Alkali metal rare earth oxide NaRO2 crystal and growth method and application thereof

Abstract

The invention belongs to the technical field of crystal materials, and particularly relates to an alkali metal rare earth oxide NaRO2 crystal and a growth method and application thereof. According to the invention, the problem of crystal growth is solved by finding a proper fluxing agent system (sodium hydroxide, sodium carbonate or a sodium carbonate-sodium hydroxide mixture), NaRO2 (R = rare earth element) single crystal with a delafossite structure is grown for the first time, and octahedral single crystal with a pyrochore structure is synthesized and grown for the first time. The crystal growth conditions are simple, the growth efficiency is high, the growth period is short, high-quality single crystals are very easy to obtain, the size of the single crystals can be further regulated and controlled by regulating and controlling the conditions such as the growth period and the cooling rate, and the method is convenient and rapid and has good application prospects. The grown NaRO2 compound single crystal can be used for researching magnetic resistance, quantum fluctuation, quantum entanglement or ultralow-temperature magnetic refrigeration and the like, and has a good application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of crystal materials, and in particular relates to a type of alkali metal rare earth oxide NaRO2 crystals and a growth method and application thereof. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention, and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] Lanthanide rare earth elements are an ideal platform for studying magnetism. Different electron numbers and crystal fields lead to completely different ground states, thus presenting a variety of physical properties and possibly realizing exotic quantum states (Physics, Vol. 50, No. 7, 2021, 454). For triangular lattices, the nearest neighbor Heisenberg model can form a non-collinear 120° magnetic structure, and both the next-nearest neighbor interaction and the anisotropic interaction can enhance frustration. The unique structural features of the triangular lattice are considered to be very promising candidate materials for realizing the quantum spin liquid state. In particular, the rare earth compound ARCh2 system has recently attracted attention (A = alkali metal, R = lanthanide metal, Ch = oxygen element, Chinese Physics Letters, 2018, 35(11): 117501), among which the triangular lattice structure of NaYbO2 (Nature Physics, 2019, 15(10): 1058), KYbO2 (Physical Review B, 2023, 107(22): 224416), NaYbS2 (Physical Review B, 2019, 100(24): 241116), NaYbSe2 (Physical Review X, 2021, 11(2):021044) and other materials have been found to behave like quantum spin liquids in preliminary measurements; and the rare earth compounds NaErO2 and NaHoO2 have a magnetic susceptibility that decreases rapidly with increasing temperature at low temperatures, which makes the system compounds likely to have a large magnetocaloric effect and have important applications in ultra-low temperature magnetic refrigeration and other fields (Journal of Solid State Chemistry, 2003, 176(1):266). By changing the rare earth elements and adjusting the crystal field parameters, we can continue to explore more novel physical phenomena including hidden order, spin fragmentation, string excitation, etc., which has important research value.

[0004] The growth of NaRO2 (R = rare earth element) single crystal material is still a great challenge, mainly for the following two reasons: on the one hand, the current research on the material is still in the powder research stage, and there is no good way to obtain single crystals for basic physics research (electricity, magnetism, thermal, etc.); on the other hand, the material has poor stability, is easy to decompose at high temperatures (T>200℃), and Na ions are easily lost in water. The single crystal of this material has been slow to grow, which has greatly restricted the progress of basic and applied research.

[0005] For the ARCh2 system, crystals other than oxygen have been successfully prepared: in 2018, Liu Weiwei and others from the Institute of Physics, Chinese Academy of Sciences, used Se as flux, Na2Se, Yb and Se powders, and kept warm at 1000°C for 48 hours to successfully cultivate high-quality 2-3 mm NaYbSe2 single crystals (Chinese Physics Letters, 2018, 35(11):117501); in 2021, the research group used the self-fluxing method to prepare 2-4 mm KErTe2 and KLuTe2 single crystals using K, Er / Lu, and Te elemental raw materials (Chinese Physics B: 2021, 30(10):577); in 2018, M. Baenitz used argon gas flow to bring CS2 vapor into the hot zone to introduce a sulfur source to obtain NaYbS2 and NaLuS2 crystals, and millimeter-sized layered crystals were obtained (Physical Review B, 2018, 98(22):220409).

