An intrinsic superlattice single crystal material and a method for preparing the same

Abstract

This invention discloses an intrinsic superlattice single-crystal material and its preparation method, belonging to the field of single-crystal growth technology. The single crystal has the chemical formula BaLaMnSb4, and its crystal structure consists of alternating stacks of BaMnSb2 and LaSb2 layers in an intrinsic superlattice configuration perpendicular to the layer direction. This invention utilizes a self-fluxing method to grow a novel magnetic topological material, BaLaMnSb4, with an intrinsic superlattice. This single crystal has a structure composed of BaMnSb2 and LaSb2 layers... ­2 The alternating intrinsic superlattice structure, with its high single-crystal quality, few defects, and large size, is an ideal research platform for magnetic topological materials.

Description

Technical Field

[0001] This invention relates to the field of single crystal growth technology for magnetic materials, specifically an intrinsic superlattice single crystal material and its preparation method. Background Technology

[0002] BaMnSb2 is a magnetic topological material that has been extensively studied in recent years. This compound consists of Sb, Ba, and MnSb4 layers stacked along the c-axis, with Sb atoms arranged in a zigzag chain pattern between the layers. Both theoretical calculations and experiments have confirmed the existence of a Dirac-type linear dispersion band near the Fermi level in BaMnSb2. Furthermore, due to the antiferromagnetic order provided by Mn, this system becomes one of the few ideal platforms for realizing magnetic topological states. Researchers have observed the quantum Hall effect in BaMnSb2 single crystals, indicating that its electronic states possess high coherence and topological nontriviality.

[0003] LaSb₂ is another type of correlated electron system with a layered structure. Its crystal structure consists of alternating layers of La and Sb atoms, with Sb atoms forming a one-dimensional zigzag chain structure within the layers, highly similar to the Sb atom arrangement in BaMnSb₂. LaSb₂ exhibits charge density waves, extremely high magnetoresistivity (up to 10000%), and possible topological electronic states, making it a research hotspot in condensed matter physics. However, LaSb₂ itself lacks long-range magnetic order and cannot independently serve as a research platform for magnetic topological physics.

[0004] In recent years, constructing superlattice structures by alternately stacking different two-dimensional materials at the atomic scale has become an important means of controlling the electronic transport properties of materials. Artificial superlattices are typically formed by periodically stacking two or more materials, with period lengths ranging from a few nanometers to tens of nanometers, significantly larger than the original lattice constant. In contrast, intrinsic superlattices are formed naturally driven by the thermodynamics within the material, with period lengths that are integer multiples or simple fractional multiples of the unit cell lattice constant. They exhibit no abrupt changes in chemical composition at the interfaces and serve as important structural carriers connecting microscopic interactions and macroscopic quantum properties. Material systems with intrinsic superlattice structures can directly demonstrate strongly correlated physics and exhibit competitive or synergistic relationships with quantum order phenomena such as superconductivity and charge density waves, which is of great significance for understanding unconventional superconductivity and designing novel quantum materials.

[0005] In the electronic state distribution of three-dimensional momentum space, compounds formed by Sb and Mn readily exhibit anisotropic linear dispersion near the Fermi level. Due to the antiferromagnetic order of Mn, the AMnSb2 (A = Ca, Sr, Ba, Eu, Yb) system has become a research hotspot for magnetic topological materials. Among them, BaMnSb2 has a space group of I4 / mmm, and theoretical predictions have been experimentally confirmed to exhibit Dirac fermion behavior. As an asymmetric crystal, LaSb2 is composed of alternating layers of La and Sb atoms, with Sb atoms forming a one-dimensional zigzag chain structure within the layers. This structural feature is highly similar to the Sb atom arrangement in BaMnSb2. LaSb2 has attracted considerable attention due to its charge density wave, superconductivity, extremely high magnetoresistivity, and potential topological properties.

