A method for preparing a metastable phase rare earth nickel-based oxide electronic phase change material

Abstract

The application relates to a preparation method of a metastable phase rare earth nickel-based strong correlation oxide material, and belongs to the field of phase change materials and functional materials. The target rare earth nickel-based oxide is used as a homogeneous seed crystal to promote a non-uniform nucleation process and reduce the positive Gibbs free energy of a synthesis reaction, so that a thermodynamic metastable phase rare earth nickel-based oxide ceramic is prepared under high oxygen pressure conditions. By adjusting the types and proportions of Re and B elements, the distortion degree of NiO6 and BO6 octahedrons is influenced, so that the phase transition temperature and the electric transport characteristics of the metastable phase rare earth nickel-based oxide are adjusted; the synthesis pressure of the material can be obviously reduced, the process flow of the prepared material is simplified, and the metastable phase rare earth nickel-based oxide can be prepared in a large amount to meet the preparation requirements of strong correlation logic devices, sudden change type sensitive resistor devices and infrared camouflage devices.

Description

Technical Field

[0001] This invention belongs to the fields of oxide semiconductors, phase change materials and functional materials. Background Technology

[0002] Among numerous oxide semiconductors, metastable rare-earth nickel-based oxides ReNiO3 exhibit a typical CaTiO3 perovskite structure, where Re is primarily composed of rare-earth and alkaline-earth elements. ReNiO3 possesses a characteristic temperature (T0). MIT The phase transition characteristics of metal-insulators triggered by ) at T MIT The above exhibits an orthorhombic crystal structure (space group: Pbnm), at which point ReNiO3 has high crystal symmetry and exhibits metallic properties; when the temperature decreases to T... MIT When ReNiO3 transforms into a monoclinic crystal structure (space group: P21 / n), the nickel element undergoes valence bond disproportionation and reduces the symmetry of the NiO6 octahedron. The electrical transport properties of ReNiO3 change from metallic to semiconductor. [1-3] The electrical transport properties of metastable rare-earth nickel-based oxides can be modulated by adjusting the type of Re site elements. As the radius of rare-earth ions decreases, the distortion of the NiO6 octahedron in ReNiO3 gradually increases, improving the stability of the semiconductor phase relative to the metallic phase and lowering the metal-insulator transition temperature T. MIT This also increases accordingly. Therefore, by designing the average ionic radius of rare earth elements occupying the Re sites in the ReNiO3 perovskite structure, T can be achieved. MIT Continuous adjustment over a wide temperature range. In practical applications, this characteristic facilitates the fabrication of wide-temperature-range, abrupt-change thermistor devices, which have considerable application value in fields such as strongly correlated logic devices and infrared camouflage devices. [4-6] .

[0003] Currently, the synthesis of metastable rare-earth nickel-based oxides relies on high-pressure synthesis and high-oxygen-pressure co-solvent reaction. The high-pressure synthesis method first involves mixing rare-earth oxides, NiO, and KClO4, sealing the mixture in a platinum capsule, and then using a cylindrical graphite heater and a large press at 950 °C and 6 GPa to synthesize the material. The high-oxygen-pressure co-solvent reaction method first involves weighing the corresponding oxide raw materials according to stoichiometric ratios, weighing the co-solvent according to the proportions, and mixing it with the oxides. After homogeneous mixing, the mixture is placed in a high-pressure tube furnace and heated at 800 °C and 7 MPa to obtain rare-earth nickel-based oxide bulk materials. These bulk materials are then ground into powder, and the co-solvent and other water-soluble impurities are removed by washing, sonication, and centrifugation. After drying, metastable rare-earth nickel-based oxide powder is obtained. A binder is added to the powder, which is then cold-pressed into sheets and sintered under the same high-oxygen-pressure conditions to obtain metastable rare-earth nickel-based oxide ceramics. Existing methods for synthesizing metastable rare earth nickel-based oxides are cumbersome, requiring synthesis under high pressure at the GPa level or removal of the co-solvent, and cannot produce metastable rare earth nickel-based oxide ceramics in one step. In addition, the high oxygen pressure co-solvent reaction method requires the co-solvent to completely dissolve the raw material oxide, and the target yield is limited by the amount of co-solvent used, which cannot meet the needs of large-scale production of metastable rare earth nickel-based oxide ceramics.

[0004] In summary, there is currently a lack of an effective method in the field to achieve rapid, efficient, and large-scale preparation of metastable rare-earth nickel-based oxide ceramics, which limits the application of this material in strongly correlated logic devices and abruptly sensitive resistor devices.

[0005] [1]CATALAN G. Progress in perovskite nickelate research [J]. PhaseTransitions, 2008, 81(7-8): 729-49.

[0006] [2]MARíA LUISA M. Structural, magnetic and electronic properties of perovskites (R = rare earth) [J]. J Phys: Condens Matter, 1997, 9(8): 1679.

[0007] [3]VARIGNON J, GRISOLIA MN, ÍñIGUEZ J, et al. Complete phase diagram of rare-earth nickelates from first-principles [J]. npj Quantum Materials, 2017, 2 (1)

[0008] [4]SHAHSAFI A, RONEY P, ZHOU Y, et al. Temperature-independent thermal radiation [J]. Proc Natl Acad Sci USA, 2019, 116(52): 26402-6.

[0009] [5]TORRISS B, CHAKER M, MARGOT J. Electrical and Fourier transforminfrared properties of epitaxial SmNiO3 tensile strained thin film [J]. ApplPhys Lett, 2012, 101(9).

