Preparation method of refrigeration device based on Mg3Bi2-based single crystal thermoelectric material

Abstract

The invention relates to the field of thermoelectric semiconductor materials, and provides a refrigeration device preparation method based on an Mg3Bi2-based single crystal thermoelectric material, which comprises a single crystal thermoelectric material preparation step and a refrigeration device preparation step, the preparation method of the single crystal thermoelectric material comprises the following steps: a raw material weighing step: magnesium, bismuth, antimony and tellurium elements are weighed according to the nominal value of Mg < 3.05 > Bi < 1.997-x > Sb < x > Te < 0.003 >, and x is equal to 0.1-1.5; the raw materials are placed in a temperature-resistant container to be smelted, and molten liquid is obtained; a single crystal forming step: controlling the temperature drop rate of the melt, cooling the melt to form a single crystal nucleation point in the melt, continuously cooling the melt, and growing the single crystal nucleation point to form a single crystal to obtain the single crystal thermoelectric material; the preparation method of the refrigeration device comprises the following steps: preparing an n-type thermoelectric single leg from a single-crystal thermoelectric material, and welding the n-type thermoelectric single leg and a p-type thermoelectric single leg to form a single-stage thermoelectric refrigeration device and a double-stage thermoelectric refrigeration device. The Mg3Bi2-based single-crystal thermoelectric material prepared by the invention is good in thermoelectric performance, good in joint quality of a refrigeration device and wide in application prospect.

Description

Technical Field

[0001] This invention relates to the field of thermoelectric semiconductor materials, and specifically to a method for fabricating a refrigeration device based on Mg3Bi2-based single-crystal thermoelectric material. Background Technology

[0002] Thermoelectric semiconductor materials are functional materials that can directly convert heat energy into electrical energy using the Seebeck and Peltier effects. Compared to traditional heat engines, thermoelectric energy conversion technology is a novel energy technology that is all-solid-state, zero-emission, and sustainable, with broad application prospects in fields such as instrumentation, medicine, space exploration, and the automotive industry. The performance of thermoelectric cooling devices is directly related to the thermoelectric figure of merit (zT) of the selected materials. Because they typically operate in environments below room temperature, the performance of these devices largely depends on the material properties in the sub-temperature region.

[0003] Bi2Te3 alloy (Bi2Te 3-x Se x Since its discovery in the 1950s, Bi2Te3-based alloys have held a leading position in thermoelectric refrigeration materials. However, the poor mechanical properties, strong anisotropy, and high cost of raw materials of Bi2Te3-based alloys have limited the large-scale application of their refrigeration devices. (Electronic type Mg3Sb) 2-x Bi x The conduction band of a thermoelectric material has a higher degeneracy (N0) than the valence band. v =6), giving it a higher Seebeck coefficient and conductivity; on the other hand, Mg3Sb 2-x Bi x It has a low intrinsic thermal conductivity, which can be further reduced through alloying, resulting in a rapid improvement in thermoelectric properties. Mg3Sb 2-x Bi x Polycrystalline materials exhibit excellent thermoelectric properties in the sub-room to room temperature range (250K-300K). By using methods such as slow cooling, fluxing, and Bridgman methods, single-crystal samples with fewer defects can be grown, which can reduce the scattering of charge carriers by crystal defects and grain boundaries, improve the carrier mobility, and further enhance the thermoelectric quality of single-crystal samples. This makes them a promising candidate for commercially viable environmentally friendly thermoelectric cooling devices.

[0004] Full-size thermoelectric cooling devices are composed of multiple pairs of n-type and p-type semiconductor thermoelectric single-leg units connected together. Optimization of thermoelectric cooler structures focuses on different numbers and forms, as different numbers of stages are themselves an optimization. Researchers have compared the performance of single-stage and two-stage thermoelectric coolers, showing that two-stage thermoelectric coolers have higher energy efficiency and can achieve larger cooling temperature differences. Especially in working environments requiring larger cooling temperature differences and meeting different depths of cooling needs, thermoelectric cooling devices require multi-layer design and construction. Thermoelectric cooling devices are increasingly widely used in various fields of production and daily life due to their advantages such as small size, light weight, accurate temperature control, and rapid cooling. For example, when infrared detectors operate at room temperature, the difference between the received signal and the environmental background is small, resulting in long component response times and poor performance. Multi-stage thermoelectric cooling devices can provide a stable, lower-temperature operating environment to improve the performance of infrared detectors. Therefore, using electronic Mg3Sb... 2-x Bi x Based on basic alloy materials, two-stage thermoelectric refrigeration devices can be built, which has great application potential to overcome the technical bottleneck of low thermoelectric conversion efficiency and realize the commercialization of affordable, stable and high mechanical performance refrigeration devices.

[0005] Currently, only n-type Bi₂(Te,Se)₃ and p-type (Bi,Sb)₂Te₃-based alloys have been successfully commercialized for multi-stage thermoelectric cooling devices. This is not only because Bi₂Te₃-based alloys possess excellent thermoelectric figures of merit (zT = approximately 0.9 at room temperature for n-type materials and approximately 1.4 for p-type materials), but also because they exhibit excellent chemical stability, making them less prone to performance degradation during the fabrication of single thermoelectric legs and device assembly. Performance testing of commercial Bi₂Te₃-based thermoelectric cooling devices revealed that, at a hot-end temperature of around 300K, the maximum single-stage cooling temperature difference is 64K, and the maximum cooling temperature difference for two-stage devices can reach 79K, still some distance from commercially available lightweight cooling products. To overcome the bottleneck in thermoelectric cooling performance and develop new commercially viable environmentally friendly energy devices, three aspects should be considered: improving the performance of thermoelectric semiconductor materials, selecting and preparing the bonding layer, and optimizing the welding process.

[0006] The room-temperature thermoelectric figure of merit of polycrystalline Mg3Bi2-based alloys has exceeded 0.9. However, polycrystalline materials are often prepared using non-thermodynamic equilibrium methods such as ball milling, suspension melting, and arc melting. During synthesis, various crystal defects, such as stacking faults, dislocations, vacancies, and interstitial atoms, are inevitably introduced. High concentrations of crystal defects inevitably affect the scattering mechanism of charge carriers, limiting the improvement of thermoelectric material performance. Therefore, optimizing thermoelectric coolers requires eliminating grain boundary scattering of charge carriers and improving the material's carrier mobility by preparing ideal single-crystal semiconductor materials. Furthermore, two-stage thermoelectric cooling devices based on Mg3Bi2 single crystals have not yet been reported. This is mainly because the growth of multi-element, highly doped single-crystal materials is inherently challenging. Multi-stage devices not only require high quality and large size of the single-crystal thermoelectric leg but also need to ensure stable performance and mass production, which places extremely high demands on the single-crystal growth environment and synthesis technology.

