Method for preparing functional materials by liquid metal assisted pressureless rapid joule heating sintering

Abstract

This invention relates to a method for preparing bismuth telluride-based thermoelectric materials by liquid metal-assisted pressureless rapid Joule sintering. The method involves uniformly mixing liquid metal with functional material precursor powder, followed by cold pressing or heated assisted pressing to obtain a preform, and finally performing rapid Joule sintering to obtain the functional material. The functional material includes at least one of bismuth telluride-based thermoelectric materials, germanium telluride-based and cadmium telluride-based optoelectronic functional materials, lead telluride-based functional semiconductor materials, and tin selenide-based functional semiconductor materials. In the optimized method, the liquid metal uniformly coats the matrix material during the mixing stage, acts as a lubricating medium and pore-filling medium during the cold pressing stage to promote powder particle rearrangement and initial densification, and at least partially diffuses into the matrix and / or grain boundaries during the rapid Joule sintering stage, participating as a dopant element to regulate the thermoelectric properties of the material. This method enables rapid densification of functional materials at low temperatures under short-process conditions and significantly improves their corresponding properties.

Description

Technical Field

[0001] This invention belongs to the field of functional materials preparation technology, and particularly relates to a method for preparing bismuth telluride-based thermoelectric materials by liquid metal-assisted pressureless rapid Joule heating sintering. Background Technology

[0002] Functional materials refer to materials with specific functions such as electrical, thermal, magnetic, optical, acoustic, mechanical, chemical, or energy conversion, and are widely used in energy conversion, electronic devices, sensing, thermal management, information storage, and advanced manufacturing. For many inorganic functional materials, powder metallurgy is one of the important methods for preparing bulk materials, which usually includes powder preparation, forming, and sintering densification. However, due to the frictional resistance between powder particles, limited particle rearrangement, and limited initial forming density, existing powder metallurgy routes usually require high-temperature and high-pressure processes such as hot pressing sintering, spark plasma sintering, or hot deformation, as well as corresponding specialized equipment, to achieve final densification of the bulk material under the combined action of high temperature and external pressure. Therefore, this approach has problems such as long process flow, high dependence on equipment, high requirements for molds and pressure systems, high energy consumption, and high preparation costs.

[0003] Thermoelectric materials are a typical example of functional materials, capable of direct and reversible conversion of thermal energy into electrical energy based on the Seebeck, Peltier, and Thomson effects. They are characterized by the absence of mechanical transmission parts, compact structure, fast response, and high reliability. Among them, bismuth telluride-based thermoelectric materials, due to their excellent thermoelectric properties in the room temperature and near-room temperature range, have been widely used in thermoelectric power generation, thermal management of electronic devices, and solid-state refrigeration, and are one of the representative thermoelectric semiconductor material systems in functional materials.

[0004] Taking the preparation of bismuth telluride-based thermoelectric materials as an example, the problems existing in the powder metallurgy route mentioned above are also prominent, and are further affected by factors such as the layered structure of the material itself, the volatility of components, and the sensitivity of thermoelectric properties to composition and defect states. Existing bulk preparation methods for bismuth telluride-based thermoelectric materials can be mainly divided into directional solidification and powder metallurgy sintering methods according to the forming and densification processes. Directional solidification can obtain single crystals, near-single crystals, or columnar crystals with strong orientation, which is beneficial for leveraging the excellent thermoelectric transport properties of bismuth telluride-based materials along specific crystal orientations; however, this type of method usually suffers from problems such as long preparation cycles, low production efficiency, large microstructure size, difficulty in controlling compositional uniformity, and significant material anisotropy. Furthermore, bismuth telluride-based materials have a layered crystal structure, and the strongly oriented bulk obtained by directional solidification is prone to cracking along cleavage planes during subsequent cutting, processing, and assembly, making it difficult to simultaneously achieve high thermoelectric performance, microstructure uniformity, processing reliability, and large-scale preparation efficiency.

[0005] Powder metallurgy sintering typically involves two routes: one involves first obtaining an alloy ingot through melting, annealing, or zone melting, then crushing, grinding, or ball milling the ingot to obtain a powder precursor, followed by bulk densification using processes such as hot pressing sintering, spark plasma sintering, or hot deformation; the other involves directly preparing a powder precursor from elemental raw materials through mechanical alloying or high-energy ball milling, followed by bulk material preparation via hot pressing sintering or spark plasma sintering. While these methods can shorten the preparation cycle, refine grains, and improve microstructure uniformity to some extent, they still generally rely on external pressure for final densification during the sintering or hot deformation stages, requiring the use of high-temperature, high-pressure sintering equipment, mold systems, pressure systems, and temperature control systems, resulting in high equipment costs and energy consumption. Furthermore, in bismuth telluride-based materials, low-melting-point or volatile components such as Te are more prone to volatilization or compositional deviation during prolonged high-temperature melting, annealing, hot pressing sintering, spark plasma sintering, or hot deformation, thus affecting the phase composition stability and thermoelectric property consistency of the material.

[0006] Therefore, for functional materials, including bismuth telluride-based thermoelectric materials, developing a preparation method that can improve powder forming behavior, enhance the structural integrity of bulk precursors, reduce external pressure dependence during sintering, and achieve rapid densification under conditions of short process cycles and low energy consumption has significant engineering application value. For bismuth telluride-based thermoelectric materials, this method also needs to consider composition control, defect control, and thermoelectric performance control to meet their requirements for phase composition stability and consistency of thermoelectric transport properties.

[0007] The inventors discovered that introducing liquid metal into functional material powder systems and combining it with pre-forming and pressureless rapid Joule sintering processes allows the liquid metal to act as a lubricant, fill gaps, and promote powder particle rearrangement during the forming stage. In the subsequent rapid Joule sintering stage, it further promotes interparticle bonding, interface control, and sintering densification, thus facilitating the rapid densification of functional materials without applying external sintering pressure. Taking the preparation of bismuth telluride-based thermoelectric materials as an example, when using Ga-In liquid metal, it not only acts as a lubricating and pore-filling medium to promote the forming and initial densification of the powder precursor during the forming stage, but also at least partially distributes or diffuses into the bismuth telluride matrix and / or grain boundary regions during pressureless rapid Joule sintering, participating as a component to regulate the thermoelectric properties of the material.

[0008] It should be noted that, regarding bismuth telluride-based thermoelectric materials, while existing technologies have disclosed Ga-doped or Ga-Cu dual-doped bismuth telluride-based thermoelectric materials, and densification can be achieved through hot pressing sintering, spark plasma sintering, hot deformation, or texturing treatment, these methods typically rely on melting and casting, hot pressing sintering, SPS pressure sintering, or high-temperature hot deformation processes. They do not utilize Ga-In liquid metal as a lubricating medium and pore-filling medium during the powder forming stage, nor do they leverage its bulking effect to achieve rapid Joule heating sintering without external sintering pressure. The essential difference of this invention lies in the fact that the liquid metal promotes powder particle rearrangement, fills interparticle pores, and improves the structural integrity of the bulk precursor during the forming stage. During pressureless rapid Joule heating sintering, it further promotes interfacial bonding and densification. Taking the preparation of bismuth telluride-based thermoelectric materials as an example, Ga and In can also at least partially enter the matrix and / or grain boundary regions, participating in the regulation of composition and thermoelectric properties. Summary of the Invention

[0009] To address the problems of existing functional material preparation processes that typically rely on melting and casting, hot pressing and sintering, spark plasma sintering, high-pressure hot extrusion or hot deformation to prepare bulk materials, which have issues such as long process flow, high equipment dependence, high external pressure requirements, and difficulty in simultaneously achieving densification and performance control, this invention provides a method for preparing functional materials by Ga-In liquid metal-assisted pressureless rapid Joule thermal sintering.