[0010] [6]GIRARDOT C, KREISEL J, PIGNARD S, et al. Raman scattering investigation across the magnetic and metal-insulator transition in rareearth nickelateRNiO3 (R=Sm, Nd) thin films [J]. Phys Rev B, 2008, 78(10) Summary of the Invention

[0011] The purpose of this invention is to provide a method for the mass production of metastable rare-earth nickel-based oxide ceramics. The main concept is to provide homogeneous rare-earth nickel-based oxide nuclei to the oxide raw materials, promote the heterogeneous nucleation and growth process of the crystals, reduce the forward Gibbs free energy of the synthesis reaction, and thus prepare metastable rare-earth nickel-based oxide ceramics in one step without further removal of the flux, which can meet the potential application requirements of abrupt change sensitive resistor devices.

[0012] A method for preparing metastable rare earth nickel-based oxide materials, characterized in that:

[0013] 1) Design the metastable phase rare earth nickel-based oxide material composition based on the target electrical transport and phase transition characteristics. Based on the selected material composition, select the precursors of Re, Ni and transition elements and weigh them according to the stoichiometric ratio of the target metastable phase rare earth nickel-based oxide.

[0014] 2) Weigh out the target metastable rare earth nickel-based oxide with a Ni element precursor molar ratio of 0.1-50% according to the amount of precursor used, and use it as a nucleation seed crystal. Mix the seed crystal with the precursor thoroughly and cold press it into a sheet.

[0015] 3) Select the heat treatment temperature and oxygen pressure according to the target metastable rare earth nickel-based oxide: Heat the cold-pressed reactant to a high temperature in a high oxygen pressure atmosphere and hold for 0.1-48 h. After holding, slowly cool to room temperature, take out the sample, grind it into powder, and then cold-press it into a sheet again. Heat it to a high temperature in a high oxygen pressure atmosphere and hold for 0.1-48 h. Repeat the above operation 1-5 times until pure metastable rare earth nickel-based oxide ceramic is obtained.

[0016] 4) Based on metastable rare earth nickel-based oxide ceramics, further introduce electrode and other functional layer materials to prepare abrupt change thermistor devices and strongly correlated logic devices; or grind them into powder to prepare infrared camouflage coatings and laser protection coatings;

[0017] The above steps enable the efficient synthesis of rare earth nickel-based oxides that exhibit both metal-insulator phase transition and hydrogen-induced electronic phase transition and are in a thermodynamically metastable phase. The method used does not contain any liquid phase substances, is simple to operate, and can achieve large-scale production. By controlling the ratio of precursor to seed crystal, oxygen partial pressure, and heat treatment process, the hardness, morphology, and electrical transport properties of metastable rare earth nickel-based oxide ceramics can be controlled.

[0018] Furthermore, the chemical composition of the metastable rare earth nickel-based oxide synthesized in step 1) is ReNi 1-x B x O3; where Re is a single rare earth element or a combination of multiple rare earth elements, including La, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, Y; B is a single transition metal element or a combination of multiple transition metal elements, including Cr, Mn, Fe, Co; by designing the elemental composition at the Re and B sites, the phase transition temperature and the degree of resistivity abrupt change in rare earth nickel-based oxide metal insulators can be controlled. In a preferred embodiment, the sintered Nd... 0.5 Sm 0.5 The electrical transport properties of NiO3 were characterized, and Nd was measured. 0.5 Sm 0.5 The phase transition temperature of NiO3 is around 300 K, which falls within the range of phase transition temperatures for NdNiO3 and SmNiO3; in another preferred embodiment, the sintered NdNi... 0.9 Mn 0.1 The electrical transport properties of O3 were characterized, and it was found that the doping of Mn element modulates the phase transition temperature of NdNiO3 from around 200 K to around 100 K.

[0019] Further, the precursors mentioned in step 1) include oxides of rare earth elements, Ni, and transition elements, as well as carbonates, nitrates, and acetates. For carbonate, nitrate, and acetate precursors, the corresponding oxides of rare earth elements, Ni, and transition elements can be obtained by pre-calcination decomposition. The pre-calcination temperature should be 1-200 °C higher than the decomposition temperature of the corresponding carbonate, nitrate, or acetate. In a preferred embodiment, the raw materials for preparing EuNiO3 are Eu2O3, NiCO3, and EuNiO3 seed crystals. The decomposition temperature of NiCO3 is 270 °C. The NiCO3 powder is pre-calcined at 470 °C and then mixed with other powders. In another preferred embodiment, the raw materials for preparing GdNiO3 are Gd2O3, Ni(CH3COO)2, and GdNiO3 seed crystals. The decomposition temperature of Ni(CH3COO)2 is 310 °C. The raw material powders are mixed and then pre-calcined at 311 °C.

[0020] Further, the particle size of the metastable rare-earth nickel-based oxide nucleation seed crystal in step 2) is 0.1-100 μm, preferably 1-10 μm; by changing the size of the seed crystal grains, the heterogeneous nucleation process can be controlled, thereby further controlling the purity, electrical transport properties, and mechanical properties of the metastable rare-earth nickel-based oxide ceramic; in a preferred example, the raw material for preparing PrNiO3 is Pr6O 11 In another preferred embodiment, the raw materials for preparing NdNiO3 are Nd2O3, NiO, and 1 μm NdNiO3 seed crystals. After the raw materials are mixed evenly, a binder is added and the mixture is cold-pressed into a block.

[0021] Further, in step 3), the mechanical pressure range during cold pressing is 0.01-10 GPa, preferably 0.1-1 GPa. The density of the cold-pressed block can be controlled by changing the powder sample mass, the size of the cold-pressing mold, and the pressure of the tablet press, thereby further controlling the thermodynamic process during sintering. In a preferred example, the mechanical pressure of cold pressing when preparing PrNiO3 ceramic is 1 GPa, 0.2 g of raw material powder is weighed, a mold with a diameter of 6 mm is used, and the corresponding tablet press pressure is 3t. In another preferred example, when preparing Ho… 0.8 Y 0.2 The mechanical pressure for cold pressing of NiO3 ceramics is 0.1 GPa. Weigh 2.2 g of raw material powder, use a mold with a diameter of 20 mm, and the corresponding tablet press pressure is 3 t.

