature of 50-100°C for 4-10 hours. The dried calcined product is placed in a mortar for grinding for 5-20 minutes to obtain particles with uniform dispersion and spherical morphology (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 high entropy oxide powder.

[0043] Embodiment 1

[0044] Step 1: Weigh the raw materials and mix the molten salt

[0045] Using pure Na2CO3, Bi2O3, BaCO3, SrCO3, CaCO3 and TiO2 as raw materials, according to the chemical formula (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 ) The molar ratio of Na, Bi, Ba, Sr, Ca and Ti elements in TiO3 is as follows: weigh the corresponding masses of Na2CO3, Bi2O3, BaCO3, SrCO3, CaCO3 and TiO2, and the molar ratio is Na2CO3:Bi2O3:BaCO3:SrCO3:CaCO3:TiO2=1:1:2:2:2:10; add NaC1-KCl to the weighed raw materials, the mass ratio of the raw materials to NaC1-KCl is 1:1, and the mass ratio of NaC1 to KCl in the composite salt NaC1-KCl is 1:1, to obtain an oxide mixture containing molten salt;

[0046] Step 2: Grind and dry

[0047] The oxide mixture containing molten salt obtained in step 1 is put into a mortar, and ground with ethanol as the liquid medium for 0.5 seconds to obtain a uniformly mixed wet material, and then the particle size of the particles in the wet material is tested by a laser particle size analyzer to be 1-10 μm; the wet material is put into an oven for drying at a drying temperature of 50° C. for 10 hours to obtain a dried oxide mixture;

[0048] Step 3: Low temperature calcination

[0049] The oxide mixture dried in step 2 is placed in an alumina crucible, and then placed in a muffle furnace for calcination at a temperature of 700° C. for 2 h at a heating rate of 2° C. / min in an air atmosphere, and then cooled to room temperature in the furnace to obtain a calcined product after cooling;

[0050] Step 4: Preparation (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 high entropy oxide powder

[0051] The cooled calcined product obtained in step 3 was repeatedly rinsed with deionized water and filtered. The Cl - until the washing liquid contains no Cl - The concentration of silver nitrate is 1-2 mol / L, the content of silver nitrate is 3-5 drops, and the filtrate does not change color within 5-30 minutes, which proves that the filtrate does not contain Cl - ; will not contain Cl - The calcined product was washed once with ethanol, filtered, and then placed in an oven for drying at a temperature of 50°C for 10 h. The dried calcined product was ground in a mortar for 5 min to obtain (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 high entropy oxide powder.

[0052] Embodiment 2

[0053] Step 1: Weigh the raw materials and mix the molten salt

[0054] Using pure Na2CO3, Bi2O3, BaCO3, SrCO3, CaCO3 and TiO2 as raw materials, according to the chemical formula (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2) The molar ratio of Na, Bi, Ba, Sr, Ca and Ti elements in TiO3 is as follows: weigh the corresponding masses of Na2CO3, Bi2O3, BaCO3, SrCO3, CaCO3 and TiO2, and the molar ratio is Na2CO3:Bi2O3:BaCO3:SrCO3:CaCO3:TiO2=1:1:2:2:2:10; add NaCl to the weighed raw materials, the mass ratio of the oxide mixture to NaCl is 1:2, and obtain an oxide mixture containing molten salt;

[0055] Step 2: Grind and dry

[0056] The oxide mixture containing molten salt obtained in step 1 is put into a mortar and ground with ethanol as the liquid medium for 1.5 hours to obtain a uniformly mixed wet material. The particle size of the particles in the wet material is tested by a laser particle size analyzer to be 1-10 μm; the wet material is put into an oven for drying at a drying temperature of 65° C. for 8 hours to obtain a dried oxide mixture;

[0057] Step 3: Low temperature calcination

[0058] The oxide mixture dried in step 2 is placed in an alumina crucible, and then placed in a muffle furnace for calcination at a temperature of 750° C., a holding time of 4 h, a heating rate of 3° C. / min, and an air atmosphere, and then cooled to room temperature with the furnace to obtain a cooled calcined product;

[0059] Step 4: Preparation (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 high entropy oxide powder

[0060] The cooled calcined product obtained in step 3 was repeatedly rinsed with deionized water and filtered. The Cl - until the washing liquid contains no Cl - The concentration of silver nitrate is 1-2 mol / L, the content of silver nitrate is 3-5 drops, and the filtrate does not change color within 5-30 minutes, which proves that the filtrate does not contain Cl - ; will not contain Cl - The calcined product was washed once with ethanol, filtered, and then placed in an oven for drying at a temperature of 65°C for 8 hours. The dried calcined product was ground in a mortar for 10 minutes to obtain (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 high entropy oxide powder.