[0010] The preparation of functional materials by liquid metal-assisted rapid Joule thermal sintering includes the following steps:

[0011] After the liquid metal and the functional material precursor powder are mixed evenly, the mixture is cold-pressed or heated to form a blank. Finally, the blank is subjected to rapid Joule heating sintering without applying external mechanical pressure for sintering densification to obtain the functional material.

[0012] Preferably, the functional material includes at least one of bismuth telluride-based thermoelectric materials, germanium telluride-based and cadmium telluride-based optoelectronic functional materials, lead telluride-based functional semiconductor materials, and tin selenide-based functional semiconductor materials.

[0013] The liquid metal is a low-melting-point metal or low-melting-point alloy that is liquid, near-liquid, or semi-liquid at room temperature, mixing temperature, or forming temperature. The low-melting-point metal or low-melting-point alloy is selected from one or more of gallium-based liquid metals, indium-based low-melting-point alloys, tin-based low-melting-point alloys, and bismuth-based low-melting-point alloys. Preferably, the liquid metal is selected from one or more of Ga, Ga-In alloys, Ga-In-Sn alloys, Ga-Sn alloys, Ga-In-Zn alloys, Ga-In-Sn-Zn alloys, In-Sn alloys, Bi-In alloys, Sn-Bi alloys, and Bi-In-Sn alloys. More preferably, the liquid metal is Ga-In liquid metal.

[0014] When the functional material is a bismuth telluride-based thermoelectric material or a germanium telluride-based optoelectronic material, the preferred preparation method is as follows:

[0015] (1) Mechanical alloying treatment of bismuth telluride-based raw materials or mechanical alloying treatment of germanium telluride-based raw materials to obtain powder precursors;

[0016] (2) The Ga-In liquid metal is mixed with the powder precursor obtained in step (1) to obtain a composite powder, wherein the amount of Ga added is greater than 0 and not higher than 4 at.%, preferably 0.02~3 at.%, more preferably 0.5~2 at.%, and the amount of In added is greater than 0 and not higher than 0.66 at.%, preferably 0.02~0.5 at.%, more preferably 0.05~0.3 at.%. at.%, where at.% is the atomic percentage relative to the total number of atoms of all elements in the obtained bismuth telluride-based thermoelectric material. When the Ga and In contents are too low, the spreading, wetting, interstitial filling, and lubrication effects of the Ga-In liquid metal between powder particles are insufficient, making it difficult to fully promote particle rearrangement and preliminary densification of the precursor, which is detrimental to obtaining a structurally complete and highly dense bulk material through subsequent pressureless rapid Joule thermal sintering. When the Ga content is too high, excess Ga tends to accumulate or segregate at the matrix or grain boundaries, enhancing carrier scattering and reducing mobility, and even causing phase composition deviation or second phase formation. When the In content is too high, it may excessively control antisite defects and carrier concentration, causing the carrier concentration to deviate from the optimal range and leading to a decrease in power factor or thermoelectric figure of merit. Therefore, controlling Ga and In within the above ranges is beneficial for achieving a balance between the liquid metal's role in promoting molding and densification and the regulation of thermoelectric transport properties.

[0017] (3) The composite powder is cold-pressed to obtain a bulk precursor;

[0018] (4) The bulk precursor is subjected to rapid Joule thermal sintering under vacuum or protective atmosphere and without external sintering pressure to obtain a sintered body of bismuth telluride-based thermoelectric material; wherein, the Ga-In liquid metal in step (3) not only acts as a lubricating medium to reduce the frictional resistance between powder particles and between powder and mold, and promotes particle rearrangement, but also acts as an interstitial medium to enter the pores and gaps between particles, thereby improving the initial density of the precursor; in the subsequent pressureless rapid Joule thermal sintering process, the Ga-In liquid metal diffuses at least partially into the bismuth telluride-based matrix and / or grain boundary region, and participates in the regulation of the material composition and thermoelectric properties as a dopant element; this method does not require the raw materials to be melted into ingots first, nor does it require high-pressure hot extrusion to achieve bulk densification.

[0019] Preferably, the bismuth telluride-based thermoelectric material is selected from bismuth telluride-based materials, bismuth-antimony-telluride thermoelectric materials, bismuth-telluride-selenium thermoelectric materials, and any of the aforementioned materials in a further doping or composite modification system. Specifically, the bismuth telluride-based thermoelectric material is selected from at least one of the following: bismuth telluride-based materials, bismuth-antimony-telluride thermoelectric materials, bismuth-telluride-selenium thermoelectric materials, bismuth-antimony-selenium thermoelectric materials, bismuth-telluride-selenium thermoelectric materials, doped bismuth telluride-based materials, doped bismuth-antimony-telluride thermoelectric materials, doped bismuth-telluride-selenium thermoelectric materials, doped bismuth-antimony-selenium thermoelectric materials, modified bismuth telluride-based materials, modified bismuth-antimony-telluride thermoelectric materials, modified bismuth-telluride-selenium thermoelectric materials, and modified bismuth-antimony-selenium thermoelectric materials.

[0020] Preferably, the bismuth-antimony-tellurium thermoelectric material is a p-type bismuth telluride-based thermoelectric material with a Bi-Sb-Te-based system, and the bismuth-tellurium-selenium thermoelectric material is an n-type bismuth telluride-based thermoelectric material with a Bi-Te-Se-based system.

[0021] Preferably, the Ga-In liquid metal is an alloy system composed of Ga and In that is in a liquid or near-liquid state at room temperature or a mixed temperature.

[0022] Preferably, the mechanical alloying treatment is carried out by vibratory ball milling, and the loading and sealing are completed under an inert atmosphere; the ball-to-material ratio is 10:1, the ball milling method is dry milling, the ball milling jar and the ball milling media are made of stainless steel, the vibration frequency is 1060 reciprocating vibrations per minute, and the total ball milling time is not less than 5 minutes, preferably 30 minutes to 3 hours, and more preferably 1 to 2 hours.

[0023] Preferably, in step (2), Ga and In are first mixed to form a homogeneous liquid system, and then mixed with the powder precursor; the mixing is carried out by grinding and mixing, and the mixing time is not less than 30 min.

[0024] Preferably, the ratio of Ga to In is such that the formed Ga-In system is in a liquid or near-liquid state at room temperature, mixing temperature, or molding temperature. Preferably, based on a total Ga and In atomic number of 100 at.%, the Ga ratio is 80–99 at.% and the In ratio is 1–20 at.%; more preferably, the Ga ratio is 83–95 at.% and the In ratio is 5–17 at.%. Within this range, the Ga-In system has a low melting point and good fluidity, which is beneficial for its spreading and filling between powder particles, and plays a lubricating and rearrangement-promoting role during cold pressing. If the In ratio is too low, the low melting point and fluidity advantages of the Ga-In system are weakened; if the In ratio is too high, the carrier regulation effect of In after entering the matrix or grain boundaries may be too strong, easily causing the carrier concentration to deviate from the optimal range and weakening the thermoelectric performance.