[0006] Currently, there are no reports on the formation of a new compound BaLaMnSb4 by alternating stacking of BaMnSb2 and LaSb2 in an intrinsic superlattice, nor are there any publicly available methods for the single-crystal growth of this compound. Summary of the Invention

[0007] In view of this, the present invention provides an intrinsic superlattice single crystal material and its preparation method. The BaLaMnSb4 single crystal is formed by the natural alternation of BaMnSb2 and LaSb2 layers at the atomic scale. It has high crystal quality and can reach the millimeter scale in size, providing an ideal natural quantum material platform for studying magnetic topological physics, the coupling effect of charge density waves and magnetic order.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] In a first aspect, this invention discloses an intrinsic superlattice single-crystal material with the chemical formula BaLaMnSb4. Its crystal structure consists of alternating stacks of BaMnSb2 and LaSb2 layers in an intrinsic superlattice configuration perpendicular to the layer direction. This invention utilizes a self-flush method to grow a novel magnetic topological material, BaLaMnSb4, with an intrinsic superlattice structure. This single crystal exhibits high quality, few defects, and a large size, making it an ideal research platform for magnetic topological materials.

[0010] Furthermore, the lamellar area of ​​the single crystal material is not less than 2 mm. 2 The thickness is not less than 0.5 mm.

[0011] Furthermore, the single crystal exhibits charge density wave phase transition characteristics in the temperature range of 220-240 K.

[0012] Secondly, this invention discloses a method for preparing the intrinsic superlattice single crystal material as described above, comprising the following steps:

[0013] S1: Under an inert gas atmosphere, Ba source, La source, Mn source and Sb source are mixed in an atomic ratio of Ba:La:Mn:Sb = (0.7-0.9):(0.05-0.15):1:x and placed in a high-temperature resistant container; wherein, the molar ratio of x to Mn is greater than 4:1, so that Sb acts as a flux during crystal growth;

[0014] Low purity of raw materials and the introduction of impurities are significant reasons for low single crystal quality during single crystal growth. This invention treats the Ba and La blocks before use, removing the surface oxide layer in a glove box, and uses Sb as a flux to prevent the introduction of other impurity elements. These methods ensure the purity of the raw materials, achieving uniform and high-quality single crystal growth.

[0015] S2: Place the high-temperature resistant container containing the raw materials into a sealed container, evacuate the vacuum, and then seal it.

[0016] S3: Heat the sealed container to 750-850℃ and keep it at that temperature to allow the raw materials to fully melt and mix.

[0017] S4: Cool the sealed container to 550-650℃ to separate the solid and liquid, remove excess flux, and obtain BaLaMnSb4 single crystal after cooling.

[0018] Furthermore, in step S1, 4 < x < 10.

[0019] Furthermore, the Ba source is Ba lumps with a purity of not less than 99.99%, the La source is La lumps with a purity of not less than 99.5%, the Mn source is Mn powder with a purity of not less than 99.95%, and the Sb source is Sb particles with a purity of ≥99.9999%.

[0020] Furthermore, in step S1, the inert gas atmosphere is specifically: a high-purity argon atmosphere with an oxygen content of <0.1 PPM and a water content of <0.1 PPM.

[0021] Furthermore, in step S2, the vacuum level is lower than 2 × 10⁻⁶. -3 Pa.

[0022] Furthermore, in step S4, the sealed container is cooled to 550-650℃ at a rate of 1-3℃ / h. When the quartz tube (sealed container) is in the muffle furnace, excessively rapid heating and cooling can cause thermal stress buildup, leading to tube breakage and exposure of the raw material to air, resulting in experimental failure. Additionally, if the quartz tube has sharp points, heat will accumulate at those points, potentially causing breakage; therefore, sharp points should be minimized. This invention precisely controls the heating and cooling rates, effectively reducing thermal stress buildup in the quartz tube and preventing breakage. This improvement not only effectively prevents oxidation of the raw material during growth but also prevents oxidation of the single crystal sample due to quartz tube breakage during centrifugation, thus improving the quality of the single crystal.

[0023] During crystal growth, oxygen and water have a significant impact on experimental results, and inadequate sealing is a major cause of raw material oxidation and crystal growth failure. This invention, when using a propane flame to seal the tube, first rotates it once in the middle of the quartz column, then once at the top, causing the upper part of the quartz tube to significantly retract. After the quartz tube cools down, the upper part is knocked off, and the broken area is then heated with a propane flame to soften and smooth it. By optimizing the sealing effect, the problems of raw material oxidation and low single crystal quality caused by air can be effectively avoided.

