Hexagonal scandium hydride and preparation method thereof

Abstract

The invention discloses a hexagonal scandium hydrogen compound and a preparation method thereof, and the preparation method comprises the following steps: taking a borane ammine complex as a solid hydrogen source, tabletting the borane ammine complex and elemental scandium through a mold, and stacking according to'hydrogen source-scandium-hydrogen source '; loading the assembly into a CVD diamond single crystal tube with holes, and carrying out secondary wrapping with NaCl to form a sealed reaction unit; carrying out segmented pressurization / depressurization in a cubic press, electrifying and segmented heating under the condition of 800-1200 DEG C, and carrying out pressure maintaining and cooling to complete synthesis; according to the method, local high hydrogen partial pressure is established under the action of moderate high pressure and double-layer sealing, external introduction of high-pressure hydrogen is avoided, and the equipment complexity and the safety risk are reduced; the product prepared by the invention is hexagonal-phase ScH3, can stably exist at normal temperature and normal pressure, and is different from cubic-phase ScH3 which can only be synthesized under an extreme high-pressure condition and cannot be kept stable after pressure relief, XRD and structure refinement are consistent with the standard, and the process can be repeated and amplified.

Description

Technical Field

[0001] This invention relates to the field of superconducting materials and high-pressure synthesis technology, and more specifically, to a hexagonal scandium hydrogen compound and its preparation method. Background Technology

[0002] Superconducting materials possess advantages such as high current-carrying capacity and low loss. The zero-resistance property of superconductors can be used to manufacture superconducting cables, enabling efficient power transmission; their perfect diamagnetism can be utilized to create superconducting magnetic levitation trains and frictionless bearings. However, traditional superconducting materials have relatively low superconducting transition temperatures, typically requiring liquid nitrogen or liquid helium environments to operate, severely limiting their wide-ranging applications at room temperature and pressure. Therefore, developing novel materials with higher superconducting transition temperatures has become an important research goal in the field of superconductivity.

[0003] In recent years, hydrogen-rich compounds based on the chemical precompression effect have been considered one of the most promising candidate systems for achieving high-temperature superconductivity. Previous studies have shown that some hydrogen-rich compounds can form stable phases under high pressure and exhibit excellent superconducting properties. For example, in the early stages, superconductivity was observed in the silane (SiH4) system at pressures above 60 GPa, and a superconducting transition temperature of 17 K was achieved at 90 GPa. These results verified the possibility of achieving high-temperature superconductivity in hydride systems under high pressure. Subsequently, multiple experimental and theoretical studies have further discovered several hydrogen-rich compounds with high superconducting transition temperatures, driving rapid development in this field.

[0004] However, existing hydride superconductors generally suffer from the following limitations: on the one hand, most materials require extremely high pressures (typically exceeding 100 GPa) to remain stable, and are prone to decomposition or instability under normal temperature and pressure conditions; on the other hand, existing synthesis processes rely on the direct introduction of high-purity hydrogen under ultra-high pressure, resulting in high equipment costs, stringent experimental conditions, limited production, and safety hazards due to the potential for hydrogen explosion. Therefore, these materials are difficult to prepare in a controlled manner and achieve industrial application.

[0005] In transition metal hydride systems, scandium hydrides are predicted to possess potentially excellent superconducting properties due to their unique electronic structure. However, currently reported scandium hydrides are limited to cubic phase structures, which require extreme pressures exceeding 100 GPa to obtain and cannot remain stable at room temperature and pressure, thus losing their practical application value. Therefore, how to synthesize a novel scandium hydride compound that can exist stably at room temperature and pressure under controlled conditions and has potential application prospects has become an important problem that urgently needs to be solved. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for preparing hexagonal scandium hydride compounds, so as to solve the problem that the synthesis of existing scandium hydrides depends on ultra-high pressure and external hydrogen gas, which is not only harsh and has safety risks, but also the resulting phase is unstable at room temperature and pressure.

[0007] To overcome the shortcomings of the prior art, the present invention provides a method for preparing hexagonal scandium hydrogen compounds, comprising the following steps: S1: After compressing elemental scandium and borane-amine complex into tablets, the tablets are stacked in the order of borane-amine complex-scandium-borane-amine complex to form an assembly; S2: The assembly is first encapsulated using a CVD single crystal tube, and then encapsulated a second time using NaCl to form a sealed reaction unit; S3: The reaction unit is placed in a high-pressure device, and segmented pressurization and pressure holding are carried out within a pressure range of 2±0.2 GPa to 5±1.0 GPa. During the pressurization and pressure holding process, preliminary heating and heat holding treatment and high-temperature heat holding treatment at 800–1200℃ are carried out in sequence to prepare hexagonal scandium hydrogen compound.