[0007] The performance of thermoelectric cooling devices depends not only on the high performance of the thermoelectric materials but also, and perhaps more importantly, on the quality of the device's junctions. Mg3Bi2-based alloys have poor chemical stability, readily reacting with water, and at high temperatures, Mg atoms escape, reducing the carrier concentration and weakening the Seebeck coefficient, leading to deterioration in thermoelectric performance. Therefore, optimizing the interface and welding processes of the bonding layer without compromising the thermoelectric properties of the materials, and minimizing device losses, are crucial considerations in device fabrication. In the welding of two-stage cooling devices, solder paste with a low melting point should be selected, and conventional segmented, step-by-step assembly methods should be avoided to prevent performance degradation of the Mg3Bi2-based materials due to repeated welding. Furthermore, repeated welding may cause interface problems at the bonding layer, putting the device junctions at risk of failure. Therefore, selecting appropriate bonding layer materials and welding methods is critical for Mg3Bi2-based single-crystal cooling devices. Summary of the Invention

[0008] In view of this, the present invention provides a method for preparing a refrigeration device based on Mg3Bi2-based single crystal thermoelectric material. The prepared Mg3Bi2-based single crystal thermoelectric material has excellent thermoelectric properties, the refrigeration device has excellent joint quality, and it has broad application prospects.

[0009] This invention provides a method for fabricating a refrigeration device based on Mg3Bi2-based single-crystal thermoelectric material, comprising: a single-crystal thermoelectric material fabrication step and a single- or double-stage refrigeration device fabrication step;

[0010] The preparation steps of the single-crystal thermoelectric material include:

[0011] Raw material weighing steps: according to Mg 3.05 Bi 1.997-x Sb x Te 0.003The nominal weights of magnesium, bismuth, antimony, and tellurium are given, where x = 0.1-1.5;

[0012] Raw material smelting step: The magnesium, bismuth, antimony and tellurium elements weighed in the weighing step are placed in a heat-resistant container and smelted to obtain a molten liquid;

[0013] Single crystal formation step: control the rate of temperature decrease of the melt to cool the melt so that single crystal nucleation points can be formed in the melt. The melt continues to cool, and the single crystal nucleation points grow to form a single crystal, thereby obtaining a single crystal thermoelectric material.

[0014] The fabrication steps of the single-stage and dual-stage thermoelectric devices include: fabricating the single-crystal thermoelectric material into an n-type thermoelectric single leg, and welding the n-type thermoelectric single leg to a p-type thermoelectric single leg to form a single-stage and dual-stage thermoelectric cooling device.

[0015] Optionally, the heat-resistant container includes an inert metal tube such as niobium or tantalum (niobium tube is used as an example in this invention), and the raw material smelting step includes a packaging step:

[0016] The magnesium, bismuth, antimony, and tellurium elements weighed in the raw material weighing step are placed in a niobium tube and the niobium tube is sealed in a protective gas atmosphere, including argon, helium, or nitrogen.

[0017] The pressure of the protective gas inside the niobium tube is 0.02-0.15 MPa, and the niobium tube is sealed in a quartz tube.

[0018] Optionally, the raw material smelting step includes:

[0019] Heating steps:

[0020] The quartz tube is placed in a heating device, which heats the raw material to 1200-1300K at a set heating rate, causing the raw material to form a liquid compound, and maintaining this temperature for 24 to 72 hours.

[0021] Single crystal formation steps: The liquid compound is subjected to a flow rate of 0.1 to 15 K h. -1 The temperature is cooled to 900 to 950 K at a rate that, during the cooling process, the liquid compound passes its solid-liquid phase transition point and slowly precipitates along the tube wall to form Mg. 3.05 Bi 1.997-x Sb x Te 0.003 Single crystal nucleation sites are formed. As the temperature decreases, the single crystal gradually grows. The annealing time is set to achieve elemental homogenization of the compound before cooling to room temperature.

[0022] Optionally, in the heating step, the quartz tube is placed in a heating device, which heats it to 1223K within 12 hours and maintains it at this temperature for 48 hours.

[0023] Optionally, in the single crystal formation step, the liquid compound is prepared at 3K h. -1 The rate of cooling is slowed down to 923K.

[0024] Specifically, the single-crystal thermoelectric material prepared according to the above-described method for preparing Mg3Bi2-based single-crystal thermoelectric materials includes the following steps in the fabrication of the refrigeration device:

[0025] The single-crystal thermoelectric material is prepared into an n-type thermoelectric single leg, and the n-type thermoelectric single leg is welded with a p-type thermoelectric single leg to form a single-stage thermoelectric refrigeration device.

[0026] Specifically, fabricating the single-crystal thermoelectric material into an n-type thermoelectric single leg includes:

[0027] Single-crystal thermoelectric material is cut into single-crystal substrates. Silver powder and Mg2Ni powder are then formed on both sides of the substrates in a mold. After sintering at a set temperature and pressure for a set time, a thermoelectric substrate is obtained. This substrate is then cut to a set size to obtain an n-type thermoelectric single leg: Ag / Mg2Ni / Mg3Bi. 1.497 Sb 0.5 Te 0.003 / Mg2Ni / Ag single leg.

[0028] Optionally, the mold is a graphite mold, and the thermoelectric substrate is obtained by plasma discharge sintering at 623K and 3.5kN for 5 minutes.

[0029] Optionally, the p-type thermoelectric single leg is a p-type Bi2Te3 single leg prepared by electroplating Ni, and Al2O3 ceramic with deposited Ni metal is used as the upper and lower substrates of the device. An n-type Ag / Mg2Ni / Mg3Bi with a set logarithmic number is bonded using SnBi solder paste. 1.497 Sb 0.5 Te 0.003 / Mg2Ni / Ag single leg and p-type Bi2Te3 single leg prepared by electroplating Ni are soldered onto the substrate in one-step reflow soldering, thereby preparing a set of full-size Mg3Bi2-based single-crystal single-stage refrigeration devices with a set logarithm.

[0030] Optionally, the one-step reflow soldering method includes: using a reflow oven at 1K s -1 The temperature was raised to 408 K at a heating rate of [unspecified rate] and held at 393 K for 2 min; then, [the temperature was further increased] at 1 K s [unspecified rate]. -1 The temperature was increased to 453 K at a heating rate of [value missing], held at this temperature for 45 s, and finally increased by 1 K / s. -1 The cooling rate is used to cool it to room temperature.

