CN115787060A - Rare earth perovskite nickel oxide high-pressure fluxing agent method crystal growth and application - Google Patents

Abstract

The invention relates to the crystal growth and application of rare earth perovskite nickel oxide compound high-pressure flux method. NiO and R ₂ O ₃ are used as raw materials, and R is a rare earth element. The crystal growth is carried out under the condition of filling oxygen with an alkali flux system. Raise the temperature to 400-500°C to fully melt the raw materials, then cool down to the growth temperature to grow the crystal, the oxygen pressure range is 5-300bar, the growth temperature is 150-450°C, and the rare earth perovskite nickel oxide compound RNiO ₃ crystal is obtained after the growth is completed . The invention utilizes an alkali flux system to reduce the RNiO ₃ crystal growth temperature to below 500°C and the required oxygen pressure to below 300bar, which greatly reduces the risk in the growth process, increases the crystal size, and obtains RNiO crystals under lower conditions. Relatively larger-sized RNiO ₃ crystals were obtained, and the crystal size can reach 45‑60 μm.

Description

Crystal growth and application of rare earth perovskite nickel oxide compound by high pressure flux method

technical field

The present invention relates to the crystal growth and application of rare earth perovskite nickel oxide compound high-pressure flux method and belongs to the technical field of crystal materials.

Background technique

In 1911, the discovery of the superconducting properties of mercury started the study of superconducting materials. The superconducting materials discovered so far are mainly divided into conventional superconductors and unconventional superconductors. The superconducting origin of conventional superconductors can be perfectly explained by BCS theory, but for unconventional superconductors such as copper-based and iron-based high-temperature superconductors, there is no unified and quantitative theoretical explanation for their superconducting mechanism. At present, the key basic scientific issues of superconductivity research focus on the mechanism of high-temperature superconductivity and the design and discovery of room-temperature superconductors. The discovery of new high-temperature superconductors will provide new material platforms and ideas for solving the worldwide problem of high-temperature superconducting mechanism.

In August 2019, Professor Hwang's research group at Stanford University successfully prepared Nd _0.8 Sr _0.2 NiO ₂ thin films on SrTiO ₃ substrates by laser pulse deposition, and discovered superconductivity with a critical transition temperature of 9-15K. Subsequently, superconductivity was discovered in R _1-x Sr _x NiO ₂ (R=Nd, Pr, La), La _1-x Ca _x NiO ₂ and Nd ₆ Ni ₅ O ₁₂ thin films. However, superconductivity was not found in polycrystalline materials, which may be due to poor sample quality. Due to the limited detection volume of the film, tests such as neutron scattering cannot be carried out, which seriously hinders the study of its superconducting mechanism. In addition, basic scientific issues related to the research of nickel-based superconductivity, such as what is the magnetic ground state of rare earth perovskite? Are there competing orders such as charge density waves and spin density waves? Does the pseudogap phase also exist above the temperature range of the superconducting phase? Exotic metal? Single crystal is an ideal platform to solve the above key basic scientific problems and study the anisotropic physical properties of nickel-based materials.

Monovalent nickel oxides are difficult to obtain directly through chemical reactions. Therefore, in order to prepare high-quality RNiO ₂ single crystals, high-quality RNiO ₃ parent phase single crystals must be prepared first, so the growth of RNiO ₃ single crystals is a low-cost research method. Nickel oxide superconductivity needs to overcome the difficulties. At present, there are two methods for synthesizing trivalent nickel parent phase single crystal, one is the high-pressure flux method, and the other is the high-pressure floating zone method. Both methods require a high oxygen pressure to stabilize the trivalent nickel ions. As the radius of rare earth ions decreases, the required oxygen pressure will also continue to increase, which has high requirements for equipment. At present, RNiO ₃ single crystals grown by high-pressure flux mostly use chloride as flux to grow under high temperature and high isostatic pressure conditions, but it is still impossible to obtain large-sized RNiO ₃ single crystals. At present, there are reports in the literature that 10-15 μm RNiO ₃ (R=Nd, Sm, Gd, Dy) with a size of 10-15 μm was grown under the condition of 2000 bar oxygen pressure and 1000 ° C by using chloride as a flux.