[0006] Anisotropic NaRO2 (R = rare earth element) single crystals are an ideal material platform for studying their physical properties. However, the growth of NaRO2 single crystals is an unresolved issue. At present, its polycrystalline powder can only be prepared by solid phase sintering (Nature Physics, 2019, 15 (10): 1058), but polycrystalline powders have many crystal defects and the stoichiometric ratio is difficult to accurately control. Since it is currently impossible to grow high-quality single crystal samples, further in-depth experimental research is still lacking. Therefore, it is urgent to develop a process for preparing alkali metal rare earth oxide NaRO2 single crystals to promote basic research and applied research on this series of crystals. Summary of the invention

[0007] In view of the problems existing in the prior art, the present invention provides a type of alkali metal rare earth oxide NaRO2 crystal and a growth method and application thereof. The present invention adopts a new flux system of sodium hydroxide, sodium carbonate or a sodium carbonate-sodium hydroxide mixture to simply and efficiently obtain single crystals of alkali metal rare earth oxide NaRO2 compounds with structures of delafossite (α phase) and pyrochlore (β phase), wherein the single crystal of the delafossite structure is grown for the first time, and the material of the pyrochlore structure is synthesized and grown as a single crystal for the first time.

[0008] In order to achieve the above object, the present invention adopts the following technical solution:

[0009] The first aspect of the present invention provides a method for preparing the growth of alkali metal rare earth oxide NaRO2 crystals, wherein NaOH, Na2CO3 or a mixture thereof is used as a flux, mixed with a precursor substance of a rare earth element R to prepare a crystal growth material, and NaRO2 single crystals are obtained by spontaneous crystallization.

[0010] Preferably, the precursor material of the rare earth element R is selected from one or more of rare earth oxides and their corresponding sulfates, nitrates, chlorides and prefabricated NaRO2 crystals.

[0011] Preferably, in the alkali metal rare earth oxide NaRO2 single crystal, R is selected from one or more of lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium.

[0012] Preferably, the method comprises: using NaOH, Na2CO3 or a mixture thereof as a flux, mixing it with a precursor of the rare earth element R to prepare a crystal growth material, heating the crystal growth material to melt it, cooling it to a growth temperature after keeping it warm, and growing a crystal to obtain a NaRO2 single crystal.

[0013] Preferably, the melting process is to heat up to 400-1200°C at a heating rate of <200°C / h and keep the temperature for 5-72h; further preferably, the melting process is to heat up to 450-1100°C at a heating rate of ≤100°C / h and keep the temperature;

[0014] Preferably, the cooling rate of the cooling process is 0.01-10°C / h, and the crystal nucleation and growth temperature range is 400-1200°C; further preferably, the cooling rate of the cooling process is 0.1-2°C / h, and the crystal nucleation and growth temperature range is 450-1100°C;

[0015] Preferably, the crystal growth period of the alkali metal rare earth oxide NaRO2 single crystal is 3 days or more, more preferably 3 to 5 days, and more preferably 3 days.

[0016] Preferably, the growth temperature is 1000-1200° C. to obtain α-NaRO2; the growth temperature is 400-1050° C. to obtain β-NaRO2.

[0017] Preferably, when the flux is selected from a mixture of NaOH and Na2CO3, the mass ratio of NaOH and Na2CO3 is (1-100):(1-100); the mass ratio of the precursor of the rare earth element R to the flux is 1:(5-40), further preferably 1:(8-20), and more preferably 1:(8-15).

[0018] Preferably, the reaction atmosphere of the mixed reaction is selected from one or more of air, nitrogen, argon, hydrogen and carbon dioxide.

[0019] The second aspect of the present invention provides a type of alkali metal rare earth oxide NaRO2 crystals obtained by the above-mentioned growth method.

[0020] Preferably, the alkali metal rare earth oxide NaRO2 crystal includes α-NaRO2 and β-NaRO2; the α-NaRO2 compound single crystal morphology is a layered morphology, and the unit cell parameters are α=β=90°andγ=120°, and the length and width of the α-NaRO2 compound single crystal are 20 to 250 microns.