[0022] Further, in step 3), the heating and holding temperature required are jointly controlled by the ratio of precursor to seed crystal and the seed crystal grain size. The holding temperature is 300-1100 ℃. By changing the holding temperature, the diffusion rate of the raw materials and the non-uniform nucleation process can be controlled, thereby further controlling the mechanical properties of rare earth nickel-based oxide ceramics. Preferably, the holding temperature is 800 ℃. The single holding time is 0.1-48 h. By changing the holding time, the purity of the metastable rare earth nickel-based oxide can be controlled. Preferably, the single holding time is 24 h. The oxygen pressure is 0.2-50 MPa. By changing the oxygen pressure, the thermodynamic process of the reaction can be controlled, thereby controlling the electrical transport properties of rare earth nickel-based oxide ceramics. Preferably, the oxygen pressure is 1-10 MPa. MPa; By grinding the sample into powder and sintering it multiple times, the mixing degree between the homogeneous crystal nuclei and the oxide raw materials can be controlled, thereby further controlling the purity and electrical transport properties of rare earth nickel-based oxides. The preferred number of sintering times is 1-5 times. In one preferred example, the raw materials for preparing SmNiO3 are Sm2O3, NiO, and SmNiO3 seed crystals. After the raw materials are mixed evenly, a binder is added and cold-pressed into sheets. After holding at 1 MPa oxygen pressure and 800 ℃ for 24 h, SmNiO3 ceramic is obtained. In another preferred example, NdNi is prepared. 0.9 Fe 0.1 The raw materials for O3 are Nd2O3, NiO, Fe2O3, and NdNi. 0.9 Fe 0.1 O3 seed crystals were obtained by uniformly mixing raw materials, adding binder, cold pressing into sheets, and holding at 10 MPa oxygen pressure and 800 °C for 24 h. The sintered blocks were then ground into powder, and binder was added again, followed by holding at 10 MPa oxygen pressure and 800 °C for 24 h. This process was repeated four times to obtain NdNi. 0.9 Fe 0.1 O3 ceramics.

[0023] This invention relates to a technique for preparing thermodynamically metastable rare-earth nickel-based oxide ceramics under high oxygen pressure conditions by using a target rare-earth nickel-based oxide as a homogeneous seed crystal to promote a heterogeneous nucleation process and reduce the forward Gibbs free energy of the synthesis reaction. Compared with traditional high-pressure synthesis methods, this method can significantly reduce the synthesis pressure of the material, enabling the synthesis of thermodynamically metastable phase materials under MPa-level pressure. Compared with high-oxygen-pressure co-solvent reaction methods, this method simplifies the material preparation process, directly obtaining high-quality rare-earth nickel-based oxide ceramics without the need for additional co-solvents, reducing preparation costs, and enabling large-scale preparation of metastable rare-earth nickel-based oxides. This method allows for the control of the type and ratio of Re and B site elements, affecting the distortion degree of NiO6 and BO6 octahedra, thereby controlling the phase transition temperature and electrical transport properties of metastable rare-earth nickel-based oxides. The prepared ceramics can be applied to strongly correlated logic devices and abruptly-type thermistor devices. The prepared ceramics can be further ground into powder and applied to the preparation of infrared camouflage coatings and laser protective coatings. Attached Figure Description

[0024] Figure 1 The X-ray diffraction pattern of PrNiO3 powder prepared using the seed crystal method proposed in this invention shows that the main phase of the prepared powder is PrNiO3.

[0025] Figure 2 The X-ray diffraction pattern of SmNiO3 powder prepared using the seed crystal method proposed in this invention shows that the main phase of the prepared powder is SmNiO3.

[0026] Figure 3 The X-ray diffraction pattern of GdNiO3 powder prepared using the seed crystal method proposed in this invention shows that the main phase of the prepared powder is GdNiO3.

[0027] Figure 4 The electrical transport characteristic curves of NdNiO3 ceramics prepared using the seed crystal method proposed in this invention show that NdNiO3 ceramics exhibit a metal-insulator transition near 200 K.

[0028] Figure 5 The electrical transport characteristic curves of SmNiO3 ceramics prepared using the seed crystal method proposed in this invention show that SmNiO3 ceramics exhibit a metal-insulator transition near 400 K. Detailed Implementation

[0029] Unless otherwise specified, all raw materials used in this invention are commercially available or prepared according to conventional methods in the art. Unless otherwise defined or stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of skill in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to the methods of this invention.

[0030] Other aspects of the invention will be apparent to those skilled in the art from the disclosure herein.

[0031] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer.

[0032] Example 1: The raw material powders used in this experiment were Nd₂O₃, NiO, and NdNiO₃. First, the corresponding oxide powders were weighed according to the elemental ratio of Nd:Ni = 1:1. The raw material powders were poured into an agate mortar and mixed. Then, NdNiO₃ with a particle size of 1 μm was added as a homogeneous seed crystal according to the ratio of Nd₂O₃:NdNiO₃ = 1:0.01, and grinding continued until homogeneous. 0.2 g of the mixed powder was weighed and added to a polyvinyl alcohol solution. After grinding and drying, it was cold-pressed into discs with a diameter of 6 mm under a pressure of 3 t. After pre-firing to remove the polyvinyl alcohol, it was placed in a high-pressure furnace and oxygen was introduced to 7 MPa. The temperature was raised to 800 ℃ and held for 24 h, and finally slowly cooled to room temperature. The sintered block was removed, ground into a uniform and fine powder, and polyvinyl alcohol solution was added. It was then cold-pressed into discs, pre-fired, and placed in a high-pressure furnace and oxygen was introduced to 7 MPa. The temperature was raised to 800 ℃ and held for 24 h, and finally slowly cooled to room temperature. Repeat the above process 5 times to obtain NdNiO3 ceramic. Introducing electrodes into the ceramic can further prepare a mutation-type thermistor device. Grinding the NdNiO3 ceramic into powder can also be further applied to infrared camouflage coatings.