Contents of the invention

Aiming at the deficiencies of the existing technology, especially the technical defects that the existing growth temperature and pressure are too high and the obtained crystal size is too small, the present invention provides crystal growth and application of rare earth perovskite nickel oxide compound high-pressure flux method. The invention obtains larger-sized RNiO ₃ crystals under the condition of lowering the growth temperature and oxygen pressure by exploring a novel flux system.

Technical scheme of the present invention is as follows:

A rare earth perovskite nickel oxide compound high-pressure flux method crystal growth method, including the following steps:

Using NiO and R ₂ O ₃ as raw materials, R is a rare earth element (R=Pr-Dy), and the alkali flux system is used for crystal growth under the condition of filling oxygen. First, the temperature is raised to 400-500°C to fully melt the raw materials, and then the temperature is lowered. The crystal is grown at the growth temperature, the oxygen pressure range is 5-300bar, and the growth temperature is 150-450°C. After the growth is completed, the rare earth perovskite nickel oxide compound RNiO ₃ crystal is obtained.

The RNiO ₃ crystal prepared by the present invention has a metal-insulator phase transition. It is a metal at high temperature and belongs to the orthorhombic crystal system. The space group is Pbnm. The phase transition temperature increases with the decrease of the R ion radius, and exists below T _N antiferromagnetic order. RNiO ₃ is the parent phase material for preparing low-valent nickel oxide compound RNiO ₂ . The powder X-ray diffractometer data of the prepared RNiO ₃ crystal is consistent with the powder diffraction standard PDF card, indicating that the grown crystal RNiO ₃ crystal has a perovskite structure confirmed by single crystal analysis.

Compared with the prior art, the crystal size of _RNiO3 prepared by the method of the invention is greatly improved, and the crystal size can reach 45-60 μm.

The RNiO ₃ crystal prepared by the present invention is black, cuboid in shape, stable at room temperature, and has no decomposition and deliquescence phenomenon. The growth cycle can be adjusted according to requirements to obtain high-quality RNiO ₃ single crystals for physical testing.

The RNiO ₃ single crystal prepared by the present invention has a metal-insulator phase transition, for example, the metal-insulator phase transition of NdNiO ₃ occurs around 160K.

According to the present invention, preferably, R=Nd, Sm, Gd or Dy.

According to the present invention, preferably, the alkali flux is a mixture of one or more of NaOH and KOH; when the flux is a NaOH-KOH mixed system, the molar ratio of NaOH-KOH is preferably 1:1.

According to the present invention, preferably, the mass ratio of the raw material to the flux is 0.15: (1-2).

According to the present invention, preferably, during cooling down to the growth temperature, the cooling rate is 15-0.4°C/h, more preferably 10-0.5°C/h.

According to the present invention, oxygen is continuously added during the growth process to maintain the partial pressure of oxygen.

According to the present invention, preferably, the growth temperature is 170-360°C, which can be 200°C, 250°C, 350°C; preferably, the oxygen pressure range is 5-270bar, which can be 80bar, 90bar, 100bar, 110bar, 200bar, 240bar , 260bar, 300bar.

According to the present invention, preferably, the growth cycle of RNiO ₃ crystals is 3-12 days.

According to the present invention, preferably, the growth conditions of RNiO ₃ crystals are: cooling down to 250-200° C. at a rate of 0.5-10° C./h, and the growth period is 3-12 days.