[0021] The third aspect of the present invention provides a β-NaRO2 single crystal having a pyrochlore structure, wherein the β-NaRO2 compound single crystal has an octahedral morphology; the β-NaRO2 single crystal has a hexagonal morphology. The space group and unit cell parameters are α=β=90°andγ=120°;

[0022] Preferably, the length and width of the octahedral single crystal of the β-NaRO2 compound are 15 to 50 microns;

[0023] Preferably, the method for growing the β-NaRO2 single crystal comprises: using a mixture of NaOH and Na2CO3 as a flux, mixing it with a precursor of a rare earth element R to prepare a crystal growth material, heating the crystal growth material to melt it, cooling it to a growth temperature after keeping it warm, and growing the crystal to obtain a β-NaRO2 single crystal with a pyrochlore structure;

[0024] Further preferably, the precursor of the rare earth element R is selected from rare earth oxides such as Ho2O3, Er2O3, Tm2O3, Yb2O3 or Lu2O;

[0025] Further preferably, the melting process is to heat up to 400-1200°C at a heating rate of <200°C / h and keep the temperature for 5-72h; further preferably, the melting process is to heat up to 450-1100°C at a heating rate of ≤100°C / h;

[0026] Preferably, the cooling rate of the cooling process is 0.01-10°C / h, and the temperature is slowly reduced to allow the crystals to nucleate and grow, and the crystal nucleation and growth temperature range is 400-1200°C; further preferably, the cooling rate of the cooling process is 0.1-2°C / h, and the crystal nucleation and growth temperature range is 450-1100°C;

[0027] Preferably, the crystal growth period of the β-NaRO2 single crystal is 3 days or more, more preferably 3 to 5 days, and more preferably 3 days.

[0028] A fourth aspect of the present invention provides the use of the above-mentioned alkali metal rare earth oxide crystals in the study of magnetic frustration, quantum fluctuations, quantum entanglement or ultra-low temperature magnetic refrigeration.

[0029] The beneficial effects achieved by one or more technical solutions of the present invention are as follows:

[0030] (1) The present invention overcomes the crystal growth problem by finding a suitable flux system (sodium hydroxide, sodium carbonate or a sodium carbonate-sodium hydroxide mixture), grows a delafossite structure NaRO2 (R = rare earth element) single crystal for the first time, and synthesizes and grows a pyrochlore structure octahedral single crystal for the first time.

[0031] (2) The conditions required for growing the crystals of the present invention are simple, and the growth efficiency is high and the growth cycle is short, so it is very easy to obtain high-quality single crystals. The size of the single crystal can be further controlled by adjusting the growth cycle and the cooling rate, which is convenient and quick.

[0032] (3) The NaRO2 compound single crystal grown by the present invention can be used to study magnetic frustration, quantum fluctuations, quantum entanglement or ultra-low temperature magnetic refrigeration, etc., and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0034] Figure 1 is a microscopic morphology of a layered α-NaYbO2 crystal prepared in Example 1 of the present invention;

[0035] Figure 2is the powder X-ray powder diffraction pattern of the layered α-NaYbO2 crystal prepared in Example 1 of the present invention;

[0036] Figure 3 is a microscopic morphology image of an octahedral β-NaYbO2 crystal prepared in Example 2 of the present invention;

[0037] Figure 4 is the powder X-ray powder diffraction pattern of the octahedral β-NaYbO2 crystal prepared in Example 2 of the present invention;

[0038] Figure 5 is a microscopic morphology of NaLuO2 crystals prepared in Example 3 of the present invention;

[0039] Figure 6 is the powder X-ray powder diffraction pattern of the NaLuO2 crystal prepared in Example 3 of the present invention;

[0040] Figure 7 is a microscopic morphology of NaTmO2 crystals prepared in Example 4 of the present invention;

[0041] Figure 8 is the powder X-ray powder diffraction pattern of the NaTmO2 crystal prepared in Example 4 of the present invention;

