CN117127260B - Method for growing perovskite nickel oxide compound monocrystal under normal pressure - Google Patents

Abstract

The invention relates to a method for growing perovskite nickel oxide single crystal under normal pressure, which takes Ni source and La ₂O₃ as raw materials, adopts anhydrous K ₂CO₃ or a mixture of Na ₂CO₃ and NaCl as fluxing agent, heats the raw materials to melt, then cools the raw materials to the growth temperature, carries out crystal growth under normal pressure, and removes the fluxing agent after the growth is finished to obtain La _n+1Ni_nO_3n+1 (n=2, 3) crystal. The invention uses the fluxing agent method, does not need high pressure, breaks away from the high oxygen pressure condition for the first time, realizes the growth of perovskite nickel oxide compound R _n+1Ni_nO_3n+1 (n=2-7) monocrystal under normal pressure, greatly reduces the threshold of crystal growth, reduces the danger in the growth process, solves the key problem of a material platform for the research of a nickel-based high-temperature superconducting mechanism, and has important basic research value and potential application prospect.

Description

A method for growing perovskite nickel oxide single crystal under normal pressure

Technical Field

The invention relates to a method for growing a perovskite nickel-oxygen compound single crystal under normal pressure, belonging to the technical field of crystal materials.

Background technique

Understanding the interplay of lattice, charge, spin, and orbital degrees of freedom and the physical properties they govern, such as superconductivity, colossal magnetoresistance, metal-insulator phase transitions, and multiferroics, is a central challenge in the study of strongly correlated materials. Nickel oxides have attracted widespread attention due to their important physical properties for fundamental research and technology, including superconductivity at ambient pressure in infinite-layer square coordination oxides R _1-x A _x NiO ₂ (R＝La, Pr, Nd, A＝Sr; R＝La, A＝Ca) and pentalayer Nd ₆ Ni ₅ O ₁₂ and high-temperature superconductivity with a critical transition temperature as high as 80K in La ₃ Ni ₂ O ₇ at 14.0-43.5 GPa, metal-insulator phase transition and multiferroicity in RNiO ₃ (R＝Pr-Lu), charge/spin stripe phase in R _2-x Sr _x NiO ₄ (R＝La-Nd) and La ₄ Ni ₃ O ₈ , large orbital polarization and metallic behavior similar to high-temperature superconducting cuprates in Pr ₄ Ni ₃ O ₈ , and trilayer nickel oxide R ₄ Ni ₃ O _10. (R＝La, Pr, Nd) metal-metal phase transition produced by the interweaving of charge and spin density waves. However, some key basic scientific issues surrounding nickel oxide physics remain unresolved, including but not limited to the origin of superconductivity in square planar nickel oxides at normal pressure and La ₃ Ni ₂ O ₇ at high pressure, the role of hydrogen in superconductivity, the crystal structure and magnetic ground state of RNiO ₂ , the magnetic ground state of RNiO ₃ , etc. Anisotropic single crystals are an ideal material platform for solving the above key basic scientific issues.

The growth of bulk nickel oxide single crystals is still a great challenge: (1) Currently, low-valent nickel oxides containing Ni ⁺ cannot be directly synthesized, but are prepared by topological reduction of nickel oxides with a valence >2+; (2) Perovskite nickel oxides with a nickel valence >2+ all need to be grown under high oxygen pressure. For example, under oxygen pressures of 30-150, 20 _{, 15 , 290 and 140 bar, people have grown LaNiO3, La4Ni3O10, La3Ni2O7 , PrNiO3 and Pr4Ni3O10 bulk single} crystals with edge sizes greater than 1 mm using the floating zone crystal growth technique. However _, high-pressure floating zone furnaces are expensive, have a high-pressure oxygen atmosphere, and have very high safety requirements, which greatly limits the progress of basic and applied research.

