Method for preparing functional material by using two-state powder and joul heat sintering

Abstract

This invention discloses a method for preparing functional materials by synergistic Joule heating sintering of dual-state powders. First and second ball-milled powders are prepared according to a target composition. The first ball-milled powder undergoes a first rapid Joule heating pretreatment to obtain a pre-Joule-heat-treated powder. The second ball-milled powder, used as the ball-milling active powder, is mixed with the pre-Joule-heat-treated powder, cold-pressed, and then rapidly Joule-heat-sintered without external densification pressure to obtain a sintered functional material. Optional post-current treatment is performed. The two types of powders have the same, similar, or complementary compositions, and the overall composition after mixing corresponds to the target functional material. The pre-Joule-heat-treated powder provides the phase composition basis, while the ball-milling active powder participates in local reactions, particle bonding, and pore filling, achieving rapid and complete forming. The post-current treatment is used to regulate the phase composition, defect state, and functional properties. This method is applicable to the rapid preparation and optional post-treatment of inorganic functional materials.

Description

[0001] manual

[0002] A method for preparing functional materials by synergistic Joule thermal sintering of dual-state powders Technical Field

[0003] This invention belongs to the field of functional materials preparation technology, specifically relating to a method for preparing functional materials based on the synergistic rapid Joule heat sintering of pre-Joule heat-treated powder and ball-milled active powder, and further relating to a method for regulating the microstructure and properties of functional materials through current post-processing. More specifically, this invention relates to a rapid preparation and post-processing method applicable to inorganic functional materials, particularly chalcogenide functional materials, Zintl phase functional materials, intermetallic compound functional materials, and bismuth telluride-based thermoelectric functional materials. Background Technology

[0004] Functional materials refer to materials with specific functions such as electrical, thermal, optical, magnetic, acoustic, mechanical, chemical, or energy conversion. They are widely used in energy conversion, electronic devices, sensing, thermal management, information storage, phase change control, and advanced manufacturing. For many inorganic functional materials, powder metallurgy and sintering densification are important methods for preparing bulk materials. The functional properties of these materials are usually closely related to phase composition, degree of crystallization, density, defect state, grain boundary structure, and carrier transport behavior. Therefore, the preparation process not only needs to achieve bulk forming and densification but also needs to consider phase formation and functional property control.

[0005] Existing methods for preparing bulk inorganic functional materials typically include traditional sintering, hot pressing, spark plasma sintering, hot deformation, or prolonged annealing. While these methods can produce bulk materials, they often suffer from long processing cycles, high dependence on equipment, high external pressure requirements, high energy consumption, and difficulties in simultaneously achieving material phase formation, densification, and functional performance control. For functional materials containing volatile components, low-melting-point components, or complex multi-component compositions, prolonged high-temperature treatment may lead to component volatilization, compositional deviation, impurity phase formation, or performance fluctuations.

[0006] Rapid Joule heat treatment and rapid Joule sintering (RJT) offer advantages such as rapid heating, short processing time, and low energy consumption, making them promising candidates for the rapid preparation of functional materials. However, for routes involving direct RJT sintering of elemental powders, short-time ball-milled powders, or mechanically activated powders, the powders must simultaneously complete phase formation reactions, particle bonding, and sintering densification within a very short time. This can easily lead to problems such as incomplete reactions, unstable phase composition, localized overheating, thermal stress concentration, bulk cracking, or insufficient density. On the other hand, if pre-treated or pre-synthesized powders are used for re-sintering, although their phase composition is relatively stable, the powder reactivity and sintering driving force may be insufficient. Hot pressing sintering is required to promote interparticle bonding, pore filling, and rapid densification. Therefore, relying solely on ball-milled activated powders or pre-Joule heat-treated powders makes it difficult to simultaneously achieve phase stability, sintering activity, and bulk integrity during short-time RJT sintering.

[0007] Taking bismuth telluride-based thermoelectric functional materials as an example, bismuth telluride-based materials are a mature thermoelectric functional material system used in the room temperature and near-room temperature range. Typical systems include Bi-Sb-Te p-type materials and Bi-Te-Se n-type materials. The performance of these materials is highly sensitive to phase composition, carrier concentration, defect state, grain boundary state, and density. Under rapid Joule heating sintering conditions, if the powder phase formation reaction, particle bonding, and densification processes cannot proceed in a coordinated manner, the bulk integrity and thermoelectric transport performance can easily be affected. In addition to bismuth telluride-based materials, inorganic functional materials such as lead telluride-based, tin selenide-based, germanium telluride-based, magnesium bismuth-based, or magnesium bismuth antimony-based materials also commonly involve issues such as powder reaction, rapid phase formation, sintering densification, and post-processing performance control.

[0008] Furthermore, conventional heat treatment or annealing is commonly used in the preparation of functional materials to improve phase composition and defect states. However, conventional heat treatment mainly relies on temperature and time, has a relatively long processing cycle, and has limited ability to rapidly regulate electrical transport properties. For functional materials such as thermoelectric materials that are sensitive to electrical transport properties, if a post-treatment with current is introduced after rapid Joule sintering, it is possible to promote phase composition optimization, defect state regulation, and carrier transport behavior improvement in a shorter time, thereby achieving further synergy between sintering densification and functional performance regulation.

[0009] It should be noted that while rapid Joule heating sintering, conventional heat treatment, current treatment, or electric field-assisted treatment can each be used for material preparation or performance regulation, simply listing or sequentially combining these processes cannot naturally solve the problem of the difficulty in simultaneously achieving phase formation reaction, particle bonding, pore filling, densification, and bulk crack prevention during the rapid sintering of functional materials. For elemental powders or short-time ball-milled powders, if rapid Joule heating sintering is directly performed, the powder needs to simultaneously complete the formation of the target main phase, particle bonding, and sintering within a very short time. This can easily lead to problems such as insufficient reaction, residual impurities, unstable phase composition, and impaired functional performance. For powders that have already undergone pretreatment or pre-synthesis, although their phase composition is relatively stable, the powder's reactivity and sintering activity are reduced. During re-sintering, it is difficult to fully promote interparticle bonding and pore filling, which can easily lead to problems such as thermal stress concentration, bulk cracking, or insufficient density. Therefore, this invention does not simply connect ball milling, rapid Joule heating sintering, and current post-treatment in series. Instead, it addresses the coupling contradiction between phase formation, connection, and densification in the rapid Joule heating sintering stage by constructing a dual-state powder system with different thermal histories and reaction states: a portion of the ball-milled powder undergoes a first rapid Joule heating pretreatment to form pre-Joule-heat-treated powder, providing a pre-reacted, partially or basically phase-formed phase composition basis; the other portion of the ball-milled powder, without the first rapid Joule heating pretreatment, serves as a ball-milled active powder, acting as a reactive auxiliary sintering component matching the same system or composition during subsequent rapid Joule heating sintering, participating in local reactions, particle connection, and pore filling. Furthermore, after obtaining the complete sintered body, this invention performs current post-treatment, placing the functional material sintered body in a current-passing circuit. During the energization process, it is simultaneously subjected to rapid Joule heating and current / electric field effects, further regulating phase composition, defect states, and electrical transport properties. This treatment differs from ordinary heat treatment that only uses an external heat source and where the sample is not in an energized circuit. Therefore, the steps of this invention have a continuous cooperative relationship addressing the same technical problem, and are not a mechanical superposition of known process steps.

[0010] Therefore, it is necessary to develop a rapid preparation method suitable for functional materials, enabling the phase stability provided by pre-Joule heat-treated powders to synergistically combine with the reactivity and sintering activity provided by ball-milled active powders. Furthermore, the phase composition, defect state, and functional properties of the functional materials can be further controlled through current post-treatment. This method is particularly suitable for the rapid preparation of inorganic functional materials such as bismuth telluride-based thermoelectric functional materials, and can also provide a reference for the rapid sintering and performance control of other chalcogenide functional materials, Zintl phase thermoelectric functional materials, and intermetallic compound functional materials. Summary of the Invention

[0011] To address the problems of rapid cracking during the existing functional material preparation process, difficulty in synchronizing phase formation and densification, and limited means and long control cycles for subsequent phase composition, defect state, and functional performance, this invention provides a method for preparing functional materials by synergistic Joule thermal sintering of dual-state powders. Furthermore, the phase composition, defect state, and functional performance of the obtained functional materials can be further controlled by current post-processing.

[0012] The core of this invention lies in: preparing a first ball-milled powder and a second ball-milled powder according to the composition of the target functional material; subjecting the first ball-milled powder to a first rapid Joule heating pretreatment to obtain a pre-Joule-heat-treated powder; mixing the pre-Joule-heat-treated powder with a ball-milled active powder and cold-pressing it into a block, wherein the ball-milled active powder is the second ball-milled powder that has not undergone the first rapid Joule heating pretreatment. The pre-Joule-heat-treated powder and the ball-milled active powder have the same, similar, or complementary compositions, and the overall composition of the mixture corresponds to the composition of the target functional material. In the subsequent rapid Joule heating sintering process, the ball-milled active powder, as a reactive auxiliary sintering component, participates in local reactions, particle bonding, and pore filling, thereby improving the integrity of the block structure, reducing the risk of cracking during rapid sintering, and promoting sintering densification. Furthermore, this invention controls the phase composition, defect state, and functional properties of the sintered body through current post-treatment, thereby achieving synergy between rapid sintering preparation and subsequent performance optimization.

[0013] To achieve the above objectives, the present invention provides a method for preparing functional materials by synergistic Joule thermal sintering of dual-state powders, comprising the following steps:

[0014] (1) Prepare ball milled powder according to the composition of the target functional material. The ball milled powder includes a first ball milled powder and a second ball milled powder. The first ball milled powder and the second ball milled powder have the same, similar or complementary composition. After the treatment in step (2), the overall composition of the pre-joule heat-treated powder and the ball milled active powder after mixing corresponds to the composition of the target functional material.