[0008] Compared with existing technologies, the preparation method of hexagonal scandium hydride of the present invention has the following advantages: The preparation method utilizes the hydrogen released by the decomposition of borane-ammonia complexes under high temperature and high pressure conditions as a hydrogen source, avoiding the complex processes and explosion risks associated with external hydrogen supply. Furthermore, the synthesis pressure and temperature are directly controlled using a domestically produced six-sided top press, achieving rapid synthesis of high-purity SCH3 within a relatively low pressure range. By employing the initial encapsulation of CVD single crystal tubes and the secondary encapsulation with NaCl to construct a stable and sealed reaction unit, the purity of the reaction environment is maintained, and the risks associated with CVD are avoided. The invention addresses the cracking caused by the brittleness of single-crystal tubes. Simultaneously, it utilizes amorphous boron to replace traditional pyrophyllite and redesigns the steel cap structure, effectively reducing temperature loss and improving the temperature uniformity of the reaction chamber. Precise control of the synthesis temperature during the reaction ensures the controllable formation of the target hexagonal scandium hydride. This invention boasts advantages such as simplified process, shorter cycle time, mild conditions, high safety, and good stability. It not only successfully obtained hexagonal ScH3 that can exist stably at room temperature and pressure but also provides a feasible reference route for the synthesis of other rare earth transition metal hydrides and lays the foundation for research on high-temperature superconducting materials.

[0009] In one possible implementation, in step S1, the tableting method is as follows: using a 1mm mold to press elemental scandium and the borane-ammonia complex into tablets respectively.

[0010] Compared with existing technologies, the above-mentioned technical solution can make the raw materials uniform in shape and controllable in size, ensuring full contact between scandium and hydrogen source sheets during stacking. Furthermore, the thin sheet material obtained by molding can effectively shorten the diffusion path and increase the contact area, which can promote the full reaction between borane-ammonia complex and scandium when decomposing and releasing hydrogen gas, thereby improving the hydrogen diffusion rate and reaction uniformity, and avoiding incomplete reaction caused by excessively large block size.

[0011] In one possible implementation, in step S2, the CVD single crystal tube is a diamond single crystal tube, and the diamond single crystal tube has a hole with a diameter of 1.5 mm inside to accommodate the assembly.

[0012] Compared with the prior art, the above technical solution can provide a sealed space with high strength, high hardness and high chemical stability for the reaction unit under high temperature and high pressure. In this embodiment, the diamond single crystal tube has excellent mechanical strength and chemical resistance, and can maintain structural integrity under high pressure. The size of the internal pores matches the assembly, ensuring that the assembly is stably placed and maintaining the confined space, avoiding hydrogen leakage and foreign impurities from entering, while preventing the container from cracking due to high pressure.

[0013] As a preferred embodiment, step S3 includes the following pressurization and pressure holding operations: Initial pressurization: Increase the pressure to 2±0.2 GPa within 300 s and maintain the pressure for 200±20 s; Repressurize: Increase the pressure from 2±0.2 GPa to 5±1.0 GPa within 300 s and hold the pressure for 1500±150 s; Initial pressure reduction: Reduce the pressure from 5±1.0 GPa to 2±0.2 GPa within 500 s, and maintain the pressure for 200±20 s; Final depressurization: Reduce the pressure from 2±0.2 GPa to atmospheric pressure.

[0014] Compared with existing technologies, the above-mentioned technical solution, through the procedural control of "segmented pressurization-pressure holding-segmented depressurization", first stabilizes the reaction environment under medium pressure, and then gradually increases it to the target high pressure, so that the release of hydrogen source and the hydrogenation process of scandium are under control; after the reaction is completed, the gradual depressurization can reduce the distortion or breakage of crystal structure when the pressure is released; this embodiment avoids the impact of a single rapid pressurization and depressurization on the sample and packaging material by completing the staged pressurization and depressurization in a short time.

[0015] In one possible implementation, step S3 includes the following operations: Preliminary heating and heat preservation treatment: heating begins when the initial pressure reaches 2±0.2 GPa, and the temperature is raised to 200 ℃ within 100 s. This temperature is maintained until the end of the 2±0.2 GPa pressure preservation stage, so as to promote the decomposition of borane-ammonia complex to release hydrogen and remove residual moisture. High-temperature heat preservation treatment: When entering the repressurization stage and the pressure rises to 5±1.0 GPa, continue to heat up to 800-1200 ℃ and keep warm for 20 min; Cooling phase: After the heat preservation is completed, the sample is naturally cooled to room temperature under the condition of maintaining 5±1.0 GPa during the repressurization phase.

[0016] Compared with existing technologies, the above-mentioned technical solution enables continuous process control of "low-temperature hydrogen release - high-temperature synthesis - high-pressure cooling" during the synthesis process. By first promoting the slow decomposition of the borane-ammonia complex at low temperature, hydrogen is stably released and residual moisture is removed at the same time, avoiding chamber impact or sample contamination caused by sudden hydrogen release. Subsequently, the main reaction is carried out under high temperature and high pressure, allowing scandium to fully combine with hydrogen to generate the target compound. Maintaining high pressure during the cooling stage helps stabilize the product structure and eliminate defects. This improves hydrogen utilization efficiency, reduces the formation of secondary phases, and improves the integrity and stability of the crystal.

[0017] In one possible implementation, the heating temperature in step S3 is 800°C.

[0018] Compared with the prior art, the above technical solution can ensure the reaction is complete while avoiding the formation of secondary phases or decomposition of scandium hydrogen compounds due to excessively high temperatures. In the method of the present invention, 800 °C is in the suitable temperature range for hydrogen source decomposition and scandium hydrogen bonding. This can ensure the stable release of hydrogen from the borane-ammonia complex and enable scandium atoms to have sufficient diffusion activity to complete the hydrogenation reaction. Under this embodiment, the reaction proceeds more uniformly, the product phase has higher purity, and crystal defects are reduced.