[0031] Optionally, the method for fabricating a refrigeration device based on Mg3Bi2-based single-crystal thermoelectric material further includes a fabrication step for a two-stage thermoelectric refrigeration device:

[0032] n-type Ag / Mg2Ni / Mg3Bi prepared by plasma discharge sintering 1.497 Sb 0.5 Te 0.003 / Mg2Ni / Ag is used as an n-type thermoelectric leg. p-type Bi2Te3 thermoelectric particles prepared by electroplating Ni are used as p-type thermoelectric legs. They are placed sequentially on a ceramic substrate coated with low-temperature SnBi solder paste according to the set points to form the first-stage thermoelectric particle array. Then the ceramic substrate is placed into the mold base to form the lower substrate of the first stage of the device.

[0033] Next, insert four frustum-shaped pins into the frustum-shaped holes in the mold base. Then, place the n-type thermoelectric single leg and the p-type thermoelectric single leg on the solder paste-coated ceramic substrate according to the predetermined positions. With the help of the four frustum-shaped pins, place the ceramic substrate on the thermoelectric particle array of the first stage of the device to form the upper substrate of the first stage of the device. Insert four perforated positioning rods into the four frustum-shaped pins respectively. At the same time, the distance between each pair of mirror-arranged positioning rods is consistent with the length or width of the upper substrate of the second stage of the device. Place the solder paste-coated ceramic substrate on the thermoelectric particle array of the first stage of the device according to the positioning of the perforated positioning rods to form the upper substrate of the second stage of the device. Then remove the perforated positioning rods, then remove the pins. Finally, remove the multi-stage device from the mold base and complete the fabrication of the two-stage thermoelectric cooling device through one reflow soldering.

[0034] The present invention provides a method for fabricating a refrigeration device based on Mg3Bi2-based single-crystal thermoelectric material. The method utilizes single-crystal material to prepare single-stage, double-stage, or multi-stage thermoelectric refrigeration devices with thermoelectric single legs. The prepared Mg3Bi2-based single-crystal thermoelectric material has excellent thermoelectric performance and provides an integrated double-stage construction design, which simplifies the assembly steps, reduces assembly difficulty, and avoids the thermal effects of repeated welding on material properties, joint interfaces, and substrate materials. The refrigeration device has excellent joint quality and broad application prospects. Attached Figure Description

[0035] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0036] Figure 1 (a) Single-crystal Mg3Sb provided in an embodiment of the present invention 1.497 Sb 0.5 Te0.003 X-ray diffraction pattern of thermoelectric material along the in-plane direction;

[0037] Figure 1 (b) Single-crystal Mg3Sb provided in an embodiment of the present invention 1.497 Sb 0.5 Te 0.003 Single-crystal X-ray diffraction pattern of thermoelectric materials;

[0038] Figure 2 Single-crystal Mg3Sb provided as an embodiment of the present invention 1.497 Sb 0.5 Te 0.003 Comparison of the thermoelectric figure of merit of thermoelectric materials with that of commercial n-type Bi2Te3-based thermoelectric materials;

[0039] Figure 3 (a) Single-crystal Mg3Sb provided in an embodiment of the present invention 1.497 Sb 0.5 Te 0.003 Thermoelectric properties (resistivity) along the in-plane and out-of-plane;

[0040] Figure 3 (b) Single-crystal Mg3Sb provided in an embodiment of the present invention 1.497 Sb 0.5 Te 0.003 Thermoelectric properties along the in-plane and out-of-plane (Sebeck coefficient);

[0041] Figure 3 (c) Single-crystal Mg3Sb provided in the embodiments of the present invention 1.497 Sb 0.5 Te 0.003 Thermoelectric performance diagrams (power factor) along the in-plane and out-of-plane;

[0042] Figure 3 (d) is a single-crystal Mg3Sb provided in an embodiment of the present invention. 1.497 Sb 0.5 Te 0.003 Thermoelectric properties (thermal conductivity) along the in-plane and out-of-plane;

[0043] Figure 3 (e) Single-crystal Mg3Sb provided in the embodiments of the present invention 1.497 Sb 0.5 Te 0.003 Thermoelectric properties (thermoelectric figure of merit) along the in-plane and out-of-plane;

[0044] Figure 3 (f) is a single-crystal Mg3Sb provided in an embodiment of the present invention. 1.497 Sb 0.5 Te 0.003Thermoelectric properties along the in-plane and out-of-plane (relationship between carrier mobility and temperature).

[0045] Figure 4 (a) A single-crystal Mg3Bi provided in an embodiment of the present invention 1.997-x Sb x Te 0.003 Thermoelectric properties (resistivity) at temperatures of 300K-600K;

[0046] Figure 4 (b) Single-crystal Mg3Bi provided in the embodiments of the present invention 1.997-x Sb x Te 0.003 Thermoelectric properties (Zebeck coefficient) at temperatures between 300K and 600K;

[0047] Figure 4 (c) Single-crystal Mg3Bi provided in the embodiments of the present invention 1.997-x Sb x Te 0.003 Thermoelectric properties (thermal conductivity) at temperatures between 300K and 600K;

[0048] Figure 4 (d) is a single-crystal Mg3Bi provided in an embodiment of the present invention. 1.997-x Sb x Te 0.003 Thermoelectric performance diagram (thermoelectric figure of merit) at temperatures of 300K-600K;

[0049] Figure 5 The n-type Mg3Bi provided in the embodiments of the present invention 1.497 Sb 0.5 Te 0.003 Schematic diagram of the assembly process of a two-stage refrigeration device with p-type commercial (Bi,Sb)3Te2 thermoelectric material;

[0050] Figure 6 The n-type Mg3Bi provided in the embodiments of the present invention 1.497 Sb 0.5 Te 0.003 Maximum cooling temperature difference diagram of a single-stage refrigeration device with p-type (Bi,Sb)2Te3 thermoelectric material at hot end temperatures of 303K, 325K, and 350K.

[0051] Figure 7 (a) Based on n-type Mg3Bi provided in the embodiments of the present invention 1.497 Sb 0.5 Te 0.003 Diagram of a two-stage refrigeration performance testing device for p-type commercial (Bi,Sb)3Te2 thermoelectric material;

[0052] Figure 7 (b) Based on n-type Mg3Bi provided in the embodiments of the present invention 1.497 Sb 0.5 Te 0.003 A diagram showing the cooling performance of a two-stage refrigeration device using p-type commercial (Bi,Sb)3Te2 thermoelectric material at a hot junction temperature of 350K (a schematic diagram of the relationship between cooling power and temperature difference under different test currents).

