A cubic phase AgBiTe2 thermoelectric material, its preparation method and application

Abstract

The application belongs to the technical field of thermoelectric materials, and particularly relates to a cubic phase AgBiTe2 thermoelectric material and a preparation method and application thereof. AgBiTe2 is a promising I-V-VI2 thermoelectric candidate material with intrinsic low lattice thermal conductivity, and its practical application is seriously hindered by the instability of the cubic phase thermodynamics. In this work, we propose an entropy engineering strategy by PbTe alloying to stabilize the cubic phase in the whole working temperature range. Based on this robust matrix, Cd doping is used to decouple electron-phonon transport, which proves that Cd doping can effectively optimize the n-type carrier concentration, and at the same time induce the change of energy band structure, thereby significantly improving the Seebeck coefficient. Microstructurally, Cd supersaturation induces a layered defect architecture composed of Cd-rich inclusions and dense dislocations. These multi-scale features and intrinsic cationic disorder cooperatively scatter phonons, further improving the transport properties of carriers and practical application scenarios.

Description

Technical Field

[0001] This invention belongs to the field of thermoelectric materials technology, and specifically relates to a cubic phase AgBiTe2 thermoelectric material, its preparation method, and its application. Background Technology

[0002] The urgent need for sustainable energy solutions has significantly increased due to the depletion of fossil fuels and escalating environmental problems. Thermoelectric (TE) technology offers a promising pathway for direct thermoelectric conversion, characterized by its operational flexibility, quiet operation, and environmental compatibility. The efficiency of thermoelectric materials is measured by dimensionless performance indicators. zT=S 2 Quantization is performed. σT / ( K e + K L ),in S , σ , T , K e as well as K L These represent the Seebeck coefficient, electrical conductivity, absolute temperature, electronic thermal conductivity, and lattice thermal conductivity, respectively. Therefore, a high power factor ( PF=S 2 σ Combining with low thermal conductivity is crucial for maximizing... zT It is crucial. However, S , σ and κ e The strong interdependence of carrier concentrations limits the independent optimization of these parameters. To address this trade-off, various strategies for decoupling these parameters have been developed, including band convergence, resonant levels, and carrier energy filtering, all aimed at simultaneously improving electrical transport properties.

[0003] Typically, high-performance thermoelectric materials are degenerate semiconductors with high crystal symmetry and inherently low lattice thermal conductivity. Historically, cubic salt compounds (space group: Fm3mCompounds such as PbTe, PbSe, and SnTe have attracted widespread attention due to their superior thermoelectric properties. The high crystal symmetry in these systems promotes band degeneracy and multi-valley transport, thereby enhancing electrical conductivity without significantly reducing the Seebeck coefficient. Driven by the search for novel thermoelectric candidates, research has expanded to ternary IV-VI2 chalcogenides crystallized in salt structures. Among them, AgBiTe2 has become a particularly promising candidate due to its inherently ultra-low lattice thermal conductivity, a property derived from strong anharmonic lattice vibrations. However, AgBiTe2 exhibits thermodynamic instability at room temperature and tends to decompose into a Bi2Te3 phase containing dissolved silver, possibly accompanied by the formation of Ag2Te or other Ag-Te phases. This phase heterogeneity severely degrades the transport properties of the support and hinders practical applications. Therefore, stabilizing the cubic phase of AgBiTe2 across the entire operating temperature range is a key prerequisite for realizing its thermoelectric potential. Summary of the Invention

[0004] To address the shortcomings of the prior art, the present invention aims to provide a cubic phase AgBiTe2 thermoelectric material, its preparation method, and its application. This cubic phase AgBiTe2 thermoelectric material solves the problem in the prior art where AgBiTe2 exhibits thermodynamic instability at room temperature, does not tend to decompose into the Bi2Te3 phase containing dissolved silver, and does not accompany the formation of Ag2Te or other Ag-Te phases. At the same time, it improves the transport characteristics of the carrier and its practical application.

[0005] To address the aforementioned technical problems, this invention provides a cubic AgBiTe2 thermoelectric material. This cubic AgBiTe2 thermoelectric material is an entropy-mediated structure-stabilized AgBiTe2-based thermoelectric material combined with carrier optimization, and its chemical formula is (AgBi1- y Cd y Te2) 1-x (|PbTe|) x , x It is 0.3~0.5. y The value is 0.04~0.08.