[0015] (2) The first ball-milled powder is subjected to a first rapid Joule heat pretreatment to obtain pre-Joule heat-treated powder;

[0016] (3) The pre-Joule heat-treated powder obtained in step (2) is mixed with the ball-milled active powder to obtain a mixed powder, wherein the ball-milled active powder is a second ball-milled powder that has not undergone the first rapid Joule heat pretreatment;

[0017] (4) The mixed powder obtained in step (3) is cold-pressed to obtain a bulk precursor;

[0018] (5) The bulk precursor obtained in step (4) is subjected to rapid Joule thermal sintering to obtain functional materials;

[0019] (6) Optionally, the functional material obtained in step (5) may be further subjected to current post-processing.

[0020] The pre-Joule heat-treated powder and the ball-milled active powder have the same, similar or complementary composition, and the overall composition after mixing the two corresponds to the composition of the target functional material; the ball-milled active powder acts as a reactive auxiliary sintering component in the rapid Joule heat sintering process in step (5), participating in local reactions, particle connection and pore filling.

[0021] Preferably, the functional material is an inorganic functional material. More preferably, the inorganic functional material is one of the following: chalcogenide functional materials, functional semiconductor materials, thermoelectric functional materials, optoelectronic functional materials, phase change functional materials, Zintl phase functional materials, or intermetallic compound functional materials, or a material possessing multiple of the above functional properties simultaneously. More preferably, the functional material is a bismuth telluride-based thermoelectric functional material.

[0022] Preferably, the first and second ball-milled powders can originate from the same batch of ball-milled powders or can be prepared separately. The first ball-milled powder undergoes a first rapid Joule heating pretreatment to form a pre-Joule heat-treated powder, and the second ball-milled powder serves as the ball-milled active powder. The pre-Joule heat-treated powder and the ball-milled active powder can have the same, similar, or complementary compositions, and the overall composition of the mixture corresponds to the composition of the target functional material. Thus, the ball-milled active powder is not an external heterogeneous sintering aid, but a reactive auxiliary sintering component that is in the same system or matches the composition of the target functional material, and can participate in local reactions, particle bonding, and pore filling during rapid Joule heating sintering.

[0023] Preferably, the pre-Joule heat-treated powder is not limited to a fully phase-formed powder; it can be a phase-formed powder, a basically phase-formed powder, a partially phase-formed powder, a partially reactive powder, a pre-crystallized powder, or a combination thereof. That is, full phase formation is not a necessary condition for the pre-Joule heat-treated powder. As long as the phase composition, degree of crystallization, reaction state, or sintering behavior of the first ball-milled powder changes relative to the powder that has not undergone this pretreatment after the first rapid Joule heat pretreatment, it belongs to the pre-Joule heat-treated powder of this invention.

[0024] Preferably, the ball milling process in step (1) employs one or more of the following: dry ball milling, wet ball milling, vibratory ball milling, planetary ball milling, or high-energy ball milling. More preferably, the ball milling process employs dry high-energy vibratory ball milling, with an inert atmosphere, a ball-to-material ratio of 10:1, and the ball milling jar and grinding media made of stainless steel or hard steel. The vibration frequency is 1060 reciprocating vibrations per minute, and the ball milling time is 1–120 min, more preferably 5–20 min.

[0025] Preferably, the first rapid Joule heating pretreatment in step (2) is performed on a first ball-milled powder that has not been cold-pressed. The first ball-milled powder is loaded into an electrically conductive device in powder form to form an electrically conductive powder system, and then subjected to the first rapid Joule heating pretreatment. The first rapid Joule heating pretreatment is performed under vacuum or a protective atmosphere, preferably argon.

[0026] Preferably, the first rapid Joule heating pretreatment includes a rapid heating stage, an optional holding stage, and a cooling stage; the temperature of the first rapid Joule heating pretreatment is determined based on the phase formation temperature, component volatility characteristics, and thermal stability of the target functional material. More preferably, when the functional material is a bismuth telluride-based thermoelectric functional material, the first rapid Joule heating pretreatment includes: heating from room temperature to 300–460 °C within 1–600 s, holding at that temperature for 0–600 s, and then cooling to room temperature within 1–600 s; wherein, holding at that temperature for 0 s indicates that after heating to the target temperature, no constant temperature holding stage is set and the cooling stage is directly initiated. More preferably, heating from room temperature to 400 °C within 60 s, holding at that temperature for 60 s, and then cooling to room temperature within 60 s.

[0027] Preferably, in step (3), the mass ratio of the pre-Joule heat-treated powder to the ball-milled active powder is 75:25 to 99:1, more preferably 80:20 to 96:4, further preferably 88:12 to 95:5, and even more preferably 93:7. When the proportion of pre-Joule heat-treated powder is too low, the proportion of components that have already undergone pre-reaction or partially formed phases in the mixed powder is insufficient. In the subsequent rapid Joule heat sintering process, a large number of phase-forming reactions still need to be completed in a short time, which is not conducive to the rapid formation of the target main phase or pure phase. Problems such as insufficient reaction, residual impurities, or unstable phase composition are likely to occur. Controlling the ratio of the two within the above range is beneficial to taking into account phase stability, sintering activity, and bulk structural integrity.

[0028] Preferably, the mixing method in step (3) is manual grinding and mixing with a mortar and pestle, mechanical stirring and mixing, ball milling and mixing, planetary mixing, or other mixing methods that can uniformly disperse the two types of powders. More preferably, the mixing method is manual grinding and mixing with a mortar and pestle, the mixing time is 30 min, and the mixing atmosphere is argon.

[0029] Preferably, the cold pressing in step (4) is performed using a single-stage or multi-stage pressurization method. The single-stage pressurization method involves increasing the pressure to the target cold pressing pressure in one step; the multi-stage pressurization method involves sequentially increasing the pressure to two or more pressure stages. Preferably, the cold pressing pressure is 200–900 MPa, and the total holding time is 0–600 s; more preferably, the cold pressing pressure is 650 MPa, and the total holding time is 0 s. Preferably, no release agent is used during the cold pressing process. The resulting block precursor can maintain its preset shape and is suitable for subsequent rapid Joule heating sintering.

[0030] Preferably, the rapid Joule heating sintering in step (5) is carried out under vacuum or protective atmosphere conditions, preferably argon. No external mechanical pressure for densification is applied during the rapid Joule heating sintering stage; the contact forces required for equipment clamping, electrode contact, or sample support are not considered external sintering pressures.

[0031] Preferably, the rapid Joule heating sintering object in step (5) is a mixed powder compact obtained by cold pressing. The rapid Joule heating sintering includes a rapid heating stage, an optional holding stage, and a cooling stage; the rapid Joule heating sintering temperature is determined according to the phase formation temperature of the target functional material, the sintering densification requirements, the component volatility characteristics, and the thermal stability. More preferably, when the functional material is a bismuth telluride-based thermoelectric functional material, the rapid Joule heating sintering includes: heating from room temperature to 300-460 °C within 1-600 s, holding for 0-600 s, and then cooling to room temperature within 1-600 s; wherein, holding for 0 s indicates that after heating to the target temperature, no constant temperature holding stage is set and the cooling stage is directly entered. More preferably, heating from room temperature to 400 °C within 60 s, holding for 60 s, and then cooling to room temperature within 60 s.

[0032] Preferably, the functional material sintered body obtained in step (5) can maintain a complete block morphology; more preferably, the functional material sintered body obtained does not crack.

[0033] Preferably, the relative density of the resulting functional material sintered body is not less than 85%; more preferably, the relative density is not less than 90%; and even more preferably, the relative density is not less than 95%.

[0034] Preferably, the current post-processing in step (6) is performed under a vacuum or inert atmosphere. The current post-processing can be DC current post-processing, AC current post-processing, pulsed current post-processing, or a combination thereof. More preferably, the current post-processing is AC current post-processing.

[0035] Preferably, the current post-treatment in step (6) includes a rapid heating stage, an optional holding stage, and a cooling stage. The current post-treatment involves applying a direct current, an alternating current, a pulsed current, or a combination thereof to the functional material sintered body, causing it to heat to 200–500 °C within 10–300 s, hold for 0–300 s, and then cool to room temperature. More preferably, for bismuth telluride-based thermoelectric functional materials, the current post-treatment includes heating to 400 °C within 60 s from room temperature, holding for 0 s, and then cooling to room temperature within 60 s. When the holding time is 0 s, it indicates that the cooling stage is directly entered after heating to the target treatment temperature. During the current post-treatment, the current post-treatment uses a target temperature-time program as the control target. The current, voltage, power, and / or duty cycle are adjusted according to the sample size, sample resistance, sample cross-sectional area, electrode spacing, electrode contact state, and real-time sample temperature to ensure that the functional material sintered body reaches the preset heating rate and target treatment temperature. Specifically, the device's set voltage can be 1–60 V, preferably 10–50 V, and more preferably 40 V; the actual current passing through the sample circuit can be 0.1–50 A, preferably 1–20 A, and more preferably 1–15 A; the equivalent current density, based on the equivalent cross-sectional area in the sample's current-carrying direction, can be 0.1–100 A / cm², preferably 5–80 A / cm²; the device's output power can be 1–1000 W, preferably 10–600 W; and the electrode spacing can be 0.5–100 mm, preferably 1–20 mm. When using pulsed current, the duty cycle can be 1%–90%, preferably 10%–70%. These parameters are not independent fixed combinations, but are matched and adjusted according to the target temperature-time program, sample size, sample resistance, sample cross-sectional area, electrode spacing, and electrode contact state.