Another method is the combination of flux method and high oxygen pressure technology, but it is more difficult to grow crystals using the high _pO2 flux method. The reported growth technology of _RNiO3 single crystals with an edge size of about 100 microns has extremely harsh growth conditions of 900-1500°C and pressure of 4-4.5GPa. Recently, Klein et al. used LiCl-KCl as flux and successfully grew RNiO ₃ (R=Nd, Sm, Gd, Dy, Y, Ho, Er, Lu) microcrystals at oxygen partial pressure pO ₂ =2000bar and T=850℃, with the maximum size of 75 microns. For example, the Chinese patent document CN115787060A previously applied by the applicant discloses the crystal growth and application of rare earth perovskite nickel oxide compound high pressure flux method, using NiO and R ₂ O ₃ as raw materials, R is a rare earth element, using an alkali flux system to fill with oxygen to grow crystals, first heating to 400-500℃ to fully melt the raw materials, then cooling to the growth temperature to grow crystals, and after the growth is completed, rare earth perovskite nickel oxide compound RNiO ₃ crystals are obtained, with a crystal size of up to 45-60μm. This technology greatly reduces the growth temperature and oxygen pressure.

In general, whether it is the high-pressure floating zone method or the high-pressure flux method, the growth of high-valent nickel-oxygen compound single crystals requires high oxygen pressure conditions, has stringent requirements on equipment, high cost, and high threshold. The growth of high-valent nickel-based oxide single crystals under normal pressure is an unresolved issue and there have been no successful reports.

Summary of the invention

In view of the shortcomings of the prior art, especially the difficulties of high oxygen pressure and expensive equipment in the growth of high-valent nickel oxide single crystals, the present invention provides a method for growing perovskite nickel oxide single crystals under normal pressure. The present invention adopts a new flux system, wherein the flux system is _potassium carbonate ( _K2CO3 ) or a sodium carbonate- _sodium chloride mixture ( _Na2CO3 -NaCl), and for the first time breaks away from high oxygen pressure conditions, thereby achieving the growth of perovskite nickel oxide Rn _{+1Ni nO3n +1} (n=2-7) single crystals under normal pressure.

To achieve the above objectives, the present invention is implemented through the following technical solutions:

A method for growing a perovskite nickel oxide single crystal under normal pressure, wherein the perovskite nickel oxide has a general formula of R _n+1 Ni _n O _3n+1 , n=2-7, and R is a rare earth element. The method comprises the following steps:

Take the raw materials Ni source and rare earth element oxide according to the stoichiometric ratio, use _anhydrous potassium carbonate ( _K2CO3 ) or sodium carbonate- _sodium chloride mixture ( _Na2CO3 -NaCl) as flux, first heat up to melt the raw materials, then cool down to the growth temperature, and grow crystals under normal pressure. When the growth is completed, a perovskite nickel oxide single crystal is obtained.

Preferably according to the present invention, in the general formula of the perovskite nickel oxide compound Rn _{+1Ni nO3n +1} , R is selected from lanthanum (La), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) or lutetium (Lu).

More preferably, R is selected from lanthanum (La) alone, or a mixture of lanthanum (La) and other rare earth ions.

Preferably, according to the present invention, in the general formula of the perovskite nickel oxide compound Rn _{+1Ni nO3n +1} , n=2 or 3.

According to the preferred embodiment of the present invention, the Ni source is Ni or NiO. The present invention includes but is not limited to Ni and NiO, as long as a Ni source can be provided.

Preferably, according to the present invention, when anhydrous potassium carbonate (K ₂ CO ₃ ) is used as a flux, the molar ratio of the Ni source to the flux is 1:(10-100).

More preferably, the molar ratio of the Ni source to the flux is 1:(30-70).

Preferably, according to the present invention, when a sodium carbonate-sodium chloride mixture (Na ₂ CO ₃ -NaCl) is used as a flux, the total mass of raw materials: mass of flux = 1: (5-40), and the molar ratio of Na ₂ CO ₃ : NaCl = (3-20): (5-15).

