Alkali rare earth oxide naRO2 crystal and its growth method and application

Abstract

The application belongs to the technical field of crystal materials, and particularly relates to an alkali rare earth oxide NaRO2 crystal and a growth method and application thereof. The application breaks through the crystal growth problem by finding a suitable flux system (sodium hydroxide, sodium carbonate or a sodium carbonate-sodium hydroxide mixture), first grows a delafossite structure NaRO2 (R=rare earth element) single crystal, and simultaneously first synthesizes and grows an octahedral single crystal with a pyrochlore structure. The crystal growth condition involved in the application is simple, the growth efficiency is high, the growth cycle is short, and high-quality single crystals can be easily obtained; the size of the single crystals can be further regulated by regulating the growth cycle and the cooling rate, which is convenient and fast; the grown NaRO2 compound single crystals can be used for studying magnetic frustration, quantum fluctuation, quantum entanglement or super-low-temperature magnetic refrigeration, and have good application prospects.

Description

Technical Field

[0001] This invention belongs to the field of crystal materials technology, specifically relating to a class of alkali metal rare earth oxide NaRO2 crystals, their growth methods, and applications. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Lanthanum group rare earth elements provide an ideal platform for studying magnetism. Different numbers of electrons and crystal fields lead to drastically different ground states, resulting in a rich variety of physical properties and the potential to achieve 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 next-nearest-neighbor interactions and anisotropic interactions can enhance frustration. The unique structural features of triangular lattices are considered promising candidate materials for realizing quantum spin liquid states, especially the rare earth compound ARCh2 system, which has recently attracted attention (A = alkali metal, R = lanthanide metal, Ch = chalcogenide, Chinese Physics Letters, 2018, 35(11):117501). Among them, the triangular lattice structures of NaYbO2 (Nature Physics, 2019, 15(10):1058), KYbO2 (Physical Review B, 2023, 107(22):224416), NaYbS2 (Physical Review B, 2019, 100(24):241116), and NaYbSe2 (Physical Review B, 2019, 100(24):241116) are particularly noteworthy. Quantum spin liquid behavior has been found in preliminary measurements of several materials, including X, 2021, 11(2):021044; and the rare earth compounds NaErO2 and NaHoO2 have a large magnetocaloric effect due to the rapid decrease in magnetic susceptibility with increasing temperature at low temperatures, which may 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, and string excitation, which has important research value.

[0004] The growth of NaRO2 (R = rare earth element) single crystals remains a significant challenge, primarily due to two reasons: Firstly, current research on this material is still largely confined to powder metallurgy, and there is currently no effective method to obtain single crystals suitable for fundamental physics research (electrical, magnetic, thermal, etc.). Secondly, this material exhibits poor stability, readily decomposing at high temperatures (T>200℃) and easily losing Na ions in water. The prolonged inability to grow single crystals of this material has severely limited the progress of both fundamental and applied research.

[0005] For the ARCH2 system, crystals other than oxygen have been successfully prepared: In 2018, Liu Weiwei et al. from the Institute of Physics, Chinese Academy of Sciences, successfully cultivated high-quality 2-3 mm NaYbSe2 single crystals using Se as a flux and Na2Se, Yb and Se powders at 1000℃ for 48 hours (Chinese Physics Letters, 2018, 35(11):117501); In 2021, the same 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 introduced sulfur source by using argon gas flow to bring CS2 vapor into the hot zone to obtain NaYbS2 and NaLuS2 crystals, which can obtain millimeter-sized layered crystals (Physical Review B, 2018, 98(22):220409).

[0006] Anisotropic NaRO2 (R = rare earth element) single crystals are an ideal material platform for studying their properties; however, the growth of NaRO2 single crystals remains an unresolved issue. Currently, polycrystalline powders can only be prepared by solid-state sintering (Nature Physics, 2019, 15(10):1058), but polycrystalline powders suffer from numerous crystal defects and difficulty in precisely controlling stoichiometry. Due to the inability 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 advance the fundamental and applied research of this series of crystals. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a class of alkali metal rare earth oxide NaRO2 crystals, their growth methods, and applications. This invention uses a novel 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 delafossite (α phase) and pyrochlore (β phase) structures. The delafossite structure single crystal is grown for the first time, while the pyrochlore structure material is synthesized and grown into single crystals for the first time.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing alkali metal rare earth oxide NaRO2 crystals, wherein the method uses NaOH, Na2CO3 or a mixture thereof as flux to mix with a precursor material of rare earth element R to prepare a crystal growth material, and obtains NaRO2 single crystals through 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 pre-prepared 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 includes: using NaOH, Na2CO3 or a mixture thereof as flux, mixing with a precursor material of rare earth element R to prepare a crystal growth material, heating to melt the crystal growth material, holding at the temperature and then cooling to the growth temperature to grow a crystal to obtain NaRO2 single crystal.