[0024] Furthermore, in step S1, during the ingredient preparation process, the Ba source, La source, and Mn source are evenly placed at the bottom of the high-temperature resistant container, and then the Sb source is placed on top.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] The BaLaMnSb4 single crystal synthesized in this invention possesses a unique intrinsic superlattice structure, formed by the natural alternation of BaMnSb2 and LaSb2 layers at the atomic scale. This crystal exhibits high crystal quality, low defect density, and millimeter-scale dimensions. This single crystal is the first to couple a magnetic topological layer (BaMnSb2) and a charge density wave layer (LaSb2) within the same intrinsic superlattice system, demonstrating a clear charge density wave phase transition near 230 K while maintaining good metallic conductivity. This material provides an ideal natural quantum material platform for studying the competition and cooperation mechanisms between magnetic order, topological electronic states, and charge density waves, and is expected to advance experimental research in cutting-edge fields such as unconventional superconductivity, quantum critical behavior, and low-dimensional correlation physics.

[0027] This invention employs a self-fluxing method to grow BaLaMnSb4 single crystals. By controlling the raw material ratio and heating / cooling rates, atomic-level spontaneous alternating stacking of BaMnSb2 and LaSb2 layers is achieved within a closed vacuum system, successfully obtaining a previously unreported intrinsic superlattice phase. This method utilizes excess Sb as both a reactant and a flux, avoiding the introduction of impurities. In-situ separation of the crystal and melt is achieved through high-temperature centrifugation, resulting in a simple and reproducible process. Compared to traditional solid-state reaction methods and artificially stacked heterojunction processes, this invention requires no complex equipment, offers controllable single crystal growth cycles, and produces products with high purity and good crystal integrity, providing a generalizable preparation paradigm for the exploration of novel intrinsic superlattice quantum materials. Attached Figure Description

[0028] Figure 1 An optical photograph of the BaLaMnSb4 single crystal prepared in Example 1 of this invention.

[0029] Figure 2 This is the energy dispersive spectroscopy (EDS) spectrum of the BaLaMnSb4 single crystal prepared in Example 1 of this invention.

[0030] Figure 3 The X-ray diffraction pattern is shown for the BaLaMnSb4 single crystal prepared in Example 1 of this invention.

[0031] Figure 4 This is a transmission electron microscope image of the BaLaMnSb4 single crystal prepared in Example 1 of the present invention.

[0032] Figure 5 High-resolution transmission electron microscope image and elemental plane distribution diagram of the BaLaMnSb4 single crystal prepared in Example 1 of this invention.

[0033] Figure 6 The resistivity of the BaLaMnSb4 single crystal prepared in Example 1 of this invention is shown as a function of temperature. Detailed Implementation

[0034] To facilitate understanding of the present invention, a more comprehensive description will be given below with reference to specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0036] Example 1

[0037] This embodiment provides a method for preparing BaLaMnSb4 single crystals with an intrinsic superlattice structure. The specific steps are as follows:

[0038] S1: Raw material preparation and pretreatment

[0039] The experiment was conducted in a glove box filled with high-purity argon gas, ensuring that the oxygen content and water content inside the box were <0.1 ppm and <0.1 ppm, respectively. The raw materials used in the experiment included: Ba blocks (Aladdin, purity ≥99.99%), La blocks (Aladdin, purity ≥99.5%), Mn powder (Aladdin, purity ≥99.95%), and Sb granules (Aladdin, purity ≥99.9999%). The pretreated alumina crucible, quartz tube (inner diameter 17 mm, outer diameter 19 mm, length approximately 25 cm), and quartz column (diameter 16 mm) were removed from the vacuum drying oven.

[0040] The quartz tube and quartz column were ultrasonically cleaned in anhydrous ethanol for 15 minutes, then wiped clean with a lint-free cloth and dried at 150°C. The alumina crucible was baked at 1500°C for 4 days to remove any impurities such as binders that might be present. The treated alumina crucible, quartz tube, and quartz column were placed in the glove box transition chamber and transferred to the glove box after three gas purging cycles. In the glove box, the oxide layer on the surface of the Ba and La blocks was scraped off using a clean tool until the metallic luster was exposed, and surface debris was gently wiped away with lint-free paper.