[0019] In one possible implementation, the high-pressure device is a six-sided top press, and the aperture of its reaction chamber is 2 mm.

[0020] Compared with existing technologies, the above-mentioned technical solution can provide a larger effective reaction space and ensure uniform pressure distribution. The six-sided top press has the characteristics of multi-directional force and can form an approximately isotropic pressure field in the reaction chamber. The 2 mm orifice can not only meet the sample assembly requirements, but also effectively maintain pressure stability and temperature uniformity.

[0021] In one possible implementation, in step S3, the heating method is to generate Joule heating by passing electricity through graphite, and to control the temperature with the help of insulation materials; at the same time, multi-point thermocouple monitoring is used in conjunction with compensation current adjustment to achieve precise control of the synthesis temperature.

[0022] Compared with existing technologies, the above-mentioned technical solution can achieve rapid and uniform heating of samples under high temperature and high pressure, and maintain dynamic temperature stability. The Joule heating generated by the graphite through electric current has high efficiency and can achieve rapid heating in a limited space. The heat insulation material can reduce heat loss and maintain a stable thermal field. Multi-point thermocouples monitor the temperature distribution at different locations in real time, and the temperature deviation is corrected by adjusting the compensation current.

[0023] Another technical problem to be solved by the present invention is to provide a hexagonal scandium hydrogen compound to overcome the shortcomings of existing scandium hydrogen compounds, which can only form a cubic phase under extreme high pressure and are unstable at room temperature and pressure, and cannot be stored and used for a long time.

[0024] To address the aforementioned technical problems, this invention provides a hexagonal scandium hydrogen compound, which is prepared by the above-described preparation method and has a hexagonal crystal structure, maintaining stability under normal temperature and pressure conditions.

[0025] Compared with existing technologies, the hexagonal scandium hydrogen compound provided by this invention has the following advantages: This invention achieves controlled hydrogen release in a high-pressure reaction chamber using a solid hydrogen source, ensuring the sufficiency and uniformity of the hydrogenation process; through programmed pressure management of "2 GPa pretreatment + 5 GPa main reaction," the bonding between scandium and hydrogen is gradually completed and stably embedded in the hexagonal lattice; simultaneously, cooling under high pressure effectively suppresses structural rearrangement and defect generation, thus achieving the preparation of stable hexagonal scandium hydrogen compounds under relatively mild conditions. Unlike existing technologies that rely on ultra-high pressures of hundreds of GPa to obtain the cubic phase, this invention utilizes the in-situ decomposition of borane-ammonia complexes under high pressure to release hydrogen gas. Combined with a double-sealed reaction space and segmented pressurization / heating process, it directly induces scandium and hydrogen to combine and form a hexagonal crystal structure. The structure of this invention is always under controlled high-temperature and high-pressure environment during formation and can still be maintained at room temperature and pressure after stabilization and cooling, thus avoiding the instability defect of rapid decomposition or transformation of cubic scandium hydrogen compounds after pressure relief. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the assembly of the high-temperature and high-pressure composite block using a domestically produced hinged six-sided top press. Among them, 1. steel cap; 2. molybdenum sheet; 3. graphite tube; 4. graphite sheet; 5. pyrophyllite plug; 6. magnesium oxide tube; 71. boron nitride tube; 72. boron nitride sheet; 8. thermocouple; 9. amorphous boron block.

[0027] Figure 2 This is a schematic diagram of the assembly of Sc metal elemental and borane ammonia complex; Figure 3 This is a schematic diagram of the pressurization process of a six-sided top press. Figure 4 This is a process curve of preparing SchH3 at 5 GPa and 800 °C in Example 1; Figure 5 X-ray diffraction patterns of SCH3 prepared at different temperatures under 5 GPa conditions; Figure 6 The X-ray diffraction results of SCH3 prepared under conditions of 5 GPa and 800 °C in Example 1 are compared with the refined structural diagram of standard SCH3. Figure 7 This is a schematic diagram of the hexagonal phase structure of SchH3 in this invention. Detailed Implementation

[0028] First, those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention. Those skilled in the art can make adjustments as needed to adapt to specific application scenarios.

[0029] In the description of the embodiments of the present invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present invention based on the specific circumstances.

[0030] This invention provides a method for preparing a hexagonal scandium hydrogen compound, comprising the following steps: S1: After compressing elemental scandium and borane-amine complex into tablets, the tablets are stacked in the order of borane-amine complex-scandium-borane-amine complex to form an assembly; S2: The assembly is first encapsulated using a CVD single crystal tube, and then encapsulated a second time using NaCl to form a sealed reaction unit; S3: The reaction unit is placed in a high-pressure device, and segmented pressurization and pressure holding are carried out within a pressure range of 2±0.2 GPa to 5±1.0 GPa. During the pressurization and pressure holding process, preliminary heating and heat holding treatment and high-temperature heat holding treatment at 800–1200℃ are carried out in sequence to prepare hexagonal scandium hydrogen compound.

[0031] As a preferred embodiment, in step S1, the tableting method is as follows: using a 1mm mold to press elemental scandium and borane-amine complex into tablets respectively.

[0032] As a preferred embodiment, in step S2, the CVD single crystal tube is a diamond single crystal tube, and the diamond single crystal tube has a hole with a diameter of 1.5 mm inside to accommodate the assembly.