According to the present invention, the crystal growth method of rare earth perovskite nickel oxide compound high-pressure flux method, a preferred embodiment, includes the following steps:

(1) NiO, R ₂ O ₃ , and R are rare earth elements, mixed according to the stoichiometric ratio, mixed evenly, pressed into tablets, added to the prepared flux system, mixed evenly, to obtain a crystal growth material;

The flux is: NaOH-KOH, wherein the molar ratio of NaOH to KOH is (0-1):1;

The mass ratio of the raw material to the flux is 0.15: (1-2);

(2) Put the crystal growth material obtained in step (1) into a platinum crucible, fill it with oxygen, adjust the pressure, raise the temperature to 400-500°C, keep warm to fully melt the raw material, and then cool down to grow the crystal to obtain the rare earth perovskite nickel Oxygen compound RNiO ₃ crystal;

The crystal growth temperature range is 170-400° C., the oxygen pressure range is 5-300 bar, and the cooling rate is 10-0.5° C./h.

In the above crystal growth process of the present invention, the chemical reaction formula involved is: R ₂ O ₃ +2NiO+0.5O ₂ →2RNiO ₃ .

According to the present invention, the coupling effect between lattice-charge-spin-orbit in the perovskite nickel-oxygen compound _RNiO3 crystal makes it have the potential for practical application in frontier research fields such as new morphology computing, bioelectronic interface and electrocatalysis . For example, it can be used as a parent phase material to prepare low-priced nickel oxide compound RNiO ₂ crystals; applications in the field of new morphology computing, for neuromorphic computing, etc.; applications in the field of biology, for the development of electrochemical biosensors; in the field of electrocatalysis applications for electrochemical catalysts.

The beneficial effects of the present invention are as follows:

1. It has been reported in the literature (Klein et al. Cryst. Growth Des. 21, 4230-4241 (2021)) that RNiO ₃ crystals were grown under the conditions of 2000 bar oxygen pressure and 1000 °C using chloride as a flux. In contrast, the present invention uses the alkali flux system for the first time: one is to reduce the growth temperature of RNiO ₃ (R=Pr-Dy) crystals to below 400°C; the other is to reduce the oxygen pressure required for growth to below 300bar, greatly reducing Minimize the danger in the growth process and the requirements for equipment; the third is to increase the crystal size on this basis, and obtain relatively larger RNiO ₃ crystals under lower conditions, and the crystal size can reach 45-60 μm.

2. The conditions required by the flux growth method adopted in the present invention are easy to realize, easy to operate, and the required raw materials are simple and easy to purchase. The growth period is 3-12 days to obtain a large-sized RNiO ₃ single crystal.

Description of drawings

Fig. 1 is the NdNiO prepared by embodiment ₁ The microscopic morphology figure of the crystal;

Fig. 2 is the NdNiO prepared by embodiment 1 The _XRD figure of the crystal;

Fig. 3 is the NdNiO prepared by embodiment ₂ The microscopic morphology figure of the crystal;

Fig. 4 is the NdNiO prepared by embodiment 2 The _XRD figure of the crystal;

Fig. 5 is the NdNiO prepared by embodiment ₃ The microscopic morphology figure of the crystal;

Fig. 6 is the NdNiO prepared by embodiment ₃ XRD figure of the crystal;

Fig. 7 is the NdNiO prepared by embodiment ₄ The microscopic morphology figure of the crystal;

Fig. 8 is the _NdNiO3 crystal XRD pattern prepared by embodiment 4;

Fig. 9 is the NdNiO prepared in embodiment ₅ The microscopic morphology figure of the crystal;

Fig. 10 is the _NdNiO3 crystal XRD figure prepared by embodiment 5;

Fig. 11 is the GdNiO prepared in embodiment ₆ The microscopic morphology figure of the crystal;

Fig. 12 is the XRD figure of the _GdNiO3 crystal prepared by embodiment 6;

Fig. 13 is the SmNiO prepared in embodiment ₇ The microscopic morphology figure of the crystal;

Fig. 14 is the XRD figure of the _SmNiO crystal prepared in embodiment 7;

Fig. 15 is the DyNiO prepared in embodiment ₈ The microscopic morphology figure of the crystal;

Fig. 16 is the _DyNiO3 crystal XRD figure prepared by embodiment 8;

FIG. 17 is an XRD pattern of the material prepared in Comparative Example 1.

Detailed ways

The present invention will be further described below in conjunction with specific examples, but not limited thereto. The flux ratios mentioned below are all molar ratios.