[0041] S2: Ingredients and Loading

[0042] Weigh the above high-purity raw materials according to the molar ratio of Ba : La : Mn : Sb = 0.8 : 0.1 : 1 : 5.5. When loading, first place the Ba and La blocks at the bottom of the alumina crucible, then add the Mn powder, and finally cover the top layer with Sb particles.

[0043] S3: Quartz tube packaging

[0044] Insert a small amount of quartz wool into the bottom of the quartz tube beforehand. Place the alumina crucible containing the raw material into the quartz tube, and then insert a section of quartz wool on top of the crucible to leave space for centrifugation. Finally, place the quartz column in the tube. Temporarily seal the opening of the quartz tube with sealing film and remove it from the glove box.

[0045] Quickly connect the quartz tube to the vacuum system for evacuation. First, evacuate to a low vacuum level, then fill with high-purity argon gas for cleaning; repeat this process three times. Finally, evacuate until the internal pressure is below 2 × 10⁻⁶. -3After Pa, a hydrogen-oxygen flame (or propane-oxygen flame) is used for melting and sealing. The gas ratio is adjusted to ensure the flame temperature is sufficient to melt the quartz tube while maintaining a vacuum inside. During sealing, the middle of the quartz column is first heated to melt it and allow it to adhere to the tube wall. Then, the upper part of the quartz column is heated to retract it, facilitating the subsequent removal of excess tube material. After the quartz tube cools, the excess portion at the top is knocked off, and the broken edge is melted and polished with a flame to eliminate sharp parts.

[0046] S4: Crystal growth

[0047] Place the sealed quartz tube vertically into a large alumina crucible and then into a muffle furnace. Set the heating program: raise the temperature from room temperature to 800°C at a rate of 20°C / h, hold for 10 hours to allow the raw materials to fully melt and mix evenly. Then slowly cool the temperature to 610°C at a rate of 2°C / h.

[0048] S5: Centrifugation and Post-processing

[0049] When the furnace temperature drops to 610℃, quickly remove the quartz tube, invert it and place it in a centrifuge. Centrifuge at 2000 r / min for 3 minutes to separate the excess liquid Sb flux from the crystallized solid using centrifugal force.

[0050] After the quartz tube has cooled to room temperature naturally, it is transferred to a glove box. The quartz tube is carefully broken open, and the crystal is removed to obtain a plate-like BaLaMnSb4 single crystal with a metallic luster. The single crystal size obtained in this embodiment can reach approximately 2 mm × 1 mm × 0.5 mm (e.g., ...). Figure 1 (As shown).

[0051] Example 2

[0052] This embodiment provides a method for preparing BaLaMnSb4 single crystals with an intrinsic superlattice structure. Compared with Example 1, the main difference is the adjustment of the ratio of Ba source to La source. The specific steps are as follows:

[0053] S1: Raw material preparation and pretreatment

[0054] The alumina crucible, quartz tube, and quartz column were cleaned, dried, and pretreated according to the method in Example 1. The surfaces of Ba blocks (purity ≥99.99%), La blocks (purity ≥99.5%), and Mn powder (purity ≥99.95%) were cleaned in a high-purity argon glove box with oxygen content <0.1 ppm and water content <0.1 ppm.

[0055] S2: Ingredients and Loading

[0056] Weigh the above high-purity raw materials according to the molar ratio of Ba : La : Mn : Sb = 0.8 : 0.1 : 1 : 5.5. When loading, first place the Ba and La blocks at the bottom of the alumina crucible, then add the Mn powder, and finally cover the top layer with Sb particles.

[0057] S3: Quartz tube packaging

[0058] Following the method in Example 1, an alumina crucible containing the raw material was placed into a quartz tube, stuffed with quartz wool and a quartz column, temporarily sealed with sealing film, and then removed. A vacuum system was connected, and the tube was evacuated until the pressure inside was below 2 × 10⁻⁶. -3 Pa, using an oxyhydrogen flame to melt and seal.

[0059] S4: Crystal growth

[0060] Place the sealed quartz tube vertically in the muffle furnace. Set the heating program: raise the temperature from room temperature to 800°C at a rate of 20°C / h, hold for 10 hours to allow the raw materials to fully melt and mix evenly. Then slowly cool the temperature to 580°C at a rate of 2.5°C / h.