Preferably, according to the present invention, the temperature is first raised to melt the raw material, and then cooled to the growth temperature, the growth temperature is 890-1200° C., and during the cooling process to the growth temperature, the cooling rate is <20° C./h.

More preferably, the cooling rate is ≤1.0°C/h.

Preferably according to the present invention, the growth period of the crystal is ≥ 2 days.

A perovskite nickel oxide compound single crystal, wherein the perovskite nickel oxide compound has a general formula of R _n+1 Ni _n O _3n+1 , n=2-7, and R is a rare earth element, and is prepared by the above method.

The above-mentioned perovskite nickel oxide single crystals are used to study the mechanism of high-temperature superconductivity, metal-metal phase transition, charge order, spin order, etc., and as a parent phase, three-layer and two-layer equiplanar coordinated T' structure crystals are prepared by topological reduction to study the interaction between charge-spin-lattice-orbital;

In the field of fuel cells, used in solid-state fuel cells,

In the field of electrochemistry, it acts as an electrochemical catalyst.

Taking R as lanthanum (La) as an example, the present invention uses anhydrous potassium carbonate (K ₂ CO ₃ ) or a sodium carbonate-sodium chloride mixture (Na ₂ CO ₃ -NaCl) as a flux to successfully grow two-layer perovskite nickel oxide La ₃ Ni ₂ O ₇ crystals or three-layer perovskite nickel oxide La ₄ Ni ₃ O ₁₀ .

By optimizing the growth conditions of the present invention, a titanium ore nickel oxide compound La ₃ Ni ₂ O ₇ crystal with a size greater than 100 μm can be obtained. The obtained two-layer perovskite nickel oxide compound La ₃ Ni ₂ O ₇ crystal is black, has a layered structure, and is stacked in a rectangular shape. It is stable at room temperature and has no decomposition and deliquescence phenomenon. Its powder X-ray diffractometer test data is consistent with the powder diffraction standard PDF card, indicating that the grown crystal is a La ₃ Ni ₂ O ₇ crystal. The structure obtained by single crystal analysis is a monoclinic P2 ₁ /m space group, and the unit cell parameters are β＝104.817(1)°.

By optimizing the growth conditions of the present invention, a titanium ore nickel oxide compound La ₄ Ni ₃ O ₁₀ crystal with a size greater than 180 μm can be obtained. The obtained three-layer perovskite nickel oxide compound La ₄ Ni ₃ O ₁₀ is black, has a layered structure, is stacked in a rectangular shape, is stable at room temperature, has no decomposition and deliquescence phenomenon, has a metal-metal phase transition, and has a phase transition temperature of approximately 140 K. Its powder X-ray diffractometer test data is consistent with a powder diffraction standard PDF card, indicating that the grown crystal is a La ₄ Ni ₃ O ₁₀ crystal, and its structure is also confirmed by single crystal analysis.

The method of the present invention is not limited to this, and is also applicable to praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

The technical features and advantages of the present invention are as follows:

1. This has been reported previously (Zhang, J. et al. Phys. Rev. Mater. 4, 83402 (2020);

Liu, Z., Sun. et al. Sci. China Phys. Mech. Astron. 66, 217411 (2023).) used high-pressure floating zone technology to grow La ₄ Ni ₃ O ₁₀ and La ₃ Ni ₂ O ₇ crystals at 20 bar and 15 bar oxygen pressures, respectively. In comparison, the present invention uses a flux method to explore the flux system, and obtains submillimeter-scale perovskite nickel oxide R _{n+ 1} Ni _n O _3n+1 (n=2~7) single crystals at normal pressure for the first time, breaking through the limitation that high-oxidation nickel oxide bulk single crystals can only grow under high oxygen pressure, greatly reducing the difficulty of crystal preparation. The growth conditions are easy to achieve, the operation is simple, the growth cycle is short, and it is easy to obtain larger-sized perovskite nickel oxide R _n+1 Ni _n O _3n+1 (n=2~7) single crystals. Further reducing the rate can improve the crystal quality, and further increasing the amount of raw materials can obtain larger-sized single crystals.