[0013] Preferably, the melting process involves heating to 400–1200°C at a heating rate of <200°C / h and holding at that temperature for 5–72 hours; more preferably, the melting process involves heating to 450–1100°C at a heating rate of ≤100°C / h and holding at that temperature.

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

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

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

[0017] Preferably, when the flux is selected from a mixture of NaOH and Na2CO3, the mass ratio of NaOH to 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), more preferably 1:(8-20), and even 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] In a second aspect, the present invention provides a type of alkali metal rare earth oxide NaRO2 crystal, which is obtained by the above-described growth method.

[0020] Preferably, the alkali metal rare earth oxide NaRO2 crystal comprises α-NaRO2 and β-NaRO2; the single crystal morphology of the α-NaRO2 compound is layered, and the cell parameters are as follows: α = β = 90° and γ = 120°, and the length and width dimensions of the single crystal of the α-NaRO2 compound are 20 to 250 micrometers.

[0021] A third aspect of the present invention provides a β-NaRO2 single crystal with a pyrochlore structure, wherein the compound single crystal morphology of the β-NaRO2 is octahedral; the β-NaRO2 single crystal is hexagonal. Space group, cell parameters are α=β=90°andγ=120°;

[0022] Preferably, the octahedral single crystal of the β-NaRO2 compound has length and width dimensions of 15–50 micrometers;

[0023] Preferably, the growth method of the β-NaRO2 single crystal includes: using a mixture of NaOH and Na2CO3 as a flux, mixing it with a precursor material of rare earth element R to prepare a crystal growth material, heating to melt the crystal growth material, holding it at the temperature and then cooling it to the growth temperature to grow the crystal and obtain a β-NaRO2 single crystal with a pyrochlore structure.

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

[0025] More preferably, the melting process involves heating to 400–1200°C at a heating rate of <200°C / h and holding at that temperature for 5–72 hours; more preferably, the melting process involves heating to 450–1100°C at a heating rate of ≤100°C / h.

[0026] Preferably, the cooling rate of the cooling process is 0.01 to 10 °C / h, and the slow cooling allows crystal nucleation and growth, with the crystal nucleation and growth temperature range being 400 to 1200 °C; more preferably, the cooling rate of the cooling process is 0.1 to 2 °C / h, with the crystal nucleation and growth temperature range being 450 to 1100 °C.

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

[0028] A fourth aspect of the present invention provides the application 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) This invention overcomes the crystal growth problem by finding a suitable flux system (sodium hydroxide, sodium carbonate or sodium carbonate-sodium hydroxide mixture), and grows NaRO2 (R = rare earth element) single crystal with delafossite structure for the first time. At the same time, it synthesizes and grows octahedral single crystal with pyrochlore structure for the first time.

[0031] (2) The crystals grown by this invention require simple conditions, have high growth efficiency, short growth cycle, and are easy to obtain high-quality single crystals. The size of the single crystals can be further controlled by adjusting the growth cycle and 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. Attached Figure Description

[0033] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

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

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

[0036] Figure 3 This is a microscopic morphology diagram of the octahedral β-NaYbO2 crystal prepared in Example 2 of this invention;

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

[0038] Figure 5 This is a microscopic morphology diagram of the NaLuO2 crystal prepared in Example 3 of this invention;

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

[0040] Figure 7 This is a microscopic morphology diagram of the NaTmO2 crystal prepared in Example 4 of this invention;

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

[0042] Figure 9 These are the magnetic susceptibility test data of the octahedral β-NaYbO2 crystal prepared in Example 2 of this invention in the range of 0.4 to 300 K. Detailed Implementation

[0043] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0044] Given that anisotropic NaRO2 (R = rare earth element) single crystals are currently an ideal material platform for studying their properties, the growth of NaRO2 single crystals remains an unresolved issue. Currently, polycrystalline powders can only be prepared through solid-state sintering, but polycrystalline powders suffer from numerous crystal defects and difficulties in precisely controlling stoichiometry. Due to the inability to grow high-quality single-crystal samples, further in-depth experimental research is relatively lacking. Therefore, there is an urgent need to develop a process for preparing alkali metal rare earth oxide NaRO2 single crystals to advance fundamental and applied research on this series of crystals.