[0033] Example 2: The raw material powders used in this experiment were Pr6O 11 NiO, PrNiO3. First, press Pr6O 11Oxide raw materials were weighed in a NiO:PrNiO3 ratio of 1:6. 10 μm PrNiO3 powder was weighed as a homogeneous seed crystal according to a NiO:PrNiO3 ratio of 1:0.05. The oxide raw materials and the homogeneous seed crystal were poured into an agate mortar and mixed for 20 min. 0.2 g of the mixed powder was weighed and 2 drops of polyvinyl alcohol solution were added. After mixing thoroughly, a pressure of 2.5 t was applied and cold-pressed into a disc with a diameter of 6 mm. The disc was pre-fired in air at 600 ℃ for 2 h to remove polyvinyl alcohol. Then, it was held at 800 ℃ and 7 MPa oxygen pressure for 24 h. Finally, it was slowly cooled to room temperature to obtain PrNiO3 ceramic. The proportion of PrNiO3 phase in the sample was 96.26%, requiring no further grinding and sintering. Introducing electrodes into PrNiO3 ceramic can further enable the fabrication of magnetoelectronic devices. Grinding PrNiO3 ceramic into powder can also be further applied to infrared camouflage coatings.

[0034] Example 3: The raw materials used in this experiment were Sm2O3, NiO, and SmNiO3 with a diameter of 1 μm. First, the oxide powder and homogeneous seed crystals were weighed according to the ratio of Sm2O3:NiO:SmNiO3 = 1:2:0.04. The above raw materials were poured into an agate mortar and mixed evenly, then placed into a quartz tube and placed in a high-pressure tube furnace under an oxygen pressure of 1 MPa. After being kept at 800 ℃ for 24 h, the tube was taken out, ground into powder, and polyvinyl alcohol solution was added. The powder was then cold-pressed into discs with a diameter of 6 mm using a tablet press under a pressure of 3 t. The discs were pre-fired in air at 600 ℃ for 4 h to remove polyvinyl alcohol. After that, the discs were placed in a high-pressure tube furnace and kept at 800 ℃ under an oxygen pressure of 1 MPa for 24 h. Then, they were slowly cooled to room temperature to obtain SmNiO3 ceramic. Introducing electrodes into SmNiO3 ceramics can produce abrupt change thermistor devices, and grinding SmNiO3 ceramics into powder can further be applied to infrared camouflage coatings.

[0035] Example 4: The raw material powders used in this experiment include Sm2O3, Nd2O3, NiO, and Nd2O3. 0.5 Sm 0.5 NiO3. First, weigh out the corresponding oxide powders according to the elemental ratio of Nd:Sm:Ni = 1:1:1, pour them into an agate mortar and mix evenly. Then mix them according to the ratio of NiO:Nd... 0.5 Sm 0.5 Weigh out Nd3 in a ratio of 1:0.1 using NiO3. 0.5 Sm 0.5 NiO3, Nd 0.5 Sm 0.5NiO3 was ball-milled to a particle size of 1 μm and then added to an agate mortar for further grinding for 20 min. 0.2 g of the mixed powder was weighed out, and 1 drop of polyvinyl alcohol solution was added. After mixing and drying, the mixture was poured into a 6 mm diameter mold and cold-pressed into sheets under a mechanical pressure of 2 GPa. The sheets were then pre-calcined in air to remove polyvinyl alcohol and placed in a high-pressure tube furnace. The furnace was held at 10 MPa oxygen pressure and 800 °C for 24 h. After slow cooling to room temperature, the sheets were removed and ground into powder until uniform and fine. Polyvinyl alcohol solution was added again, and the sheets were cold-pressed into sheets. The mixture was held at 10 MPa oxygen pressure and 800 °C for 24 h and then slowly cooled to room temperature. The sheets were then ground into powder. 0.2 g of the powder was weighed out, and 4 drops of polyvinyl alcohol solution were added. After mixing evenly, the powder was cold-pressed into discs with a diameter of 6 mm. The discs were pre-calcined in air at 600 °C for 4 h to remove polyvinyl alcohol. Finally, the mixture was held at 10 MPa oxygen pressure and 800 °C for 24 h and then slowly cooled to obtain Nd2O3. 0.5 Sm 0.5 NiO3 ceramics. In Nd... 0.5 Sm 0.5 Introducing electrodes into NiO3 ceramics can produce abrupt change thermistor devices, and grinding the ceramics into powder can further be applied to infrared camouflage coatings.

[0036] Example 5: The powder used in this experiment was Nd2O3, NiO, MnO2, with a particle size of 10 μm. 0.9 Mn 0.1 O3. First, weigh the oxide powder according to the ratio Nd2O3:NiO:MnO2 = 1:1.8:0.2, and then weigh the Nd2O3:NdNiO powder according to the ratio Nd2O3:NdNiO:MnO2 = 1:1.8:0.2. 0.9 Mn 0.1 Homogeneous seed crystals were weighed out in a ratio of O3:1:0.02, and NdNi was processed using a ball mill. 0.9 Mn 0.1 O3 was ball-milled to a particle size of 1 μm. The above raw materials were poured into an agate mortar and mixed evenly. 0.2 g of powder was weighed and 2 drops of polyvinyl alcohol solution were added. After mixing evenly, 3 t mechanical pressure was applied and cold-pressed into discs with a diameter of 6 mm. The discs were pre-fired in air at 600 ℃ for 4 h to remove polyvinyl alcohol. The discs were then placed in a high-pressure tube furnace and charged with 7 MPa oxygen pressure. They were kept at 800 ℃ for 24 h and slowly cooled to room temperature. The discs were then ground into powder, and a binder was added. The powder was then cold-pressed into sheets and kept at 800 ℃ and 7 MPa oxygen pressure for another 24 h. This process was repeated 3 times to obtain NdNi. 0.9 Mn 0.1 O3 ceramics. In NdNi 0.9 Mn 0.1 Introducing electrodes into O3 ceramics can create abrupt change thermistor devices, and grinding the ceramics into powder can further be applied to infrared camouflage coatings.