[0025] Preferably, the cold pressing pressure in step (3) is not less than 500 MPa and the holding time is not less than 1 min. The cold pressing can be carried out by one-time pressing or staged cold pressing. The staged cold pressing includes graded pressure increase, graded pressure holding and / or repeated pressure increase-depressurization process.

[0026] Preferably, the rapid Joule heating sintering in step (4) is carried out under a vacuum or argon protective atmosphere; when the rapid Joule heating sintering is carried out under vacuum conditions, the vacuum degree of the furnace cavity is less than 2.2 × 10⁻⁶. -3 Pa; When the rapid Joule heating sintering is carried out under an argon protective atmosphere, the furnace cavity is under a slight negative pressure, with a gauge pressure of -0.07 MPa.

[0027] Preferably, the pressureless rapid Joule heating sintering process in step (4) includes a rapid heating stage, a holding stage, and a rapid cooling stage; the rapid heating stage involves heating from room temperature to 280-440 °C within 1-600 s, holding for 0-600 s, and then cooling to room temperature or no higher than 100 °C within 1-600 s; when the holding time is 0 s, it indicates that the rapid cooling stage is directly entered after heating to the target sintering temperature. More preferably, the temperature is heated from room temperature to 350-420 °C within 30-90 s, held for 30-180 s, and then cooled to room temperature within 30-120 s; more preferably, the temperature is heated from room temperature to 400-410 °C within 60 s, held for 60 s, and then cooled to room temperature within 60 s.

[0028] Preferably, the relative density of the sintered bulk bismuth telluride-based thermoelectric material is greater than 90%, more preferably greater than 95%, and even more preferably greater than or equal to 98%.

[0029] Preferably, the functional material includes Ga. 0.1In 0.0165 Bi 0.3835 Sb 1.5 Te 3、 Ga 0.05 In 0.00825 Bi 0.44175 Sb 1.5 Te3, Ga 0.048 In 0.008 Bi 0.144 Sb 1.8 Te3, Ga 0.048 In 0.008 Bi 0.244 Sb 1.7 Te3, Ga 0.048 In 0.008 Bi 0.344 Sb 1.6 Te3, Ga 0.0667 In 0.011 Bi 1.9223 Te 2.7 Se 0.3 Ga 0.02 In 0.0033 Ge 0.9767 Te, Ga 0.02 In 0.0033 Pb 0.9767 Te, Ga 0.02 In 0.0033 Sn 0.9769 At least one of Se.

[0030] Beneficial effects

[0031] Compared with the prior art, the present invention has at least the following beneficial effects:

[0032] Firstly, by introducing an appropriate amount of Ga-In liquid metal with a suitable Ga / In ratio into the bismuth telluride-based powder system, it plays a lubricating and interstitial role during the cold pressing stage, which helps to reduce interparticle frictional resistance, promote particle rotation and rearrangement, and improve the initial density of the bulk precursor. In the subsequent pressureless rapid Joule thermal sintering process, the Ga-In liquid metal further promotes interparticle diffusion, interfacial bonding, and sintering densification, thereby improving the final density of the sintered bulk.

[0033] Secondly, Ga-In liquid metal diffuses into the bismuth telluride matrix and / or grain boundary region at least partially during the subsequent rapid Joule thermal sintering process. Thus, it not only exists as a densification medium, but also participates in the material composition regulation and thermoelectric property regulation as a performance regulation element, realizing the dual functions of "forming to promote densification" and "post-sintering performance regulation".

[0034] Third, the process route that combines pre-process cold pressing with subsequent pressureless rapid Joule thermal sintering can achieve rapid densification of materials in a shorter processing time, and helps to reduce the risk of volatilization of low-melting-point components at high temperatures and suppress abnormal grain growth.

[0035] Fourth, the rapid Joule thermal sintering process of this invention does not apply external sintering pressure, unlike traditional hot pressing, spark plasma sintering, or hot extrusion processes that rely on external pressure for densification. Furthermore, this invention does not require the raw materials to be melted into ingots beforehand, nor does it require ingot powdering and high-temperature, high-pressure hot extrusion. Instead, it uses Ga-In liquid metal to assist in cold pressing pre-densification of the powder, and completes rapid, low-temperature Joule thermal sintering densification without external sintering pressure. This process route helps reduce equipment dependence, shorten equipment downtime, and reduce energy consumption, making it suitable for the rapid preparation and further engineering scale-up of bismuth telluride-based thermoelectric materials.

[0036] Fifth, the present invention can produce a dense and high-performance product without special texturing treatment. Attached Figure Description

[0037] Figure 1 Ga prepared in Example 1 0.1 In 0.0165 Bi 0.3835 Sb 1.5 XRD pattern of Te3 sample;

[0038] Figure 2 Ga prepared in Example 2 0.05 In 0.00825 Bi 0.44175 Sb 1.5 XRD pattern of Te3 sample;

[0039] Figure 3 Ga prepared in Example 3 0.0667 In 0.011 Bi 1.9223 Te 2.7 Se 0.3 XRD pattern of the sample. Detailed Implementation

[0040] The present invention will be further described below with reference to specific embodiments, examples, and comparative examples, but the present invention is not limited to the embodiments described below. Those skilled in the art can make appropriate adjustments to the raw material system, the amount of Ga-In liquid metal added, the cold pressing conditions, and the pressureless rapid Joule heating sintering conditions according to the composition of the target bismuth telluride-based thermoelectric material, and such adjustments should all fall within the protection scope of the present invention.

[0041] It should be noted that the "pressureless rapid Joule thermal sintering" described in this invention refers to the absence of external sintering pressure during the rapid Joule thermal sintering stage. The preceding cold pressing step is used to obtain a bulk precursor with a certain initial density and shape stability, and is not part of the external pressure applied during the sintering stage. This invention differs from the electromagnetic melting-ingot powdering-hot extrusion route. It does not require the raw material to be melted into an ingot first, nor does it require densification through high-pressure hot extrusion at high temperatures. Instead, it utilizes the lubrication, gap-filling, and rearrangement-promoting effects of Ga-In liquid metal during the cold pressing stage to enable the bulk precursor to achieve densification through rapid Joule thermal sintering without external sintering pressure.

[0042] This embodiment provides a method for preparing bismuth telluride-based thermoelectric materials by Ga-In liquid metal-assisted pressureless rapid Joule heating sintering, comprising the following steps:

[0043] Step 1: Preparation of bismuth telluride-based powder precursor; Weigh the raw materials according to the stoichiometric ratio of the target bismuth telluride-based thermoelectric material, place the raw materials and grinding balls in a ball mill jar, and perform mechanical alloying treatment under an inert atmosphere to obtain a powder precursor with uniform composition distribution and high surface activity.

[0044] Preferably, the bismuth telluride-based thermoelectric material is selected from bismuth telluride-based materials, bismuth-antimony-telluride thermoelectric materials, bismuth-telluride-selenium thermoelectric materials, and any of the aforementioned materials in a further doping or composite modification system; the bismuth-antimony-telluride thermoelectric material can be a p-type bismuth telluride-based thermoelectric material with a Bi-Sb-Te-based system, and the bismuth-telluride-selenium thermoelectric material can be an n-type bismuth telluride-based thermoelectric material with a Bi-Te-Se-based system.