[0042] Fig. 9 These are the magnetic susceptibility test data of the octahedral β-NaYbO2 crystal prepared in Example 2 of the present invention in the range of 0.4 to 300K. DETAILED DESCRIPTION

[0043] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0044] Given that the anisotropic NaRO2 (R = rare earth element) single crystal is an ideal material platform for studying its physical properties, however, the growth of NaRO2 single crystal is an unresolved issue. Currently, its polycrystalline powder can only be prepared by solid-phase sintering, but polycrystalline powder has many crystal defects and the stoichiometric ratio is difficult to accurately control. Since it is currently impossible to grow high-quality single crystal samples, further in-depth experimental research is still relatively lacking. Therefore, it is urgent to develop a process for preparing alkali metal rare earth oxide NaRO2 single crystals to promote basic research and applied research on this series of crystals.

[0045] The first typical embodiment of the present invention provides a method for preparing the growth of alkali metal rare earth oxide NaRO2 crystals, wherein NaOH, Na2CO3 or a mixture thereof is used as a flux, mixed with a precursor substance of a rare earth element R to prepare a crystal growth material, and NaRO2 single crystals are obtained by spontaneous crystallization.

[0046] In one or more examples of this embodiment, the precursor material of the rare earth element R is selected from one or more of rare earth oxides and their corresponding sulfates, nitrates, chlorides and prefabricated NaRO2 crystals.

[0047] In one or more embodiments of this embodiment, in the alkali metal rare earth oxide NaRO2 single crystal, R is selected from one or more of lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium.

[0048] In one or more embodiments of this implementation mode, the method includes: using NaOH, Na2CO3 or a mixture thereof as a flux, mixing it with a precursor of the rare earth element R to prepare a crystal growth material, heating the crystal growth material to melt it, keeping it warm and then cooling it to the growth temperature, and growing the crystal to obtain a NaRO2 single crystal.

[0049] In one or more examples of this implementation mode, the melting process is to heat the material to 400-1200° C. at a heating rate of <200° C. / h and keep the temperature therefor for 5-72 hours.

[0050] In one or more examples of this implementation mode, the melting process is to increase the temperature to 450-1100° C. at a heating rate of ≤100° C. / h and keep the temperature.

[0051] In one or more examples of this implementation mode, the cooling rate of the cooling process is 0.01-10°C / h, and the temperature range of crystal nucleation and growth is 400-1200°C.

[0052] In one or more examples of this implementation mode, the cooling rate of the cooling process is 0.1-2°C / h, and the temperature range of crystal nucleation and growth is 450-1100°C.

[0053] In one or more examples of this implementation mode, the crystal growth period of the alkali metal rare earth oxide NaRO2 single crystal is 3 days or more, more preferably 3 to 5 days, and more preferably 3 days.

[0054] In one or more examples of this implementation mode, the growth temperature is 1000-1200° C. to obtain α-NaRO2; the growth temperature is 400-1050° C. to obtain β-NaRO2.

[0055] In one or more embodiments of this embodiment, when the flux is selected from a mixture of NaOH and Na2CO3, the mass ratio of NaOH and Na2CO3 is (1-100):(1-100); the mass ratio of the precursor of the rare earth element R to the flux is 1:(5-40), further preferably 1:(8-20), and more preferably 1:(8-15).

[0056] In one or more examples of this embodiment, the reaction atmosphere of the mixed reaction is selected from one or more of air, nitrogen, argon, hydrogen, and carbon dioxide.

[0057] A second typical embodiment of the present invention provides a type of alkali metal rare earth oxide NaRO2 crystals obtained by the above-mentioned growth method.

[0058] In one or more examples of this embodiment, the alkali metal rare earth oxide NaRO2 crystal includes α-NaRO2 and β-NaRO2; the α-NaRO2 compound single crystal morphology is a layered morphology, and the unit cell parameters are α=β=90°andγ=120°; the length and width of the α-NaRO2 compound single crystal are 20 to 250 microns.