[0036] Preferably, for bismuth telluride-based thermoelectric functional materials, current post-processing can promote the formation of the main phase or improve the purity of the main phase, reduce impurity or residual phases, and regulate its thermoelectric transport properties. More preferably, the current post-processing is DC current post-processing, AC current post-processing, pulsed current post-processing, or a combination thereof; wherein, DC current post-processing can increase the absolute value of the Seebeck coefficient, and AC current post-processing can increase the absolute value of the Seebeck coefficient while maintaining a high level of conductivity. By controlling the current mode, target temperature-time program, and current, voltage, power, and / or duty cycle of the current post-processing, the phase composition, defect state, and thermoelectric transport properties of the bismuth telluride-based thermoelectric functional materials can be further controlled.

[0037] Beneficial effects

[0038] Compared with the prior art, the present invention has at least the following beneficial effects:

[0039] Firstly, this invention combines pre-Joule heat-treated powder with ball-milled active powder. The pre-Joule heat-treated powder provides a pre-reacted, partially or basically phase-formed phase composition basis, which helps reduce the phase-forming reaction burden in subsequent rapid Joule heat sintering. The ball-milled active powder provides high reactivity and sintering activity, promoting particle connection, pore filling and complete block formation. The two work synergistically in the rapid Joule heat sintering process, which is beneficial to achieve rapid phase formation, particle bonding and sintering densification in a short time.

[0040] Secondly, the ball-milled active powder and the pre-Joule heat-treated powder in this invention have the same, similar, or complementary compositions, and the overall composition of the mixture corresponds to the composition of the target functional material. Therefore, the ball-milled active powder is different from external heterogeneous sintering aids; rather, it is a reactive auxiliary sintering component that matches the system or composition. It can participate in local reactions, particle bonding, and pore filling during rapid Joule heat sintering, which helps reduce the risk of cracking, promotes the formation of sintered bodies, and reduces the adverse effects of external impurities or heterogeneous components on the performance of the target functional material.

[0041] Thirdly, this invention introduces current post-treatment after rapid Joule heating sintering, which can regulate the phase composition, defect state, and target functional properties of the functional material. For bismuth telluride-based thermoelectric functional materials, experimental results show that the phase composition of the sample is purer after current post-treatment, and the absolute value of the Seebeck coefficient is significantly improved. In particular, AC current post-treatment can improve the absolute value of the Seebeck coefficient while maintaining a high level of conductivity, which is beneficial to improving thermoelectric transport performance.

[0042] Fourth, this invention does not apply external mechanical pressure for densification during the rapid Joule heating sintering stage, unlike processes such as hot pressing sintering, spark plasma sintering, and high-pressure hot deformation, which rely on external pressure for densification. Furthermore, this invention combines a first rapid Joule heating pretreatment, ball milling of active powder to assist rapid Joule heating sintering, and current post-treatment, which shortens the preparation process, reduces dependence on equipment pressure systems, and improves the efficiency of rapid preparation and subsequent performance control of functional materials. Attached Figure Description

[0043] Figure 1 Bi2Te prepared in Example 1 2.7 Se 0.3 Sample XRD pattern;

[0044] Figure 2 Cu obtained in Example 4 0.01 Bi2Te 2.7 Se 0.3 XRD pattern of the sample. Detailed Implementation

[0045] 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 following embodiments. Those skilled in the art can make appropriate adjustments to the compositional relationship, powder ratio, rapid Joule heating pretreatment parameters, rapid Joule heating sintering parameters, cold pressing parameters and current post-treatment parameters of the first ball-milled powder and the second ball-milled powder according to the composition, phase formation characteristics, sintering activity, densification behavior and functional performance requirements of the target functional material.

[0046] It should be noted that the "pre-Joule heat-treated powder" mentioned in this invention refers to the powder obtained after the first ball-milled powder undergoes a first rapid Joule heat pretreatment. This powder is not limited to a fully phase-forming powder; it can be a powder that has already formed the target main phase, or it can be a basically phase-forming powder, a partially phase-forming powder, a partially reactive powder, a pre-crystallized powder, or a combination thereof. In other words, as long as the phase composition, degree of crystallization, reaction state, or sintering behavior of the first ball-milled powder changes relative to the original ball-milled powder after the first rapid Joule heat pretreatment, it can be used as the pre-Joule heat-treated powder described in this invention.

[0047] The "ball-milled active powder" described in this invention refers to a second ball-milled powder that has undergone ball milling but has not undergone a first rapid Joule heating pretreatment. The ball-milled active powder and the pre-Joule-heat-treated powder may have the same, similar, or complementary compositions, and the overall composition of the mixture corresponds to the composition of the target functional material. During rapid Joule heating sintering, the ball-milled active powder is not an external heterogeneous sintering aid, but rather a reactive auxiliary sintering component that is in the same system or matches the composition of the target functional material. It can participate in local reactions, particle bonding, interfacial bonding, and pore filling during rapid Joule heating sintering, thereby improving the integrity of the bulk structure and promoting sintering formation.

[0048] The "rapid Joule heating pretreatment" described in this invention refers to a process in which an electric current or electric field is applied to powder, causing the powder to rapidly heat up and undergo pre-reaction, partial phase formation, crystallization, or state control within a short period of time. The rapid Joule heating pretreatment is primarily used to adjust the powder state and is not necessarily intended to obtain sintered bulk materials.

[0049] The "rapid Joule thermal sintering" described in this invention refers to a process in which a bulk precursor is rapidly heated by an electric current or electric field, achieving particle bonding, interface connection, and sintering within a short time. Preferably, no external mechanical pressure for densification is applied during the rapid Joule thermal sintering stage; the contact forces required for equipment clamping, electrode contact, or sample support are not considered external sintering pressures.

[0050] The "current post-treatment" described in this invention refers to applying direct current, alternating current, pulsed current, or a combination thereof to a functional material sintered body after rapid Joule heating, placing the sintered body in a current-passing circuit. During the energizing process, rapid Joule heating and the influence of current / electric field are simultaneously achieved to further regulate phase composition, defect state, electrical transport behavior, grain boundary state, or other functional properties. This current post-treatment differs from ordinary heat treatment that only uses an external heat source and does not place the sample in a current-passing circuit.

[0051] This embodiment provides a method for preparing functional materials by synergistic Joule thermal sintering of dual-state powders, including the following steps, and may further perform current post-processing as needed:

[0052] Step 1: Preparation of the first and second ball-milled powders. Raw materials are weighed according to the composition of the target functional material, and the raw materials are ball-milled to obtain ball-milled powders. The ball-milled powders include the first and second ball-milled powders, wherein the first ball-milled powder is used for the subsequent first rapid Joule heating pretreatment, and the second ball-milled powder is not subjected to the first rapid Joule heating pretreatment and is used as the ball-milled active powder.

[0053] The first and second ball-milled powders can originate from the same batch of ball-milled powders or can be prepared separately. The first and second ball-milled powders can have the same or similar target composition, or they can have different but complementary compositions; when they have complementary compositions, the overall elemental composition of the mixture after mixing them in a predetermined ratio corresponds to the composition of the target functional material.

[0054] Preferably, the functional material is an inorganic functional material. More preferably, the inorganic functional material is one of the following: chalcogenide functional materials, functional semiconductor materials, thermoelectric functional materials, optoelectronic functional materials, phase change functional materials, Zintl phase functional materials, or intermetallic compound functional materials, or a material possessing multiple of the above functional properties simultaneously. More preferably, the functional material is a bismuth telluride-based thermoelectric functional material.

[0055] In one specific embodiment, the functional material is a Bi-Te-Se type n-type bismuth telluride-based thermoelectric functional material, and the target composition can be Bi2Te. 2.7 Se 0.3 In other embodiments, the functional material may also be a Bi-Sb-Te type p-type bismuth telluride-based thermoelectric functional material, a germanium telluride-based phase change functional material, a lead telluride-based functional material, a tin selenide-based functional material, a magnesium bismuth-based or magnesium bismuth antimony-based Zintl phase thermoelectric functional material, etc.

[0056] Preferably, the ball milling process employs one or more of the following: dry ball milling, wet ball milling, vibratory ball milling, planetary ball milling, or high-energy ball milling. More preferably, the ball milling process employs high-energy vibratory ball milling, with an inert atmosphere, a ball-to-material ratio of 10:1, and the milling jar and milling media made of stainless steel or hard steel. The vibration frequency is 1060 reciprocating vibrations per minute, and the milling time is 1–120 min, more preferably 5–20 min.

[0057] Step 2: Preparation of pre-Joule heat-treated powder. The first ball-milled powder obtained in Step 1 is subjected to a first rapid Joule heat pretreatment to obtain pre-Joule heat-treated powder.

[0058] Preferably, the object of the first rapid Joule heating pretreatment is the first ball-milled powder that has not been cold-pressed, that is, the first ball-milled powder is placed in an electrically conductive device in powder form to form an electrically conductive powder system, and then the first rapid Joule heating pretreatment is performed. The first rapid Joule heating pretreatment can be carried out under vacuum or a protective atmosphere, preferably argon.

[0059] Preferably, the first rapid Joule heating pretreatment includes a rapid heating stage, an optional holding stage, and a cooling stage. More preferably, when the functional material is a bismuth telluride-based thermoelectric functional material, the first rapid Joule heating pretreatment includes: heating from room temperature to 300–460 °C within 1–600 s, holding at that temperature for 0–600 s, and then cooling to room temperature within 1–600 s; wherein, holding at that temperature for 0 s indicates that after heating to the target temperature, no constant temperature holding stage is set and the cooling stage is directly initiated. More preferably, heating from room temperature to 400 °C within 60 s, holding at that temperature for 60 s, and then cooling to room temperature within 60 s.