[0006] Preferably, the chemical formula of the cubic AgBiTe2 thermoelectric material is (AgBi1- y Cd y Te2) 1-x (|PbTe|) x ,and x The values ​​are 0.3, 0.4, and 0.5. y The values ​​are 0.04, 0.06, and 0.05.

[0007] Preferably, the chemical formula of the cubic AgBiTe2 thermoelectric material is (AgBi 0.94 Cd0.06 Te 2 ) 0.6 (|PbTe|) 0.4 .

[0008] Preferably, the chemical formula is (AgBi) 0.94 Cd 0.06 Te 2 ) 0.6 (|PbTe|) 0.4 The cubic AgBiTe2 thermoelectric material achieved a 0.31 W / m² output in a helium atmosphere at 303 K–632 K. -1 K -1 The ultra-low lattice thermal conductivity and peak value of 0.51 zT .

[0009] This invention provides a method for preparing cubic AgBiTe2 thermoelectric materials, comprising the following steps: High-purity metallic silver particles, bismuth particles, tellurium particles, lead particles, and cadmium particles are weighed and mixed, then vacuum-sealed and heated to melt to obtain a melt. The melt was cooled to 923K and annealed at this temperature for 48 hours; after annealing, it was slowly cooled to room temperature to obtain ingots. After grinding the ingots into fine powder, they are hot-pressed into cylindrical blocks.

[0010] Preferably, the purity of the silver particles, bismuth particles, tellurium particles, lead particles, and cadmium particles is 99.999%.

[0011] Preferably, the mass ratio of the silver particles, bismuth particles, tellurium particles, lead particles, and cadmium particles is 64.772:115.357~120.372:204.16:82.88:2.698~5.396.

[0012] Preferably, the step of heating the silver particles, bismuth particles, tellurium particles, lead particles, and cadmium particles to melt to obtain a melt is as follows: the silver particles, bismuth particles, tellurium particles, lead particles, and cadmium particles placed in a sealed vacuum environment are heated to 1273K within 10 hours and held at this temperature for 6 hours to obtain a melt.

[0013] Preferably, the hot pressing temperature of the ingot is 823K, the axial pressure of the hot pressing is 50MPa, and the hot pressing time is 7min to obtain a cylindrical block with a diameter of 12mm and a thickness of 2mm~3mm.

[0014] This invention provides an application of cubic phase AgBiTe2 thermoelectric material in thermoelectric power generation devices.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention employs an entropy engineering strategy, introducing PbTe and AgBiTe2 for alloying, successfully stabilizing the cubic rock salt phase of AgBiTe2 in the room-to-mid-temperature range, thus regulating the material's structural stability and thermoelectric properties, and obtaining a high-performance thermoelectric material. It does not tend to decompose into the Bi2Te3 phase containing dissolved silver, nor does it involve the formation of Ag2Te or other Ag-Te phases. This is because the high configurational entropy inherent in the cubic AgBiTe2 thermoelectric material lowers the Gibbs free energy, thereby promoting the formation of a stable and highly symmetric single-phase solid solution. The introduction of PbTe not only contributes to the configuration entropy, but more importantly, it has a high degree of synergy with AgBiTe2 in terms of crystal field effect and electronic structure. The mechanism for solving the thermodynamic instability of AgBiTe2 and improving its thermoelectric performance is mainly manifested in the following ways: (1) In the synergistic mechanism for the stability of cubic phase, PbTe, a group IV-VI rock salt mineral structure compound, and AgBiTe2, a group IV-VI2 rock salt mineral structure compound, have the isomorphic property of complete miscibility at high temperature. The introduction of PbTe not only increases the mixing entropy of the cation sublattice, but more importantly, the 6s ions provided by Pb atoms 3 Lone pair electrons and the 6s electrons of Bi in AgBiTe2 2 The lone pairs of electrons form a synergistic lattice distortion suppression effect, effectively compensating for Ag. + -Bi 3+ The ordering trend effectively prevents the transformation to hexagonal or rhombohedral structures during the cooling process. This synergistic effect based on electronic structure and crystal field matching allows the material to achieve single cubic phase locking from room temperature to operating temperature without the need for high-content alloying, fundamentally avoiding the tendency to decompose into Ag-containing Bi2Te3 impurity phases or Ag2Te secondary phases. (2) In different kinetic mechanisms for impurity phase suppression, the introduction of PbTe changes the local chemical environment inside the lattice. The occupation of Pb atoms in the cation sublattice increases the Ag content. +The migration barrier inhibits the long-range diffusion of Ag through the pinning effect. Therefore, the material of the present invention is not only thermodynamically stable due to entropy increase, but also kinetically inhibits the atomic-scale segregation process, ensuring that the material does not decompose into Bi2Te3-based solid solution or Ag-Te compound during long-term thermal cycling. (3) In the coordinated regulation of carriers and phonons based on stable cubic phase, firstly, the introduction of PbTe itself has a positive effect on the band structure of the material. Due to the matching of PbTe and AgBiTe2 at the band edge states, the band gap increases significantly after alloying. The mechanism is that the introduction of Pb atoms changes the crystal field environment of the cation sublattice, which makes the energy of the conduction band bottom (mainly contributed by the cation s state and Te p state) rise; at the same time, the 6p state of Pb hybridizes with the valence band state of Ag / Bi, causing the valence band top to shift slightly downward, thereby effectively widening the band gap. The increase in band gap effectively suppresses the intrinsic excitation of minority carriers (i.e., bipolar effect) at high temperatures and reduces the contribution of bipolar diffusion to thermal conductivity, which is one of the key factors for improving the high-temperature thermoelectric performance of materials.