[0045] In one specific embodiment, mechanical alloying is completed by loading materials in an argon-filled glove box, followed by sealing the ball mill jar and performing vibratory ball milling; the ball-to-material ratio of the vibratory ball mill is 10:1, the ball milling method is dry grinding, the ball mill jar and the ball milling media are made of stainless steel, the vibration frequency is 1060 reciprocating vibrations per minute, and the total ball milling time is 1.5 hours.

[0046] Step 2: Mixing Ga-In liquid metal with the powder precursor; Ga and In are placed in a mixing container or mixing device, and after mixing to form a homogeneous Ga-In liquid metal system, the powder precursor obtained in Step 1 is added, and mixing continues to obtain a composite powder; the premixing of Ga and In and the mixing of Ga-In liquid metal with the powder precursor can be carried out by grinding, mechanical stirring, planetary mixing, or other mixing methods that can uniformly disperse Ga-In liquid metal between powder particles. Preferably, the mixing is carried out at room temperature, and the mixing time is not less than 30 minutes.

[0047] The amount of Ga added is greater than 0 and not more than 4 at.%, and the amount of In added is greater than 0 and not more than 0.66 at.%, where at.% is the atomic percentage relative to the total number of atoms of all elements in the resulting bismuth telluride-based thermoelectric material. Ga-In liquid metal is in a liquid or near-liquid state at room temperature and can spread, wet, and fill gaps between powder particles.

[0048] Step 3: Cold pressing; The composite powder obtained in Step 2 is loaded into a mold and cold pressed under pressure to obtain a bulk precursor with a preset shape. During this process, Ga-In liquid metal acts as a lubricating medium, reducing frictional resistance between powder particles and between the powder and the mold, promoting particle rearrangement; it also acts as a gap-filling medium, entering the pores and gaps between particles to increase the initial density of the bulk precursor. Preferably, the cold pressing pressure is not less than 500 MPa, and the holding time is not less than 1 min. The cold pressing mold can be selected according to the size and shape of the target sample, including but not limited to cylindrical, cuboid, sheet-like, or other preset shaped molds. The size and shape of the resulting bulk precursor correspond to the cavity of the cold pressing mold. No additional release agent is needed during the cold pressing process, and the resulting bulk precursor can be stably demolded while maintaining structural integrity.

[0049] Step 4: Place the bulk precursor obtained in Step 3 in a rapid Joule thermal sintering equipment and perform rapid Joule thermal sintering under vacuum or protective atmosphere conditions without applying external sintering pressure to obtain a dense bismuth telluride-based thermoelectric material sintered body.

[0050] In the pressureless rapid Joule heating process, in addition to promoting interparticle diffusion, interfacial bonding and sintering densification, Ga-In liquid metal also diffuses into the bismuth telluride matrix and / or grain boundary region at least partially, acting as a dopant element to regulate the composition and thermoelectric properties of the material.

[0051] Preferably, the pressureless rapid Joule heating sintering is performed under a vacuum or argon protective atmosphere. When the pressureless rapid Joule heating sintering is performed under vacuum conditions, the vacuum degree of the furnace cavity is less than 2.2 × 10⁻⁶. -3 Pa; When the pressureless rapid Joule thermal sintering is carried out under an argon protective atmosphere, the furnace cavity is under a slight negative pressure, with a gauge pressure of -0.07 MPa.

[0052] In one specific embodiment, the pressureless rapid Joule heating sintering process is as follows: the temperature is raised to 400 ℃ within 60 s from room temperature, held at that temperature for 60 s, and then cooled to room temperature within 60 s.

[0053] In an embodiment of the present invention, the relative density of the sintered bulk of the bismuth telluride-based thermoelectric material obtained is greater than 95%, including 95% to 98%.

[0054] In this invention, the relative density is calculated according to the following formula: Relative density (%) = ρ 实测 / ρ 理论 ×100%, where ρ 实测 ρ is the measured density calculated from the sample mass and geometric volume. 理论 The theoretical density of the bismuth telluride-based material corresponding to the target composition.

[0055] Example 1

[0056] This embodiment employs a Ga-In liquid metal-assisted pressureless rapid Joule thermal sintering method to prepare bismuth-antimony-tellurium-based p-type bismuth telluride thermoelectric materials. The target composition is written as: Ga 0.1 In 0.0165 Bi 0.3835 Sb 1.5 Te3, Ga, and In correspond to 2 at.% and 0.33 at.% of the total number of atoms of all elements in the obtained material, respectively, falling within the range of Ga and In addition amounts specified in this invention.

[0057] 1. Raw material pretreatment: Weigh Bi, Sb and Te raw materials and mix them according to the corresponding stoichiometric ratio; in an argon-filled glove box, load the raw materials and grinding balls into a stainless steel ball mill jar, seal it and place it in a vibrating ball mill for mechanical alloying treatment.

[0058] The ball-to-material ratio was 10:1, the ball milling method was dry milling, the ball milling jar and the ball milling media were made of stainless steel, the vibration frequency was 1060 reciprocating vibrations per minute, the ball milling program was set to 30 min × 3 ball milling cycles, with a 15 min break between adjacent ball milling cycles, and the total ball milling time was 1.5 h, to obtain the powder precursor.

[0059] 2. Ga-In liquid metal mixing: Ga and In are mixed in a grinding mortar at an atomic stoichiometric ratio of 0.1:0.0165 and ground at room temperature to form a homogeneous Ga-In liquid metal system. Then, the system is added to the powder precursor obtained in step 1 according to the designed composition and ground for another 30 min to obtain the composite material.

[0060] 3. Cold pressing: The composite powder is loaded into a cold pressing mold, and a pressure of 700 MPa is applied using a cold press and held for 1 minute to obtain a bulk precursor.

[0061] 4. Pressureless rapid Joule thermal sintering: The bulk precursor is placed in a rapid Joule thermal sintering apparatus and subjected to pressureless rapid Joule thermal sintering under a vacuum or argon protective atmosphere without applying external sintering pressure; when using vacuum conditions, the vacuum degree of the furnace cavity is less than 2.2 × 10⁻⁶. -3Pa; When using an argon protective atmosphere, the furnace cavity is under a slight negative pressure, with a gauge pressure of -0.07 MPa; The specific sintering process is as follows: from room temperature, the temperature is raised to 400 ℃ within 60 s, held for 60 s, and then cooled to room temperature within 60 s.

[0062] 5. Result Characterization: The mass and volume of the obtained sample were measured, and the results showed that the relative density of the sample was greater than 95%. Figure 1 The XRD results show that the obtained sample is a bismuth telluride-based single-phase material with a thermoelectric figure of merit (ZT) of 1.15 at 300 K and 1.03 at 450 K. The maximum ZT value is obtained at 350 K, which is 1.34.

[0063] Comparative Example 1

[0064] This comparative example illustrates the impact of Ga-In liquid metal on the stability of powder cold pressing and the feasibility of subsequent pressureless rapid Joule thermal sintering.

[0065] Except for not adding Ga-In liquid metal and adjusting the basic composition to Bi 0.5 Sb 1.5 Except for Te3, the other process conditions were the same as in Example 1. The number of samples was 10.