[0037] Example 6: The powders used in this experiment were Eu2O3, NiCO3, and EuNiO3 with a particle size of 2 μm. First, Eu2O3 and NiCO3 powders were weighed according to the elemental ratio Eu:Ni = 1:1. The NiCO3 powder was placed in an air furnace and pre-calcined at 470 °C for 12 h, then poured into an agate mortar. Homogeneous seed crystal EuNiO3 was weighed according to the ratio NiCO3:EuNiO3 = 1:0.05, poured into the mortar, and polyvinyl alcohol solution was added and mixed with the above powders for 20 min. Weigh 0.2 g of the ground and dried powder, apply 3 t of mechanical pressure to the tablet using a tablet press, cold press it into a tablet, pre-fire it and place it in a high-pressure tube furnace, press it into an oxygen chamber to 7 MPa, hold it at 800 ℃ for 24 h, slowly cool it down, take out the sintered block and grind it into powder, add polyvinyl alcohol solution, cold press it into a small disc with a diameter of 6 mm, pre-fire it in air at 600 ℃ for 4 h to remove polyvinyl alcohol, then place it in a high-pressure tube furnace and hold it at 7 MPa oxygen pressure for 24 h. Repeat the above process 4 times, and slowly cool it down to obtain EuNiO3 ceramic. Further introducing electrodes into the ceramic can prepare magnetoelectronic devices. Grinding EuNiO3 ceramic into powder can also be further applied to infrared camouflage coatings.

[0038] Example 7: The raw materials used in this experiment included Gd2O3, Ni(CH3COO)2, and GdNiO3 seed crystals. The corresponding oxide powders and homogeneous seed crystals were weighed according to the ratio Gd2O3:Ni(CH3COO)2:GdNiO3 = 1:2:0.1. The weighed raw material powders were poured into an agate mortar and mixed evenly. The mixture was then pre-fired in an air furnace at 311 °C for 12 h. 0.2 g of the pre-fired powder was weighed and added to a polyvinyl alcohol solution, then ground for 20 min. A mechanical pressure of 3 t was applied, and the mixture was cold-pressed into discs with a diameter of 6 mm. After pre-firing to remove the polyvinyl alcohol binder, the discs were placed in a quartz tube and placed in a high-pressure tube furnace at 800 °C and 8 MPa oxygen pressure for 24 h. After slow cooling, the discs were removed, ground into powder, and polyvinyl alcohol solution was added. 0.2 g of the powder was weighed and cold-pressed into discs using a 6 mm diameter mold. The discs were then pre-fired in air at 600 °C for 1 h. After removing polyvinyl alcohol, the material is placed in a high-pressure tube furnace and filled with oxygen at 8 MPa. It is then kept at 800°C for 24 hours. This process is repeated four times to obtain GdNiO3 ceramic. Electrodes can be further introduced into the ceramic to prepare magnetoelectronic devices. Grinding the GdNiO3 ceramic into powder can also be further applied to infrared camouflage coatings.

[0039] Example 8: The raw materials used in this experiment are Nd₂O₃, NiO, Fe₂O₃, and NdNi. 0.9 Fe 0.1O3 seed crystals were prepared by weighing the corresponding oxide powders Nd₂O₃, NiO, and Fe₂O₃ according to the elemental ratio Nd:Ni:Fe = 10:9:1. The powders were then poured into an agate mortar and mixed thoroughly. Afterwards, the NiO:NdNi ratio was adjusted to... 0.9 Fe 0.1 Weigh out homogeneous seed crystals (O3 = 10:1), pour them into an agate mortar and mix with the previously prepared oxide powder. Then add polyvinyl alcohol solution and continue grinding for 20 min. Cold press the mixture into multiple small discs using a 6 mm diameter mold. Pre-fire at 600 °C in air for 1 h to remove polyvinyl alcohol. Place the mixture in a high-pressure tube furnace and press it under 10 GPa oxygen pressure. Hold it at 800 °C for 24 h. After cooling to room temperature, remove the sintered discs and grind them into powder. Add binder and cold press into sheets. Hold the sheets at 800 °C and 10 MPa for 24 h. Repeat the above process 5 times. Finally, slowly cool to room temperature to obtain NdNi. 0.9 Fe 0.1 O3 ceramics, by further introducing electrodes into the ceramics, can be used to fabricate abrupt changeover thermistor devices, using NdNi 0.9 Fe 0.1 O3, when ground into powder, can be further applied to infrared camouflage coatings.

[0040] Example 9: The raw material powders used in this experiment include Ho2O3, Y2O3, NiNO3, and Ho. 0.8 Y 0.2 NiO3 seed crystals. First, weigh out Ho2O3, Y2O3, and NiNO3 powders according to the elemental ratio Ho:Y:Ni = 8:2:10. After mixing the powders evenly, place them in an air furnace and pre-calcine at 300℃ for 12 hours. Then, prepare NiO:Ho seed crystals according to the ratio... 0.8 Y 0.2 Weigh a homogeneous seed crystal (NiO3 = 10:1), and grind it with the pre-sintered powder in an agate mortar for 20 minutes. Weigh 2.2 g of the powder, add 0.5 mL of polyvinyl alcohol solution, and continue grinding. Press the powder into a disc using a 20 mm diameter mold under 3 t pressure. Pre-sinter the disc at 600 °C in air for 3 h to remove the polyvinyl alcohol. Then, place it in a high-pressure tube furnace and hold it at 800 °C and 9 MPa for 24 h. After slow cooling, remove the sintered block and grind it into powder. Add polyvinyl alcohol solution and cold press it into a disc with a diameter of 20 mm. Hold the disc at 800 °C and 9 MPa oxygen pressure for 24 h. Repeat the above process 4 times. After cooling to room temperature, obtain Ho. 0.8 Y 0.2 NiO3 ceramics, with the further introduction of electrodes, can be used to fabricate magnetoelectronic devices, and Ho... 0.8 Y 0.2 NiO3, when ground into powder, can be further applied to infrared camouflage coatings.