Example 1

Mix NiO and Nd ₂ O ₃ according to the stoichiometric ratio, mix them evenly and press into tablets, add them to the flux system NaOH-KOH (NaOH:KOH=1:1), the mass ratio of NiO, Nd ₂ O ₃ raw materials to flux The ratio is 0.15:1, and it is loaded into an alumina crucible with a volume of Φ40mm×60mm. Put the crucible into the high-pressure furnace and fill it with high-purity oxygen so that the O ₂ pressure = 2bar. Heat up to 400°C to melt it. At this time, the oxygen pressure in the furnace reaches 5bar. Fully keep the heat and cool down to 170°C. 10°C/h to make it spontaneously crystallize. During the heat preservation and cooling process, maintain the oxygen pressure at 100bar+/-10bar. The growth cycle is 3 days to obtain NdNiO ₃ microcrystals.

The microscopic morphology of NdNiO ₃ crystallites was tested, as shown in Figure 1. It can be seen from Fig. 1 that the obtained NdNiO ₃ crystallite has a crystal size of 1-10 μm.

The X-ray powder diffraction pattern of the tested NdNiO ₃ crystallites is shown in Figure 2. It can be seen from Figure 2 that it is consistent with the standard card (PDF#04-013-9190), indicating that the obtained NdNiO ₃ crystal is orthorhombic.

Example 2

Mix NiO and Nd ₂ O ₃ according to the stoichiometric ratio, mix them evenly and press into tablets, add them to the flux system NaOH-KOH (NaOH:KOH=1:1), the mass ratio of NiO, Nd ₂ O ₃ raw materials to flux The ratio is 0.15:1, and it is loaded into an alumina crucible with a volume of Φ40mm×60mm. Put the crucible into the high-pressure furnace, fill it with high-purity oxygen, make the O ₂ pressure = 88bar, heat up to 400°C to make it melt, at this time the oxygen pressure in the furnace reaches 200bar, fully keep warm, cool down to 170°C, and the cooling speed 10°C/h to make it spontaneously crystallize. During the heat preservation and cooling process, maintain the oxygen pressure at 200bar+/-10bar, and the growth cycle is 3 days to obtain NdNiO ₃ crystals.

The microscopic morphology of NdNiO ₃ crystals was tested, as shown in Figure 3. It can be seen from Fig. 3 that the obtained NdNiO ₃ crystallite has a crystal size of 10-20 μm.

The X-ray powder diffraction pattern of the tested NdNiO ₃ crystal is shown in Figure 4. It can be seen from Figure 4 that its X-ray powder diffraction pattern is consistent with the standard card (PDF#04-013-9190), indicating that the obtained NdNiO ₃ crystal is orthorhombic.

Example 3

Mix NiO and Nd ₂ O ₃ according to the stoichiometric ratio, mix them evenly and press into tablets, add them to the flux system NaOH-KOH (NaOH:KOH=1:1), the mass ratio of NiO, Nd ₂ O ₃ raw materials to flux The ratio is 0.15:1, and it is loaded into an alumina crucible with a volume of Φ40mm×60mm. Put the crucible into a high-pressure furnace and fill it with high-purity oxygen so that the O ₂ pressure = 102bar, and heat up to 400°C to melt it. At this time, the oxygen pressure in the furnace reaches 200bar, fully keep it warm, and cool down to 360°C. 5°C/h, keep warm for 2h, cool down to 260°C, and cool down at a rate of 1°C/h to make it spontaneously crystallize. During the heat preservation and cooling process, keep the oxygen pressure at 200bar+/-10bar, and grow in 7 days to obtain NdNiO ₃ crystals.

Test the microscopic morphology of NdNiO ₃ crystals, as shown in Figure 5. It can be seen from Fig. 5 that the obtained NdNiO ₃ crystallite has a crystal size of 20-40 μm.