[0066] Specifically, weigh out Bi, Sb, and Te raw materials, and mix them according to the formula. 0.5 Sb 1.5 The raw materials were prepared according to the stoichiometric ratio corresponding to Te3; the powder precursor was obtained by vibratory ball milling under the same mechanical alloying conditions as in Example 1. Subsequently, without adding Ga and In, the obtained powder precursor was directly loaded into a cold pressing mold and cold-pressed at 700 MPa for 1 min, and then processed according to the same pressureless rapid Joule thermal sintering process as in Example 1.

[0067] The results show that without the addition of Ga-In liquid metal, the powder precursor is difficult to form a structurally complete and stably demolded bulk precursor after cold pressing. Some samples cracked during demolding. Even after further pressureless rapid Joule sintering, the uncrackled samples also cracked, making it difficult to obtain a complete sintered bulk body that meets the performance testing requirements. Compared with the complete sintered bulk body with a relative density greater than 95% obtained in Example 1, Comparative Example 1, due to the lack of Ga-In liquid metal, failed to obtain a structurally complete bulk sample. The obtained sample cracked and could not be processed into a regular sample that meets the thermoelectric performance testing requirements; therefore, ZT testing at 300 K was not performed. Combining Example 1 and Comparative Example 1, it can be seen that Ga-In liquid metal plays a lubricating, gap-filling, and particle rearrangement-promoting role in the cold pressing stage, which is crucial for obtaining a structurally complete bulk precursor and achieving subsequent pressureless rapid Joule sintering densification.

[0068] Comparative Example 2

[0069] This comparative example uses a pressureless rapid Joule thermal sintering method with Ga as the sole addition to prepare bismuth-antimony telluride-based p-type bismuth telluride thermoelectric materials. The target composition is written as: Ga 0.1165 Bi 0.3835 Sb 1.5 Te 3， In this composition, the total number of atoms is 5, and Ga accounts for 2.33 at.% of the total number of atoms in the material. In this comparative example, the number of Ga atoms added is 0.1165, which is the same as the total number of Ga and In atoms added in Example 1.

[0070] 1. Raw material pretreatment: Weigh Bi, Sb, and Te raw materials, and prepare them according to Bi... 0.3835 Sb 1.5 The raw materials were prepared according to the stoichiometric ratio corresponding to Te3; in an argon-filled glove box, the raw materials and grinding balls were loaded into a stainless steel ball mill jar, sealed, and then placed in a vibrating ball mill for mechanical alloying treatment.

[0071] The ball-to-material ratio was 10:1, the ball milling method was dry milling, the ball milling jar and the ball milling media were made of stainless steel, the vibration frequency was 1060 reciprocating vibrations per minute, the ball milling program was set to 30 min × 3 ball milling cycles, with a 15 min break between adjacent ball milling cycles, and the total ball milling time was 1.5 h, to obtain the powder precursor.

[0072] 2. Ga elemental mixing: Add Ga to the powder precursor obtained in step 1 according to the stoichiometric ratio, and continue grinding for 30 min to obtain composite powder.

[0073] 3. Cold pressing: The composite powder is loaded into a cold pressing mold, and a pressure of 700 MPa is applied using a cold press and held for 1 minute to obtain a bulk precursor.

[0074] 4. Pressureless rapid Joule thermal sintering: The bulk precursor is placed in a rapid Joule thermal sintering apparatus and subjected to pressureless rapid Joule thermal sintering under a vacuum or argon protective atmosphere without applying external sintering pressure; when using vacuum conditions, the vacuum degree of the furnace cavity is less than 2.2 × 10⁻⁶. -3 Pa; When using an argon protective atmosphere, the furnace cavity is under a slight negative pressure, with a gauge pressure of -0.07 MPa; The specific sintering process is as follows: from room temperature, the temperature is raised to 400 ℃ within 60 s, held for 60 s, and then cooled to room temperature within 60 s.

[0075] 5. Result Characterization: Mass and volume measurements of the obtained samples showed a relative density of 79% and a ZT value of only 0.85 at 300 K. This result indicates that, under the same total metal addition conditions, while adding Ga alone can introduce Ga, it does not form a Ga-In low-melting-point liquid alloy system. This makes it difficult to fully utilize the lubricating, gap-filling, and particle rearrangement-promoting effects of the liquid metal during the cold pressing stage, and also makes it difficult to achieve a densification effect comparable to Example 1 during subsequent pressureless rapid Joule sintering. Therefore, this invention differs from existing Ga doping modification techniques; its technical effect does not originate from Ga doping alone, but rather from the synergistic effect of the Ga-In low-melting-point liquid metal system in promoting densification during forming, promoting bonding during pressureless rapid Joule sintering, and controlling the composition / performance after sintering.

[0076] Comparative Example 3

[0077] This comparative example uses a pressureless rapid Joule thermal sintering method with sole In addition to prepare bismuth-antimony telluride-based p-type bismuth telluride thermoelectric materials. The target composition is written as: In. 0.1165 Bi 0.3835 Sb 1.5 Te 3， In this comparative example, the number of In atoms added is 0.1165, the same as the total number of Ga and In atoms added in Example 1. In this composition, the total number of atoms is 5, and In accounts for 2.33 at.% of the total number of atoms in the material.

[0078] 1. Raw material pretreatment: Weigh Bi, Sb, and Te raw materials, and prepare them according to Bi... 0.3835 Sb 1.5 The raw materials were prepared according to the stoichiometric ratio corresponding to Te3; in an argon-filled glove box, the raw materials and grinding balls were loaded into a stainless steel ball mill jar, sealed, and then placed in a vibrating ball mill for mechanical alloying treatment.

[0079] The ball-to-material ratio was 10:1, the ball milling method was dry milling, the ball milling jar and the ball milling media were made of stainless steel, the vibration frequency was 1060 reciprocating vibrations per minute, the ball milling program was set to 30 min × 3 ball milling cycles, with a 15 min break between adjacent ball milling cycles, and the total ball milling time was 1.5 h, to obtain the powder precursor.

[0080] 2. In elemental mixing: Add In to the powder precursor obtained in step 1 according to the stoichiometric ratio, and continue grinding for 30 min to obtain composite powder.

[0081] 3. Cold pressing: The composite powder is loaded into a cold pressing mold, and a pressure of 700 MPa is applied using a cold press and held for 1 min to obtain a bulk precursor.

[0082] 4. Pressureless rapid Joule thermal sintering: The bulk precursor is placed in a rapid Joule thermal sintering apparatus and subjected to pressureless rapid Joule thermal sintering under a vacuum or argon protective atmosphere without applying external sintering pressure; when using vacuum conditions, the vacuum degree of the furnace cavity is less than 2.2 × 10⁻⁶. -3 Pa; When using an argon protective atmosphere, the furnace cavity is under a slight negative pressure, with a gauge pressure of -0.07 MPa; The specific sintering process is as follows: from room temperature, the temperature is raised to 400 ℃ within 60 s, held for 60 s, and then cooled to room temperature within 60 s.

[0083] 5. The obtained samples cracked during cold pressing or subsequent pressureless rapid Joule sintering, making it difficult to obtain a complete sintered block that meets the performance testing requirements. This result indicates that the addition of In alone cannot effectively replace the lubrication, gap filling, and particle rearrangement promotion functions of the Ga-In low-melting-point liquid metal system during the forming stage. It is also difficult to support the subsequent pressureless rapid Joule sintering to obtain a structurally complete sintered block. The obtained samples cracked and could not be processed into regular samples that meet the thermoelectric performance testing requirements; therefore, ZT testing at 300 K was not performed.