[0041] Example 10: The raw material powders used in this experiment included Dy2O3, Co3O4, NiO, and DyNi powder with a diameter of 10 μm. 0.8 Co 0.2 O3 seed crystals. First, weigh the corresponding oxide powders according to the elemental ratio Dy:Ni:Co = 1:0.8:0.2, then weigh the NiO:DyNi seed crystals. 0.8 Co 0.2 Weigh DyNi with O3 = 10:1 0.8 Co 0.2 O3 homogeneous seed crystals were ball-milled to a particle size of 1 μm. The seed crystals were then mixed evenly with the aforementioned oxide powder in an agate mortar. 0.2 g of the powder was weighed, and one drop of polyvinyl alcohol solution was added. Mixing continued for 10 min. The mixture was then cold-pressed into sheets using a 6 mm diameter mold under 3 t pressure. The sheets were held at 500 °C in air for 1 h to remove the polyvinyl alcohol solution. The pre-sintered small discs were placed in quartz tubes and placed in a high-pressure tube furnace filled with 7 MPa of oxygen. The furnace was then held at 900 °C for 24 h. The sintered blocks were ground into uniform powder, and polyvinyl alcohol solution was added. The mixture was then cold-pressed into sheets and sintered again at 900 °C and 7 MPa for 24 h. This process was repeated three times to obtain DyNi. 0.8 Co 0.2 O3 ceramics, by further introducing electrodes into the ceramics, can be used to fabricate strongly correlated logic devices, and DyNi 0.8 Co 0.2 O3, when ground into powder, can be further applied to laser protective coatings.

[0042] Example 11: The raw materials used in this experiment are Ho2O3, CrO2, NiO, and HoNi. 0.9 Cr 0.1 O3 powder. First, prepare it in the following ratio: Ho2O3:CrO2:NiO:HoNi. 0.9 Cr 0.1 Weigh out the oxide powders and homogeneous seed crystals in a ratio of O3:5:1:9:1. Pour the powders into an agate mortar and mix thoroughly. Weigh 0.2 g of the mixture and add it to a polyvinyl alcohol solution, continuing to mix. Pour the dried powder into a 6 mm diameter cold-press mold and apply a mechanical pressure of 2 GPa for 5 min. Place the cold-pressed block in an air furnace and hold it at 500 ℃ for 1 h to remove the polyvinyl alcohol. Place the pre-fired block in a high-pressure tube furnace and hold it at 900 ℃ and 5 MPa for 24 h. After cooling to room temperature, remove the sintered block and grind it into powder. Add polyvinyl alcohol solution again and cold-press it into sheets. Pre-fire at 500 ℃ for 2 h, then hold it at 900 ℃ and 5 MPa for 24 h. After slow cooling, obtain HoNi. 0.9 Cr 0.1O3 ceramics, by further introducing electrodes into the ceramics, can be used to fabricate strongly correlated logic devices, and HoNi 0.9 Cr 0.1 O3, when ground into powder, can be further applied to infrared camouflage coatings.

[0043] Example 12: The raw material powders used in this experiment were Er₂O₃, NiO, and ErNiO₃. First, the corresponding oxide powders were weighed according to the ratio Er:Ni = 1:1. The raw material powders were poured into an agate mortar and mixed. Then, 1 μm ErNiO₃ was added as a homogeneous seed crystal according to the ratio Er₂O₃:ErNiO₃ = 1:0.01, and grinding continued until homogeneous. 0.2 g of the mixed powder was weighed and added to a polyvinyl alcohol solution. After grinding and drying, it was cold-pressed into discs with a diameter of 6 mm. After pre-firing, it was placed in a high-pressure furnace and oxygen was introduced to 7 MPa. The temperature was raised to 800 ℃ and held for 24 h, then slowly cooled to room temperature. The agglomerated powder was removed and re-ground. A binder was added, and it was cold-pressed into discs, placed in a high-pressure furnace, and held at 800 ℃ and 7 MPa for 24 h, then slowly cooled to room temperature. Repeat the above process 5 times to obtain ErNiO3 ceramic. Introducing electrodes into the ceramic can further prepare a sudden change thermistor device. Grinding ErNiO3 ceramic into powder can also be further applied to infrared camouflage coatings.

[0044] Example 13: The raw material powders used in this experiment include Tm2O3, Yb2O3, NiO, and Tm. 0.5 Yb 0.5 NiO3. First, weigh out the corresponding oxide powders according to the elemental ratio Tm:Yb:Ni = 1:1:1, pour them into an agate mortar and mix evenly. Then, mix NiO:Tm... 0.5 Yb 0.5 Weigh out Tm at a NiO3 ratio of 1:0.1. 0.5 Yb 0.5 NiO3, Tm 0.5 Yb 0.5 NiO3 was ball-milled to a particle size of 1 μm and then added to an agate mortar for further grinding for 20 min. 0.2 g of the mixed powder was weighed out, and 1 drop of polyvinyl alcohol solution was added. After mixing and drying, the mixture was poured into a 6 mm diameter mold and cold-pressed into sheets under a mechanical pressure of 2 GPa. The sheets were then pre-calcined in air to remove the polyvinyl alcohol, placed in a quartz tube, and kept in a high-pressure tube furnace at 10 MPa oxygen pressure and 800 °C for 24 h. After slowly cooling to room temperature, the sheets were removed and ground into powder until the powder was uniform and fine. Polyvinyl alcohol solution was added again, and the sheets were cold-pressed into sheets. The process was repeated three times, with the powder kept at 10 MPa oxygen pressure and 800 °C for 24 h. After slow cooling, Tm was obtained. 0.5 Yb 0.5 NiO3 ceramics. In Tm 0.5 Yb0.5 Introducing electrodes into NiO3 ceramics can produce abrupt change thermistor devices, and grinding the ceramics into powder can further be applied to infrared camouflage coatings.