[0053] Figure 7 (c) Based on n-type Mg3Bi provided in the embodiments of the present invention 1.497 Sb 0.5 Te 0.003 A diagram showing the cooling performance of a two-stage refrigeration device using p-type commercial (Bi,Sb)3Te2 thermoelectric material at a hot junction temperature of 350K (a schematic diagram of the relationship between cooling power and test current under different cooling temperature differences).

[0054] Figure 7 (d) is an embodiment of the present invention based on n-type Mg3Bi 1.497 Sb 0.5 Te 0.003 A diagram showing the cooling performance of a two-stage refrigeration device using p-type commercial (Bi,Sb)3Te2 thermoelectric material at a hot junction temperature of 350K (a schematic diagram of the relationship between cooling efficiency and temperature difference under different test currents).

[0055] Figure 7 (e) Based on n-type Mg3Bi provided in the embodiments of the present invention 1.497 Sb 0.5 Te 0.003 A diagram showing the cooling performance of a two-stage refrigeration device using p-type commercial (Bi,Sb)3Te2 thermoelectric material at a hot junction temperature of 350K (a schematic diagram of the relationship between cooling efficiency and current under different cooling temperature differences).

[0056] Figure 7 (f) is an embodiment of the present invention based on n-type Mg3Bi 1.497 Sb 0.5 Te 0.003 A two-stage refrigeration device using p-type commercial (Bi,Sb)3Te2 thermoelectric material at a hot junction temperature of 350K is shown in the following graph: (Schematic diagram of the relationship between actual refrigeration temperature difference, simulated refrigeration temperature difference and optimal current at different hot junction temperatures).

[0057] Figure 8 A three-dimensional schematic diagram of a two-stage cooling device provided in an embodiment of the present invention;

[0058] Figure 9 This is a three-dimensional schematic diagram of the assembly process of a two-stage refrigeration device provided in an embodiment of the present invention. Detailed Implementation

[0059] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0060] The terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this invention are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or apparatuses.

[0061] In this document, references to "embodiment" or "implementation" mean that a particular feature, structure, or characteristic described in connection with an embodiment or implementation may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0062] This invention provides a method for fabricating a refrigeration device based on Mg3Bi2-based single-crystal thermoelectric material, comprising: a single-crystal thermoelectric material preparation step and a refrigeration device preparation step; the single-crystal thermoelectric material preparation step includes: a raw material weighing step: according to Mg... 3.05 Bi 1.997-x Sb x Te 0.003 The nominal weights of magnesium, bismuth, antimony, and tellurium are measured, where x = 0.1-1.5. The raw material smelting step involves placing the raw materials in a heat-resistant container and smelting them to obtain a molten liquid. The single crystal formation step involves controlling the rate of temperature decrease of the molten liquid to allow it to cool and form single crystal nucleation points. As the molten liquid continues to cool, the single crystal nucleation points grow to form a single crystal, thus obtaining a single-crystal thermoelectric material. The refrigeration device fabrication step includes: preparing the single-crystal thermoelectric material into an n-type thermoelectric single leg, and welding the n-type thermoelectric single leg to a p-type thermoelectric single leg to form a single- or double-stage thermoelectric refrigeration device. The Mg3Bi2-based single-crystal thermoelectric material prepared by this invention exhibits excellent thermoelectric performance, and the refrigeration device has excellent joint quality, showing broad application prospects.

[0063] This invention provides a method for fabricating a refrigeration device based on Mg3Bi2-based single-crystal thermoelectric material, including: a single-crystal thermoelectric material fabrication step and a refrigeration device fabrication step (single-stage and double-stage refrigeration device fabrication steps);

[0064] The preparation steps of the single-crystal thermoelectric material include:

[0065] Raw material weighing steps: according to Mg 3.05 Bi 1.997-x Sb x Te 0.003 The nominal weights of magnesium, bismuth, antimony, and tellurium are given, where x = 0.1-1.5;

[0066] Raw material smelting step: The magnesium, bismuth, antimony and tellurium elements weighed in the weighing step are placed in a heat-resistant container and smelted to obtain a molten liquid;

[0067] Single crystal formation step: control the rate of temperature decrease of the melt to cool the melt so that single crystal nucleation points can be formed in the melt. The melt continues to cool, and the single crystal nucleation points grow to form a single crystal, thereby obtaining a single crystal thermoelectric material.

[0068] The steps for fabricating the refrigeration device include:

[0069] The single-crystal thermoelectric material is prepared into an n-type thermoelectric single leg and welded with a p-type thermoelectric single leg to form a single-stage thermoelectric refrigeration device.

[0070] In this embodiment of the invention, the prepared single-crystal thermoelectric material has high purity and uniformity, which can effectively improve the optimal average thermoelectric figure of merit (zT) in the temperature range of 250K-300K, and has broad application prospects.

[0071] Specifically, the heat-resistant container includes inert metal tubes such as niobium and tantalum (niobium tubes are used as an example in this invention), and the raw material smelting step includes a packaging step:

[0072] The magnesium, bismuth, antimony, and tellurium elements weighed in the raw material weighing step are placed inside a niobium tube, and the niobium tube is sealed under a protective gas atmosphere, including argon, helium, or nitrogen. The pressure of the protective gas inside the niobium tube is 0.02-0.15 MPa, and the niobium tube is sealed in a quartz tube under vacuum.

[0073] In specific applications, Mg 3.05 Bi 1.997-x Sb x Te 0.003 In this context, x can be 0.1 ≤ x ≤ 1.5. In this invention, x is taken as 0.5.

[0074] Specifically, the raw material smelting step includes:

[0075] Heating steps:

[0076] The quartz tube is placed in a heating device, which heats the raw material to 1200-1300K at a set heating rate, causing the raw material to form a liquid compound, and holds it at this temperature for 24 to 72 hours. In specific applications, the raw material can be heated to other suitable ranges such as 1220K, 1240K, 1260K, and 1280K. In this embodiment, the raw material is heated to 1223K. The holding time can be other suitable ranges such as 24, 36, 48, and 60 hours.