[0033] As a preferred embodiment, step S3 includes the following pressurization and pressure holding operations: Initial pressurization: Increase the pressure to 2±0.2 GPa within 300 s and maintain the pressure for 200±20 s; Repressurize: Increase the pressure from 2±0.2 GPa to 5±1.0 GPa within 300 s and hold the pressure for 1500±150 s; Initial pressure reduction: Reduce the pressure from 5±1.0 GPa to 2±0.2 GPa within 500 s, and maintain the pressure for 200±20 s; Final depressurization: Reduce the pressure from 2±0.2 GPa to atmospheric pressure.

[0034] As a preferred embodiment, in step S3, the preliminary heating and heat preservation treatment and the high-temperature heat preservation treatment operations include: Preliminary heating and heat preservation treatment: heating begins when the initial pressure reaches 2±0.2 GPa, and the temperature is raised to 200 ℃ within 100 s. This temperature is maintained until the end of the 2±0.2 GPa pressure preservation stage, so as to promote the decomposition of borane-ammonia complex to release hydrogen and remove residual moisture. High-temperature heat preservation treatment: When entering the repressurization stage and the pressure rises to 5±1.0 GPa, continue to heat up to 800-1200 ℃ and keep warm for 20 min; Cooling phase: After the heat preservation is completed, the sample is naturally cooled to room temperature under the condition of maintaining 5±1.0 GPa during the repressurization phase.

[0035] As a preferred embodiment, the high-pressure device is a six-sided top press, and the aperture of its reaction chamber is 2 mm.

[0036] As a preferred embodiment, in step S3, the heating method is to generate Joule heat by passing electricity through graphite, and to control the temperature with the help of insulation materials; at the same time, multi-point thermocouple monitoring is used in conjunction with compensation current adjustment to achieve precise control of the synthesis temperature.

[0037] The present invention also provides a hexagonal scandium hydride, which is prepared by the above preparation method and has a hexagonal crystal structure, and can remain stable under normal temperature and pressure conditions.

[0038] This invention uses a borane-ammonia complex as a solid hydrogen source, which is stacked and assembled with elemental scandium tablets to achieve in-situ hydrogen release in a closed, small-scale reaction space. A dense reaction unit is formed through the initial encapsulation of a CVD single-crystal tube and a secondary encapsulation with NaCl, maintaining a high partial pressure and high purity environment for hydrogen locally. This avoids the equipment complexity and safety hazards associated with externally supplied high-pressure hydrogen in traditional methods. The method of this invention can complete the reaction at a pressure of 2–5 GPa and a temperature of 800–1200 °C, significantly lower than the hundreds of GPa levels reported in traditional methods. Because the reaction space is closed and the hydrogen source is controllable, the scandium hydride obtained by this method can directly and stably form a hexagonal crystal structure and remain stable at room temperature and pressure. This invention simplifies hydrogenation conditions and improves safety through a synergistic design of "solid hydrogen source—double-layer sealing—moderate high-pressure reaction," while lowering the synthesis threshold and making the controllable synthesis of hexagonal scandium hydride possible.

[0039] The product obtained by this invention is a hexagonal phase SCH3 that can exist stably at room temperature and pressure, unlike the cubic phase SCH3 in the prior art which can only be obtained under extreme high pressure and becomes unstable after depressurization. Furthermore, the pressurization-heating-depressurization process used in this invention is an unconventional segmented curve. By continuously connecting the initial low-temperature holding stage with the high-temperature reaction stage, the release of hydrogen source and lattice stability are effectively controlled, avoiding the defect generation caused by the traditional single pressurization / heating method. This invention also innovates in assembly structure, using a CVD single crystal tube and NaCl dual encapsulation to construct a dense reaction unit, and introducing multi-point thermocouples and amorphous boron materials to achieve precise control of temperature and pressure fields and effective isolation of samples, thereby significantly improving the safety and reproducibility of the synthesis process.