[0061] Embodiment 3

[0062] Step 1: Weigh the raw materials and mix the molten salt

[0063] Using pure Na2CO3, Bi2O3, BaCO3, SrCO3, CaCO3 and TiO2 as raw materials, according to the chemical formula (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 ) The molar ratio of Na, Bi, Ba, Sr, Ca and Ti elements in TiO3 is as follows: weigh the corresponding masses of Na2CO3, Bi2O3, BaCO3, SrCO3, CaCO3 and TiO2, and the molar ratio is Na2CO3:Bi2O3:BaCO3:SrCO3:CaCO3:TiO2=1:1:2:2:2:10; add KC1 to the weighed raw materials, the mass ratio of the oxide mixture to KC1 is 1:3, and obtain an oxide mixture containing molten salt;

[0064] Step 2: Grind and dry

[0065] The oxide mixture containing molten salt obtained in step 1 is put into a mortar and ground with ethanol as the liquid medium for 2.5 hours to obtain a uniformly mixed wet material. The particle size of the particles in the wet material is tested by a laser particle size analyzer to be 1-10 μm; the wet material is put into an oven for drying at a drying temperature of 85° C. for 6 hours to obtain a dried oxide mixture;

[0066] Step 3: Low temperature calcination

[0067] The oxide mixture dried in step 2 is placed in an alumina crucible, and then placed in a muffle furnace for calcination at a temperature of 800° C. for 6 h at a heating rate of 4° C. / min in an air atmosphere, and then cooled to room temperature in the furnace to obtain a calcined product after cooling;

[0068] Step 4: Preparation (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 high entropy oxide powder

[0069] The cooled calcined product obtained in step 3 was repeatedly rinsed with deionized water and filtered. The Cl - until the washing liquid contains no Cl -The concentration of silver nitrate is 1-2 mol / L, the content of silver nitrate is 3-5 drops, and the filtrate does not change color within 5-30 minutes, which proves that the filtrate does not contain Cl - ; will not contain Cl - The calcined product was washed once with ethanol, filtered, and then placed in an oven for drying at 85°C for 6 hours. The dried calcined product was ground in a mortar for 15 minutes to obtain (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 high entropy oxide powder.

[0070] Embodiment 4

[0071] Step 1: Weigh the raw materials and mix the molten salt

[0072] Using pure Na2CO3, Bi2O3, BaCO3, SrCO3, CaCO3 and TiO2 as raw materials, according to the chemical formula (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 ) The molar ratio of Na, Bi, Ba, Sr, Ca and Ti elements in TiO3 is as follows: weigh the corresponding masses of Na2CO3, Bi2O3, BaCO3, SrCO3, CaCO3 and TiO2, and the molar ratio is Na2CO3:Bi2O3:BaCO3:SrCO3:CaCO3:TiO2=1:1:2:2:2:10; add NaC1-KCl to the weighed raw materials, the mass ratio of the oxide mixture to NaC1-KCl is 1:4, and the mass ratio of NaC1 to KCl in the composite salt NaC1-KCl is 1:2, to obtain an oxide mixture containing molten salt;

[0073] Step 2: Grind and dry

[0074] The oxide mixture containing molten salt obtained in step 1 is put into a mortar and ground with ethanol as the liquid medium for 3 hours to obtain a uniformly mixed wet material. The particle size of the particles in the wet material is tested by a laser particle size analyzer to be 1-10 μm; the wet material is put into an oven for drying at a drying temperature of 100° C. for 4 hours to obtain a dried oxide mixture;

[0075] Step 3: Low temperature calcination

[0076] The oxide mixture dried in step 2 is placed in an alumina crucible, and then placed in a muffle furnace for calcination at a temperature of 850° C. for 8 h at a heating rate of 5° C. / min in an air atmosphere, and then cooled to room temperature in the furnace to obtain a calcined product after cooling;

[0077] Step 4: Preparation (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 high entropy oxide powder

[0078] The cooled calcined product obtained in step 3 was repeatedly rinsed with deionized water and filtered. The Cl - until the washing liquid contains no Cl - The concentration of silver nitrate is 1-2 mol / L, the content of silver nitrate is 3-5 drops, and the filtrate does not change color within 5-30 minutes, which proves that the filtrate does not contain Cl - ; will not contain Cl - The calcined product was washed once with ethanol, filtered, and then placed in an oven for drying at a temperature of 100°C for 4 hours. The dried calcined product was ground in a mortar for 20 minutes to obtain particles with uniform dispersion and spherical morphology (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 high entropy oxide powder.