[0016] Based on this, the present invention further optimizes the performance by using Cd doping. The mechanism of action includes (1) specific regulation of band structure. In the PbTe alloy matrix, due to the resonance energy level effect between the band edge of Pb and AgBiTe2, the promotion effect of Cd doping (substituting Bi sites) on band convergence is more significant. The introduction of Cd not only regulates the carrier concentration, but more importantly, induces multi-valley convergence at the bottom of the conduction band, thereby significantly improving the Seebeck coefficient while maintaining high conductivity. (2) Enhancement effect of multi-scale phonon scattering. In the entropy-stable PbTe-AgBiTe2 system, the random occupation of Ag / Pb / Bi / Cd on the cation sublattice leads to more severe local lattice distortion. The Pb-Te bond has higher polarizability and more compliant bonding characteristics, which makes the mass fluctuations and stress field fluctuations in the lattice more intense, thus showing a better suppression effect on mid-to-high frequency phonon scattering. Furthermore, the supersaturated doping of Cd induces a hierarchical defect architecture composed of Cd-enriched nano-inclusions and dense dislocations, which, in synergy with the inherent cation disorder, effectively reduces the lattice thermal conductivity across the entire scale.

[0017] In summary, this invention, through PbTe alloying, not only stabilizes the cubic phase using entropy engineering, but also solves the technical challenges of easy decomposition, unstable phase composition, and significant high-temperature bipolar effects in existing AgBiTe2-based materials by leveraging the unique crystal field synergy, kinetic suppression mechanism, and bandgap modulation between PbTe and AgBiTe2. Combining Cd doping with the decoupling modulation of band structure and phonon transport, Cd doping is used to decouple electron-phonon transport, demonstrating that Cd doping can adjust the band structure and effectively optimize the n-type carrier concentration, which is beneficial for band convergence and induces changes in the band structure, thereby significantly improving the Seebeck coefficient. Furthermore, in entropy-stable systems, the random occupancy of cations on the sublattice induces severe lattice distortion and mass fluctuations. These characteristics form multi-scale phonon scattering centers, effectively suppressing lattice thermal conductivity. In addition, Cd supersaturation induces a layered defect architecture composed of Cd-rich inclusions and dense dislocations. These multi-scale characteristics, combined with the disordered phonon scattering of intrinsic cations, ultimately led to the fabrication of AgBiTe2-based thermoelectric materials with highly stable structures and excellent thermoelectric properties. Attached Figure Description