[0077] Single crystal formation steps: The liquid compound is subjected to a flow rate of 0.1 to 15 K h. -1 The temperature is cooled to 900 to 950 K at a rate that, during the cooling process, the liquid compound passes its solid-liquid phase transition point and slowly precipitates along the tube wall to form Mg. 3.05 Bi 1.997-x Sb x Te 0.003 Single-crystal nucleation sites are established, and as the temperature decreases, the single crystal gradually grows. After a set annealing time to achieve elemental homogenization of the compound, it is cooled to room temperature in the furnace. In specific applications, the cooling rate can also be 1 K h. -1 2K h -1 3K h -1 4K h -1 5K h -1 Or other suitable range.

[0078] Specifically, in the heating step, the quartz tube is placed in a heating device, which heats it to 1223K within 12 hours and maintains it at this temperature (1223K) for 48 hours.

[0079] Specifically, in the single crystal formation step, the liquid compound is prepared at 3K h. -1 The rate of cooling is slowed down to 923K.

[0080] Because Mg is highly reactive and volatile, it readily reacts with crucibles made of materials such as quartz, Al2O3, and graphite. Therefore, in this embodiment, an inert metal tube (niobium tube as an example in this invention) is used as the first container. The niobium tube itself is highly inert, does not readily react with the participating elements (magnesium, bismuth, antimony, and tellurium) in this embodiment, and is heat-resistant, allowing the reactants to melt at high temperatures and the elements to be fully mixed. An arc welding machine can be used to seal the raw materials in the niobium tube (the inner diameter of the niobium tube can be 22 mm, and the length can be 100 mm) under an argon atmosphere. The pressure of the protective gas inside the niobium tube is 0.02-0.15 MPa. Then, the niobium tube is sealed in a quartz tube under vacuum, which avoids the corrosive effect of oxygen on the niobium tube. The raw materials are heated to 1223 K within 12 hours and maintained at this temperature for 48 hours. High-temperature convection ensures uniform mixing of the elements and complete reaction. Then, the mixture is heated at 3 K h... -1 The tube is slowly cooled to 923 K. During this slow cooling process, the liquid compound passes its solid-liquid phase transition point and slowly precipitates along the tube wall, forming Mg. 3.05 Bi 1.497 Sb 0.5 Te 0.003 Single-crystal nucleation sites were observed, and the single crystals gradually grew as the temperature decreased. After a final 72-hour annealing to homogenize the compound, it was furnace-cooled to room temperature. Once the temperature program was complete, peeling open the metal tube revealed 2-3 distinct layered Mg crystals. 3.05 Bi 1.497 Sb 0.5 Te 0.003 Single crystals grow along the tube wall towards the center. The lamellar single crystals are peeled off along the in-plane ((0001) cleavage plane) and out-of-plane directions using a blade or wire cutter. The X-ray diffraction pattern in the in-plane direction is as follows: Figure 1 As shown in Figure a, the peak intensity along the (000l) direction macroscopically demonstrates the quality of the single-crystal material. Mg 3.05 Bi 1.497 Sb 0.5 Te 0.003 Single-crystal X-ray diffraction patterns such as Figure 1 As shown in b, crystallographic information such as atomic types, atomic occupancy, crystal structure, and bonding environment of the single crystal was obtained from a microscopic perspective. The obtained single-crystal thermoelectric material was cleaved along the ab direction, and its thermoelectric figure of merit zT was compared with that of commercial n-type Bi₂Te₃-based thermoelectric materials. Figure 2 Comparison reveals that the thermoelectric figure of merit of the single-crystal material of this invention is superior to that of commercial n-type thermoelectric materials across the entire temperature range of 300-600K. The thermoelectric performance of the obtained large-size single crystals was tested along the in-plane and out-of-plane directions in the sub-room temperature to mid-temperature range (250K-600K), and the results are as follows. Figure 3 As shown. The extremely high carrier mobility results in an average thermoelectric figure of merit zT for the material at 250K-300K.avg The value was increased to 0.97, which is the highest value reported to date. This embodiment also prepared and characterized a series of Mg3Bi with different Sb and Bi contents. 1.997-x Sb x Te 0.003 Single-crystal materials, their thermoelectric properties are as follows Figure 4 As shown. During the synthesis of polycrystalline materials, various types of crystal defects are inevitably introduced. High concentrations of crystal defects will inevitably affect the scattering mechanism of charge carriers in the material, limiting the improvement of thermoelectric material performance. The Mg3Bi2-based single-crystal thermoelectric material provided in this invention has ultra-high carrier mobility, increasing the average thermoelectric figure of merit zT of the material in the 250K-300K range. avg Increased to 0.97.

[0081] Specifically, fabricating the single-crystal thermoelectric material into an n-type thermoelectric single leg includes:

[0082] The single-crystal thermoelectric material is cut into a single-crystal substrate. Then, in a mold, a structure is formed with silver powder and Mg2Ni powder respectively deposited on both sides of the single-crystal substrate. From the bottom of the mold cavity upwards, there are five layers: a silver powder layer, a Mg2Ni powder layer, the single-crystal substrate, a Mg2Ni powder layer, and another silver powder layer, forming a five-layer hamburger structure. The mold is placed in a sintering device (such as a plasma discharge sintering device) and sintered at a set temperature and pressure for a set time to obtain the thermoelectric substrate. The thermoelectric substrate is then cut to a set size to obtain an n-type thermoelectric single leg, namely: Ag / Mg2Ni / Mg3Bi. 1.497 Sb 0.5 Te 0.003 / Mg2Ni / Ag single leg.

[0083] Specifically, the mold is a graphite mold, which is plasma-discharge sintered at 623K and 3.5kN for 5 minutes in a plasma discharge sintering equipment. The thermoelectric substrate is then cut into 2×2mm (2mm in length and width) single legs for later use using wire cutting.

[0084] Specifically, the p-type thermoelectric single leg is a p-type Bi2Te3 single leg prepared by electroplating Ni. In specific applications, Al2O3 ceramic with deposited Ni metal is used as the upper and lower substrates of the device, and an n-type Ag / Mg2Ni / Mg3Bi with a set logarithmic number is bonded using SnBi solder paste. 1.497 Sb 0.5 Te 0.003 / Mg2Ni / Ag single leg and p-type Bi2Te3 single leg prepared by electroplating Ni are soldered onto the substrate in one-step reflow soldering, thereby preparing a set of full-size Mg3Bi2-based single-crystal single-stage refrigeration devices with a set logarithm.

[0085] Specifically, the one-step reflow soldering method includes: using a reflow oven, at 1K s -1 The temperature was raised to 408 K at a heating rate of [unspecified rate] and held at 393 K for 2 min; then, [the temperature was further increased] at 1 K s [unspecified rate]. -1 The temperature was increased to 453 K at a heating rate of [value missing], held at this temperature for 45 s, and finally increased by 1 K / s. -1 The cooling rate is used to cool it to room temperature.