[0084] Example 2

[0085] This embodiment employs a Ga-In liquid metal-assisted pressureless rapid Joule thermal sintering method to prepare another Ga-In-added bismuth-antimony telluride-based p-type bismuth telluride thermoelectric material. The target composition is written as: Ga 0.05 In 0.00825 Bi 0.44175 Sb 1.5 Te 3， In this composition, Ga and In correspond to 1 at.% and 0.165 at.% of the total atomic number of all elements in the obtained material, respectively, falling within the range of Ga and In addition amounts defined by this invention. The difference between this embodiment and Example 1 lies in the amount of Ga-In liquid metal added; the remaining preparation steps and process conditions are the same as in Example 1.

[0086] 1. Raw material pretreatment: Weigh Bi, Sb, and Te raw materials, and prepare them according to B... i0.44175 Sb 1.5 The raw materials and grinding balls were mixed according to the stoichiometric ratio corresponding to Te3. In a glove box filled with argon, the raw materials and grinding balls were loaded into a stainless steel ball mill jar, sealed, and then placed in a vibrating ball mill for mechanical alloying treatment.

[0087] The ball-to-material ratio was 10:1, the ball milling method was dry milling, the ball milling jar and the ball milling media were made of stainless steel, the vibration frequency was 1060 reciprocating vibrations per minute, the ball milling program was set to 30 min × 3 ball milling cycles, with a 15 min break between adjacent ball milling cycles, and the total ball milling time was 1.5 h, to obtain the powder precursor.

[0088] 2. Ga-In liquid metal mixing: Ga and In are placed in a grinding mortar at an atomic stoichiometric ratio of 0.05:0.00825 and ground and mixed at room temperature to form a homogeneous Ga-In liquid metal system. Then, the powder precursor obtained in step 1 is added and the mixture is manually ground in the grinding mortar for 30 min to uniformly disperse the Ga-In liquid metal between the powder particles, thus obtaining a composite powder.

[0089] 3. Cold pressing: The composite powder is loaded into a cold pressing mold, and a pressure of 700 MPa is applied using a cold press for 1 min to obtain a block precursor. No additional release agent is required during the cold pressing process, and the resulting block precursor can be stably demolded while maintaining structural integrity.

[0090] 4. Pressureless rapid Joule thermal sintering: The bulk precursor is placed in a rapid Joule thermal sintering apparatus and subjected to pressureless rapid Joule thermal sintering under a vacuum or argon protective atmosphere without applying external sintering pressure; when using vacuum conditions, the vacuum degree of the furnace cavity is less than 2.2 × 10⁻⁶. -3 Pa; When using an argon protective atmosphere, the furnace cavity is under a slight negative pressure, with a gauge pressure of -0.07 MPa; The specific sintering process is as follows: from room temperature, the temperature is raised to 400 ℃ within 60 s, held for 60 s, and then cooled to room temperature within 60 s.

[0091] 5. The mass and volume of the obtained sample were measured, and the results showed that the relative density of the sample was greater than 95%. Figure 2 The XRD results show that the obtained sample is a bismuth telluride-based single-phase material; the ZT value is 1.31 at 300 K and the thermoelectric figure of merit ZT is 1.22 at 450 K. It obtains the maximum ZT value at 350 K, which is 1.50.

[0092] Example 3

[0093] This embodiment employs a Ga-In liquid metal-assisted pressureless rapid Joule thermal sintering method to prepare bismuth telluride selenide-based n-type bismuth telluride thermoelectric materials. The target composition is written as: Ga 0.0667 In 0.011 Bi 1.9223 Te 2.7 Se 0.3 In this composition, the total number of atoms is 5, and Ga and In correspond to 1.334 at.% and 0.22 at.% of the total number of atoms of all elements in the obtained material, respectively, falling within the range of Ga and In addition amounts defined by this invention. The difference between this embodiment and Embodiments 1 and 2 is that the prepared material is a bismuth telluride selenide-based n-type bismuth telluride thermoelectric material.

[0094] 1. Raw material pretreatment: Weigh Bi, Te, and Se raw materials, and prepare them according to Bi...1.9223 Te 2.7 Se 0.3 The ingredients are prepared according to the corresponding stoichiometric ratio. In an argon-filled glove box, the raw materials and grinding balls are loaded into a stainless steel ball mill jar, sealed, and then placed in a vibratory ball mill for mechanical alloying treatment.

[0095] The ball-to-material ratio was 10:1, the ball milling method was dry milling, the ball milling jar and the ball milling media were made of stainless steel, the vibration frequency was 1060 reciprocating vibrations per minute, the ball milling program was set to 30 min × 3 ball milling cycles, with a 15 min break between adjacent ball milling cycles, and the total ball milling time was 1.5 h, to obtain the powder precursor.

[0096] 2. Ga-In liquid metal mixing: Ga and In are placed in a grinding mortar at a stoichiometric ratio of 0.0667:0.011 and manually ground and mixed at room temperature to form a homogeneous Ga-In liquid metal system; then the powder precursor obtained in step 1 is added and the mixture is manually ground in the grinding mortar for 30 min to uniformly disperse the Ga-In liquid metal between the powder particles, thus obtaining a composite powder.

[0097] 3. Cold pressing: The composite powder is loaded into a cold pressing mold, and a pressure of 700 MPa is applied using a cold press for 1 min to obtain a block precursor. No additional release agent is required during the cold pressing process, and the resulting block precursor can be stably demolded while maintaining structural integrity.

[0098] 4. Pressureless rapid Joule thermal sintering: The bulk precursor is placed in a rapid Joule thermal sintering equipment and subjected to pressureless rapid Joule thermal sintering under a vacuum or argon protective atmosphere without applying external sintering pressure.

[0099] When vacuum conditions are used, the vacuum level in the furnace cavity is less than 2.2 × 10⁻⁶. -3 Pa; When using an argon protective atmosphere, the furnace cavity is under a slight negative pressure, with a gauge pressure of -0.07 MPa.

[0100] The specific sintering process is as follows: the temperature is raised to 400 ℃ within 60 s from room temperature, held for 60 s, and then cooled to room temperature within 60 s.

[0101] The mass and volume of the obtained samples were measured, and the results showed that the relative density of the samples was greater than 95%. Figure 3 The XRD results show that the obtained sample is a bismuth telluride-based single-phase material with a ZT value of 1.2 at 300 K and a thermoelectric figure of merit ZT of 1.19 at 450 K. It obtains the maximum ZT value at 350 K, which is 1.32.

[0102] Example 4

[0103] This embodiment illustrates the effect of rapid Joule heating holding time on the densification and thermoelectric properties of bismuth-antimony-tellurium-based p-type bismuth telluride thermoelectric materials. The target composition used in this embodiment is the same as in Example 2, except that the holding time for pressureless rapid Joule heating in step 4 is extended from 60 s to 120 s. The remaining raw material ratios, mechanical alloying, Ga-In liquid metal mixing, cold pressing, sintering atmosphere, and heating / cooling conditions are all the same as in Example 2.