2. Taking R as lanthanum (La) as an example, the present invention uses anhydrous potassium carbonate (K ₂ CO ₃ ) or a sodium carbonate-sodium chloride mixture (Na ₂ CO ₃ -NaCl) as a flux to successfully grow larger-sized two-layer perovskite nickel oxide La ₃ Ni ₂ O ₇ crystals or three-layer perovskite nickel oxide La ₄ Ni ₃ O ₁₀ , which are stable at room temperature without decomposition and deliquescence.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a microscopic morphology of La ₄ Ni ₃ O ₁₀ crystal prepared in Example 1;

FIG2 is a powder XRD pattern of La ₄ Ni ₃ O ₁₀ crystals prepared in Example 1;

FIG3 is a microscopic morphology of La ₄ Ni ₃ O ₁₀ crystal prepared in Example 2;

FIG4 is a powder XRD pattern of La ₄ Ni ₃ O ₁₀ crystals prepared in Example 2;

FIG5 is a microscopic morphology of La ₄ Ni ₃ O ₁₀ crystal prepared in Example 3;

FIG6 is a powder XRD pattern of La ₄ Ni ₃ O ₁₀ crystals prepared in Example 3;

FIG7 is a microscopic morphology of La ₄ Ni ₃ O ₁₀ crystal prepared in Example 4;

FIG8 is a powder XRD pattern of La ₄ Ni ₃ O ₁₀ crystals prepared in Example 4;

FIG9 is a microscopic morphology of the La ₃ Ni ₂ O ₇ single crystal prepared in Example 5;

FIG. 10 is a powder XRD pattern of the La ₃ Ni ₂ O ₇ single crystal prepared in Example 5.

Detailed ways

The present invention is further described below in conjunction with specific examples, but is not limited thereto. The ratios of Ni source to flux mentioned below are all molar ratios, and the Ni source mentioned below is all Ni (including but not limited to Ni, NiO, etc.).

It should be noted that the following detailed descriptions are all illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and/or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and/or combinations thereof.

For La ₄ Ni ₃ O ₁₀ crystals, two flux systems are mainly used, namely K ₂ CO ₃ flux system and Na ₂ CO ₃ /NaCl flux system. For K ₂ CO ₃ flux system, the growth temperature is between 1200-890°C, Ni source: K ₂ CO ₃ (molar ratio) = 1: (10-100), the cooling rate is <10°C/h, and the growth period is ≥2 days. For Na ₂ CO ₃ /NaCl flux system, the growth temperature is between 1100-500°C, raw material: flux = 1: (5-40) (mass ratio), wherein Na ₂ CO ₃ :NaCl = (3-20): (5-15) (molar ratio), and the growth period is ≥2 days.

For La ₃ Ni ₂ O ₇ crystals, K ₂ CO ₃ flux system is mainly used.

Example 1

K ₂ CO ₃ flux system, preparation of La ₄ Ni ₃ O ₁₀ single crystal under normal pressure conditions:

(1) Ni and La ₂ O ₃ are mixed in a stoichiometric ratio, and then anhydrous K ₂ CO ₃ as a flux is added, wherein the molar ratio of Ni to anhydrous K ₂ CO ₃ is 1:65, and the mixture is mixed to obtain a crystal growth material;

(2) The crystal growth material is loaded into an alumina crucible with a volume of Φ30 mm×30 mm, and the crucible is placed in a muffle furnace. The temperature is raised to 1050°C, and after keeping the temperature for 24 hours, the temperature is lowered to 890°C at a rate of 3.3°C/h to allow spontaneous crystallization. The growth cycle is 3 days, and La ₄ Ni ₃ O ₁₀ crystals can be obtained.

The microscopic morphology of the La ₄ Ni ₃ O ₁₀ microcrystals was tested, as shown in Figure 1. As shown in Figure 1, the crystal size of the obtained La ₄ Ni ₃ O ₁₀ microcrystals is 10-50 μm.