[0045] The first typical embodiment of the present invention provides a growth method for preparing alkali metal rare earth oxide NaRO2 crystals. The method uses NaOH, Na2CO3 or a mixture thereof as flux to mix with a precursor material of rare earth element R to prepare crystal growth material, and obtains NaRO2 single crystals through spontaneous crystallization.

[0046] In one or more embodiments of this implementation, 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 pre-prepared NaRO2 crystals.

[0047] In one or more embodiments of this implementation, 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, the method includes: using NaOH, Na2CO3 or a mixture thereof as flux, mixing with a precursor material of rare earth element R to prepare a crystal growth material, heating to melt the crystal growth material, holding at the temperature and then cooling to the growth temperature to grow a crystal to obtain NaRO2 single crystal.

[0049] In one or more embodiments of this implementation, the melting process involves heating to 400–1200°C at a heating rate of <200°C / h and holding at that temperature for 5–72 hours.

[0050] In one or more embodiments of this implementation, the melting process involves heating to 450–1100°C at a heating rate of ≤100°C / h and holding at that temperature.

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

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

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

[0054] In one or more embodiments of this implementation, 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 implementation, when the flux is selected from a mixture of NaOH and Na2CO3, the mass ratio of NaOH to 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), more preferably 1:(8-20), and even more preferably 1:(8-15).

[0056] In one or more embodiments of this implementation, 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 crystal, which is obtained by the above-described growth method.

[0058] In one or more embodiments of this implementation, the alkali metal rare earth oxide NaRO2 crystal includes α-NaRO2 and β-NaRO2; the single crystal morphology of the α-NaRO2 compound is layered, and the cell parameters are as follows: α = β = 90° and γ = 120°; the length and width dimensions of the single crystal of the α-NaRO2 compound are 20 to 250 micrometers.

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

[0060] In one or more embodiments of this implementation, the compound single crystal of β-NaRO2 has a length and width dimension of 15 to 50 micrometers.

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

[0062] In one or more embodiments of this implementation, 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 embodiments of this implementation, the melting process involves heating to 400–1200°C at a heating rate of <200°C / h and holding at that temperature for 5–72 hours.

[0064] In one or more embodiments of this implementation, the melting process involves heating to 450–1100°C at a heating rate of ≤100°C / h and holding at that temperature.

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

[0066] In one or more embodiments of this implementation, 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 embodiments of this implementation, the crystal growth cycle of the alkali metal rare earth oxide NaRO2 single crystal is 3 days or more, more preferably 3 to 5 days, and even more preferably 3 days.

[0068] The fourth typical embodiment of the present invention provides the application 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 this invention, unless otherwise specified, "R" 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 mixtures thereof.

[0070] This invention uses different rare earth raw materials (R) and the flux system of this invention can 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), NaYbO2 single crystals with a quasi-two-dimensional triangular lattice (α phase) of hexagonal phase and a novel pyrochlore structure (β phase) can be prepared.

[0071] The precursor materials of rare earth element R described in this invention include, but are 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 fluxing agents sodium hydroxide, sodium carbonate, or a mixture of sodium carbonate and sodium hydroxide described in this invention are self-fluxing agents, which not only act as fluxing agents but also provide the 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 they can be tableted and then reacted and synthesized in a crucible.

[0074] The crucible used in this invention should be covered to minimize the volatilization of flux at high temperatures, prevent complete volatilization of flux, and prevent corrosion of equipment such as muffle furnaces.

[0075] This invention does not impose any special restrictions on the mixing method of the rare earth element R source and the flux; any mixing method commonly used in the art can be adopted. After mixing the rare earth element R source and the flux to obtain the crystal growth material, this invention further includes a step of sealing the crystal growth material to prevent the volatilization of the raw materials and flux; this invention does not impose any special restrictions on the sealing method; any sealing method commonly used in the art can be adopted.

[0076] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are explanations of the present invention and not limitations thereof.

[0077] Example 1 :

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

[0079] (1) Mix Na2CO3, NaOH and Yb2O3 in a mass ratio of 24:1:4 and mix them evenly to obtain crystal growth material;

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

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

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

[0083] Example 2 :

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

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

[0086] (2) The crystal growth material is loaded into an alumina crucible with a volume of Φ30mm×30mm. The crucible is placed in a muffle furnace and heated to 1050℃ at a rate of 80℃ / h. After holding at this temperature for 24h, the temperature is lowered to 950℃ at a rate of 1.4℃ / h to allow it to crystallize spontaneously. The growth cycle is 3 days, and octahedral NaYbO2 single crystals can be obtained.

[0087] The microstructure of octahedral NaYbO2 single crystals was tested, such as... Figure 3 As shown. By Figure 3 It can be seen that the length and width dimensions of the obtained octahedral NaYbO2 crystals are 20–70 μm.