[0104] 1. Raw material pretreatment: Weigh Bi, Sb and Te raw materials, and mix them according to the corresponding stoichiometric ratio of Bi, Sb and Te. In a glove box filled with argon, load the raw materials and grinding balls into a stainless steel ball mill jar, seal it and place it in a vibrating ball mill for mechanical alloying treatment.

[0105] The ball-to-material ratio was 10:1, the ball milling method was dry milling, the ball milling jar and the ball milling media were made of stainless steel, the vibration frequency was 1060 reciprocating vibrations per minute, the ball milling program was set to 30 min × 3 ball milling cycles, with a 15 min break between adjacent ball milling cycles, and the total ball milling time was 1.5 h, to obtain the powder precursor.

[0106] 2. Ga-In liquid metal mixing: Ga and In are placed in a grinding mortar at an atomic stoichiometric ratio of 0.05:0.00825 and ground and mixed at room temperature to form a homogeneous Ga-In liquid metal system. Then, the powder precursor obtained in step 1 is added and the mixture is manually ground in the grinding mortar for 30 min to uniformly disperse the Ga-In liquid metal between the powder particles, thus obtaining a composite powder.

[0107] 3. Cold pressing: The composite powder is loaded into a cold pressing mold, and a pressure of 700 MPa is applied using a cold press for 1 min to obtain a block precursor. No additional release agent is required during the cold pressing process, and the resulting block precursor can be stably demolded while maintaining structural integrity.

[0108] 4. Pressureless rapid Joule thermal sintering: The bulk precursor is placed in a rapid Joule thermal sintering apparatus and subjected to pressureless rapid Joule thermal sintering under a vacuum or argon protective atmosphere without applying external sintering pressure; when using vacuum conditions, the vacuum degree of the furnace cavity is less than 2.2 × 10⁻⁶. -3 Pa; When using an argon protective atmosphere, the furnace cavity is under a slight negative pressure, with a gauge pressure of -0.07 MPa; The specific sintering process is as follows: from room temperature, the temperature is raised to 400 ℃ within 60 s, held for 120 s, and then cooled to room temperature within 60 s.

[0109] 5. The mass and volume of the obtained sample were measured, and the results showed that the relative density of the sample was greater than 95%. The XRD results showed that the obtained sample was a bismuth telluride-based single-phase material. At 300 K, the ZT value was 1.26, and at 450 K, the thermoelectric figure of merit ZT was 1.17. The maximum ZT value was obtained at 350 K, which was 1.46.

[0110] Example 5

[0111] This embodiment illustrates the effect of ball milling time on the densification and thermoelectric properties of bismuth-antimony-tellurium p-type bismuth telluride-based thermoelectric materials. The target composition used in this embodiment is the same as in Example 2, except that the ball milling time in step 1 is extended from 1.5 h to 2 h. The remaining raw material ratios, mechanical alloying, Ga-In liquid metal mixing, cold pressing, sintering atmosphere, and heating / cooling conditions are all the same as in Example 2.

[0112] 1. Raw material pretreatment: Weigh Bi, Sb, and Te raw materials, and prepare them according to B... i0.44175 Sb 1.5 The raw materials and grinding balls were mixed according to the stoichiometric ratio corresponding to Te3. In a glove box filled with argon, the raw materials and grinding balls were loaded into a stainless steel ball mill jar, sealed, and then placed in a vibrating ball mill for mechanical alloying treatment.

[0113] The ball-to-material ratio was 10:1, the ball milling method was dry milling, the ball milling jar and the ball milling media were made of stainless steel, the vibration frequency was 1060 reciprocating vibrations per minute, the ball milling program was set to 30 min × 3 ball milling cycles, with a 15 min break between adjacent ball milling cycles, and the total ball milling time was 2 h, to obtain the powder precursor.

[0114] 2. Ga-In liquid metal mixing: Ga and In are placed in a grinding mortar at an atomic stoichiometric ratio of 0.05:0.00825 and ground and mixed at room temperature to form a homogeneous Ga-In liquid metal system. Then, the powder precursor obtained in step 1 is added and the mixture is manually ground in the grinding mortar for 30 min to uniformly disperse the Ga-In liquid metal between the powder particles, thus obtaining a composite powder.

[0115] 3. Cold pressing: The composite powder is loaded into a cold pressing mold, and a pressure of 700 MPa is applied using a cold press for 1 min to obtain a block precursor. No additional release agent is required during the cold pressing process, and the resulting block precursor can be stably demolded while maintaining structural integrity.

[0116] 4. Pressureless rapid Joule thermal sintering: The bulk precursor is placed in a rapid Joule thermal sintering apparatus and subjected to pressureless rapid Joule thermal sintering under a vacuum or argon protective atmosphere without applying external sintering pressure; when using vacuum conditions, the vacuum degree of the furnace cavity is less than 2.2 × 10⁻⁶. -3Pa; When using an argon protective atmosphere, the furnace cavity is under a slight negative pressure, with a gauge pressure of -0.07 MPa; The specific sintering process is as follows: from room temperature, the temperature is raised to 400 ℃ within 60 s, held for 60 s, and then cooled to room temperature within 60 s.

[0117] 5. The mass and volume of the obtained sample were measured, and the results showed that the relative density of the sample was greater than 95%. The XRD results showed that the obtained sample was a bismuth telluride-based single-phase material. At 300 K, the ZT value was 1.29, and at 450 K, the thermoelectric figure of merit ZT was 1.13. The maximum ZT value was obtained at 350 K, which was 1.52.

[0118] Comparative Example 4

[0119] This comparative example illustrates the effect of ball milling time on the stability of cold pressing of bismuth-antimony-tellurium p-type bismuth telluride-based thermoelectric materials and the feasibility of subsequent pressureless rapid Joule heating sintering. The target composition used in this comparative example is the same as in Example 2, except that the total ball milling time in step 1 is reduced from 1.5 h to 2 min. All other raw material ratios, Ga-In liquid metal mixing, cold pressing, sintering atmosphere, heating and cooling conditions, and holding time are the same as in Example 2.

[0120] 1. Raw material pretreatment: Weigh Bi, Sb, and Te raw materials, and prepare them according to B... i0.44175 Sb 1.5 The raw materials and grinding balls were mixed according to the stoichiometric ratio corresponding to Te3. In a glove box filled with argon, the raw materials and grinding balls were loaded into a stainless steel ball mill jar, sealed, and then placed in a vibratory ball mill for short-time ball milling.

[0121] The ball-to-material ratio was 10:1, the ball milling method was dry milling, the ball mill jar and the ball milling media were made of stainless steel, the vibration frequency was 1060 reciprocating vibrations per minute, and the ball milling program was set to 2 minutes to obtain the powder precursor.

[0122] 2. Ga-In liquid metal mixing: Ga and In are placed in a grinding mortar at an atomic stoichiometric ratio of 0.05:0.00825 and ground and mixed at room temperature to form a homogeneous Ga-In liquid metal system. Then, the powder precursor obtained in step 1 is added and the mixture is manually ground in the grinding mortar for 30 min to uniformly disperse the Ga-In liquid metal between the powder particles, thus obtaining a composite powder.

[0123] 3. Cold pressing: The composite powder is loaded into a cold pressing mold, and a pressure of 700 MPa is applied using a cold press for 1 min to obtain a block precursor. No additional release agent is required during the cold pressing process, and the resulting block precursor can be stably demolded while maintaining structural integrity.