[0059] A third typical embodiment of the present invention provides a β-NaRO2 single crystal having a pyrochlore structure, wherein the β-NaRO2 compound single crystal has an octahedral morphology; the β-NaRO2 single crystal has a hexagonal morphology. The space group and unit cell parameters are α=β=90° and γ=120°.

[0060] In one or more examples of this implementation mode, the length and width of the β-NaRO2 compound single crystal are 15 to 50 microns.

[0061] In one or more examples of this implementation mode, the method for growing the β-NaRO2 single crystal includes: using a mixture of NaOH and Na2CO3 as a flux, mixing it with a precursor of the rare earth element R to prepare a crystal growth material, heating the crystal growth material to melt it, keeping the temperature and then cooling it to the growth temperature, growing the crystal to obtain a β-NaRO2 single crystal with a pyrochlore structure.

[0062] In one or more examples of this implementation mode, the precursor material of the rare earth element R is selected from rare earth oxides such as Ho2O3, Er2O3, Tm2O3, Yb2O3 or Lu2O3.

[0063] In one or more examples of this implementation mode, the melting process is to heat the material to 400-1200° C. at a heating rate of <200° C. / h and keep the temperature therefor for 5-72 hours.

[0064] In one or more examples of this implementation mode, the melting process is to increase the temperature to 450-1100° C. at a heating rate of ≤100° C. / h and keep the temperature.

[0065] In one or more examples of this implementation mode, the cooling rate of the cooling process is 0.01-10°C / h, and the temperature range of crystal nucleation and growth is 400-1200°C.

[0066] In one or more examples of this implementation mode, the cooling process is carried out at a cooling rate of 0.1 to 2°C / h, and the crystal nucleation and growth temperature range is 450 to 1100°C.

[0067] In one or more examples of this implementation mode, the crystal growth period of the alkali metal rare earth oxide NaRO2 single crystal is 3 days or more, more preferably 3 to 5 days, and more preferably 3 days.

[0068] A fourth typical embodiment of the present invention provides the use of the above-mentioned alkali metal rare earth oxide crystals in the study of magnetic frustration, quantum fluctuations, quantum entanglement or ultra-low temperature magnetic refrigeration.

[0069] In the present invention, unless otherwise specified, "R" described below refers to 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) or a mixture thereof.

[0070] The present invention uses different R rare earth raw materials and the flux system of the present invention to prepare NaRO2 compound single crystals with different crystal structures: tetragonal phase, cubic phase, monoclinic phase, and hexagonal phase; in particular, when R is ytterbium (Yb), hexagonal phase quasi-two-dimensional triangular lattice (α phase) and novel pyrochlore structure (β phase) NaYbO2 single crystals can be prepared.

[0071] The precursor material of the rare earth element R described in the present invention includes but is not limited to rare earth oxides or their corresponding sulfates, nitrates, chlorides, etc., as long as they can provide an R source without affecting crystal growth.

[0072] The flux sodium hydroxide, sodium carbonate or sodium carbonate-sodium hydroxide mixture described in the present invention is a self-fluxing agent, which not only plays the role of a flux but also provides a necessary Na source for the growth of NaRO2 crystals.

[0073] The mixed raw materials of the present invention can be reacted directly in a crucible, or can be pressed into tablets and then reacted and synthesized in a crucible.

[0074] The crucible used in the present invention should be covered to minimize the volatilization of the flux at high temperature and prevent the flux from completely volatilizing and corroding equipment such as the muffle furnace.

[0075] The present invention does not impose any special restrictions on the mixing method of the rare earth element R source and the flux, and a mixing method commonly used in the art can be used. After the rare earth element R source and the flux are mixed to obtain a crystal growth material, the present invention also includes a step of sealing the crystal growth material to prevent the raw material and the flux from volatilizing; the present invention does not impose any special restrictions on the sealing method, and a sealing method commonly used in the art can be used.

[0076] The present invention will be further described in detail below in conjunction with specific embodiments. It should be noted that the specific embodiments are intended to explain the present invention rather than to limit it.