[0079] Comparative Example 1

[0080] Step 1: Weigh the raw materials and mix the molten salt

[0081] Using pure Na2CO3, Bi2O3, BaCO3, SrCO3, CaCO3 and TiO2 as raw materials, according to the chemical formula (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2) The molar ratio of Na, Bi, Ba, Sr, Ca and Ti elements in TiO3 is as follows: weigh the corresponding masses of Na2CO3, Bi2O3, BaCO3, SrCO3, CaCO3 and TiO2, and the molar ratio is Na2CO3:Bi2O3:BaCO3:SrCO3:CaCO3:TiO2=1:1:2:2:2:10; add NaC1-KCl to the weighed raw materials, the mass ratio of the oxide mixture to NaC1-KCl is 1:1, and the mass ratio of NaC1 to KCl in the composite salt NaC1-KCl is 1:1, to obtain an oxide mixture containing molten salt;

[0082] Step 2: Grind and dry

[0083] The oxide mixture containing molten salt obtained in step 1 is put into a mortar and ground with ethanol as the liquid medium for 0.5 h to obtain a uniformly mixed wet material. The particle size of the particles in the wet material is tested by a laser particle size analyzer to be 1-10 μm. The wet material is put into an oven for drying at a drying temperature of 50° C. for 10 h to obtain a dried oxide mixture.

[0084] Step 3: Low temperature calcination

[0085] The oxide mixture dried in step 2 is placed in an alumina crucible, and then placed in a muffle furnace for calcination at a temperature of 600° C. for a holding time of 2 h, a heating rate of 2° C. / min, and an air atmosphere, and then cooled to room temperature in the furnace to obtain a cooled calcined product;

[0086] Step 4: Preparation (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 high entropy oxide powder

[0087] The cooled calcined product obtained in step 3 was repeatedly rinsed with deionized water and filtered. The Cl - until the washing liquid contains no Cl - The concentration of silver nitrate is 1-2 mol / L, the content of silver nitrate is 3-5 drops, and the filtrate does not change color within 5-30 minutes, which proves that the filtrate does not contain Cl - ; will not contain Cl - The calcined product was washed once with ethanol, filtered, and then placed in an oven for drying at a temperature of 50°C for 10 h. The dried calcined product was ground in a mortar for 5 min to obtain (Na 0.2 Bi 0.2 Ba 0.2 Sr0.2 Ca 0.2 )TiO3 high entropy oxide powder.

[0088] This case is a comparative example. The process and parameters are the same as those in Example 1, but the calcination temperature in step 3 is 600°C. Figure 4 The diffraction peak intensity of the sample shown is relatively weak, and there are impurity peaks, indicating that single-phase perovskite-type high-entropy oxide powder cannot be prepared at this calcination temperature.

[0089] Prior to the technical solution of the present invention, there was no relevant literature reporting the use of a molten salt method to prepare a single-phase uniform (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 high entropy oxide powder, the present invention uses the molten salt method to obtain (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 high entropy oxide powder, having a single-phase perovskite structure, good dispersibility, and uniform distribution of each component element; Figure 1 As shown in the figure, when the calcination temperature is 750℃, single-phase perovskite-type high entropy oxide powders are prepared by using molten salt medium of NaCl, KCl or NaCl-KCl composite salt. The diffraction peaks of the products correspond to the diffraction peaks of the standard card one by one, among which the diffraction peak position of the main diffraction peak (101) crystal plane corresponding to 32.5° is the strongest, indicating that the obtained products have good crystallinity (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 high entropy powder. Figure 2 and Figure 3 It can be seen that when NaCl-KCl composite salt is used for preparation, the obtained (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 ) TiO3 high entropy powder particles are evenly distributed, with uniform particle size and particle size d 50 The particle size is about 0.70 μm, and the agglomeration phenomenon between particles is weaker than that of single salt. This is because the NaCl-KCl composite salt has a low melting point, and its lower vapor pressure provides a low-viscosity liquid environment, which accelerates the diffusion and transportation of raw materials and is beneficial to the mass and heat transfer of reactants. Therefore, the composite salt NaCl-KCl is more suitable for the preparation of (Na 0.2 Bi 0.2 Ba 0.2 Sr0.2 Ca 0.2 )The molten salt medium of TiO3 high entropy powder.