The X-ray powder diffraction pattern of La ₄ Ni ₃ O ₁₀ microcrystals was tested, as shown in Figure 2. As shown in Figure 2, it is consistent with the standard card (PDF#04-009-1774), indicating that La ₄ Ni ₃ O ₁₀ crystals were obtained.

Example 2

K ₂ CO ₃ flux system, preparation of La ₄ Ni ₃ O ₁₀ single crystal under normal pressure conditions:

(1) Ni and La ₂ O ₃ are mixed in a stoichiometric ratio, and then anhydrous K ₂ CO ₃ is added as a flux, Ni:K ₂ CO ₃ =1:33, and mixed evenly to obtain a crystal growth material.

(2) The crystal growth material is loaded into an alumina crucible with a volume of Φ50mm×50mm, and the crucible is placed in a muffle furnace. The temperature is raised to 1050°C, and after keeping the temperature for 48 hours, the temperature is lowered to 920°C at a rate of 0.83°C/h to allow spontaneous crystallization. The growth cycle is _{7 days, and La4Ni3O10 crystals can} be obtained.

The microscopic morphology of the La ₄ Ni ₃ O ₁₀ microcrystals was tested, as shown in Figure 3. As shown in Figure 3, the crystal size of the obtained La ₄ Ni ₃ O ₁₀ microcrystals is 40-100 μm.

The X-ray powder diffraction pattern of the La ₄ Ni ₃ O ₁₀ microcrystals was tested, as shown in Figure 4. As shown in Figure 4, it is consistent with the standard card (PDF#04-009-1774), indicating that the obtained is La ₄ Ni ₃ O ₁₀ crystals.

Example 3

K ₂ CO ₃ flux system, preparation of La ₄ Ni ₃ O ₁₀ single crystal under normal pressure conditions:

(1) Ni and La ₂ O ₃ are mixed in a stoichiometric ratio, and then anhydrous K ₂ CO ₃ is added as a flux, Ni:K ₂ CO ₃ =1:38, and mixed evenly to obtain a crystal growth material.

(2) The crystal growth material is placed in an alumina crucible with a volume of Φ50mm×50mm. The temperature is raised to 1050℃, kept at this temperature for 48h, and then lowered to 960℃ at a rate of 0.55℃/h to allow spontaneous crystallization. The growth cycle is 3 days, and La ₄ Ni ₃ O ₁₀ crystals are obtained.

The microscopic morphology of the La ₄ Ni ₃ O ₁₀ microcrystals was tested, as shown in Figure 5. As shown in Figure 5, the crystal size of the obtained La ₄ Ni ₃ O ₁₀ microcrystals is 40-180 μm.

The X-ray powder diffraction pattern of the La ₄ Ni ₃ O ₁₀ microcrystals was tested, as shown in Figure 6. As shown in Figure 6, it is consistent with the standard card (PDF#04-009-1774), indicating that the obtained product is La ₄ Ni ₃ O ₁₀ crystals.

Example 4

Na ₂ CO ₃ , NaCl flux system, preparation of La ₄ Ni ₃ O ₁₀ single crystal under normal pressure:

(1) Ni and La ₂ O ₃ are mixed in a stoichiometric ratio, and then flux Na ₂ CO ₃ and NaCl are added. The total mass ratio of Ni and La ₂ O ₃ : flux is 1:22, and the molar ratio of Na ₂ CO ₃ : NaCl is 11:9, to obtain a crystal growth material.

(2) The crystal growth material is placed in an alumina crucible with a volume of Φ40 mm×38 mm, the temperature is raised to 950°C, and after keeping the temperature for 24 hours, the temperature is lowered to 500°C at a rate of 75°C/h to allow spontaneous crystallization. The growth cycle is 2 days, and La ₄ Ni ₃ O ₁₀ crystals can be obtained.

The microscopic morphology of La ₄ Ni ₃ O ₁₀ microcrystals was tested, as shown in Figure 7. As shown in Figure 7, the crystal size of the obtained La ₄ Ni ₃ O ₁₀ microcrystals is 1-20 μm.