[0086] Specifically, the method for fabricating a refrigeration device based on Mg3Bi2-based single-crystal thermoelectric material further includes a fabrication step for a two-stage thermoelectric refrigeration device:

[0087] The upper stage of the two-stage single-crystal thermoelectric refrigeration device consists of multiple pairs of n-type thermoelectric single legs and p-type thermoelectric single legs of the same size and material;

[0088] The construction of the two-stage single-crystal thermoelectric refrigeration device is as follows:

[0089] like Figure 8 and Figure 9 As shown, n-type Mg3Bi 1.497 Sb 0.5 Te 0.003 Single-crystal thermoelectric particles are used as n-type thermoelectric single legs, and p-type Bi₂Te₃ thermoelectric particles are used as p-type thermoelectric single legs, while n-type Mg₃Bi 1.497 Sb 0.5 Te 0.003 Single-crystal thermoelectric particles and p-type Bi2Te3 thermoelectric particles are placed sequentially on a ceramic substrate coated with low-temperature SnBi solder paste according to a set position to form a first-level thermoelectric particle array. Then, the ceramic substrate is placed into a mold base 200 to form the lower substrate 110 of the first level of the device.

[0090] Next, insert four frustum-shaped pins 210 into the frustum-shaped holes of the mold base 200. Then, place the n-type thermoelectric single leg and the p-type thermoelectric single leg on the ceramic substrate coated with solder paste according to the predetermined positions. With the help of the positioning of the four frustum-shaped pins 210, place the ceramic substrate on the thermoelectric particle array of the first stage of the device to form the upper substrate 120 of the first stage of the device. Insert four perforated positioning rods 230 into the four frustum-shaped pins 210 respectively. At the same time, the distance between each pair of mirror-arranged positioning rods is consistent with the length or width of the upper substrate 130 of the second stage of the device. Place the ceramic substrate coated with solder paste on the thermoelectric particle array of the first stage of the device according to the positioning of the perforated positioning rods to form the upper substrate 130 of the second stage of the device. Then remove the perforated positioning rods 230, then remove the pins 210. Finally, remove the multi-stage device from the mold base 200 and complete the two-stage thermoelectric cooling device through one reflow soldering. The positioning rod 230 with a hole includes a rod body and a rod seat. The rod body is fixed to the rod seat, and the rod seat has a hole that can be fitted with a pin 210.

[0091] In practical applications, Mg3Bi2-based single-crystal single-stage cooling devices use Al2O3 ceramics with deposited Ni metal as the upper and lower substrates, and employ SnBi low-temperature solder paste (melting point: 411K) to bond 7 pairs of n-type Ag / Mg2Ni / Mg3Bi... 1.497 Sb 0.5 Te 0.003 The Mg2Ni / Ag single leg and the p-type Bi2Te3 single leg prepared by electroplating Ni are soldered onto the substrate in one-step reflow soldering, thereby fabricating a full-size Mg3Bi2-based single-crystal single-stage refrigeration device with 7 pairs of units.

[0092] Specifically, n-type Ag / Mg2Ni / Mg3Bi 1.497 Sb 0.5 Te 0.003 The preparation process of the / Mg2Ni / Ag single leg is as follows: single crystal Mg3Bi 1.497 Sb 0.5 Te 0.003 The wafers are wire-cut into circular pieces (diameter can be within a suitable range such as 12.7 mm) using electrical discharge machining (EDM) to serve as single-crystal substrates. Then, silver powder, Mg2Ni powder, and single-crystal Mg3Bi are mixed. 1.497 Sb 0.5 Te 0.003 The five-layer hamburger structure (on a single-crystal substrate) is sequentially loaded into a graphite mold and sintered by plasma discharge at 623K and 3.5kN for 5 minutes. The resulting disc is then cut into 2×2mm single-leg pieces using wire cutting. The preparation of Mg2Ni powder and the electroplating of Ni to prepare p-type Bi2Te3 single-leg pieces are well-known existing techniques and will not be elaborated here. In specific applications, the one-step reflow soldering method is as follows: using a reflow oven, at 1K s... -1 The temperature was raised to 408 K at a heating rate of [unspecified rate] and held at 393 K for 2 min; then, [the temperature was further increased] at 1 K s [unspecified rate]. -1 The temperature was increased to 453 K at a heating rate of [value missing] and held at this temperature for 45 s. Finally, the temperature was increased to 1 K s. -1 The cooling rate is used to cool it to room temperature.

[0093] To achieve deep and efficient cooling, this invention provides a fabrication process for a multi-stage thermoelectric cooling device, and uses COMSOL to simulate different logarithmic ratios between upper and lower stages and different area ratios of n / p type thermoelectric single legs. The lower stage of the two-stage thermoelectric cooling device consists of 17 n-type Mg3Bi... 1.497 Sb 0.5 Te 0.003 The device consists of a single leg and 17 commercially available (Bi,Sb)₂Te₃ electrodes, with the upper stage composed of 7 pairs of n / p-type thermoelectric single legs of the same size and material. The construction of the two-stage single-crystal thermoelectric cooling device is as follows: n-type Mg₃Bi 1.497Sb 0.5 Te 0.003 Single-crystal thermoelectric particles and p-type Bi₂Te₃ thermoelectric particles are sequentially placed at predetermined locations on a ceramic substrate coated with low-temperature SnBi solder paste. The ceramic substrate is then placed into a mold base to form the lower substrate of the first stage of the device. Figure 5 c. Next, insert the four frustum-shaped pins into the frustum-shaped holes in the substrate base, as follows: Figure 5 d. Once again, arrange the n-type and p-type thermoelectric particles in an array on the solder-painted ceramic substrate according to predetermined positions. Using four frustum-shaped pins for positioning, place the ceramic substrate on the thermoelectric particle array of the first stage of the device, forming the upper substrate of the first stage of the device, as shown below. Figure 5 d2. Next, insert the four perforated positioning rods into the four frustum-shaped pins as follows: Figure 5 d3. Simultaneously, the distance between each pair of mirror-aligned positioning rods matches the length or width of the upper substrate of the second stage of the device. Subsequently, the ceramic substrate coated with solder paste is placed on the thermoelectric particle array of the first stage of the device according to the positioning of the perforated positioning rods, forming the upper substrate of the second stage of the device, as shown below. Figure 5 d4. The final step is to first remove the perforated positioning rod, then remove the pin, and finally remove the multi-stage components from the base. Figure 5 d5, and the fabrication of multi-stage thermoelectric cooling devices is completed in a single reflow soldering process. This design allows for the construction of even more stages of thermoelectric cooling devices, which will not be elaborated upon here.