[0045] Example 14: The raw materials used in this experiment included Lu2O3, Ni(CH3COO)2, and LuNiO3 seed crystals. The corresponding oxide powders and homogeneous seed crystals were weighed according to the ratio Lu2O3:Ni(CH3COO)2:LuNiO3 = 1:2:0.1. The weighed raw material powders were poured into an agate mortar and mixed evenly. The mixture was then placed in an air furnace and pre-fired at 311 °C for 12 h. 0.2 g of the pre-fired powder was weighed and added to a polyvinyl alcohol solution, then ground for 20 min. A mechanical pressure of 3 t was applied, and the mixture was cold-pressed into round discs with a diameter of 6 mm. After pre-firing to remove the polyvinyl alcohol binder, the discs were placed in a quartz tube and placed in a high-pressure tube furnace at 800 °C and 10 MPa oxygen pressure for 24 h. After slow cooling, the discs were removed, ground, and then polyvinyl alcohol solution was added. 0.2 g of the powder was weighed and cold-pressed into discs using a 6 mm diameter mold. The discs were pre-fired in air at 600 °C for 1 h to remove the polyvinyl alcohol. The discs were then placed in a high-pressure tube furnace and filled with 10 t of oxygen. The process of applying an oxygen pressure of MPa and holding at 800 °C for 24 h was repeated four times to obtain LuNiO3 ceramic. Electrodes can be further introduced into the ceramic to prepare magnetoelectronic devices. Grinding the LuNiO3 ceramic into powder can also be further applied to laser protective coatings.

[0046] Example 15: The main raw material powders used in this experiment are Y2O3, NiO, and YNiO3 seed crystals. First, the corresponding oxide powders Y2O3 and NiO were weighed according to the elemental ratio Y:Ni = 1:0.05 and mixed evenly in an agate mortar. Then, YNiO3 homogeneous seed crystals were weighed according to the ratio NiO:YNiO3 = 10:1 and added to the agate mortar. The mixture was continued for 20 min. Polyvinyl alcohol solution was added as a binder. After mixing and drying, 0.2 g of powder was weighed and poured into a mold with a diameter of 6 mm. Mechanical pressure of 2 GPa was applied and the mixture was cold-pressed into sheets. After pre-firing at 500 °C for 1 h, the sheets were placed in a high-pressure tube furnace and charged with oxygen pressure of 7 MPa. The furnace was then held at 800 °C for 24 h. After slowly cooling to room temperature, the sintered blocks were removed and ground into fine and uniform powder. Polyvinyl alcohol solution was added and the sheets were cold-pressed into small round sheets with a diameter of 6 mm. The sheets were then cold-pressed again at 800 °C for 7 h. The process was repeated three times under MPa conditions for 24 hours. After cooling, YNiO3 ceramics were obtained. Electrodes were further introduced into the ceramics to prepare magnetoelectronic devices. YNiO3 ceramics were also ground into powder and applied to infrared camouflage coatings.

[0047] Example 16: The raw material powders used in this experiment include La2O3, Sm2O3, Ni(CH3COO)2, and La. 0.8 Sm0.2 NiO3 seed crystals, in the following ratio: La2O3:Sm2O3:Ni(CH3COO)2:La 0.8 Sm 0.2 Weigh out the corresponding oxide powder and homogeneous seed crystals of NiO3 (4:1:10:0.5). Pour the weighed raw material powder into an agate mortar and mix evenly. Place it in an air furnace and pre-calcine at 311 °C for 12 h. Weigh out 0.2 g of the pre-calcineed powder and add it to a polyvinyl alcohol solution. Grind for 20 min. Apply 3 t of mechanical pressure and cold press into round discs with a diameter of 6 mm. After pre-calcine to remove the polyvinyl alcohol binder, place it in a quartz tube and place it in a high-pressure tube furnace. Hold it at 800 °C and 9 MPa oxygen pressure for 24 h. After slow cooling, remove the block and grind it. Add polyvinyl alcohol solution and weigh out 0.2 g of powder. Cold press it into discs using a mold with a diameter of 6 mm. Pre-calcine in air at 500 °C for 1 h to remove polyvinyl alcohol. Continue to place it in a high-pressure tube furnace, fill it with 9 MPa oxygen pressure, and hold it at 800 °C for 24 h. Repeat the above process 4 times to obtain La. 0.8 Sm 0.2 NiO3 ceramics, with the further introduction of electrodes into the ceramics, can be used to fabricate magnetoelectronic devices, and La 0.8 Sm 0.2 NiO3 ceramics, when ground into powder, can be further applied to infrared camouflage coatings.

[0048] Example 17: The raw materials used in this experiment are Nd₂O₃, Sm₂O₃, NiO, MnO₂, and Nd₂O₃. 0.2 Sm 0.8 Ni 0.8 Mn 0.2 O3 seed crystals were prepared by weighing the corresponding oxide powders Nd₂O₃, Sm₂O₃, NiO, and MnO₂ according to the elemental ratio Nd:Sm:Ni:Mn: = 2:8:8:2. The powders were then poured into an agate mortar and mixed thoroughly. Afterwards, the NiO:Nd₂O₃ ratio was adjusted to... 0.2 Sm 0.8 Ni 0.8 Mn 0.2 Weigh out homogeneous seed crystals (O3 = 10:1), pour them into an agate mortar and mix with the previously prepared oxide powder. Then add polyvinyl alcohol solution and continue grinding for 20 min. Cold press the mixture into multiple small discs using a 6 mm diameter mold. Pre-fire at 600 °C in air for 1 h to remove polyvinyl alcohol. Place the mixture in a high-pressure tube furnace and press it under 10 GPa oxygen pressure. Hold it at 800 °C for 24 h. After cooling to room temperature, remove the sintered discs and grind them into powder. Add binder and cold press into sheets. Hold the sheets at 800 °C and 10 MPa for 24 h. Repeat the above process 5 times. Finally, slowly cool to room temperature to obtain Nd. 0.2 Sm 0.8 Ni 0.8 Mn0.2 O3 ceramics, by further introducing electrodes into the ceramics, can be used to fabricate abrupt changeover thermistor devices, using Nd... 0.2 Sm 0.8 Ni 0.8 Mn 0.2 O3, when ground into powder, can be further applied to infrared camouflage coatings.