[0090] Depend on Figure 4 As shown, the molten salt medium is NaCl-KCl, and the calcination temperature is 700℃, 750℃, 800℃, 850℃ to prepare (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 high entropy powder diffraction peaks are consistent with the standard diffraction peaks, and there are no obvious impurity peaks, indicating that these four temperatures can synthesize relatively pure target products; compared with comparative example 1, a single-phase (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 high entropy powder, further verifying that the molten salt method can be used to obtain single-phase (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 high entropy powder; at the same time, compared with the solid phase method reported in the prior art (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 ) Compared with TiO3 high entropy powder, the synthesis temperature of high entropy powder prepared by molten salt method is reduced by 200℃.

[0091] Depend on Figure 5 As shown, the (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 high entropy powder presents a spherical morphology; Figure 6 From the diffraction pattern of the sample, we can see that (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 high entropy powder is a perovskite structure, referring to Na 0.5 Bi 0.5The PDF standard cards of TiO3 (JCPDF No.46-0001), CaTiO3 (JCPDF No.75-2100), SrTiO3 (JCPDF No.35-0734), and BaTiO3 (JCPDF No.31-0174) were used to calculate the interplanar spacings of (100), (110), (210), (111), and (211) through SAED diffraction spots, respectively. All satisfy the vector sum, Figure 6 correspond Figure 5 The red circle area in .

[0092] Depend on Figure 7 As shown in the figure, the (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 high entropy powder, its particle morphology is still spherical, the particle size is about 0.50μm, the particle size is reduced, the particle dispersion is good, and there is no obvious agglomeration phenomenon. At the same time, the elements Na, Ba, Bi, Sr, Ti, Ca, O, etc. in the powder particles are evenly distributed, and there is no segregation at the particle boundary position, which further verifies that the molten salt method can prepare (Na) with uniform component distribution. 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 high entropy powder.

Claims

1. A method for preparing single-phase high entropy oxide powder based on a molten salt method, characterized in that: The steps include: Step 1: Weigh the raw materials and mix the molten salt Using pure Na2CO3, Bi2O3, BaCO3, SrCO3, CaCO3 and TiO2 as raw materials, according to the chemical formula (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 ) The molar ratio of Na, Bi, Ba, Sr, Ca and Ti elements in TiO3 is weighed; molten salt is added to the weighed raw materials, and the mass ratio of the raw materials to the molten salt is 1:(1-4), to obtain an oxide mixture containing molten salt; Step 2: Grind and dry The oxide mixture containing molten salt obtained in step 1 is ground with ethanol as a liquid medium to obtain a uniformly mixed wet material; the wet material is dried at a drying temperature of 50-100° C. for a drying time of 4-10 hours to obtain a dried oxide mixture; Step 3: Low temperature calcination The oxide mixture dried in step 2 is calcined and cooled to room temperature in the furnace to obtain a cooled calcined product; the calcination temperature is 700-850°C, the holding time is 2-8h, the heating rate is 2-5°C / min, and the atmosphere is air atmosphere; Step 4: Preparation (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 high entropy oxide powder The cooled calcined product obtained in step 3 was repeatedly rinsed with deionized water and filtered. The Cl - until the washing liquid contains no Cl - ; will not contain Cl - The calcined product is dried at a temperature of 50-100° C. for 4-10 h, and the dried calcined product is ground for 5-20 min to obtain (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 high entropy oxide powder.

2. The method for preparing single-phase high entropy oxide powder based on molten salt method according to claim 1, characterized in that: The molten salt added in step 1 is NaCl, KCl or NaCl-KCl.

3. The method for preparing single-phase high entropy oxide powder based on molten salt method according to claim 2, characterized in that: The mass ratio of NaCl to KCl in the NaCl-KCl is 1:(1-2).

4. The method for preparing single-phase high entropy oxide powder based on molten salt method according to claim 1, characterized in that: The grinding time in step 2 is 0.5-3h.

5. The method for preparing single-phase high entropy oxide powder based on molten salt method according to claim 1, characterized in that: The particle size of the wet material after grinding in step 2 is 1-10 μm.

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