[0018] Figure 1 (AgBiTe2) 1-x (|PbTe|) x 、 (AgBiTe 2 ) 0.6 (|PbTe|) 0.4 Characterization diagrams of the original AgBiTe2 synthesized under different heat treatment conditions are shown, where (a) is the room temperature XRD pattern of the original AgBiTe2 synthesized under different heat treatment conditions; and (b) is the characterization diagram of (AgBiTe2). 1-x (|PbTe|) x (c) Room temperature XRD patterns of solid solutions in the series (x = 0.3, 0.4, and 0.5); 2 ) 0.6 (|PbTe|) 0.4 Rietveld refined XRD pattern; (d) is (AgBiTe) 2 ) 0.6 (|PbTe|) 0.4 Temperature-dependent XRD pattern. (e) (AgBiTe) 2 ) 0.6 (|PbTe|) 0.4 The DSC curve; (f) is for (AgBiTe2) 1-x SEM image of the (|PbTe|) polished surface and corresponding EDS elemental distribution map.

[0019] Figure 2 (AgBiTe2) 1-x(|PbTe|) x (x = 0.3, 0.4, and 0.5) series of temperature-dependent electrical conductivity, temperature-dependent Seebeck coefficient, total thermal conductivity, and temperature dependence zT The determination diagram shows that (a) represents (AgBiTe2). 1-x (|PbTe|) x ( x (a) Temperature-dependent conductivity series of 0.3, 0.4 and 0.5, (b) for (AgBiTe2) 1-x (|PbTe|) x ( x (c) Temperature-dependent Seebeck coefficients for (AgBiTe2) are 0.3, 0.4, and 0.5; 1-x (|PbTe|) x ( x Temperature dependence of power factor for (0.3, 0.4, and 0.5); (d) for (AgBiTe2) 1-x (|PbTe|) x ( x (e) represents the total thermal conductivity of (AgBiTe2) at values ​​of 0.3, 0.4, and 0.5. 1-x (|PbTe|) x ( x (f) represents the lattice thermal conductivity of single-phase solid solutions with values ​​of 0.3, 0.4, and 0.5; (f) represents the lattice thermal conductivity of (AgBiTe2). 1-x (|PbTe|) x ( x Temperature dependence of 0.3, 0.4, and 0.5 (for values ​​of 0.3, 0.4, and 0.5). zT .

[0020] Figure 3 For (AgBi1- y Cd y Te2) 0.6 (|PbTe|) 0.4 ,( y (0.04, 0.06, and 0.08) and (AgBiTe2) 0.6 (|PbTe|) 0.4 Temperature-dependent thermoelectric performance diagram; where (a) represents the Hall carrier concentration at room temperature. (nH ) and mobility ( μH As y The function in (AgBi1- y Cd y Te2) 0.6 (|PbTe|) 0.4 (a) is the temperature-dependent conductivity variation graph; (b) is the temperature-dependent Seebeck coefficient graph; (d) is the temperature-dependent conductivity variation graph at 300K (AgBi1-y Cd y Te2) 0.6 (|PbTe|) 0.4 The absolute value of the Seebeck coefficient as a function of carrier concentration is calculated based on the SPB model. (e) is a graph showing the temperature-dependent power factor variation. (f) shows the power factor variation in the range of 303~632K. y Cd y Te2) 0.6 (|PbTe|) 0.4 Compared to previously reported (AgBiTe2) 0.7 (SnTe) 0.3-6% Comparison of average power factors of Br.

[0021] Figure 4 For thermodynamics and ZT Value diagram, where (a) is (AgBi1- y Cd y Te2) 0.6 (|PbTe|) 0.4 ,( y (0.04, 0.06, and 0.08) and (AgBiTe2) 0.6 (|PbTe|) 0.4 Temperature-dependent thermal conductivity plot; (b) is (AgBi1- y Cd y Te2) 0.6 (|PbTe|) 0.4 ,( y (0.04, 0.06, and 0.08) and (AgBiTe2) 0.6 (|PbTe|) 0.4 Temperature-dependent lattice thermal conductivity diagram; (c) is (AgBi1- y Cd y Te2) 0.6 (|PbTe|) 0.4， ( y (0.04, 0.06, and 0.08) with Ag 0.8 Na 0.94 Sb 0.6 Bi 0.4 Te 2 and (AgBiTe) 2 ) 0.7 (SnTe) 0.3-6% Br zT Comparison figure; (d) shows the average values ​​of typical silver-based IV-VI2 thermoelectric materials (AgSbTe2, AgSbSe2, AgBiSe2, AgBiTe2) at 303K and 632K. zT Value comparison chart.