[0077] Example 1 :

[0078] This embodiment provides a method for growing a layered NaYbO2 single crystal, using Na2CO3-NaOH as a flux system and Yb2O3 as a Yb source. The specific steps are as follows:

[0079] (1) Na2CO3, NaOH and Yb2O3 are mixed in a mass ratio of 24:1:4 and uniformly prepared to obtain a crystal growth material;

[0080] (2) The crystal growth material is loaded into an alumina crucible with a volume of Φ30mm×30mm, and the crucible is placed in a muffle furnace. The temperature is raised to 1100°C at a rate of 80°C / h. After keeping the temperature for 24 hours, the temperature is lowered to 1000°C at a rate of 1.4°C / h to allow spontaneous crystallization. The growth cycle is 3 days, and a layered NaYbO2 single crystal can be obtained.

[0081] Test the microstructure of layered NaYbO2 single crystals, such as Figure 1 As shown. Figure 1 It can be seen that the length and width of the obtained layered NaYbO2 crystals are between 20 and 250 μm.

[0082] Test the X-ray powder diffraction pattern of NaYbO2 single crystal after grinding, such as Figure 2 As shown. Figure 2 It can be seen that it is consistent with the standard card (PDF#01-085-7885), indicating that the obtained crystal is α-NaYbO2, and the unit cell parameters are α=β=90° and γ=120°.

[0083] Example 2 :

[0084] This embodiment provides a method for growing an octahedral NaYbO2 single crystal, using Na2CO3-NaOH as a flux system and Yb2O3 as a Yb source. The specific steps are as follows:

[0085] (1) Na2CO3, NaOH and Yb2O3 are mixed in a mass ratio of 2:5.4:1 and uniformly prepared to obtain a crystal growth material;

[0086] (2) The crystal growth material is loaded into an alumina crucible with a volume of Φ30mm×30mm, and the crucible is placed in a muffle furnace. The temperature is raised to 1050°C at a rate of 80°C / h. After keeping the temperature for 24 hours, the temperature is lowered to 950°C at a rate of 1.4°C / h to allow spontaneous crystallization. The growth cycle is 3 days, and an octahedral NaYbO2 single crystal can be obtained.

[0087] Test the microstructure of the octahedral NaYbO2 single crystal, such as Figure 3 As shown. Figure 3 It can be seen that the length and width of the obtained octahedral NaYbO2 crystals are between 20 and 70 μm.

[0088] Test the X-ray powder diffraction pattern of octahedral NaYbO2 single crystal after grinding, such as Figure 4 As shown. Figure 4 It can be seen that the results are consistent with the standard card (PDF#01-085-7885), indicating that the obtained NaYbO2 crystals are of good purity. At the same time, the single crystal analysis obtained a new pyrochlore structure (β-NaYbO2): room temperature, hexagonal The space group and unit cell parameters are α=β=90° and γ=120°.

[0089] Example 3 :

[0090] This embodiment provides a method for growing an octahedral NaLuO2 single crystal, using Na2CO3-NaOH as a flux system and Lu2O3 as a Lu source. The specific steps are as follows:

[0091] (1) Na2CO3, NaOH and Lu2O3 are mixed in a mass ratio of 7.5:1:1 and uniformly prepared to obtain a crystal growth material;

[0092] (2) The crystal growth material is loaded into an alumina crucible with a volume of Φ30mm×30mm, and the crucible is placed in a muffle furnace. The temperature is raised to 1000°C at a rate of 80°C / h. After keeping the temperature for 24 hours, the temperature is lowered to 950°C at a rate of 1.4°C / h to allow spontaneous crystallization. The growth cycle is 3 days, and an octahedral NaLuO2 single crystal can be obtained.

[0093] Test the microstructure of the octahedral NaLuO2 single crystal, such as Figure 5 As shown. Figure 5 It can be seen that the length and width dimensions of the obtained octahedral NaLuO2 crystals are between 20 and 40 μm.

[0094] Test the X-ray powder diffraction pattern of octahedral NaLuO2 single crystal after grinding, such as Figure 6 As shown. Figure 6 It can be seen that it is consistent with the standard card (PDF#04-018-7651), indicating that the obtained crystal is β-NaLuO2. The room temperature single crystal diffraction experiment confirms that it belongs to hexagonal The space group and unit cell parameters are α=β=90° and γ=120°.