[0088] X-ray powder diffraction pattern of octahedral NaYbO2 single crystal after grinding, as shown. Figure 4 As shown. By Figure 4 As can be seen, it is consistent with the standard card (PDF#01-085-7885), indicating that a NaYbO2 crystal of good purity was obtained. Furthermore, single-crystal analysis revealed a new pyrochlore structure (β-NaYbO2): room temperature, hexagonal. Space group, cell parameters are α=β=90° and γ=120°.

[0089] Example 3 :

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

[0091] (1) Mix Na2CO3, NaOH and Lu2O3 in a mass ratio of 7.5:1:1 and mix them evenly to obtain crystal growth material;

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

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

[0094] X-ray powder diffraction patterns of octahedral NaLuO2 single crystals after grinding were tested, as shown in the figure. Figure 6 As shown. By Figure 6 As can be seen, it is consistent with the standard card (PDF#04-018-7651), indicating that the obtained crystal is β-NaLuO2. Room temperature single-crystal diffraction experiments confirmed that it belongs to the hexagonal category. Space group, cell parameters are α=β=90° and γ=120°.

[0095] Example 4 :

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

[0097] (1) Mix Na2CO3 and Tm2O3 at a mass ratio of 10:1 to obtain crystal growth material;

[0098] (2) The crystal growth material is loaded into an alumina crucible with a volume of Φ30mm×30mm. The crucible is placed in a muffle furnace and heated to 1000℃ at a rate of 80℃ / h. After holding at the temperature for 24h, the temperature is lowered to 950℃ at a rate of 1℃ / h. The crystal is allowed to cool down and crystallize spontaneously for 2 days to obtain octahedral NaTmO2 single crystals.

[0099] The microstructure of octahedral NaTmO2 single crystals was tested, such as... Figure 7 As shown. By Figure 7 It can be seen that the length and width dimensions of the obtained octahedral NaTmO2 crystals are 20–30 μm.

[0100] X-ray powder diffraction patterns of octahedral NaTmO2 single crystals after grinding were tested, as shown in the figure. Figure 8 As shown. By Figure 8 As can be seen, it is consistent with the standard card (PDF#00-047-1678), indicating that β-NaTmO2 crystals were obtained. Room temperature single-crystal diffraction experiments confirmed that it belongs to the hexagonal class. Space group, cell parameters are α=β=90° and γ=120°.

[0101] Example 5 :

[0102] This embodiment provides the magnetic susceptibility of the pyrochlore-structured 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 testing platform. The mass of the β-NaYbO2 sample tested was 42 mg. Figure 9 As shown.

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

[0105] Depend on Figure 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 Figure 9 (c) It can be seen that under a magnetic field of 20 Oe, the three curves of ZFC, FC-C and FC-W coincide in the temperature range of 0.4 to 1.8 K, the sample is paramagnetic and no spin freezing characteristics were found.

[0107] Depend on Figure 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 at frequencies of 10, 467 and 996 Hz, it can be seen that no signs of spin freezing or frequency dependence were observed in the sample.

[0108] The spin fault-blocking factor f is a physical quantity that measures the fault-blocking strength of a material, defined as f = |θ cw | / Tc, if f>10, it indicates strong spin fault blocking; the larger f is, the stronger the fault blocking and the stronger the interaction between spins. For β-NaYbO2, θ cw The temperature is -7K, and it does not exhibit long-range magnetic order or spin glass states even at a low temperature of 0.4K. It can be expressed as T c We use 0.4K to estimate the lower limit of f, i.e., f > 17.5. Such a large spin frustration f indicates that this material is a potential quantum spin liquid material, with good prospects in the study of magnetic frustration, quantum fluctuations, and quantum entanglement.

[0109] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A growth method for producing an alkali rare earth oxide NaRO2 crystal, characterized by, The method uses NaOH, Na2CO3 or a mixture thereof as a fluxing agent, 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; 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 pre-prepared NaRO2 crystals; The alkali rare earth oxide NaRO2 single crystal has R selected from one or more of lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium; The growth method comprises: using NaOH, Na2CO3 or a mixture thereof as a fluxing agent, mixing with a precursor of a rare earth element R to prepare a crystal growth material, melting the crystal growth material by heating, cooling to a growth temperature after holding, and growing crystals to obtain a NaRO2 single crystal; The melting process is heating to 400-1200℃ at a heating rate <200℃ / h and holding for 5-72h; the cooling rate of the cooling process is 0.01-10℃ / h, and the crystal nucleation and growth temperature range is 400-1200℃; and the crystal growth period of the alkali rare earth oxide NaRO2 single crystal is 3 days or more.