[0061] S5: Centrifugation and Post-processing

[0062] When the furnace temperature drops to 580°C, the quartz tube is quickly removed, inverted, and placed in a centrifuge. It is centrifuged at 2000 r / min for 5 minutes to remove excess liquid Sb flux. After the quartz tube cools naturally to room temperature, it is transferred to a glove box, broken open, and the crystal is removed to obtain a plate-like BaLaMnSb4 single crystal with a metallic luster. The single crystal size obtained in this embodiment can reach approximately 1.8 mm × 1.2 mm × 0.4 mm.

[0063] X-ray diffraction analysis showed that the diffraction pattern of the product obtained in this example was basically consistent with that of Example 1, with sharp diffraction peaks indicating that it could be identified as the same phase. Energy dispersive spectroscopy analysis showed that its atomic ratio of Ba:La:Mn:Sb was close to 1:1:1:4. Transmission electron microscopy confirmed that the crystal also has an intrinsic superlattice structure with alternating BaMnSb2 and LaSb2 layers.

[0064] Example 3

[0065] This embodiment provides a method for preparing BaLaMnSb4 single crystals with an intrinsic superlattice structure. Compared with Example 1, the main adjustments are to the cooling rate and centrifugation temperature. The specific steps are as follows:

[0066] S1: Raw material preparation and pretreatment

[0067] The alumina crucible, quartz tube, and quartz column were cleaned, dried, and pretreated according to the method in Example 1. The surfaces of Ba blocks (purity ≥99.99%), La blocks (purity ≥99.5%), and Mn powder (purity ≥99.95%) were cleaned in a high-purity argon glove box with oxygen content <0.1 ppm and water content <0.1 ppm.

[0068] S2: Ingredients and Loading

[0069] Weigh the above high-purity raw materials according to the molar ratio of Ba : La : Mn : Sb = 0.8 : 0.1 : 1 : 5.5. When loading, first place the Ba and La blocks at the bottom of the alumina crucible, then add the Mn powder, and finally cover the top layer with Sb particles.

[0070] S3: Quartz tube packaging

[0071] Following the method in Example 1, an alumina crucible containing the raw material was placed into a quartz tube, stuffed with quartz wool and a quartz column, temporarily sealed with sealing film, and then removed. A vacuum system was connected, and the tube was evacuated until the pressure inside was below 2 × 10⁻⁶. -3 Pa, using an oxyhydrogen flame to melt and seal.

[0072] S4: Crystal growth

[0073] Place the sealed quartz tube vertically in the muffle furnace. Set the heating program: raise the temperature from room temperature to 800°C at a rate of 20°C / h, hold for 10 hours to allow the raw materials to fully melt and mix evenly. Then slowly cool the temperature to 620°C at a rate of 1.5°C / h.

[0074] S5: Centrifugation and Post-processing

[0075] When the furnace temperature drops to 620°C, the quartz tube is quickly removed, inverted, and placed in a centrifuge. It is centrifuged at 2000 r / min for 3 minutes to remove excess liquid Sb flux. After the quartz tube cools naturally to room temperature, it is transferred to a glove box, broken open, and the crystal is removed to obtain a plate-like BaLaMnSb4 single crystal with a metallic luster. The single crystal size obtained in this embodiment can reach approximately 2.2 mm × 1.5 mm × 0.6 mm.

[0076] X-ray diffraction analysis showed that the diffraction pattern of the product obtained in this example was basically consistent with that of Example 1, with sharp diffraction peaks indicating that it could be identified as the same phase. Energy dispersive spectroscopy analysis showed that its atomic ratio of Ba:La:Mn:Sb was close to 1:1:1:4. Transmission electron microscopy confirmed that the crystal also possessed an intrinsic superlattice structure with alternating stacked BaMnSb2 and LaSb2 layers. Electrical transport tests showed that the crystal also exhibited charge density wave (CDW) phase transition characteristics near 230 K.