The X-ray powder diffraction pattern of the tested NdNiO ₃ crystal is shown in Figure 6. It can be seen from Figure 6 that its X-ray powder diffraction pattern is consistent with the standard card (PDF#04-013-9190), indicating that the obtained NdNiO ₃ crystal is orthorhombic.

Example 4

Mix NiO and Nd ₂ O ₃ according to the stoichiometric ratio, mix them evenly and press into tablets, add them to the flux system NaOH-KOH (NaOH:KOH=0:1), the mass ratio of NiO, Nd ₂ O ₃ raw materials to flux 0.15:2, put it into a platinum crucible with a volume of Φ40mm×60mm, put a platinum wire into it to induce crystallization, put the crucible into a high-pressure furnace, fill it with high-purity oxygen, make the _O2 pressure = 106bar, and raise the temperature to 400 ℃ to make it melt, at this time the oxygen pressure in the furnace reaches 240bar, fully keep warm, cool down to 360°C, cool down at a rate of 5°C/h, keep warm for 2h, cool down to 260°C, cool down at a rate of 1°C/h, make it spontaneously crystallize, keep warm During the cooling process, the oxygen pressure is maintained at 240bar+/-10bar, and the growth period is 7 days to obtain NdNiO ₃ crystals.

The microscopic morphology of NdNiO ₃ crystals was tested, as shown in Figure 7. It can be seen from Fig. 7 that the obtained NdNiO ₃ crystallite has a crystal size of 30-40 μm.

The X-ray powder diffraction pattern of the tested NdNiO ₃ crystal is shown in Figure 8. It can be seen from Figure 8 that its X-ray powder diffraction pattern is consistent with the standard card (PDF#04-013-9190), indicating that the obtained NdNiO ₃ crystal is orthorhombic.

Example 5

Mix NiO and Nd ₂ O ₃ according to the stoichiometric ratio, mix them evenly and press into tablets, add them to the flux system NaOH-KOH (NaOH:KOH=0:1), the mass ratio of NiO, Nd ₂ O ₃ raw materials to flux 0.15:2, put it into a platinum crucible with a volume of Φ40mm×60mm, put a platinum wire into it to induce crystallization, put the crucible into a high-pressure furnace, fill it with high-purity oxygen, make the _O2 pressure = 112bar, and raise the temperature to 400 ℃ to make it melt, at this time the oxygen pressure in the furnace reaches 260bar, fully keep warm, cool down to 350°C, cool down at a rate of 2.5°C/h, keep warm for 2h, cool down to 250°C, cool down at a rate of 0.5°C/h, make it spontaneously crystallize, keep warm During the cooling process, the oxygen pressure is maintained at 260bar+/-10bar, and the growth period is 12 days to obtain NdNiO ₃ crystals.

The microscopic morphology of NdNiO ₃ crystals was tested, as shown in Figure 9. It can be seen from Fig. 9 that the obtained NdNiO ₃ crystallite has a crystal size of 40-60 μm.

The X-ray powder diffraction pattern of the tested NdNiO ₃ crystal is shown in Figure 10. It can be seen from Figure 10 that its X-ray powder diffraction pattern is consistent with the standard card (PDF#04-013-9190), indicating that the obtained NdNiO ₃ crystal is orthorhombic.

Example 6

Mix NiO and Gd ₂ O ₃ according to the stoichiometric ratio, mix them evenly and press into tablets, add them to the flux system NaOH-KOH (NaOH:KOH=1:1), the mass ratio of NiO, Gd ₂ O ₃ raw materials to flux 0.15:2, put it into a platinum crucible with a volume of Φ40mm×60mm, put a platinum wire to induce crystallization, put the crucible into a high-pressure furnace, fill it with high-purity oxygen, make PO ₂ =112bar, and heat up to 400°C Make it melt, at this time the oxygen pressure in the furnace reaches 260bar, fully keep warm, cool down to 350°C, cool down at a rate of 2.5°C/h, keep warm for 2h, cool down to 250°C, cool down at a rate of 0.5°C/h, make it spontaneously crystallize, keep warm and During the cooling process, the oxygen pressure is maintained at 260bar+/-10bar, and the growth period is 3 days to obtain GdNiO ₃ crystals.