2. The growth method of claim 1, wherein, The melting process is heating to 450-1100℃ at a heating rate ≤100℃ / h and holding.

3. The growth method of claim 1, wherein, The cooling rate of the cooling process is 0.1-2℃ / h, and the crystal nucleation and growth temperature range is 450-1100℃.

4. The growth method of claim 1, wherein, The crystal growth period of the alkali rare earth oxide NaRO2 single crystal is 3-5 days.

5. The growth method of claim 4, wherein, The crystal growth period of the alkali rare earth oxide NaRO2 single crystal is 3 days.

6. The growth method of claim 1, wherein, The growth temperature is 1000-1200℃, and α -NaRO2; the growth temperature is 400-1050℃, and β -NaRO2.

7. The growth method of claim 1, wherein, When the fluxing agent is a mixture of NaOH and Na2CO3, the mass ratio of NaOH to Na2CO3 is (1-100):(1-100); and the mass ratio of the precursor of the rare earth element R to the fluxing agent is 1:(5-40).

8. The growth method of claim 7, wherein, The mass ratio of the precursor of the rare earth element R to the fluxing agent is 1:(8-20).

9. The growth method of claim 8, wherein, The mass ratio of the precursor of the rare earth element R to the fluxing agent is 1:(8-15).

10. The growth method of claim 1, wherein, The reaction atmosphere of the mixing reaction is selected from one or more of air, nitrogen, argon, hydrogen and carbon dioxide.

11. An alkali rare earth oxide NaRO2 crystal, characterized by, Obtained by the growth method according to any one of claims 1-10.

12. The alkali rare earth oxide NaRO2 crystal of claim 11, wherein, comprising α NaRO2and β NaRO2; the compound single crystal morphology of the a-NaRO2is lamellar morphology, the cell parameters are a= b= 3.3506(1) Å, c=16.5230(8) Å, α=β=90º and γ=120º; the length and width size of the compound single crystal of the a-NaRO2is 20~250 microns.

13. A substance with a pyrochlore structure β -NaRO2 single crystal, characterized in that, The β The compound of NaRO2 has an octahedral morphology; the β The single crystal of NaRO2 is hexagonal R m space group, and the cell parameters are a = 6.7 ± 0.1 Å, b = 6.7 ± 0.1 Å, and c = 16.5 ± 0.2 Å. The β The compound of NaRO2 has a single crystal length and width size of 15-50 microns. The β The growth method of the NaRO2 single crystal includes: preparing a crystal growth material by mixing a mixture of NaOH and Na2CO3 as a flux with a precursor of a rare earth element R, melting the crystal growth material by heating, cooling to a growth temperature after keeping the temperature, and growing a crystal to obtain a NaRO2 single crystal having a pyrochlore structure. β The NaRO2 single crystal The precursor of the rare earth element R is a rare earth oxide, and the rare earth oxide is Ho2O3, Er2O3, Tm2O3, Yb2O3 or Lu2O3; The melting process is heating to 400-1200℃ at a heating rate <200℃ / h and holding for 5-72h; The cooling rate of the cooling process is 0.01-10℃ / h, and the crystal nucleation and growth temperature range is 400-1200℃; The β The crystal growth period of the NaRO2 single crystal is 3 days or more.

14. The pyrochlore structure as described in claim 13 β -NaRO2 single crystal, characterized in that, The melting process is heating to 450-1100℃ at a heating rate ≤100℃ / h and holding.

15. The material of claim 13 having a pyrochlore structure, wherein: 0 < x < 0.1, 0 < y < 0.1, and 0 < z < 0.

1. β - a NaRO2 single crystal, characterized in that, The cooling rate of the cooling process is 0.1-2℃ / h, and the crystal nucleation and growth temperature range is 450-1100℃.

16. The material of claim 13 having a pyrochlore structure, wherein: 0 < x < 0.1, 0 < y < 0.1, and 0 < z < 0.

1. β - a NaRO2 single crystal, characterized in that, The β The crystal growth period of NaRO2 single crystals is 3-5 days.

17. The material of claim 13 having a pyrochlore structure, wherein: 0 < x < 0.1, 0 < y < 0.1, and 0 < z < 0.

1. β - a NaRO2 single crystal, characterized in that, The β The crystal growth period of NaRO2 single crystals was 3 days.

18. Use of the alkali rare earth oxide NaRO2 crystal obtained by the growth method according to any one of claims 1 to 10 in the study of magnetic frustration, quantum fluctuation, quantum entanglement or super-low temperature magnetic refrigeration.

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