[0124] 4. Pressureless rapid Joule thermal sintering: The bulk precursor is placed in a rapid Joule thermal sintering apparatus and subjected to pressureless rapid Joule thermal sintering under a vacuum or argon protective atmosphere without applying external sintering pressure; when using vacuum conditions, the vacuum degree of the furnace cavity is less than 2.2 × 10⁻⁶. -3 Pa; When using an argon protective atmosphere, the furnace cavity is under a slight negative pressure, with a gauge pressure of -0.07 MPa; The specific sintering process is as follows: from room temperature, the temperature is raised to 400 ℃ within 60 s, held for 60 s, and then cooled to room temperature within 60 s.

[0125] 5. The obtained samples cracked during the subsequent pressureless rapid Joule heating sintering process, making it difficult to obtain a complete sintered block that meets the performance testing requirements.

[0126] Comparative Example 5

[0127] This comparative example illustrates the effect of pressureless rapid Joule heating sintering temperature on the bulk structural stability, densification, and thermoelectric properties of bismuth-antimony-telluride p-type bismuth telluride-based thermoelectric materials. The target composition used in this comparative example is the same as in Example 2, except that the target temperature for pressureless rapid Joule heating sintering in step 4 is increased from 400 °C to 450 °C. To maintain an average heating and cooling rate similar to that of Example 2, the heating and cooling times are adjusted accordingly to 67.5 s. The remaining raw material ratios, mechanical alloying, Ga-In liquid metal mixing, cold pressing, sintering atmosphere, and holding time are all the same as in Example 2.

[0128] 1. Raw material pretreatment: Weigh Bi, Sb and Te raw materials and mix them according to the stoichiometric ratio corresponding to the design composition. In an argon-filled glove box, load the raw materials and grinding balls into a stainless steel ball mill jar, seal it and place it in a vibrating ball mill for mechanical alloying treatment.

[0129] The ball-to-material ratio was 10:1, the ball milling method was dry milling, the ball milling jar and the ball milling media were made of stainless steel, the vibration frequency was 1060 reciprocating vibrations per minute, the ball milling program was set to 30 min × 3 ball milling cycles, with a 15 min break between adjacent ball milling cycles, and the total ball milling time was 1.5 h, to obtain the powder precursor.

[0130] 2. Ga-In liquid metal mixing: Ga and In are placed in a grinding mortar at an atomic stoichiometric ratio of 0.05:0.00825 and ground and mixed at room temperature to form a homogeneous Ga-In liquid metal system. Then, the powder precursor obtained in step 1 is added according to the designed composition, and the mixture is manually ground in the grinding mortar for 30 min to uniformly disperse the Ga-In liquid metal between the powder particles to obtain a composite powder.

[0131] 3. Cold pressing: The composite powder is loaded into a cold pressing mold, and a pressure of 700 MPa is applied using a cold press for 1 min to obtain a block precursor. No additional release agent is required during the cold pressing process, and the resulting block precursor can be stably demolded while maintaining structural integrity.

[0132] 4. Pressureless rapid Joule thermal sintering: The bulk precursor is placed in a rapid Joule thermal sintering apparatus and subjected to pressureless rapid Joule thermal sintering under a vacuum or argon protective atmosphere without applying external sintering pressure; when using vacuum conditions, the vacuum degree of the furnace cavity is less than 2.2 × 10⁻⁶. -3 Pa; When using an argon protective atmosphere, the furnace cavity is under a slight negative pressure, with a gauge pressure of -0.07 MPa; The specific sintering process is as follows: from room temperature, the temperature is raised to 450 ℃ within 67.5 s, held for 60 s, and then cooled to room temperature within 67.5 s.

[0133] 5. The results show that after pressureless rapid Joule heating sintering at 450 °C, the obtained bulk precursor exhibited surface bulging, overall distortion, and surface darkening. It was difficult to maintain a regular and complete bulk morphology after sintering, making it impossible to obtain a complete sintered bulk that meets the requirements for dimensional processing and performance testing. This result indicates that for this embodiment, excessively high rapid Joule heating temperatures can damage the stability of the bulk structure, potentially causing problems such as localized overheating, uneven liquid phase distribution, component volatilization, or compositional deviation. Therefore, the rapid Joule heating temperature needs to be controlled within an appropriate range; the 400 °C used in Example 2 is more conducive to balancing rapid densification and bulk structural integrity.

[0134] Example 6

[0135] This embodiment employs a Ga-In liquid metal-assisted pressureless rapid Joule thermal sintering method to prepare germanium-tellurium-based optoelectronic functional materials. The target composition is written as: Ga 0.02 In 0.0033 Ge 0.9767 Te. In this composition, the total number of atoms is 2, and Ga and In correspond to 1.00 at.% and 0.165 at.% of the total number of atoms of all elements in the obtained material, respectively. This embodiment is used to illustrate that the method of the present invention is applicable not only to bismuth telluride-based thermoelectric materials, but also to the rapid preparation of germanium telluride-based chalcogenide phase change optoelectronic functional materials.

[0136] 1. Raw material pretreatment: Weigh Ge and Te raw materials according to their corresponding stoichiometric ratios; in an argon-filled glove box, load the raw materials and grinding balls into a stainless steel ball mill jar, seal it, and place it in a vibratory ball mill for mechanical alloying treatment. The ball-to-material ratio is 10:1, the ball milling method is dry grinding, the ball mill jar and grinding media are made of stainless steel, the vibration frequency is 1060 reciprocating vibrations per minute, and the total ball milling time is 1 hour, yielding a germanium-tellurium-based powder precursor.

[0137] 2. Ga-In liquid metal mixing: Ga and In are placed in a grinding mortar at an atomic stoichiometric ratio of 0.02:0.0033 and ground and mixed at room temperature to form a homogeneous Ga-In liquid metal system; then the germanium-tellurium-based powder precursor obtained in step 1 is added according to the designed composition, and the mixture is manually ground in the grinding mortar for 30 min to uniformly disperse the Ga-In liquid metal between the powder particles to obtain a composite powder.

[0138] 3. Cold pressing: The composite powder is loaded into a cold pressing mold, and a pressure of 700 MPa is applied using a cold press for 1 min to obtain a block precursor. No additional release agent is required during the cold pressing process, and the resulting block precursor can be stably demolded while maintaining structural integrity.

[0139] 4. Pressureless rapid Joule thermal sintering: The bulk precursor is placed in a rapid Joule thermal sintering apparatus and subjected to pressureless rapid Joule thermal sintering under a vacuum or argon protective atmosphere without applying external sintering pressure; when using vacuum conditions, the vacuum degree of the furnace cavity is less than 2.2 × 10⁻⁶. -3 Pa; When using an argon protective atmosphere, the furnace cavity is under a slight negative pressure, with a gauge pressure of -0.07 MPa; The specific sintering process is as follows: from room temperature, the temperature is raised to 440 ℃ within 60 s, held for 60 s, and then cooled to room temperature within 60 s.

[0140] The obtained sample maintains a complete bulk morphology, and its main phase is GeTe phase with a density of 85%. At 300 K, the ZT value is 0.4, and at 450 K, the thermoelectric figure of merit ZT is 0.9. It reaches its maximum ZT value of 1.9 at 650 K.

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