[0060] After the first rapid Joule heat pretreatment, the first ball-milled powder forms a pre-Joule heat-treated powder. The pre-Joule heat-treated powder can be in a pre-reacted, partially phased, basically phased, or pre-crystallized state, which helps to reduce the phase-forming reaction burden in the subsequent rapid Joule heat sintering process and promotes the rapid formation of the target main phase.

[0061] Step 3: Preparation of the mixed powder. The pre-Joule heat-treated powder obtained in Step 2 is mixed with the second ball-milled powder to obtain the mixed powder. The second ball-milled powder is a ball-milled active powder that has undergone ball milling but has not undergone the first rapid Joule heat pretreatment.

[0062] The pre-Joule heat-treated powder and the ball-milled active powder can have the same, similar, or complementary compositions, and the overall composition of the mixture corresponds to the composition of the target functional material. Therefore, the ball-milled active powder is not an external heterogeneous sintering aid, but a reactive auxiliary sintering component that is in the same system or matches the composition of the target functional material, and can participate in local reactions, particle bonding, and pore filling during subsequent rapid Joule heat sintering.

[0063] Preferably, the mass ratio of pre-Joule heat-treated powder to ball-milled active powder is 75:25–99:1, more preferably 80:20–96:4, further preferably 88:12–95:5, and even more preferably 93:7. When the proportion of pre-Joule heat-treated powder is too low, the proportion of components that have already undergone pre-reaction or partial phase formation in the mixed powder is insufficient. During the subsequent rapid Joule heat sintering process, a significant amount of phase-forming reaction still needs to be completed in a short time, which is not conducive to the rapid formation of a pure phase and can easily lead to problems such as insufficient reaction, residual impurities, or unstable phase composition. Controlling the ratio within the above range is beneficial for balancing phase stability, sintering activity, and the integrity of the bulk structure.

[0064] Preferably, the mixing method in step 3 is manual grinding and mixing with a mortar and pestle, mechanical stirring and mixing, ball milling and mixing, planetary mixing, or other mixing methods that can uniformly disperse the two types of powders. More preferably, the mixing method is manual grinding and mixing with a mortar and pestle, the mixing time is 30 minutes, and the mixing atmosphere is argon.

[0065] Step 4: Cold pressing. The mixed powder obtained in step 3 is loaded into a mold and cold pressed to obtain a block precursor.

[0066] Preferably, the cold pressing in step (4) is performed using a single-stage or multi-stage pressurization method. The single-stage pressurization method involves increasing the pressure to the target cold pressing pressure in one step; the multi-stage pressurization method involves sequentially increasing the pressure to two or more pressure stages. Preferably, the cold pressing pressure is 200–900 MPa, and the total holding time is 0–600 s; more preferably, the cold pressing pressure is 650 MPa, and the total holding time is 0 s. Preferably, no release agent is used during the cold pressing process. The resulting block precursor can maintain its preset shape and is suitable for subsequent rapid Joule heating sintering.

[0067] Step 5: Rapid Joule thermal sintering. The bulk precursor obtained in Step 4 is placed in a rapid Joule thermal sintering apparatus and subjected to rapid Joule thermal sintering under vacuum or protective atmosphere conditions, without applying external mechanical pressure for densification, to obtain a sintered functional material.

[0068] In rapid Joule heating sintering, pre-Joule heat-treated powders provide a pre-reacted, partially or essentially phase-formed phase composition, which is beneficial for the rapid formation of the target main phase. Ball-milled active powders provide high reactivity and sintering activity, participating in localized reactions, particle bonding, and pore filling, thereby enhancing interparticle bonding, improving the continuity of the bulk structure, and reducing the risk of deformation and cracking during rapid heating and cooling. The synergistic effect of both helps to achieve rapid phase formation, bulk integrity, and sintering densification in a relatively short time.

[0069] Preferably, the rapid Joule sintering is performed under vacuum or a protective atmosphere, preferably argon. Preferably, the rapid Joule sintering object is a mixed powder compact obtained by cold pressing. The rapid Joule sintering includes a rapid heating stage, an optional holding stage, and a cooling stage; the rapid Joule sintering temperature is determined based on the phase formation temperature of the target functional material, the sintering densification requirements, the component volatility characteristics, and the thermal stability. More preferably, when the functional material is a bismuth telluride-based thermoelectric functional material, the rapid Joule sintering includes: heating from room temperature to 300–460 °C within 1–600 s, holding at that temperature for 0–600 s, and then cooling to room temperature within 1–600 s; wherein, holding for 0 s indicates that after heating to the target temperature, no isothermal holding stage is set, and the cooling stage is directly initiated. More preferably, the temperature is increased to 400 °C within 60 s from room temperature, held for 60 s, and then cooled to room temperature within 60 s.

[0070] Preferably, the resulting sintered functional material can maintain a complete block morphology; more preferably, the resulting sintered functional material does not crack.

[0071] Preferably, the relative density of the resulting functional material sintered body is not less than 85%; more preferably, the relative density is not less than 90%; and even more preferably, the relative density is not less than 95%.

[0072] Optional Step 6: Current Post-treatment. Based on the phase composition, defect state, and functional performance control requirements of the target functional material, the sintered body of the functional material obtained in Step 5 can be further subjected to current post-treatment. In this current post-treatment process, the current serves not only as the energy input for rapid heating but also as an electrical loading condition acting on the sintered body of the functional material. Therefore, under similar temperature-time programs, the control effect of current post-treatment on phase composition, defect state, and electrical transport properties is not equivalent to that of ordinary heat treatment.

[0073] Preferably, the current post-processing is performed under a vacuum or inert atmosphere. The current post-processing can be DC current post-processing, AC current post-processing, pulsed current post-processing, or a combination thereof. More preferably, the current post-processing is AC current post-processing.

[0074] Preferably, the current post-processing in step (6) includes a rapid heating stage, an optional holding stage, and a cooling stage. The current post-processing involves applying a direct current, alternating current, pulsed current, or a combination thereof to the functional material sintered body, causing it to heat to 200–500 °C within 10–300 s, hold for 0–300 s, and then cool to room temperature. More preferably, for bismuth telluride-based thermoelectric functional materials, the current post-processing includes heating to 400 °C within 60 s from room temperature, holding for 0 s, and then cooling to room temperature within 60 s. When the holding time is 0 s, it indicates that the cooling stage begins directly after reaching the target processing temperature. During the current post-processing, the current, voltage, power, and / or duty cycle are adjusted according to the sample size, sample resistance, electrode spacing, contact state, and target temperature-time program.

[0075] Preferably, for bismuth telluride-based thermoelectric functional materials, current post-processing can promote the formation of the main phase or improve the purity of the main phase, reduce impurity or residual phases, and regulate its thermoelectric transport properties. More preferably, the current post-processing is DC current post-processing, AC current post-processing, pulsed current post-processing, or a combination thereof; wherein, DC current post-processing can increase the absolute value of the Seebeck coefficient, and AC current post-processing can increase the absolute value of the Seebeck coefficient while maintaining a high level of conductivity. By controlling the current mode, target temperature-time program, and current, voltage, power, and / or duty cycle of the current post-processing, the phase composition, defect state, and thermoelectric transport properties of the bismuth telluride-based thermoelectric functional materials can be further controlled.

[0076] In this invention, the relative density is calculated according to the following formula:

[0077] 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 This refers to the theoretical density of the material corresponding to the target function.

[0078] Example 1

[0079] This embodiment illustrates a preferred implementation method for preparing bismuth telluride-based thermoelectric functional materials by synergistic rapid Joule heat sintering of pre-Joule heat-treated powder and ball-milled active powder, followed by AC current post-treatment, as well as the phase composition, bulk integrity, and thermoelectric transport properties of the resulting materials.

[0080] This embodiment employs a method of ball-milled active powder-assisted pre-Joule heat treatment followed by rapid Joule heat sintering and AC current post-treatment to prepare bismuth telluride-based thermoelectric functional materials, with a target composition of Bi2Te.2.7 Se 0.3 .

[0081] 1. Ball milling powder preparation: Weigh Bi, Te, and Se raw materials (particle size of raw materials is 2 mm), and mill them according to the formula Bi2Te 2.7 Se 0.3 The raw materials were prepared according to the corresponding stoichiometric ratio. Under an argon atmosphere, the raw materials and grinding balls were loaded into a ball mill jar, sealed, and then subjected to dry vibration ball milling using a high-energy vibration ball mill. The ball-to-material mass ratio was 10:1. The ball mill jar and grinding media were made of stainless steel or hard steel. The vibration frequency was 1060 reciprocating vibrations per minute, and the milling time was 15 minutes, yielding milled powder. The obtained milled powder was divided into first milled powder and second milled powder. The first milled powder was used for the first rapid Joule heat pretreatment, while the second milled powder served as the active powder without the first rapid Joule heat pretreatment.

[0082] 2. First rapid Joule heat pretreatment: Take the first ball-milled powder obtained in step 1, and directly perform the first rapid Joule heat pretreatment without cold pressing. The treatment atmosphere is argon, and the treatment process is to heat up to 400℃ within 60 s from room temperature, hold at that temperature for 60 s, and then cool down to room temperature within 60 s to obtain pre-Joule heat-treated powder.

[0083] 3. Preparation of the mixed powder: The pre-Joule heat-treated powder obtained in step 2 was mixed with the second ball-milled powder that had not undergone the first rapid Joule heat pretreatment to obtain the mixed powder. The second ball-milled powder was used as the ball-milled active powder; the mass ratio of the pre-Joule heat-treated powder to the ball-milled active powder was 93:7. The mixing method was manual grinding in a mortar and pestle for 30 minutes under an argon atmosphere.