The X-ray powder diffraction pattern of La ₄ Ni ₃ O ₁₀ microcrystals was tested, as shown in Figure 8. As shown in Figure 8, it is consistent with the standard card (PDF#04-009-1774), indicating that La ₄ Ni ₃ O ₁₀ crystals were obtained.

Example 5

_K2CO3 flux system, _{preparation of La3Ni2O7 single crystal under} normal pressure:

(1) Ni and La ₂ O ₃ are mixed in a stoichiometric ratio, and then anhydrous K ₂ CO ₃ is added as a flux, with a molar ratio of Ni:K ₂ CO ₃ = 1:37, to obtain a crystal growth material.

(2) The crystal growth material is placed in an alumina crucible with a volume of Φ35mm×50mm, the temperature is raised to 1050°C, and after keeping the temperature for 72 hours, the temperature is lowered to 1000°C at a rate of 1°C/h to allow spontaneous crystallization. The growth cycle is 6 days, and La ₃ Ni ₂ O ₇ crystals can be obtained.

The microscopic morphology of the La ₃ Ni ₂ O ₇ microcrystals obtained by testing is shown in FIG9 . As can be seen from FIG9 , the crystal size of the La ₃ Ni ₂ O ₇ microcrystals obtained is 40-105 μm.

The X-ray powder diffraction pattern of La ₃ Ni ₂ O ₇ microcrystals was tested, as shown in Figure 10. As shown in Figure 10, it is consistent with the standard card (PDF#04-009-1772), indicating that La ₃ Ni ₂ O ₇ crystals are obtained.

Claims (8)

1. A method for growing a perovskite nickel oxide single crystal under normal pressure, wherein the perovskite nickel oxide has a general formula of Rn _{+ 1Ni nO3n +1} , n=2-7, and R is selected from a single lanthanum La, and the method comprises the following steps: Take the raw materials Ni source and rare earth element oxide according to the stoichiometric ratio, use _anhydrous potassium carbonate _K2CO3 or sodium carbonate- _{sodium chloride mixture Na2CO3 -} NaCl as flux, first heat up to melt the raw materials, then cool down to the growth temperature, and grow crystals under normal pressure. When the growth is completed, a perovskite nickel oxide single crystal is obtained. 2 . The method according to claim 1 , wherein in the general formula of the perovskite nickel oxide compound R _n+1 Ni _n O _3n+1 , n=2 or 3. 3. The method according to claim 1, characterized in that the Ni source is Ni or NiO. 4. The method according to claim 1, characterized in that when anhydrous _potassium carbonate _K2CO3 is used as a flux, the molar ratio of the Ni source to the flux is 1: (30-70). 5. The method according to claim 1, characterized in that when a sodium carbonate- _{sodium chloride mixture Na2CO3 -} NaCl is used as a flux, the total mass of raw materials: the mass of flux = 1: (5-40), and the molar ratio of _Na2CO3 : _NaCl = (3-20): (5-15). 6. The method according to claim 1 is characterized in that the raw material is first heated to melt and then cooled to a growth temperature of 890-1200°C. During the cooling process to the growth temperature, the cooling rate is <20°C/h, and the growth period of the crystal is ≥2 days. 7. A perovskite nickel oxide single crystal, wherein the perovskite nickel oxide has a general formula of Rn _{+1Ni nO3n +1} , n=2-7, R is selected from lanthanum La, and is prepared by the method according to any one of claims 1-6. 8. The use of the perovskite nickel oxide single crystal according to claim 7 for studying the mechanism of high-temperature superconductivity, metal-metal phase transition, charge order, spin order, and as a parent phase to prepare three-layer and two-layer planar coordinated T' structure crystals by topological reduction to study the interaction between charge-spin-lattice-orbit; In the field of fuel cells, used in solid-state fuel cells, In the field of electrochemistry, it acts as an electrochemical catalyst.