The microscopic morphology of GdNiO ₃ crystals was tested, as shown in Figure 11. It can be seen from Fig. 11 that the crystal size of the obtained GdNiO ₃ is in the range of 1-10 μm.

The X-ray powder diffraction pattern of the tested GdNiO ₃ crystal is shown in Figure 12. It can be seen from Figure 12 that its X-ray powder diffraction pattern is consistent with the standard card (PDF#01-089-7728), indicating that the obtained GdNiO ₃ crystal is orthorhombic.

Example 7

Mix NiO and Sm ₂ O ₃ according to the stoichiometric ratio, mix them evenly and press into tablets, add them to the flux system NaOH-KOH (NaOH:KOH=1:1), the mass ratio of NiO, Sm ₂ O ₃ raw materials to flux 0.15:2, put it into a platinum crucible with a volume of Φ40mm×60mm, put the crucible into a high-pressure furnace, fill it with high-purity oxygen, make _O2 pressure = 114bar, heat up to 400°C to melt, at this time Oxygen pressure in the furnace reaches 270bar, keep warm enough, cool down to 200°C, and cool down at a rate of 10°C/h to make it spontaneously crystallize, keep the oxygen pressure at 270bar+/-10bar during the heat preservation and cooling process, and grow in 3 days, you can get SmNiO ₃ crystals.

The microscopic morphology of the SmNiO ₃ crystal was tested, as shown in Figure 13. It can be seen from Fig. 13 that the crystal size of the obtained SmNiO ₃ is 10-30 μm.

The X-ray powder diffraction pattern of the tested SmNiO ₃ crystal is shown in Figure 14. It can be seen from Figure 14 that its X-ray powder diffraction pattern is consistent with the standard card (PDF#01-071-5269), indicating that the obtained SmNiO ₃ crystal is orthorhombic.

Example 8

Mix NiO and Dy ₂ O ₃ according to the stoichiometric ratio, mix them evenly and press into tablets, add them to the flux system NaOH-KOH (NaOH:KOH=1:1), the mass ratio of NiO, Dy ₂ O ₃ raw materials to flux 0.15:2, put it into a platinum crucible with a volume of Φ40mm×60mm, put the crucible into a high-pressure furnace, fill it with high-purity oxygen, make the _O2 pressure = 101bar, and heat it up to 500°C to melt it. Oxygen pressure in the furnace reaches 260bar, keep warm enough, cool down to 200°C, and cool down at a rate of 12°C/h to make it spontaneously crystallize. During the heat preservation and cooling process, keep the oxygen pressure at 260bar+/-10bar, and the growth cycle is 3 days, you can get DyNiO ₃ crystals.

The microscopic morphology of the DyNiO ₃ crystal was tested, as shown in Figure 15. It can be seen from Fig. 15 that the obtained DyNiO ₃ crystal size is 50-70 μm.

The X-ray powder diffraction pattern of the tested DyNiO ₃ crystal is shown in FIG. 16 . It can be seen from Figure 16 that its X-ray powder diffraction pattern is consistent with the standard card (PDF #01-089-7495), indicating that the obtained DyNiO ₃ crystal is orthorhombic.

Comparative example 1

At present, it has been reported in the literature (Klein et al. Cryst. Growth Des. 21, 4230-4241 (2021)) to grow RNiO ₃ crystals under the conditions of 2000 bar oxygen pressure and 1000 °C using chloride as a flux.

In this comparative example, NiO and Nd ₂ O ₃ were dosed according to the stoichiometric ratio, mixed evenly and then pressed into tablets, and added to the flux system LiCl-KCl (LiCl:KCl=6:4), NiO, Nd ₂ O ₃ raw materials and auxiliary The flux mass ratio is 0.1:1, put it into an alumina crucible with a volume of Φ40mm×60mm, put the crucible into a high-pressure furnace, and fill it with high-purity oxygen to make the _O2 pressure = 97bar, and raise the temperature to 650°C to make it Melting, at this time the oxygen pressure in the furnace reaches 300bar, fully keep warm, cool down to 50°C, and the cooling rate is 10°C/h, it spontaneously crystallizes, maintain the oxygen pressure at 300bar+/-10bar during the heat preservation and cooling process, and the growth cycle is 5 days, get the product.