[0084] 4. Cold pressing: The mixed powder obtained in step 3 is loaded into a cold pressing mold and cold pressed under a pressure of 650 MPa for 0 s to obtain a block precursor.

[0085] 5. Rapid Joule heating: The bulk precursor obtained in step 4 is placed in a rapid Joule heating sintering apparatus and subjected to rapid Joule heating sintering under an argon protective atmosphere without applying external mechanical pressure for densification. Specifically, the temperature is raised to 400 °C within 60 s from room temperature, held for 60 s, and then cooled to room temperature within 60 s to obtain a sintered body of the bismuth telluride-based thermoelectric functional material. The resulting sintered body maintains a complete bulk morphology without significant cracking, and its relative density is approximately 95%.

[0086] 6. Alternating Current Post-treatment: The sintered body of the bismuth telluride-based thermoelectric functional material obtained in step 5 was subjected to alternating current post-treatment. The alternating current post-treatment was performed under an argon protective atmosphere, with the sample temperature program as the main control condition. The equipment voltage was set to 40 V. During the treatment, the actual current varied with the sample resistance, sample temperature, and electrode contact state, with a maximum actual current of approximately 12 A. The specific treatment process was as follows: the temperature was increased to 400 °C within 60 s from room temperature, held for 0 s, and then cooled to room temperature within 60 s. After alternating current post-treatment, the sample appearance showed no significant changes, and no cracking, deformation, or surface ablation occurred.

[0087] 7. Characterization of Results: XRD results showed that the sample obtained after AC current post-processing was dominated by the bismuth telluride-based main phase, with no obvious impurity phase peaks observed. Figure 1 Thermoelectric performance test results show that the Seebeck coefficient of the sample after AC current post-treatment is -215.8 μV / K, and the conductivity is 0.95 × 10⁻⁶. 5 Based on the measured thermal conductivity (S / m), the ZT value at 300 K is approximately 1.05.

[0088] Example 2

[0089] This embodiment illustrates the effect of DC current post-processing on the phase composition and thermoelectric transport properties of bismuth telluride-based thermoelectric functional materials, and compares it with the AC current post-processing in Example 1. The target composition of this embodiment is the same as that of Example 1, which is Bi2Te. 2.7 Se 0.3 The difference between this embodiment and Embodiment 1 is that the AC current post-processing in step 6 is replaced with DC current post-processing; except for the different current mode, the other process conditions in this embodiment are the same as in Embodiment 1. Specifically, the ball milling powder preparation, the first rapid Joule heat pretreatment, powder mixing, cold pressing, rapid Joule heat sintering, and the target temperature-time program are all the same as in Embodiment 1.

[0090] DC current post-treatment: The functional material sintered bodies prepared according to steps 1-5 of Example 1 were subjected to DC current post-treatment. The DC current post-treatment was performed under an argon protective atmosphere, with the sample temperature program as the main control condition. The specific process was as follows: the temperature was increased to 400 °C within 60 s from room temperature, held for 0 s, and then cooled to room temperature within 60 s. During the treatment, the actual current varied with the sample resistance, sample temperature, and contact state. After DC current post-treatment, the sample appearance showed no significant changes; no cracking, deformation, or surface ablation occurred.

[0091] Characterization results: XRD results showed that the sample after DC current post-treatment was a pure bismuth telluride phase. Thermoelectric performance tests showed that DC current post-treatment significantly improved the absolute value of the Seebeck coefficient, which was approximately -228.5 μV / K. The conductivity after DC current post-treatment was 0.69 × 10⁻⁶. 5 S / m; the ZT value at 300 K is approximately 0.78. DC current post-treatment gives the bismuth telluride-based thermoelectric material a high Seebeck coefficient, but compared to AC current post-treatment in Example 1, its conductivity decreases significantly.

[0092] Example 3

[0093] This embodiment illustrates that, without current post-processing, bismuth telluride-based thermoelectric functional materials can still be prepared by rapid Joule thermal sintering of pre-Joule heat-treated powder and ball-milled active powder, and is used to evaluate the phase composition and thermoelectric transport properties of the obtained materials.

[0094] The target composition in this embodiment is the same as that in Embodiment 1, which is Bi2Te. 2.7 Se 0.3 Compared with Example 1, the difference in this example is that after the functional material sintered body is prepared according to steps 1 to 5 of Example 1, no current post-treatment is performed. Specifically, after completing the ball milling powder preparation, the first rapid Joule heat pretreatment, the mixed powder preparation, cold pressing, and rapid Joule heat sintering, no alternating current post-treatment is performed.

[0095] Characterization Results: In this embodiment, no current post-treatment was performed on the functional material sintered bodies prepared according to steps 1-5 of Example 1. The results show that although bulk sintered bodies could be obtained from the untreated samples, XRD results indicated that the sample phase composition was impure, containing impurities or residual phases; its Seebeck coefficient was low, approximately -111.2 μV / K, and its conductivity was approximately 1.12 × 10⁻⁶. 5 Based on the S / m and the thermal conductivity of the sample, the ZT value at 300 K is approximately 0.30.

[0096] Comparative Example 1

[0097] This comparative example illustrates that it is difficult to obtain structurally complete sintered blocks when only pre-Joule heat-treated powder is used for subsequent rapid Joule heat sintering. The target composition of this comparative example is the same as that of Example 1, which is Bi2Te. 2.7 Se 0.3 The difference lies in that this comparative example does not include ball-milled active powder; instead, it uses only pre-Joule heat-treated powder for cold pressing and rapid Joule heat sintering. Apart from the above differences, the raw material ratios and process parameters of this comparative example are the same as in Example 1.

[0098] Cold pressing: Without adding ball milled active powder, the pre-Joule heat-treated powder obtained according to steps 1 and 2 of Example 1 is directly loaded into a cold pressing mold and cold-pressed according to the conditions of step 4 of Example 1 to obtain a block precursor. The obtained block precursor is then subjected to rapid Joule heat sintering according to the conditions of step 5 of Example 1.

[0099] Characterization of results: The results show that when cold pressing and rapid Joule sintering are performed using only pre-Joule heat-treated powder, the resulting samples crack during or after sintering and cannot be processed into regular samples that meet the requirements of thermoelectric performance testing. Therefore, ZT testing at 300 K was not performed.

[0100] Comparative Example 2

[0101] This comparative example illustrates that it is difficult to obtain structurally complete sintered blocks when only ball-milled active powder is used for rapid Joule heating sintering. The target composition of this comparative example is the same as that of Example 1, which is Bi₂Te. 2.7 Se 0.3 The difference lies in that this comparative example does not include pre-Joule heat-treated powder, but instead uses only ball-milled active powder for direct cold pressing and rapid Joule heat sintering. Apart from the above differences, the raw material ratios, ball milling parameters, cold pressing parameters, and rapid Joule heat sintering parameters of this comparative example are the same as in Example 1.

[0102] Cold pressing: The ball-milled powder obtained according to the conditions in step 1 of Example 1 is not subjected to the first rapid Joule heat pretreatment, but is directly cold-pressed according to the conditions in step 4 of Example 1 to obtain a bulk precursor. The obtained bulk precursor is then subjected to rapid Joule heat sintering according to the conditions in step 5 of Example 1.

[0103] Characterization of results: The results show that when ball-milled powder is directly cold-pressed and rapidly Joule sintered, the resulting sample cracks during or after sintering and cannot be processed into a regular sample that meets the requirements for thermoelectric performance testing. Therefore, ZT testing at 300 K was not performed.

[0104] Comparative Example 3

[0105] This comparative example illustrates the effect of a pre-Joule heat-treated powder to ball-milled active powder mass ratio of 70:30 on the rapid Joule heat sintering and current post-treatment effects of functional materials. The target composition of this comparative example is the same as that of Example 1, which is Bi2Te. 2.7 Se 0.3The difference lies in that the mass ratio of pre-Joule heat-treated powder to ball-milled active powder in this comparative example is adjusted from 93:7 in Example 1 to 70:30. Apart from the above differences, the raw material ratios, ball milling parameters, first rapid Joule heat pretreatment parameters, powder mixing method, cold pressing parameters, rapid Joule heat sintering parameters, and AC current post-treatment parameters in this comparative example are all the same as in Example 1.

[0106] Preparation of the mixed powder: The pre-Joule heat-treated powder obtained according to steps 1 and 2 of Example 1 was mixed with the second ball-milled powder that had not undergone the first rapid Joule heat pretreatment to obtain the mixed powder. The second ball-milled powder was used as the ball-milled active powder; the mass ratio of the pre-Joule heat-treated powder to the ball-milled active powder was 70:30. The mixing method was manual grinding in a mortar for 30 minutes under an argon atmosphere. The resulting mixed powder was then subjected to cold pressing, rapid Joule heat sintering, and AC current post-treatment sequentially according to steps 4-6 of Example 1.

[0107] Characterization results: The results show that when the mass ratio of pre-joule heat-treated powder to ball-milled active powder is 70:30, the obtained sample can maintain the complete block morphology and does not have obvious cracking, but the density is significantly reduced, the sample has impurity peaks, and the ZT value is 0.45.

[0108] Comparative Example 4

[0109] This comparative example is used to illustrate that conventional heat treatment is not equivalent to the current post-treatment of the present invention. The target composition of this comparative example is the same as that of Example 1, which is Bi2Te. 2.7 Se 0.3 The difference lies in that: after rapid Joule sintering in this comparative example, no current post-treatment is performed on the resulting functional material sintered body; instead, ordinary heat treatment is performed using an external heat source. The target temperature-time program and atmosphere of the ordinary heat treatment are the same as those in the AC current post-treatment in Example 1, the only difference being that the sample is not in a current-carrying circuit. Apart from the above differences, the raw material ratio, ball milling parameters, first rapid Joule heat pretreatment parameters, powder mixing parameters, cold pressing parameters, and rapid Joule heat sintering parameters of this comparative example are all the same as those in Example 1.