[0094] After single-stage and two-stage thermoelectric cooling devices based on n-type Mg3Bi2-based single-crystal thermoelectric particles and commercially available p-type Bi2Te3 thermoelectric particles were constructed, their thermoelectric cooling performance was characterized, such as... Figure 6 As shown in Figure 7. Figure 6 As shown, the single-stage thermoelectric refrigeration device can achieve a maximum cooling temperature difference of 69K when the hot end temperature is 303K, which exceeds the cooling performance of the Mg3Bi2 / Bi2Te3-based thermoelectric refrigeration devices reported to date.

[0095] Figure 7 a to Figure 7 f is based on n-type Mg3Bi 1.497 Sb 0.5 Te 0.003 Graph showing the cooling performance test of a two-stage refrigeration device using p-type commercial (Bi,Sb)3Te2 thermoelectric material; Figure 7 a is a diagram of a two-stage refrigeration device testing setup; Figure 7 b is a graph showing the cooling power versus temperature difference of a two-stage refrigeration device when the hot end temperature is 350K. Figure 7 c shows the test graph of cooling power versus test current. Figure 7 d is the graph showing the relationship between cooling efficiency and temperature difference. Figure 7e represents the relationship between cooling efficiency and current. Figure 7 f is a schematic diagram illustrating the relationship between the actual cooling temperature difference, the simulated cooling temperature difference, and the optimal current at different hot-end temperatures. The cooling power (Q) of the two-stage module at a hot-end temperature of 350K is also shown. c The relationship between temperature difference (ΔT) and temperature difference (ΔT) is as follows: Figure 7 As shown in b, the cooling power decreases linearly with increasing temperature difference. Therefore, the cooling power is maximized when the temperature difference for a given input current is zero. The relationship between cooling power and input current is as follows: Figure 7 As shown in Figure c, by applying parabolic fitting of cooling power and input current, the maximum cooling power and the optimal current (IA) within the range of ~3.5A can be determined. opt The value is approximately 2.7W. Figure 7 In d, COP also shows a good linear relationship with temperature difference. The relationship between COP and current is... Figure 7 Further details are shown in section e. The cooling temperature difference related to the input current is as follows: Figure 7 As shown in f. At hot-side temperatures of 303K, 325K, and 350K, single-crystal Mg3Bi... 1.497 Sb 0.5 Te 0.003 The maximum cooling temperature differences of the (Bi,Sb)₂Te₃-based bipolar devices were ~83.1K, ~94.5K, and ~106.8K, respectively. The theoretical cooling temperature differences under different currents and hot-junction temperatures were simulated using COMSOL software. Figure 7 The dotted line in f indicates that the predicted results match the measured data well.

[0096] The present invention provides a method for fabricating a refrigeration device based on Mg3Bi2-based single-crystal thermoelectric material. It utilizes single-crystal material to prepare single- or double-stage thermoelectric refrigeration devices with thermoelectric single legs. The prepared Mg3Bi2-based single-crystal thermoelectric material has excellent thermoelectric performance and provides an integrated double-stage construction design, which simplifies the assembly steps, reduces assembly difficulty, and avoids the thermal impact of repeated welding on material properties, joint interfaces, and substrate materials. The refrigeration device has excellent joint quality and broad application prospects.

[0097] This invention proposes a slow cooling method to prepare large-sized Mg3Sb with different Sb and Bi contents. x Bi 1.997-x Te 0.003 The growth method of single crystals was described, and the in-plane and out-of-plane thermoelectric transport properties of the single crystals were analyzed. A maximum average thermoelectric figure of merit of 0.97 was achieved in the temperature range of 250K-300K, far exceeding that of previously reported room-temperature thermoelectric materials such as Bi₂Te₃, MgAgSb, and Ag₂Se. Furthermore, Ag / Mg₂Ni / Mg₃Bi was successfully achieved using plasma discharge technology. 1.497 Sb 0.5 Te0.003 A single-crystal / Mg2Ni / Ag five-layer hamburger structure n-type thermoelectric single leg was successfully fabricated using a one-step reflow soldering method to prepare a single-leg n-type Mg3Bi-based thermoelectric single leg. 1.497 Sb 0.5 Te 0.003 This invention presents a single-stage thermoelectric cooler with a single leg of commercially available p-type (Sb,Bi)₂Te₃ thermoelectric cooler, and a two-stage thermoelectric cooler with 17 pairs of lower-stage and 7 pairs of upper-stage n- / p-type thermoelectric legs. At a hot-end temperature of 350K, the single-stage cooler achieves a maximum cooling temperature difference of 85K, while the two-stage cooler achieves a maximum cooling temperature difference of ~106.8K, outperforming commercially available n- / p-type Bi₂Te₃-based alloy thermoelectric coolers. The Mg₃Bi₂ single-crystal thermoelectric cooler exhibits a cooling temperature difference and maximum cooling power density comparable to commercial thermoelectric coolers. Therefore, this invention provides a possibility for the commercialization of Mg₃Bi₂ single-crystal thermoelectric coolers and also offers new ideas and concepts for sample preparation and device construction for other cooling materials.

[0098] In this invention, the terms "embodiment" and "implementation" mean that a specific feature, structure, or characteristic described in connection with an embodiment can be included in at least one embodiment of the invention. The appearance of these phrases in various places in the specification does not necessarily refer to the same embodiment, nor are they independent or alternative embodiments mutually exclusive with other embodiments. Those skilled in the art will understand, explicitly and implicitly, that the embodiments described in this invention can be combined with other embodiments. Furthermore, it should be understood that the features, structures, or characteristics described in the various embodiments of this invention can be arbitrarily combined to form yet another embodiment that does not depart from the spirit and scope of the technical solution of this invention, provided there is no contradiction between them.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention should not depart from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a refrigeration device based on Mg3Bi2-based single crystal thermoelectric material, characterized in that: The method comprises the following steps: preparing raw materials and subjecting them to high temperature heat preservation treatment under a protective atmosphere, and obtaining single crystal thermoelectric materials after cooling; wherein the raw materials include a magnesium source and a bismuth source; Specifically, the steps of preparing the single crystal thermoelectric material include: Raw material weighing steps: press Mg 3.05 Bi 1.997-x Sb x Te 0.003 Nominal weights of magnesium, bismuth, antimony and tellurium, where x = 0.1-1.5; Raw material smelting step: placing the magnesium, bismuth, antimony and tellurium elements weighed in the raw material weighing step in a heat-resistant container and smelting to obtain a melt; Single crystal forming step: controlling the temperature drop rate of the melt to cool the melt to form single crystal nucleation points in the melt, the melt continues to cool, the single crystal nucleation points grow to form single crystals, and single crystal thermoelectric materials are obtained; The single crystal thermoelectric material is prepared into an n-type thermoelectric single leg, and the n-type thermoelectric single leg is welded with a p-type thermoelectric single leg to form a single-stage or double-stage thermoelectric refrigeration device.