[0095] Example 4 :

[0096] This embodiment provides a method for growing an octahedral NaTmO2 single crystal, using Na2CO3 as a flux system and Tm2O3 as a Tm source. The specific steps are as follows:

[0097] (1) Na2CO3 and Tm2O3 are mixed in a mass ratio of 10:1 and uniformly prepared to obtain a crystal growth material;

[0098] (2) The crystal growth material is loaded into an alumina crucible with a volume of Φ30mm×30mm, and the crucible is placed in a muffle furnace. The temperature is increased to 1000°C at a rate of 80°C / h. After keeping the temperature for 24 hours, the temperature is decreased to 950°C at a rate of 1°C / h. The temperature is decreased and spontaneous crystallization is carried out for 2 days to obtain an octahedral NaTmO2 single crystal.

[0099] Test the microstructure of the octahedral NaTmO2 single crystal, such as Figure 7 As shown. Figure 7 It can be seen that the length and width of the obtained octahedral NaTmO2 crystals are between 20 and 30 μm.

[0100] Test the X-ray powder diffraction pattern of octahedral NaTmO2 single crystal after grinding, such as Figure 8 As shown. Figure 8 It can be seen that it is consistent with the standard card (PDF#00-047-1678), indicating that the obtained crystal is β-NaTmO2. The room temperature single crystal diffraction experiment confirms that it belongs to hexagonal The space group and unit cell parameters are α=β=90° and γ=120°.

[0101] Example 5 :

[0102] This example provides the magnetic susceptibility of the pyrochlore structure β-NaYbO2 crystal prepared in Example 2. The specific test process and data are as follows:

[0103] The sample was tested using the Quantum Design MPMS3 test platform. The mass of the tested β-NaYbO2 sample was 42 mg. Fig. 9 shown.

[0104] Depend on Fig. 9 (a) It can be seen that under a magnetic field of 20 Oe, the three curves of ZFC, FC-C and FC-W overlap in the temperature range of 1.8 to 300 K, and the sample exhibits paramagnetism, and no spin freezing characteristics are found;

[0105] Depend on Fig. 9 (b) It can be seen that the magnetic susceptibility curve can be well fitted by Curie-Weiss in the temperature range of 5 to 20 K, and the required Curie-Weiss temperature is -7 K;

[0106] Depend on Fig. 9 (c) It can be seen that under a magnetic field of 20 Oe, the three curves of ZFC, FC-C and FC-W overlap in the temperature range of 0.4 to 1.8 K, and the sample exhibits paramagnetism, and no spin freezing characteristics are found;

[0107] Depend on Fig. 9 (d) It can be seen that by conducting AC magnetic susceptibility tests on the sample in the temperature range of 0.4 to 1.28 K and at frequencies of 10, 467 and 996 Hz, it can be seen that no signs of spin freezing or frequency dependence are observed in the sample.

[0108] The spin dislocation factor f is a physical quantity that measures the dislocation strength of a material and is defined as f = |θ cw | / Tc, if f>10, it means that the spin blocking is strong. The larger the f, the stronger the blocking and the stronger the interaction between spins. For β-NaYbO2, θ cw -7K, and there is no long-range magnetic order or spin glass state at a low temperature of 0.4K. c =0.4K to estimate the lower limit of f, that is, f>17.5. Such a large spin dislocation f indicates that the material is a potential quantum spin liquid material, which has good prospects in the study of magnetic frustration, quantum fluctuations, quantum entanglement, etc.

[0109] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a growth of alkali metal rare earth oxide NaRO2 crystals, characterized in that: The method uses NaOH, Na2CO3 or a mixture thereof as flux, mixes with a precursor of a rare earth element R to prepare a crystal growth material, and obtains a NaRO2 single crystal through spontaneous crystallization.

2. The growth method according to claim 1, characterized in that The precursor of the rare earth element R is selected from one or more of rare earth oxides and their corresponding sulfates, nitrates, chlorides and prefabricated NaRO2 crystals; In the alkali metal rare earth oxide NaRO2 single crystal, R is selected from one or more of lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium.