[0077] To systematically characterize the crystal structure, chemical composition, and physical properties of the product obtained in Example 1, this application conducted the following tests on the obtained BaLaMnSb4 single crystal. First, the crystal morphology was observed using an optical microscope, and the results are as follows: Figure 1 As shown, the crystals exhibit a regular layered structure with a bright metallic luster, and their size reaches approximately 2 mm × 1 mm × 0.5 mm. The composition of the crystal micro-regions was analyzed using energy-dispersive X-ray spectroscopy (SEM-EDS) with a scanning electron microscope, and the results are as follows... Figure 2 As shown in Table 1 below, the measured atomic ratio of Ba:La:Mn:Sb is close to 1:1:1:4, which is basically consistent with the target stoichiometric ratio. X-ray diffraction (XRD) was used to analyze the phase composition of the single crystal and its ground powder, and the results are as follows: Figure 3 As shown, all diffraction peaks can be indexed to the tetragonal crystal system. The diffraction peaks are sharp and free of impurity peaks, indicating that the obtained product is a high-crystallinity pure-phase BaLaMnSb4 single crystal. Further observation of the crystal microstructure using transmission electron microscopy (TEM) yielded the following results: Figure 4 and Figure 5 As shown, the crystal is clearly composed of alternating layers of BaMnSb2 and LaSb2 along specific crystal planes in an intrinsic superlattice configuration. The layered structure is regular and ordered with clear interfaces. Finally, the electrical transport properties of the single crystal were tested using a Power Profiling System (PPMS), and the resistivity versus temperature curve is shown below. Figure 6 As shown, an anomalous resistance bulge was observed near 230 K, a feature associated with the charge density wave (CDW) phase transition, further confirming the rich quantum properties of this material. These test results demonstrate that this application successfully prepared a high-quality, novel two-dimensional magnetic material, BaLaMnSb4, with an intrinsic superlattice structure.

[0078] Table 1

[0079]

[0080] Although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0081] Therefore, the above description is only a preferred embodiment of this application and is not intended to limit the scope of this application; that is, all equivalent modifications made in accordance with the scope of the claims of this application shall be within the protection scope of the claims of this application.

Claims

1. An intrinsic superlattice single crystal material, characterized in that, Its chemical formula is BaLaMnSb4, and its crystal structure is composed of BaMnSb2 layers and LaSb2 layers stacked alternately in an intrinsic superlattice form perpendicular to the layer direction.

2. The intrinsic superlattice single crystal material of claim 1, wherein, The sheet layer area of the single crystal material is not less than 2 mm 2 , and the thickness is not less than 0.5 mm.

3. The intrinsic superlattice single crystal material of claim 1, wherein, The single crystal exhibits charge density wave phase transition characteristics in the temperature range of 220-240 K.

4. A method of producing an intrinsic superlattice single crystal material as claimed in any one of claims 1 to 3, characterised in that, Includes the following steps: S1: Under an inert gas atmosphere, Ba source, La source, Mn source and Sb source are mixed in an atomic ratio of Ba:La:Mn:Sb = (0.7-0.9):(0.05-0.15):1:x and placed in a high-temperature resistant container; wherein, the molar ratio of x to Mn is greater than 4:1, so that Sb acts as a flux during crystal growth; S2: Place the high-temperature resistant container containing the raw materials into a sealed container, evacuate the vacuum, and then seal it. S3: Heat the sealed container to 750-850℃ and keep it at that temperature to allow the raw materials to fully melt and mix. S4: Cool the sealed container to 550-650℃ to separate the solid and liquid, remove excess flux, and obtain BaLaMnSb4 single crystal after cooling.

5. The method of claim 4, wherein, In step S1, 4 < x < 10.

6. The method of claim 4, wherein, The Ba source is Ba blocks with a purity of not less than 99.99%, the La source is La blocks with a purity of not less than 99.5%, the Mn source is Mn powder with a purity of not less than 99.95%, and the Sb source is Sb particles with a purity of ≥99.9999%.

7. The method according to claim 4, characterized in that, In step S1, the inert gas atmosphere is specifically: a high-purity argon atmosphere with an oxygen content of <0.1 PPM and a water content of <0.1 PPM.

8. The method according to claim 4, characterized in that, In step S2, the vacuum degree is lower than 2 x 10 -3 Pa.

9. The method according to claim 4, characterized in that, In step S4, the sealed container is cooled to 550-650℃ at a rate of 1-3℃ / h.

10. The method according to claim 4, characterized in that, In step S1, during the ingredient preparation process, the Ba source, La source, and Mn source are evenly placed at the bottom of the high-temperature resistant container, and then the Sb source is placed on top.

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