[0110] Conventional heat treatment: The sintered functional material obtained according to steps 1-5 of Example 1 was placed in a conventional heat treatment apparatus and heat-treated under an argon protective atmosphere. The specific process was as follows: the temperature was raised to 400 °C within 60 s from room temperature, held at that temperature for 0 s, and then cooled to room temperature within 60 s. No current was applied to the sample during this process.

[0111] Characterization of results: The results show that although the samples after ordinary heat treatment underwent the same target temperature-time program as those after current post-treatment, the optimization effect on phase composition was limited. Characteristic peaks of impurity phases or residual phases could still be observed in the XRD results, and the reduction of impurity phase peaks was not as great as that of the samples after current post-treatment. At the same time, the absolute value of the Seebeck coefficient of the samples after ordinary heat treatment was not significantly improved, and the ZT value was 0.32.

[0112] Comparative Example 5

[0113] This comparative example illustrates that for bismuth telluride-based thermoelectric functional materials, excessively high rapid Joule heating sintering temperatures can easily lead to appearance degradation or performance test failures. The target composition of this comparative example is the same as that of Example 1, which is Bi₂Te. 2.7 Se 0.3 The difference lies in that the maximum temperature of rapid Joule heating sintering in this comparative example is increased from 400 °C in Example 1 to 500 °C. Apart from the above differences, the raw material ratios, ball milling parameters, first rapid Joule heating pretreatment parameters, powder mixing parameters, and cold pressing parameters are the same as in Example 1.

[0114] Rapid Joule heating: The bulk precursor obtained according to steps 1-4 of Example 1 was placed in a rapid Joule heating sintering apparatus and subjected to rapid Joule heating sintering under an argon protective atmosphere without applying external mechanical pressure for densification. Unlike Example 1, the rapid Joule heating sintering process in this comparative example was as follows: the temperature was raised to 500 °C within 60 s from room temperature, held at that temperature for 60 s, and then cooled to room temperature within 60 s to obtain a comparative sintered body.

[0115] Characterization results: The results show that when the maximum rapid Joule heating sintering temperature of the Bi2Te2.7Se0.3 system is increased to 500℃, the surface of the obtained sample turns black, and the appearance and structural state deteriorate, making it impossible to process into a regular sample that meets the requirements of thermoelectric performance testing. Therefore, ZT testing at 300 K was not performed.

[0116] Comparative Example 6

[0117] This comparative example illustrates that when powders are mixed mechanically without ball milling, it is difficult to achieve the same results as in Example 1 of the present invention. The target composition of this comparative example is the same as that of Example 1, which is Bi₂Te. 2.7 Se 0.3 The difference lies in that this comparative example does not employ high-energy vibration ball milling; instead, it uses only mortar grinding or mechanical stirring to perform ordinary mixing of Bi, Te, and Se raw materials. Apart from the above differences, the parameters for the first rapid Joule heating pretreatment, the ratio of the two types of powders, the cold pressing parameters, and the rapid Joule heating sintering parameters are the same as in Example 1.

[0118] Preparation of ordinary mixed powder: Weigh Bi, Te and Se raw materials, and mix according to Bi2Te 2.7 Se 0.3 The ingredients were prepared according to the corresponding stoichiometric ratio. Under an argon atmosphere, the raw materials were manually ground and mixed in a mortar for 30 minutes to obtain a common mixed powder. The obtained common mixed powder was divided into a first mixed powder and a second mixed powder. The first mixed powder was subjected to a first rapid Joule heat pretreatment according to the conditions of step 2 in Example 1 to obtain a comparative pretreated powder. The obtained comparative pretreated powder was mixed with the second mixed powder that had not undergone the first rapid Joule heat pretreatment at a mass ratio of 93:7, and then cold-pressed and rapidly Joule sintered sequentially according to the conditions of steps 4 and 5 in Example 1.

[0119] Characterization of Results: The results show that when powders are mixed using only conventional mechanical methods without ball milling, the reactivity and mixing uniformity of the resulting powders are insufficient. During subsequent rapid Joule heating sintering, the samples struggle to achieve sufficient formation of the target main phase, particle bonding, and pore filling, resulting in cracking of the sintered body. This prevents the formation of regular samples that meet the requirements for thermoelectric performance testing. Therefore, no subsequent AC current post-processing was performed, nor was a ZT test at 300 K conducted.

[0120] Comparative Example 7

[0121] This comparative example illustrates that when the ball milling time is too long, the powder nearly forms a bismuth telluride-based main phase during the ball milling process, leading to a decrease in the reactivity and sintering activity of the ball-milled active powder, making it difficult to exert a reactive sintering-aiding effect and affecting the integrity of the sintered sample. The target composition of this comparative example is the same as that of Example 1, which is Bi2Te. 2.7 Se 0.3 The difference lies in that the ball milling time in this comparative example is extended from 15 min in Example 1 to 4 h. Apart from the extended ball milling time, the raw material composition, ball-to-material ratio, ball milling atmosphere, first rapid Joule heat pretreatment, powder mixing ratio, cold pressing, and rapid Joule heat sintering are all the same as in Example 1.

[0122] Ball milling powder preparation: Ball milling powder was prepared according to the raw material ratio and ball milling conditions in step 1 of Example 1, except that the ball milling time was extended to 4 hours to obtain long-time ball milled powder. The obtained long-time ball milled powder was divided into first ball milled powder and second ball milled powder.

[0123] Phase characterization of ball-milled powder: The long-term ball-milled powder obtained above was characterized by XRD. The results showed that after 4 hours of high-energy vibration ball milling, the powder was close to forming a bismuth telluride-based main phase. The diffraction peaks of the original components such as Bi, Te and Se were significantly weakened or basically disappeared, indicating that the raw material powder had undergone sufficient mechanical alloying or solid-phase reaction.

[0124] Characterization results: The results show that when the ball milling time is extended to 4 h, the obtained long-time ball-milled powder is close to forming a bismuth telluride-based main phase, and the subsequent second ball-milled powder no longer has sufficient reactive sintering-aiding effect. During rapid Joule heating sintering, the mixed powder is difficult to fully achieve particle connection, pore filling and complete bulk formation. The obtained samples cannot form structurally complete bulks, or significant cracking occurs during and after sintering, making it impossible to process into regular samples that meet the requirements of thermoelectric performance testing. Therefore, ZT testing at 300 K was not performed.

[0125] Example 4

[0126] This embodiment illustrates that the method of the present invention can be applied to doped and modified bismuth telluride-based thermoelectric functional materials. This embodiment employs a method of ball-milled active powder assisted by pre-Joule heat treatment, rapid Joule heat sintering of the powder, and post-current treatment to prepare Cu-doped bismuth telluride selenide-based n-type thermoelectric functional materials, with a target composition of Cu. 0.01 Bi2Te 2.7 Se 0.3 Compared to Example 1, the difference in this example is that Cu element is introduced into the Bi-Te-Se system for doping modification. Except for the target composition and corresponding raw material ratios, the remaining process conditions in this example are the same as in Example 1.

[0127] Ball milling powder preparation: Weigh Cu, Bi, Te and Se raw materials, and process them according to Cu... 0.01 Bi2Te 2.7 Se 0.3 The ingredients are mixed according to the corresponding stoichiometric ratio, and the first ball-milled powder and the second ball-milled powder are prepared according to the ball milling conditions in step 1 of Example 1.

[0128] Characterization results: The results show that the obtained samples maintain a complete bulk morphology without obvious cracking or surface ablation, indicating that even after introducing a small amount of Cu element for doping modification into the Bi-Te-Se system, rapid sintering can still be achieved using the method of this invention. After current post-processing, XRD results show ( Figure 2 The obtained sample showed no obvious impurity peaks, indicating that the method of the present invention is applicable not only to undoped Bi2Te 2.7 Se 0.3 The system is also applicable to doped or alloyed bismuth telluride-based thermoelectric functional materials with a ZT value of 1.02 at 300K.

[0129] Example 5

[0130] This embodiment illustrates that the method of the present invention can be used in p-type bismuth telluride-based thermoelectric functional materials. The target composition of this embodiment is Bi. 0.5 Sb 1.5Te3. Compared with Example 1, the difference in this example is that the target functional material is changed from a Bi-Te-Se system n-type bismuth telluride-based thermoelectric functional material to a Bi-Sb-Te system p-type bismuth telluride-based thermoelectric functional material. Except for the target composition and the corresponding raw material ratio, the other process conditions in this example are the same as in Example 1.

[0131] Ball milling powder preparation: Weigh Bi, Sb and Te raw materials, and according to Bi 0.5 Sb 1.5 The ingredients were mixed according to the stoichiometric ratio corresponding to Te3, and the first ball-milled powder and the second ball-milled powder were prepared according to the ball milling conditions in step 1 of Example 1.

[0132] Characterization results: The results show that the obtained sample maintains a complete bulk morphology without obvious cracking. After current post-processing, XRD results show that the obtained sample is dominated by the Bi-Sb-Te bismuth telluride-based main phase, indicating that the method of the present invention is also applicable to p-type bismuth telluride-based thermoelectric functional materials, which have a ZT value of 1.25 at 300K.

[0133] Example 6

[0134] This embodiment illustrates that the method of the present invention can be used in germanium-telluride-based chalcogenide functional materials. This embodiment uses a method of ball-milled active powder assisted by pre-Joule heat treatment, rapid Joule heat sintering of the powder, and post-current treatment to prepare germanium-telluride-based functional materials, with a target composition of GeTe. Compared to Example 1, this embodiment changes the target functional material from bismuth telluride-based thermoelectric functional material to germanium-telluride-based chalcogenide functional material.