3. The growth method according to claim 1, characterized in that The method comprises: using NaOH, Na2CO3 or a mixture thereof as flux, mixing with a precursor of a rare earth element R to prepare a crystal growth material, heating the crystal growth material to melt it, cooling it to a growth temperature after keeping it warm, and growing a crystal to obtain a NaRO2 single crystal; Preferably, the melting process is to heat up to 400-1200°C at a heating rate of <200°C / h and keep the temperature for 5-72h; further preferably, the melting process is to heat up to 450-1100°C at a heating rate of ≤100°C / h and keep the temperature; Preferably, the cooling rate of the cooling process is 0.01-10°C / h, and the crystal nucleation and growth temperature range is 400-1200°C; further preferably, the cooling rate of the cooling process is 0.1-2°C / h, and the crystal nucleation and growth temperature range is 450-1100°C; Preferably, the crystal growth period of the alkali metal rare earth oxide NaRO2 single crystal is 3 days or more, more preferably 3 to 5 days, and more preferably 3 days.

4. The growth method according to claim 3, characterized in that The growth temperature is 1000-1200° C. to obtain α-NaRO2; the growth temperature is 400-1050° C. to obtain β-NaRO2.

5. The growth method according to claim 1, characterized in that When the flux is selected from a mixture of NaOH and Na2CO3, the mass ratio of NaOH and Na2CO3 is (1-100):(1-100); the mass ratio of the precursor of the rare earth element R to the flux is 1:(5-40), further preferably 1:(8-20), and more preferably 1:(8-15).

6. The growth method according to claim 1, characterized in that The reaction atmosphere of the mixed reaction is selected from one or more of air, nitrogen, argon, hydrogen and carbon dioxide.

7. An alkali metal rare earth oxide NaRO2 crystal, characterized in that: Obtained by the growth method according to any one of claims 1 to 6.

8. The alkali metal rare earth oxide NaRO2 crystal according to claim 7, characterized in that Including α-NaRO2 and β-NaRO2; the α-NaRO2 compound single crystal morphology is a layered morphology, and the unit cell parameters are α=β=90°andγ=120°; the length and width of the α-NaRO2 compound single crystal are 20 to 250 microns.

9. A β-NaRO2 single crystal having a pyrochlore structure, characterized in that: The β-NaRO2 compound single crystal morphology is octahedral; the β-NaRO2 single crystal is hexagonal The space group and unit cell parameters are Preferably, the length and width of the β-NaRO2 compound single crystal are 15 to 50 microns; Preferably, the method for growing the β-NaRO2 single crystal comprises: using a mixture of NaOH and Na2CO3 as a flux, mixing it with a precursor of a rare earth element R to prepare a crystal growth material, heating the crystal growth material to melt it, cooling it to a growth temperature after keeping it warm, and growing the crystal to obtain a β-NaRO2 single crystal with a pyrochlore structure; Further preferably, the precursor of the rare earth element R is a rare earth oxide such as Ho2O3, Er2O3, Tm2O3, Yb2O3 or Lu2O3; Further preferably, the melting process is to heat up to 400-1200°C at a heating rate of <200°C / h and keep the temperature for 5-72h; further preferably, the melting process is to heat up to 450-1100°C at a heating rate of ≤100°C / h and keep the temperature; Preferably, the cooling rate of the cooling process is 0.01-10°C / h, and the crystal nucleation and growth temperature range is 400-1200°C; further preferably, the cooling rate of the cooling process is 0.1-2°C / h, and the crystal nucleation and growth temperature range is 450-1100°C; Preferably, the crystal growth period of the β-NaRO2 single crystal is 3 days or more, more preferably 3 to 5 days, and more preferably 3 days.

10. Application of alkali metal rare earth oxide crystals obtained by the growth method according to any one of claims 1 to 6 in the study of magnetic frustration, quantum fluctuation, quantum entanglement or ultra-low temperature magnetic refrigeration.

Images