[0049] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the substantive technical content of the present invention. The substantive technical content of the present invention is broadly defined within the scope of the claims. Any technical entity or method completed by others that is completely identical to or an equivalent modification of the claims is considered to be covered within the scope of the claims.

Claims

1. A method for preparing metastable rare earth nickel-based oxide materials, characterized in that: 1) Design the metastable phase rare earth nickel-based oxide material composition based on the target electrical transport and phase transition characteristics. Based on the selected material composition, select the precursors of Re, Ni and transition elements and weigh them according to the stoichiometric ratio of the target metastable phase rare earth nickel-based oxide. 2) Weigh out the target metastable rare earth nickel-based oxide with a Ni element precursor molar ratio of 0.1-50% according to the amount of precursor used, and use it as a nucleation seed crystal. Mix the seed crystal with the precursor thoroughly and cold press it into a sheet. 3) Select the heat treatment temperature and oxygen pressure according to the target metastable rare earth nickel-based oxide: Heat the cold-pressed reactants to a high temperature of 800-1100 ℃ in a high oxygen pressure atmosphere and hold for 24-48 h. After holding, slowly cool to room temperature, take out the sample, grind it into powder, and then cold-press it into sheets again. Heat it to a high temperature of 800-1100 ℃ in a high oxygen pressure atmosphere and hold for 24-48 h. Repeat the above operation 1-5 times until pure metastable rare earth nickel-based oxide ceramics are obtained. 4) Based on metastable rare earth nickel-based oxide ceramics, further introduce electrode and other functional layer materials to prepare abrupt change thermistor devices and strongly correlated logic devices; or grind them into powder to prepare infrared camouflage coatings and laser protection coatings; The above steps enable the efficient synthesis of rare earth nickel-based oxides that exhibit both metal-insulator phase transition and hydrogen-induced electronic phase transition and are in a thermodynamically metastable phase. The method used does not contain any liquid phase substances, is simple to operate, and allows for large-scale preparation. The hardness, morphology, and electrical transport properties of metastable rare earth nickel-based oxide ceramics can be controlled by adjusting the ratio of precursor to seed crystal, oxygen partial pressure, and heat treatment process. Step 1) The chemical composition of the metastable rare earth nickel-based oxide is NdNiO3, PrNiO3, SmNiO3, Nd 0.5 Sm 0.5 NiO3, NdNi 0.9 Mn 0.1 O3, EuNiO3, GdNiO3, NdNi 0.9 Fe 0.1 O3, Ho 0.8 Y 0.2 NiO3, DyNi 0.8 Co 0.2 O3, HoNi 0.9 Cr 0.1 O3, ErNiO3, Tm 0.5 Yb 0.5 NiO3, LuNiO3, YNiO3, La 0.8 Sm 0.2 NiO3 or Nd 0.2 Sm 0.8 Ni 0.8 Mn 0.2 O3.

2. The method for preparing metastable rare earth nickel-based oxide materials as described in claim 1, characterized in that, Step 1) The precursors include oxides, carbonates, nitrates and acetates of rare earth, Ni, and transition elements; for carbonate, nitrate and acetate precursors, the corresponding oxides of rare earth, Ni and transition elements are obtained by pre-calcination decomposition; the pre-calcination temperature should be 1-200 ℃ higher than the decomposition temperature of the corresponding carbonate, nitrate and acetate.

3. The method for preparing metastable rare earth nickel-based oxide materials as described in claim 1, characterized in that, Step 2) The nucleation seed crystals of the metastable rare earth nickel-based oxide have a grain size of 0.1-100 μm; by changing the size of the seed crystal grains, the non-uniform nucleation process can be controlled, thereby further controlling the purity, electrical transport properties and mechanical properties of the metastable rare earth nickel-based oxide ceramic.

4. The method for preparing metastable rare-earth nickel-based oxide materials as described in claim 1, characterized in that, In step 3), the mechanical pressure range during the cold pressing process is 0.01-10 GPa. The density of the cold-pressed block is controlled by changing the mass of the powder sample, the size of the cold pressing mold, and the pressure of the tablet press, thereby further controlling the thermodynamic process in sintering.

5. The method for preparing metastable rare earth nickel-based oxide materials as described in claim 4, characterized in that, In step 3), the heating process requires a temperature and time that are controlled by the ratio of precursor to seed crystal and the seed crystal size. The holding temperature is 800-1100 ℃. By changing the holding temperature, the diffusion rate of the raw materials and the non-uniform nucleation process can be controlled, thereby further controlling the mechanical properties of rare earth nickel-based oxide ceramics. The purity of metastable rare earth nickel-based oxides can be controlled by changing the holding time. The oxygen pressure is 0.2-50 MPa. By changing the oxygen pressure, the thermodynamic process of the reaction can be controlled, thereby controlling the electrical transport properties of rare earth nickel-based oxide ceramics. The degree of mixing between homogeneous nuclei and oxide raw materials can be controlled by grinding the sample into powder and sintering it multiple times, thereby further controlling the purity and electrical transport properties of rare earth nickel-based oxides.

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