2. The method for preparing a refrigeration device based on Mg3Bi2-based single crystal thermoelectric material according to claim 1, characterized in that: The temperature-resistant container is an inert metal tube, and the raw material smelting step includes a packaging step: Placing the magnesium, bismuth, antimony and tellurium elements weighed in the raw material weighing step in an inert metal tube, and sealing the inert metal tube under a protective gas atmosphere including argon, helium or nitrogen; The pressure of the protective gas in the inert metal tube is 0.02-0.15 MPa, and the inert metal tube is sealed in a quartz tube.

3. The method for preparing a refrigeration device based on Mg3Bi2-based single crystal thermoelectric material according to claim 2, characterized in that: The raw material smelting step comprises: Heating steps: The quartz tube is placed in a heating device, and the heating device heats the raw material to 1200-1300K at a set heating rate to form a liquid compound from the raw material, and maintains the temperature for 24 to 72 hours; Single crystal formation step: Liquid compound is heated to 0.1 to 15 K h -1 The temperature of the tube is cooled to 900 to 950 K at a rate of 100 °C. During the cooling process, the liquid compound passes through its solid-liquid phase transition point and slowly precipitates along the tube wall to form Mg 3.05 Bi 1.997-x Sb x Te 0.003 The single crystal nucleation point, as the temperature decreases, the single crystal gradually grows, the annealing time is set, so that the compound achieves element homogenization and then cools to room temperature.

4. The method for preparing a refrigeration device based on Mg3Bi2-based single crystal thermoelectric material according to claim 3, characterized in that: In the heating step, the quartz tube is placed in a heating device, which heats the tube to 1223 K within 12 hours and maintains the temperature for 48 hours.

5. The method for preparing a refrigeration device based on Mg3Bi2-based single crystal thermoelectric material according to claim 3, characterized in that: In the single crystal forming step, the liquid compound is heated at 3K h -1 The material is slowly cooled to 923 K at a rate of 1.

6. The method for preparing a refrigeration device based on Mg3Bi2-based single crystal thermoelectric material according to any one of claims 1 to 5, characterized in that: The step of preparing the single crystal thermoelectric material into an n-type thermoelectric single leg comprises: The single crystal thermoelectric material is cut into a single crystal substrate, and then a structure is formed in a mold in which silver powder and Mg2Ni powder are respectively arranged on both sides of the single crystal substrate. After sintering at a set temperature and a set pressure for a set time, a thermoelectric substrate is obtained. The thermoelectric substrate is cut into a set size to obtain an n-type thermoelectric single leg: Ag / Mg2Ni / Mg3Bi 1.497 Sb 0.5 Te 0.003 / Mg2Ni / Ag single leg.

7. The method for preparing a refrigeration device based on Mg3Bi2-based single crystal thermoelectric material according to claim 6, characterized in that: The mold is a graphite mold, and the thermoelectric substrate is obtained by plasma discharge sintering at 523-723K and 2.5-4.5kN for 3-15 minutes.

8. The method for preparing a refrigeration device based on Mg3Bi2-based single crystal thermoelectric material according to claim 5, characterized in that: The p-type thermoelectric single leg is a p-type Bi2Te3 single leg prepared by electroplating Ni, and Al2O3 ceramics deposited with Ni metal are used as the upper and lower substrates of the device. The n-type Ag / Mg2Ni / Mg3Bi with a set number of pairs is soldered by SnBi solder paste. 1.497 Sb 0.5 Te 0.003 The / Mg2Ni / Ag single leg and the p-type Bi2Te3 single leg prepared by electroplating Ni are soldered on the substrate by a one-step reflow soldering method, thereby preparing a set of full-size Mg3Bi2-based single crystal single-stage refrigeration devices with a set number of logarithms.

9. The method for preparing a refrigeration device based on Mg3Bi2-based single crystal thermoelectric material according to claim 8, characterized in that: The one-step reflow method comprises: using a reflow oven, -1 The temperature was raised to 378-438 K at a heating rate of 0.5-2 K s and maintained at 363-423 K for 1-3 min. -1 The temperature was raised to 423-483 K at a heating rate of 0.5-2 K s -1 Cool down to room temperature at a cooling rate of .

10. The method for preparing a refrigeration device based on Mg3Bi2-based single crystal thermoelectric material according to claim 8, characterized in that: The method for preparing a refrigeration device based on Mg3Bi2-based single crystal thermoelectric material also includes the following steps for preparing a two-stage thermoelectric refrigeration device: The n-type Ag / Mg2Ni / Mg3Bi prepared by plasma spark sintering 1.497 Sb 0.5 Te 0.003 / Mg2Ni / Ag is used as the n-type thermoelectric single leg, and the p-type Bi2Te3 thermoelectric particles prepared by electroplating Ni are used as the p-type thermoelectric single leg. According to the set points, they are placed in sequence on the ceramic substrate coated with low-temperature SnBi solder paste to form the first-level thermoelectric particle array. Subsequently, the ceramic substrate is placed in the mold base to form the lower substrate of the first level of the device; Then, four truncated cone-shaped pins are inserted into the truncated cone-shaped holes of the mold base, and the n-type thermoelectric single leg and the p-type thermoelectric single leg are once again placed in sequence on the ceramic substrate coated with solder paste according to the predetermined positions. With the help of the positioning of the four truncated cone-shaped pins, the ceramic substrate is placed on the thermoelectric particle array of the first level of the device to form the upper substrate of the first level of the device. Four positioning rods with holes are respectively inserted into the four truncated cone-shaped pins. At the same time, the distance between each pair of mirror-arranged positioning rods is consistent with the length or width of the upper substrate of the second level of the device. The ceramic substrate coated with solder paste is placed on the thermoelectric particle array of the first level of the device according to the positioning of the positioning rods with holes to form the upper substrate of the second level of the device. The positioning rods with holes are removed, and then the pins are removed. Finally, the multi-stage device is removed from the mold base, and the preparation of the two-stage thermoelectric cooling device is completed through one reflow soldering.

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