The X-ray powder diffraction pattern of the test product is shown in Figure 17. It can be seen from Figure 17 that the X-ray powder diffraction pattern shows that the product is NdClO, indicating that NdNiO ₃ crystals were not obtained under the conditions of 650 ° C and 300 bar oxygen pressure using the LiCl-KCl flux system.

Claims (10)

1. The method for crystal growth of rare earth perovskite nickel oxide compound high-pressure flux method, comprising steps as follows: Using NiO and R ₂ O ₃ as raw materials, R is a rare earth element, and the alkali flux system is filled with oxygen for crystal growth. First, the temperature is raised to 400-500°C to fully melt the raw materials, and then the temperature is lowered to the growth temperature to grow the crystal. The oxygen pressure range is 5-300bar, the growth temperature is 150-450°C, and the rare earth perovskite nickel oxide compound RNiO ₃ crystal is obtained after the growth is completed. 2. The method for crystal growth of rare earth perovskite nickel oxide compound high-pressure flux method according to claim 1, characterized in that, R=Pr-Dy. 3. the method for crystal growth of rare earth perovskite nickel oxide compound high-pressure flux method crystal growth according to claim 1, is characterized in that, described alkali flux is one or more mixing in NaOH, KOH; Preferably, when the co-solvent is a NaOH-KOH mixed system, the molar ratio of NaOH-KOH is 1:1. 4. The method for crystal growth of rare earth perovskite nickel oxide compound under high pressure flux method according to claim 1, characterized in that, the mass ratio of the raw material to the flux is 0.15: (1-2). 5. The method for crystal growth of rare earth perovskite nickel oxide compound by high-pressure flux method according to claim 1, characterized in that, in the process of cooling down to the growth temperature, the cooling rate is 15-0.4° C./h. 6 . The method for crystal growth of rare earth perovskite nickel oxide compound by high-pressure flux method according to claim 1 , characterized in that the growth temperature is 170-360° C. 7. The method for crystal growth of rare earth perovskite nickel oxide compound under high pressure flux method according to claim 1, characterized in that the oxygen pressure range is 5-270bar. 8. The method for crystal growth of rare earth perovskite nickel oxide compound high-pressure flux method according to claim 1, characterized in that, _RNiO The growth cycle of the crystal is 3-12 days. 9. the method for crystal growth of rare earth perovskite nickel oxide compound high-pressure flux method according to claim 1, is characterized in that, comprises steps as follows: (1) NiO, R ₂ O ₃ , and R are rare earth elements, mixed according to the stoichiometric ratio, mixed evenly, pressed into tablets, added to the prepared flux system, mixed evenly, to obtain a crystal growth material; The flux is: NaOH-KOH, wherein the molar ratio of NaOH to KOH is (0-1):1; The mass ratio of the raw material to the flux is 0.15: (1-2); (2) Put the crystal growth material obtained in step (1) into a platinum crucible, fill it with oxygen, adjust the pressure, raise the temperature to 400-500°C, keep warm to fully melt the raw material, and then cool down to grow the crystal to obtain the rare earth perovskite nickel Oxygen compound RNiO ₃ crystal; The crystal growth temperature range is 170-400° C., the oxygen pressure range is 5-300 bar, and the cooling rate is 10-0.5° C./h. 10. the _following application of the perovskite nickel oxide compound RNiO that claim 1 grows to obtain Crystal: As a parent phase material to prepare low-valent nickel oxide compound RNiO ₂ crystals and potential nickel-based oxide superconductors; Applications in the field of new morphological computing for neuromorphic computing; Applications in the biological field for the development of electrochemical biosensors; Applications in the field of electrocatalysis for electrochemical catalysts.

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