[0040] The following specific embodiments will be used to further elaborate on the technical solution of the present invention: Example 1 This embodiment provides a hexagonal scandium hydrogen compound and its preparation method. The specific steps of the preparation method are as follows: like Figure 1 As shown, Figure 1This is a schematic diagram of the domestically produced six-sided 2 mm top assembly structure used in this embodiment. The structure includes: a steel cap 1, a molybdenum sheet 2, a graphite tube 3, a graphite sheet 4, a magnesium oxide plug 5, a sample assembly 6, a boron nitride tube 71, a boron nitride sheet 72, a thermocouple 8, and an amorphous boron block 9. Figure 2 This is a schematic diagram of the assembly of the Sc metal element and the borane ammonia complex used in the experiment. Figure 3 This is a schematic diagram of the pressurization process of a six-sided top press; its assembly and connection relationships are as follows: The steel cap 1 is set at the upper and lower ends of the overall structure to bear the axial pressure from the anvil block of the six-sided top press and to serve as an external electrode; The steel caps 1 at the upper and lower ends respectively abut against and conduct electricity with the corresponding molybdenum sheets 2; The molybdenum sheet 2 is located between the steel cap 1 and the graphite sheet 4, and is in contact with both surfaces, serving as a conductive transition layer and a stress buffer layer. The molybdenum sheet 2 and the graphite sheet 4 are electrically connected to form the end contact interface of the heating circuit; Graphite sheets 4 are disposed on both ends of graphite tube 3 and abut against molybdenum sheet 2; graphite sheets 4 are conductive to graphite tube 3, which is used to reduce end face contact resistance and uniform current distribution. The graphite tube 3 is arranged along the axial direction of the overall structure and serves as an electrically conductive heating element, with its inner cavity being the reaction chamber. The graphite tube 3 is electrically connected to the graphite sheets 4 at both ends (and in turn to the molybdenum sheet 2 and the steel cap 1) to form a complete heating circuit: steel cap 1 → molybdenum sheet 2 → graphite sheet 4 → graphite tube 3 → opposite graphite sheet 4 → opposite molybdenum sheet 2 → opposite steel cap 1; The boron nitride tube 71 is coaxially sleeved in the inner cavity of the graphite tube 3 to define the sample cavity; its two ends are sealed or covered by boron nitride sheets 7-2 to seal and isolate the sample in conjunction with the end plugs. The sample assembly 6 (the sample after encapsulation in step S1) is placed in the cavity enclosed by the boron nitride tube 71 and is limited and isolated at both ends of the axial direction by the boron nitride sheet 72 to avoid direct contact with the heating element and the pressure transmission medium. The magnesium oxide plug 5 is placed between the graphite sheet 4 and the boron nitride sheet 72. It serves as the main pressure transmission medium to uniformly transmit the pressure of the steel cap 1 to the sample area and provides electrical insulation and thermal isolation. Amorphous boron blocks 9 are arranged around graphite tube 3 and its outer periphery for circumferential pressure transmission and thermal insulation support, working together with magnesium oxide plugs 5 and boron nitride components to stabilize the pressure and temperature field. Thermocouple 8 is set along the circumference or radial direction of the sample area, with the probe located near the sample, for real-time temperature measurement; the temperature measurement signal is used to compensate for the graphite heating current to improve the measurement and control accuracy of the sample area temperature.

[0041] The sealing device used in this invention is a key step in achieving the controllable synthesis of hexagonal phase SCH3. Its structural design is highly coupled with the synthesis process: the device in this embodiment adopts a double-layer encapsulation system of CVD diamond single crystal tube and NaCl tube, which simultaneously ensures mechanical strength and chemical inertness under high temperature and high pressure conditions, effectively preventing hydrogen escape and isolating impurities, thereby maintaining a stable high hydrogen partial pressure environment in the small reaction chamber; the device in this embodiment introduces a combined pressure transmission and heat insulation system of amorphous boron block and magnesium oxide tube, which not only improves the uniformity of temperature and pressure fields, but also avoids direct contact contamination between the sample and the heating element; furthermore, the device in this embodiment allows for the deployment of multiple thermocouples and the coordination of compensation current control, ensuring precise control of the segmented heating and holding processes; it works in conjunction with the "segmented pressurization-stage heating" process proposed in this invention to form an overall technical solution of "solid hydrogen source-double-layer sealing-moderate high-pressure reaction". Therefore, it can be seen that the device of the present invention is not a general-purpose reaction chamber, but is specially designed for the controllable synthesis of scandium hydrogen compounds. Only with the linkage between the device and the method can hexagonal phase ScH3 be stably obtained under conditions far lower than the traditional extreme high pressure, and its stable existence at room temperature and pressure can be guaranteed.

[0042] S1: Raw material preparation and assembly Elemental scandium powder (Sc) and borane-amine complex powder were pressed into sheets using a 1 mm diameter mold to obtain scandium metal flakes and borane-amine complex discs. Subsequently, they were stacked in a "sandwich" manner in the order of "borane-amine complex—scandium—borane-amine complex" to form an assembly.

[0043] S2: The assembly is placed into a CVD diamond single crystal tube with a 1.5 mm diameter hole, and then further encapsulated with NaCl to obtain a sealed reaction unit.

[0044] S3: Assembly and Heating / Pressure Reaction The reaction unit obtained in step S1 is loaded into the 2 mm reaction chamber of a domestic six-sided top press. The assembly structure of the chamber includes a graphite tube and graphite sheet as heating elements, a magnesium oxide tube as insulation layer, a boron nitride tube and boron nitride sheet to wrap the sample to prevent contamination, an amorphous boron block as the pressure transmission body, and a steel cap and molybdenum sheet as conductive medium. In Example 1, the process curve of the pressurized heating reaction is shown in the figure below. Figure 4 As shown, it specifically includes: The pressurization procedure is as follows: increase to 2 GPa within 300 s and hold for 200 s; then increase to 5 GPa within 300 s and hold for 1500 s; then decrease to 2 GPa within 500 s and hold for 200 s; finally decrease to atmospheric pressure.

[0045] Simultaneously, during the aforementioned pressurization process, heating was initiated when the pressure reached 2 GPa, raising the temperature to 200°C within 100 seconds and maintaining this temperature until the end of the 2 GPa holding pressure stage. This allowed the borane-ammonia complex to decompose, releasing hydrogen and removing residual moisture. Subsequently, when the pressure further increased to 5 GPa, the temperature was raised to 800°C and maintained for 20 minutes. Throughout the entire holding and cooling process, the pressure was maintained at 5 GPa, and the sample was allowed to cool naturally to room temperature. Heating was performed using Joule heating generated by energizing graphite. Four thermocouples simultaneously monitored the chamber temperature and were adjusted using a compensation current to ensure the accuracy of the synthesis temperature. The sample obtained in Example 1 was subjected to X-ray diffraction testing (e.g., ...). Figure 5 As shown in the figure, the diffraction peaks are consistent with those of standard hexagonal phase SCH3, indicating that hexagonal phase scandium hydrogen compounds can be stably generated.