[0135] 1. Preparation of ball-milled powder: Ge and Te raw materials were weighed and proportioned according to the corresponding stoichiometric ratio of Ge and Te. Under an argon atmosphere, the raw materials and grinding balls were loaded into a ball mill jar, sealed, and then subjected to dry vibratory ball milling. The ball-to-material ratio was 10:1. The ball mill jar and grinding media were made of stainless steel or hard steel. The vibration frequency was 1060 reciprocating vibrations per minute, and the milling time was 1 hour, yielding germanium-tellurium-based ball-milled powder. The obtained ball-milled powder was divided into a first ball-milled powder and a second ball-milled powder. The first ball-milled powder was used for the first rapid Joule heating pretreatment, while the second ball-milled powder served as the ball-milled active powder without the first rapid Joule heating pretreatment.

[0136] 2. First rapid Joule heat pretreatment: Take the first ball-milled powder obtained in step 1, and directly perform the first rapid Joule heat pretreatment without cold pressing. The treatment atmosphere is argon, and the treatment process is to heat up to 450℃ within 60 s from room temperature, hold at that temperature for 60 s, and then cool down to room temperature within 60 s to obtain pre-Joule heat-treated powder.

[0137] 3. Preparation of the mixed powder: The pre-Joule heat-treated powder obtained in step 2 was mixed with the second ball-milled powder that had not undergone the first rapid Joule heat pretreatment to obtain the mixed powder. The second ball-milled powder was used as the ball-milled active powder; the mass ratio of the pre-Joule heat-treated powder to the ball-milled active powder was 93:7. The mixing method was manual grinding in a mortar and pestle for 30 minutes under an argon atmosphere.

[0138] 4. Cold pressing: The mixed powder obtained in step 3 is loaded into a cold pressing mold and cold pressed under a pressure of 650 MPa for 0 s to obtain a block precursor.

[0139] 5. Rapid Joule heating: The bulk precursor obtained in step 4 is placed in a rapid Joule heating sintering apparatus and subjected to rapid Joule heating sintering under an argon protective atmosphere without applying external mechanical pressure for densification. Specifically, the temperature is raised to 450 °C within 60 s from room temperature, held for 60 s, and then cooled to room temperature within 60 s to obtain the germanium-tellurium based functional material sintered body.

[0140] 6. Alternating Current Post-treatment: The germanium-tellurium-based functional material sintered body obtained in step 5 is subjected to an alternating current post-treatment. The current post-treatment is carried out under an argon protective atmosphere, with alternating current as the current mode. Specifically, the temperature is raised to 450 °C within 60 s from room temperature, held at that temperature for 0 s, and then cooled to room temperature within 60 s.

[0141] 7. Result Characterization: The results show that the obtained samples maintain a complete bulk morphology without significant cracking, pulverization, or surface ablation. XRD results show that the main phase of the obtained samples is GeTe phase, indicating that the method of this invention can be used for the rapid sintering and forming of germanium telluride-based chalcogenide functional materials. This result indicates that the process route of "pre-Joule heat-treated powder + ball-milled active powder" synergistic rapid Joule heat sintering and current post-treatment is not limited to bismuth telluride-based thermoelectric functional materials, but can also be extended to germanium telluride-based chalcogenide functional materials.

[0142] Example 7

[0143] This embodiment illustrates that the method of the present invention can be used in lead telluride-based chalcogenide functional materials. This embodiment uses a method of ball-milled active powder assisted by pre-Joule heat treatment, rapid Joule heat sintering of the powder, and post-current treatment to prepare lead telluride-based functional materials, with a target composition of PbTe. Compared to Example 1, this embodiment changes the target functional material from bismuth telluride-based thermoelectric functional material to lead telluride-based chalcogenide functional material.

[0144] 1. Preparation of ball-milled powder: Weigh Pb and Te raw materials and mix them according to the corresponding stoichiometric ratio of PbTe. Under an argon atmosphere, load the raw materials and grinding balls into a ball mill jar, seal it, and then perform dry vibratory ball milling using a vibratory ball mill. The ball-to-material ratio is 10:1. The ball mill jar and grinding media are made of stainless steel or hard steel. The vibration frequency is 1060 reciprocating vibrations per minute, and the milling time is 1 hour, yielding lead tellurium-based ball-milled powder. The obtained ball-milled powder is divided into a first ball-milled powder and a second ball-milled powder. The first ball-milled powder is used for the first rapid Joule heating pretreatment, while the second ball-milled powder serves as the ball-milled active powder without the first rapid Joule heating pretreatment.

[0145] 2. First rapid Joule heat pretreatment: Take the first ball-milled powder obtained in step 1, and directly perform the first rapid Joule heat pretreatment without cold pressing. The treatment atmosphere is argon, and the treatment process is to heat up to 450℃ within 60 s from room temperature, hold at that temperature for 60 s, and then cool down to room temperature within 60 s to obtain pre-Joule heat-treated powder.

[0146] 3. Preparation of the mixed powder: The pre-Joule heat-treated powder obtained in step 2 was mixed with the second ball-milled powder that had not undergone the first rapid Joule heat pretreatment to obtain the mixed powder. The second ball-milled powder was used as the ball-milled active powder; the mass ratio of the pre-Joule heat-treated powder to the ball-milled active powder was 93:7. The mixing method was manual grinding in a mortar and pestle for 30 minutes under an argon atmosphere.

[0147] 4. Cold pressing: The mixed powder obtained in step 3 is loaded into a cold pressing mold and cold pressed under a pressure of 650 MPa for 0 s to obtain a block precursor.

[0148] 5. Rapid Joule heating sintering: The bulk precursor obtained in step 4 is placed in a rapid Joule heating sintering apparatus and subjected to rapid Joule heating sintering under an argon protective atmosphere without applying external mechanical pressure for densification. Specifically, the temperature is raised to 450 °C within 60 s from room temperature, held for 60 s, and then cooled to room temperature within 60 s to obtain the sintered lead tellurium-based functional material.

[0149] 6. Alternating Current Post-treatment: The sintered lead tellurium-based functional material obtained in step 5 is subjected to alternating current post-treatment. The current post-treatment is carried out under an argon protective atmosphere. Specifically, the temperature is raised to 450°C within 60 seconds from room temperature, held at that temperature for 0 seconds, and then cooled to room temperature within 60 seconds.

[0150] 7. Result Characterization: The results show that the obtained samples maintain a complete bulk morphology without significant cracking or pulverization. XRD results show that the main phase of the obtained samples is PbTe, indicating that the method of the present invention can be used for the rapid sintering and forming of lead tellurium-based chalcogenide functional materials. This result shows that the method of the present invention is also applicable to chalcogenide functional materials containing low-melting-point or volatile components, providing a phase composition basis through pre-Joule heat treatment of powders, and promoting particle bonding and bulk forming during the subsequent rapid Joule heat sintering process by ball milling active powders.

[0151] Example 8

[0152] This embodiment illustrates that the method of the present invention can be used for tin selenide-based functional materials. This embodiment uses a method of ball-milled active powder assisted by pre-Joule heat treatment of powder followed by rapid Joule heat sintering and current post-treatment to prepare tin selenide-based functional materials, with a target composition of SnSe. Compared to Example 1, this embodiment changes the target functional material from bismuth telluride-based thermoelectric functional material to tin selenide-based functional material.

[0153] 1. Preparation of ball-milled powder: Weigh Sn and Se raw materials and mix them according to the corresponding stoichiometric ratio of Sn and Se. Under an argon atmosphere, load the raw materials and grinding balls into a ball mill jar, seal it, and then perform dry vibratory ball milling using a vibratory ball mill. The ball-to-material ratio is 10:1. The ball mill jar and grinding media are made of stainless steel or hard steel. The vibration frequency is 1060 reciprocating vibrations per minute, and the ball milling time is 1 hour, yielding tin selenium-based ball-milled powder. The obtained ball-milled powder is divided into a first ball-milled powder and a second ball-milled powder. The first ball-milled powder is used for the first rapid Joule heating pretreatment, while the second ball-milled powder serves as the ball-milled active powder without the first rapid Joule heating pretreatment.

[0154] 2. First rapid Joule heat pretreatment: Take the first ball-milled powder obtained in step 1, and directly perform the first rapid Joule heat pretreatment without cold pressing. The treatment atmosphere is argon, and the treatment process is to heat up to 500℃ within 60 s from room temperature, hold at that temperature for 60 s, and then cool down to room temperature within 60 s to obtain pre-Joule heat-treated powder.

[0155] 3. Preparation of the mixed powder: The pre-Joule heat-treated powder obtained in step 2 was mixed with the second ball-milled powder that had not undergone the first rapid Joule heat pretreatment to obtain the mixed powder. The second ball-milled powder was used as the ball-milled active powder; the mass ratio of the pre-Joule heat-treated powder to the ball-milled active powder was 93:7. The mixing method was manual grinding in a mortar and pestle for 30 minutes under an argon atmosphere.

[0156] 4. Cold pressing: The mixed powder obtained in step 3 is loaded into a cold pressing mold and cold pressed under a pressure of 650 MPa for 0 s to obtain a block precursor.

[0157] 5. Rapid Joule heating: The bulk precursor obtained in step 4 is placed in a rapid Joule heating sintering apparatus and subjected to rapid Joule heating sintering under an argon protective atmosphere without applying external mechanical pressure for densification. Specifically, the temperature is raised to 500 °C within 60 s from room temperature, held for 60 s, and then cooled to room temperature within 60 s to obtain the sintered tin selenium-based functional material.