[0046] Example 2 This embodiment provides a hexagonal scandium hydrogen compound and its preparation method, the specific steps of which are as follows: S1: Raw material preparation and assembly Elemental scandium powder (Sc) and borane-amine complex powder were pressed into sheets using a 1 mm diameter mold to obtain scandium metal flakes and borane-amine complex discs. Subsequently, they were stacked in a "sandwich" manner in the order of "borane-amine complex—scandium—borane-amine complex" to form an assembly.

[0047] S2: The assembly is placed into a CVD diamond single crystal tube with a 1.5 mm diameter hole, and then further encapsulated with NaCl to obtain a sealed reaction unit.

[0048] S3: Assembly and Heating / Pressure Reaction The reaction unit obtained in step S1 is installed into the 2 mm reaction chamber of a domestically produced six-sided top press. The assembly structure of the chamber includes: a graphite tube and graphite sheet as heating elements, a magnesium oxide tube as an insulation layer, a boron nitride tube and boron nitride sheet to wrap the sample to prevent contamination, an amorphous boron block as the pressure transmission body, and a steel cap and molybdenum sheet as conductive media.

[0049] The pressurization procedure was as follows: the pressure was increased to 1.8 GPa within 300 s and held for 180 s; then increased to 4 GPa within 300 s and held for 1350 s; then decreased to 1.8 GPa within 500 s and held for 180 s; finally, the pressure was reduced to atmospheric pressure. Simultaneously, during the aforementioned pressurization procedure, heating was initiated when the pressure reached 1.8 GPa, raising the temperature to 200 °C within 100 s and maintaining this temperature until the end of the 1.8 GPa holding pressure phase. This allowed the borane-ammonia complex to decompose, releasing hydrogen gas and removing residual moisture. Subsequently, when the pressure further increased to 4.5 GPa, the temperature was further raised to 800 °C and maintained for 20 min. Throughout the entire holding and cooling process, the pressure was maintained at 4.5 GPa, and the sample was allowed to cool naturally to room temperature.

[0050] Heating is achieved by generating Joule heat through electrolysis of graphite. Four thermocouples simultaneously monitor the cavity temperature and adjust it in conjunction with compensation current to ensure the accuracy of the synthesis temperature.

[0051] Example 3 This embodiment provides a hexagonal scandium hydrogen compound and its preparation method, the specific steps of which are as follows: S1: Raw material preparation and assembly Elemental scandium powder (Sc) and borane-amine complex powder were pressed into sheets using a 1 mm diameter mold to obtain scandium metal flakes and borane-amine complex discs. These were then stacked in a "sandwich" fashion in the order of "borane-amine complex—scandium—borane-amine complex" to form an assembly. The assembly was then placed into a CVD diamond single-crystal tube with a 1.5 mm diameter hole and further encapsulated with NaCl to obtain a sealed reaction unit.

[0052] S3: Assembly and Heating / Pressure Reaction The reaction unit obtained in step S1 is installed into the 2 mm reaction chamber of a domestically produced six-sided top press. The assembly structure of the chamber includes: a graphite tube and graphite sheet as heating elements, a magnesium oxide tube as an insulation layer, a boron nitride tube and boron nitride sheet to wrap the sample to prevent contamination, an amorphous boron block as the pressure transmission body, and a steel cap and molybdenum sheet as conductive media.

[0053] The pressurization procedure was as follows: the pressure was increased to 2.2 GPa within 300 s and held for 220 s; then increased to 6 GPa within 300 s and held for 1650 s; then decreased to 2.2 GPa within 500 s and held for 220 s; finally, the pressure was reduced to atmospheric pressure.

[0054] Simultaneously, during the aforementioned pressurization procedure, heating was initiated when the pressure reached 2.2 GPa, and the temperature was increased to 200 °C within 100 s and maintained until the end of the 2.2 GPa holding pressure stage, allowing the borane-ammonia complex to decompose, releasing hydrogen gas and removing residual moisture. Subsequently, when the pressure was further increased to 5 GPa, the temperature was further increased to 1200 °C and maintained for 20 min. Throughout the entire holding and cooling process, the pressure was maintained at 5 GPa, and the sample was allowed to cool naturally to room temperature. Heating was performed using Joule heating generated by energizing graphite, with four thermocouples simultaneously monitoring the chamber temperature and adjusting it in conjunction with compensation current to ensure the accuracy of the synthesis temperature.

[0055] Example 4 This embodiment provides a method for preparing a hexagonal scandium hydrogen compound. The process flow is basically the same as in Example 1, except that in step S3, the high-temperature holding temperature is set to 1000 °C and held at a pressure of 5 GPa for 20 min. After the reaction, the mixture is naturally cooled to room temperature under high pressure. The obtained sample is then subjected to X-ray diffraction testing (e.g., ...). Figure 5 As shown in the figure, the diffraction peaks are consistent with the standard hexagonal phase SCH3, indicating that hexagonal phase scandium hydride compounds can still be stably generated. However, compared with Example 1 (800 °C), some peaks show slight broadening, and SCH2 diffraction peaks have appeared in the product, indicating the formation of a secondary phase, which indicates that the crystal integrity has slightly decreased.

[0056] Example 5 This embodiment provides a method for preparing a hexagonal scandium hydrogen compound. The process flow is basically the same as in Example 1, except that in step S3, the high-temperature holding temperature is set to 1200 °C and held at a pressure of 5 GPa for 20 min. After the reaction, the mixture is naturally cooled to room temperature under high pressure. The obtained product is analyzed by X-ray diffraction (e.g., ...). Figure 5 As shown in the figure, the diffraction peaks generally correspond to the standard hexagonal phase SCH3, but some peak positions and intensities are shifted and impurity peaks are present compared to Example 1 and Example 4. SCH2 diffraction peaks have appeared in the product, indicating the formation of a secondary phase, which suggests that defects or secondary phases may be introduced under excessively high temperature conditions.

[0057] Comparative Example 1 To further verify the effect of temperature on the product structure, a comparative experiment was set up. The process flow was basically the same as in Example 1, except that in step S3, the high-temperature holding temperature was set to 1400 °C and held at 5 GPa for 20 min. After the reaction, the sample was naturally cooled to room temperature under high pressure. The obtained sample was then subjected to X-ray diffraction testing (e.g., ...). Figure 5As shown in the figure, a significant deviation is observed compared to standard hexagonal SCH3, with the appearance of strong impurity peaks, indicating that the stability of hexagonal SCH3 is significantly reduced under these conditions, and some products undergo decomposition or phase transformation. Therefore, 1400 ℃ exceeds the suitable reaction window and cannot stably obtain high-purity hexagonal SCH3.

[0058] Hexagonal phase ScH3 was successfully obtained under the conditions described in Examples 1-3 above, and its hexagonal phase structure is as follows: Figure 7 As shown, the sample remained stable under normal temperature and pressure; the X-ray diffraction analysis results of the ScH3 prepared in Example 1 (as shown) Figure 5 As shown in the figure, the product is consistent with the standard hexagonal phase SchH3, and the structural refinement results (as shown in the figure) indicate that the product is consistent with the standard hexagonal phase SchH3. Figure 6 (As shown) further verified the integrity of the crystal structure; the synthesis results showed that the synergistic process of low-temperature pretreatment at 2±0.2 GPa and high-temperature reaction at 5±1.0 GPa can effectively improve the hydrogenation efficiency and suppress defect formation, thereby achieving stable preparation of hexagonal scandium hydrogen compounds at lower pressure (as shown). Figure 7 (As shown).

[0059] Through Examples 1-3 above, hexagonal phase ScH3 was successfully prepared under different pressure, temperature windows, and pressure / heating / holding parameters, and remained stable at room temperature and pressure. The characterization results show that: The method of this invention employs a double-layer sealed system of "solid hydrogen source (borane-ammonia complex) - CVD single crystal tube initial encapsulation - NaCl secondary encapsulation," which can establish a local reaction environment with high hydrogen partial pressure and low impurities within a moderate pressure range of 1.8–6 GPa. The method of this invention effectively controls the hydrogen supply rate and diffusion behavior through segmented pressurization and staged heating (low-temperature hydrogen dehydration + high-temperature reaction + isobaric cooling), suppressing side reactions and defect formation. Whether under minimum operating conditions (Example 2: 1.8 / 4.0 GPa, 800 °C) or maximum operating conditions (Example 3: 2.2 / 6 GPa, 1200 °C), XRD and structural refinement results consistent with standard hexagonal structures can be obtained, indicating the reproducibility of the method of this invention. Examples 1-3 further demonstrate that this invention can stably and controllably obtain hexagonal scandium hydride compounds under pressure conditions significantly lower than traditional external high-pressure hydrogen methods, while also considering process safety and scalability. Examples 1 (800 °C), 4 (1000 °C), and 5 (1200 °C) all achieved the synthesis of hexagonal SCH3 under 5 GPa conditions. The product obtained at 800 °C was the purest, with diffraction peaks highly consistent with the standard spectrum, indicating a complete crystal structure and the highest phase purity. When the temperature was raised to 1000 °C, SCH2 diffraction peaks appeared in the product, indicating the formation of a secondary phase. Although the main phase was still hexagonal SCH3, the purity decreased. At 1200 °C, the impurity peaks were further enhanced, indicating an increase in crystal defects and secondary phase content. In Comparative Example 1 (1400 °C), the product structure was significantly deteriorated, with strong impurity peaks and a substantial decrease in the stability of the hexagonal phase. Therefore, it can be seen that the present invention effectively broadens the controllable synthesis window of hexagonal phase SCH3 through the synergistic effect of "controlled hydrogen release from solid hydrogen source + double-layer sealed confined reaction + moderate high pressure field lattice stabilization + segmented heating-isobaric cooling process", and achieves phase stabilization and defect suppression under moderate high pressure and temperature conditions. This further proves that the present invention can not only stably obtain hexagonal scandium hydrogen compounds at lower pressure, but also significantly improve the structural purity and reproducibility by precisely controlling the thermo-pressure conditions.