[0158] 6. Alternating Current Post-treatment: The sintered tin selenium-based functional material obtained in step 5 is subjected to alternating current post-treatment. The current post-treatment is carried out under an argon protective atmosphere. Specifically, the temperature is increased to 500°C within 60 seconds from room temperature, held at that temperature for 0 seconds, and then cooled to room temperature within 60 seconds.

[0159] 7. Result Characterization: The results show that the obtained samples maintain a complete bulk morphology without significant cracking, pulverization, or surface ablation. XRD results show that the main phase of the obtained samples is SnSe, indicating that the method of this invention can be used for the rapid sintering and forming of tin selenide-based functional materials. This result demonstrates that the process route of "pre-Joule heat-treated powder + ball-milled active powder" synergistic rapid Joule heat sintering and current post-treatment proposed in this invention is not only applicable to bismuth telluride-based thermoelectric functional materials, but can also be extended to tin selenide-based chalcogenide functional materials.

Claims

1. A method for preparing functional materials by synergistic Joule thermal sintering of dual-state powders, characterized in that, Includes the following steps: (1) Prepare ball-milled powder according to the composition of the target functional material, wherein the ball-milled powder includes a first ball-milled powder and a second ball-milled powder; (2) The first ball-milled powder is subjected to a first rapid Joule heat pretreatment to obtain pre-Joule heat-treated powder; (3) The pre-Joule heat-treated powder obtained in step (2) is mixed with the ball-milled active powder to obtain a mixed powder, wherein the ball-milled active powder is a second ball-milled powder that has been ball-milled but has not undergone rapid Joule heat pretreatment; (4) The mixed powder obtained in step (3) is cold-pressed to obtain a bulk precursor; (5) Without applying external mechanical pressure for densification, the bulk precursor obtained in step (4) is subjected to rapid Joule thermal sintering to obtain the functional material. Wherein, the pre-Joule heat-treated powder and the ball-milled active powder have the same, similar or complementary composition, and the overall composition after the two are mixed corresponds to the composition of the target functional material; the ball-milled active powder, as a reactive auxiliary sintering component with the same system or matching composition, participates in local reaction, particle connection and / or pore filling during the rapid Joule heat sintering process in step (5).

2. The method according to claim 1, characterized in that, The functional material is an inorganic functional material; preferably, the inorganic functional material is one or more of the following: thermoelectric functional material, chalcogenide functional material, Zintl phase functional material, intermetallic compound functional material, or compound semiconductor functional material; when the inorganic functional material is a chalcogenide functional material, the chalcogenide functional material is selected from one or more of the following: bismuth telluride-based material, germanium telluride-based material, lead telluride-based material, and tin selenide-based material; when the inorganic functional material is a Zintl phase functional material or an intermetallic compound functional material, the Zintl phase functional material or intermetallic compound functional material is selected from magnesium bismuth-based material and magnesium antimony substrate. The material is selected from one or more of the following: bismuth-telluride-based materials, magnesium-bismuth-antimony-based materials, and magnesium-bismuth-antimony-based materials. More preferably, the chalcogenide functional material is a bismuth telluride-based thermoelectric functional material, preferably a Bi-Te-Se system n-type bismuth telluride-based thermoelectric material, a Bi-Sb-Te system p-type bismuth telluride-based thermoelectric material, or a doped or composite modified system thereof. Even more preferably, the target functional material includes one or more of the following: bismuth telluride selenide system n-type bismuth telluride-based thermoelectric material, doped and modified bismuth telluride selenide system n-type bismuth telluride-based thermoelectric material, bismuth-antimony telluride system p-type bismuth telluride-based thermoelectric material, germanium telluride-based material, lead telluride-based material, and tin selenide-based material. More preferably, the target functional material is selected from Bi2Te… 2.7 Se 0.3 Cu 0.01 Bi2Te 2.7 Se 0.3 Bi 0.5 Sb 1.5 One or more of Te3, GeTe, PbTe, and SnSe.

3. The method according to claim 1 or 2, characterized in that, The pre-Joule heat-treated powder is obtained by first ball-milled powder after a first rapid Joule heat pretreatment. The pre-Joule heat-treated powder includes pre-phase powder, basic phase powder, partially phase powder, partially reactive powder, pre-crystallized powder, or a combination thereof. The ball-milled active powder is a second ball-milled powder, which is ball-milled but not subjected to the first rapid Joule heat pretreatment, and participates in local reactions, particle bonding, and pore filling during rapid Joule heat sintering. The first ball-milled powder and the second ball-milled powder originate from the same batch of ball-milled powder, or are obtained by ball-milling different raw material ratios. The pre-Joule heat-treated powder and the ball-milled active powder have the same or similar target composition, or have different compositions and the overall elemental composition of the mixture after mixing them in a predetermined ratio corresponds to the composition of the target functional material.

4. The method according to any one of claims 1 to 3, characterized in that, The ball milling process in step (1) is one or more of the following: dry ball milling, wet ball milling, vibratory ball milling, planetary ball milling, or high-energy ball milling; preferably, it is dry vibratory high-energy ball milling, the ball milling atmosphere is an inert atmosphere, the ball-to-material mass ratio is 10:1, the ball milling jar and the ball milling media are made of stainless steel or hard steel, the vibration frequency is 1060 reciprocating vibrations per minute, and the ball milling time is 1 to 120 min; more preferably, it is 5 to 20 min.

5. The method according to any one of claims 1 to 4, characterized in that, The first rapid Joule heating pretreatment in step (2) is applied to the first ball-milled powder that has not been cold-pressed. The first rapid Joule heating pretreatment is carried out under vacuum or inert atmosphere and includes heating from room temperature to the target temperature within 1 to 600 s, holding at that temperature for 0 to 600 s, and then cooling to room temperature within 1 to 600 s. The target temperature is determined according to the phase formation temperature and thermal stability of the target functional material, and is preferably 300 to 500 ℃. When the functional material is a bismuth telluride-based thermoelectric functional material, the first rapid Joule heating pretreatment preferably includes heating from room temperature to 300 to 460 ℃ within 1 to 600 s, holding at that temperature for 0 to 600 s, and then cooling to room temperature within 1 to 600 s. More preferably, the temperature is heated from room temperature to 400 ℃ within 60 s, held at that temperature for 60 s, and then cooled to room temperature within 60 s.

6. The method according to any one of claims 1 to 5, characterized in that, The mass ratio of the pre-joule heat-treated powder to the ball-milled active powder in step (3) is 75:25 to 99:1, preferably 80:20 to 96:4, more preferably 88:12 to 95:5, and even more preferably 93:7; the mixing method in step (3) is one or more of manual grinding and mixing in a mortar, mechanical stirring and mixing, ball milling and mixing or planetary mixing, and the mixing time is 1 to 60 min; preferably, the mixing method is manual grinding and mixing in a mortar, the mixing time is 30 min, and the mixing atmosphere is argon.

7. The method according to any one of claims 1 to 6, characterized in that, The cold pressing in step (4) is carried out by a single pressurization method or a multi-stage pressurization method; the single pressurization method is to pressurize the mixed powder obtained in step (3) to the target cold pressing pressure in one go and hold the pressure or not hold the pressure; the multi-stage pressurization method is to pressurize the mixed powder obtained in step (3) to two or more pressure stages in sequence, and hold the pressure or not hold the pressure in at least one pressure stage; the cold pressing pressure is 200-900 MPa, and the total holding time is 0-600 s; preferably, the cold pressing pressurization method is a single pressurization, the cold pressing pressure is 650 MPa, and the total holding time is 0 s.

8. The method according to any one of claims 1 to 7, characterized in that, The rapid Joule heating sintering in step (5) is carried out under vacuum or inert atmosphere; the rapid Joule heating sintering includes heating from room temperature to the target sintering temperature within 1 to 600 s, holding at that temperature for 0 to 600 s, and then cooling to room temperature within 1 to 600 s; wherein, the target sintering temperature is determined according to the phase formation temperature, sintering densification behavior and thermal stability of the target functional material, preferably 300 to 500 ℃; when the functional material is a bismuth telluride-based thermoelectric functional material, the target sintering temperature is preferably 300 to 460 ℃; more preferably, for bismuth telluride-based thermoelectric functional materials, the temperature is heated to 400 ℃ within 60 s from room temperature, held at that temperature for 60 s, and then cooled to room temperature within 60 s.

9. The method according to any one of claims 1 to 8, characterized in that, The process also includes post-processing the functional material obtained in step (5) with current. This post-processing is performed under vacuum or an inert atmosphere, using a current mode of direct current, alternating current, pulsed current, or a combination thereof, preferably alternating current. The post-processing includes a rapid heating stage, an optional holding stage, and a cooling stage. Direct current, alternating current, pulsed current, or a combination thereof are applied to the functional material to place it in a current-carrying loop. The post-processing uses a target temperature-time program as the control objective. By adjusting the current, voltage, power, and / or duty cycle, the functional material is heated to 200–500 °C within 10–300 s, held for 0–300 s, and then cooled to room temperature. For bismuth telluride-based thermoelectric functional materials, the post-processing preferably includes heating to 400 °C within 60 s from room temperature, holding for 0 s, and then cooling to room temperature within 60 s. Cooling to room temperature within s; preferably, during the current post-processing, the current, voltage, power and / or duty cycle are adjusted according to the sample size, sample resistance, electrode spacing, contact state and target temperature-time program.

10. The method according to claim 9, characterized in that, When the functional material is a bismuth telluride-based thermoelectric functional material, the current post-processing improves the purity of the main phase, reduces the impurity phase peaks, and / or increases the absolute value of the Seebeck coefficient of the obtained bismuth telluride-based thermoelectric functional material; preferably, when the current post-processing is AC current post-processing, the electrical conductivity of the obtained bismuth telluride-based thermoelectric functional material remains at a high level while the absolute value of the Seebeck coefficient increases.

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