[0060] In summary, the design principle of this invention is as follows: The method of this invention achieves the controllable synthesis of hexagonal phase SCH3 through a synergistic design of a solid hydrogen source, double-layer sealing, moderate high pressure, and segmented thermo-pressure coupling. During the process, the borane-ammonia complex decomposes in a controlled manner at approximately 200 °C, continuously releasing high-purity hydrogen. Combined with the double-layer encapsulation of the CVD single crystal tube and NaCl, localized high hydrogen, high pressure, and high temperature are effectively maintained while isolating impurities. The hexagonal dome device provides uniform pressure within the range of 2.0±0.2–5±1.0 GPa, reducing the hydrogen insertion barrier in scandium and stabilizing the hexagonal phase lattice. Subsequent staged heating processes achieve hydrogen release and dehydration under low pressure, promote hydrogen diffusion and combination under high pressure, and retain the target phase through isobaric cooling. Electrostatic heating of graphite combined with multi-point temperature compensation ensures temperature uniformity. Simultaneously, MgO, amorphous boron, and boron nitride components construct a pressure-transmitting, insulating, and isolating system, avoiding sample contamination and improving safety. Compared to existing methods that rely on external high-pressure hydrogen, have complex processes, and require tens to hundreds of GPa, this method offers a more comprehensive approach. The pressure-based approach of this invention enables the stable preparation of hexagonal phase SCH3 at lower pressures and moderate temperatures, significantly reducing the synthesis threshold, improving safety and reproducibility, and laying the foundation for subsequent scale-up and application.

[0061] In the description of this invention, the references to "one embodiment," "some embodiments," "in this embodiment," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0062] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a hexagonal scandium hydrogen compound, characterized in that, Includes the following steps: S1: After compressing elemental scandium and borane-amine complex into tablets, the tablets are stacked in the order of borane-amine complex-scandium-borane-amine complex to form an assembly; S2: The assembly is first encapsulated using a CVD single crystal tube, and then encapsulated a second time using NaCl to form a sealed reaction unit; S3: The reaction unit is placed in a high-pressure device, and segmented pressurization and pressure holding are carried out within a pressure range of 2±0.2 GPa to 5±1.0 GPa. During the pressurization and pressure holding process, preliminary heating and heat holding treatment and high-temperature heat holding treatment at 800–1200 ℃ are carried out in sequence to prepare hexagonal scandium hydrogen compound.

2. The method for preparing hexagonal scandium hydrogen according to claim 1, characterized in that, In step S1, the tableting method is as follows: using a 1mm mold, elemental scandium and borane-ammonia complex are respectively pressed into tablets.

3. The method for preparing hexagonal scandium hydrogen according to claim 1, characterized in that, In step S2, the CVD single crystal tube is a diamond single crystal tube, and the diamond single crystal tube has a hole with a diameter of 1.5 mm inside to accommodate the assembly.

4. The method for preparing hexagonal scandium hydrogen according to claim 1, characterized in that, In step S3, the pressurization and pressure holding operations include: Initial pressurization: Increase the pressure to 2±0.2 GPa within 300 s and maintain the pressure for 200±20 s; Repressurize: Increase the pressure from 2±0.2 GPa to 5±1.0 GPa within 300 s and hold the pressure for 1500±150 s; Initial pressure reduction: Reduce the pressure from 5±1.0 GPa to 2±0.2 GPa within 500 s, and maintain the pressure for 200±20 s; Final depressurization: Reduce the pressure from 2±0.2 GPa to atmospheric pressure.

5. The method for preparing the hexagonal scandium hydrogen compound according to claim 4, characterized in that, In step S3, the preliminary heating and heat preservation treatment and the high-temperature heat preservation treatment include the following operations: Preliminary heating and heat preservation treatment: heating begins when the initial pressure reaches 2±0.2 GPa, and the temperature is raised to 200 ℃ within 100 s. This temperature is maintained until the end of the 2±0.2 GPa pressure preservation stage, so as to promote the preliminary decomposition of the borane-ammonia complex to release hydrogen and remove residual moisture. High-temperature heat preservation treatment: When entering the repressurization stage and the pressure rises to 5±1.0 GPa, continue to heat to 800-1200 ℃ and keep warm for 20 min, so that the borane ammonia complex completely releases hydrogen gas to carry out the reaction synthesis; Cooling phase: After the heat preservation is completed, the sample is naturally cooled to room temperature under the condition of maintaining 5±1.0 GPa during the repressurization phase.

6. The method for preparing hexagonal scandium hydrogen according to claim 1, characterized in that, In step S3, the heating temperature is 800°C.

7. The method for preparing hexagonal scandium hydrogen according to claim 1, characterized in that, The high-pressure device is a six-sided top press, and the aperture of its reaction chamber is 2 mm.

8. The preparation method according to claim 1, characterized in that, In step S3, the heating method is to generate Joule heat by passing electricity through graphite, and to control the temperature with the help of insulation materials; at the same time, multi-point thermocouple monitoring is used in combination with compensation current adjustment to achieve precise control of the synthesis temperature.

9. A hexagonal scandium hydrogen compound, characterized in that, The hexagonal scandium hydrogen compound is prepared by any one of the preparation methods of claims 1-8, and the hexagonal scandium hydrogen compound has a hexagonal crystal structure and can remain stable under normal temperature and pressure conditions.

Images