[0022] Figure 5 For (AgBi) 0.94 Cd 0.06 Te 2 ) 0.6 (|PbTe|) 0.4 Microscopic characterization images. (a) is a low-magnification STEM image; the inset shows the corresponding SAED pattern along the

[100] crystal plane axis; (b) is a HAADF-STEM image, whose Burgers vector is determined as... (c) shows the half-plane inserted into the Fourier-filtered image, labeled with the symbol L, and incorporates the geometric phase analysis from (b). (d) shows the EDS spectrum of Cd enrichment; (e) shows the EDS spectrum of CdTe nanoprecipitates.

[0023] Figure 6 (AgBiTe2) 1-x (|PbTe|) x The relationship between electronic thermal conductivity and temperature for x = 0.3, 0.4 and 0.5.

[0024] Figure 7 For (AgBi1- y Cd y Te2) 0.6 (|PbTe|) 0.4 Room temperature X-ray diffraction patterns (y=0, 0.04, 0.06, 0.08).

[0025] Figure 8 Here are HAADF-STEM images of (ad) dislocations, where (a) to (d) are HAADF-STEM images at different locations. Detailed Implementation

[0026] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Unless otherwise specified, the experimental methods described in the embodiments of the present invention are conventional methods.

[0027] It should be noted that when numerical ranges are involved in this invention, it should be understood that the two endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as in Examples 1 to 6, preferred embodiments are described in this invention to avoid redundancy. However, this invention is not limited to these, but can be implemented in other ways within the scope of the technical solutions defined in the appended claims. All raw materials, reagents, instruments, and equipment used in the following embodiments of this invention can be purchased from the market or prepared by existing methods.

[0028] The following detailed description, in conjunction with embodiments of the present invention and accompanying drawings, provides a clear and complete illustration of the technical solutions in these embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0029] Example 1 A type of (AgBiTe) 2 ) 0.7 (|PbTe|) 0.3 The preparation method of [the substance] specifically includes the following steps: Weigh out metallic silver particles, bismuth particles, tellurium particles, and lead particles, all with a purity of 99.999%, and seal them in a vacuum quartz tube according to an atomic percentage of 7:7:17:3 (the mass ratio of the metallic silver particles, bismuth particles, tellurium particles, and lead particles with a purity of 99.999% is 75.509:146.286:216.92:62.16). Slowly heat the quartz tube to 1273K over 10 hours and hold it at this temperature for 6 hours to obtain a melt.

[0030] The melt was then cooled to 923K within 2 hours, annealed at this temperature for 48 hours, and then slowly cooled to room temperature for 6 hours to obtain the ingot.

[0031] The obtained ingots were manually ground into fine powder, and then hot-pressed in a graphite mold at 823K with an axial pressure of 50MPa for 7 minutes to form a cylindrical block with a diameter of 12mm and a thickness of 2mm.

[0032] Example 2 A type of (AgBiTe) 2 ) 0.6 (|PbTe|) 0.4 The preparation method of [the substance] specifically includes the following steps: Weigh out metallic silver particles, bismuth particles, tellurium particles, and lead particles, all with a purity of 99.999%, and seal them in a vacuum quartz tube according to an atomic percentage of 3:3:8:2 (the mass ratio of the metallic silver particles, bismuth particles, tellurium particles, and lead particles with a purity of 99.999% is 64.722:125.388:204.16:82.88). Slowly heat the quartz tube to 1273K over 10 hours and hold it at this temperature for 6 hours to obtain a melt.

[0033] The melt was then cooled to 923K within 2 hours, annealed at this temperature for 48 hours, and then slowly cooled to room temperature for 6 hours to obtain the ingot.

[0034] The obtained ingots were manually ground into fine powder, and then hot-pressed in a graphite mold at 823K with an axial pressure of 50MPa for 7 minutes to form a cylindrical block with a diameter of 12mm and a thickness of 3mm.

[0035] Example 3 A type of (AgBiTe) 2 ) 0.5 (|PbTe|) 0.5 The preparation method of [the substance] specifically includes the following steps: Weigh out metallic silver particles, bismuth particles, tellurium particles, and lead particles, all with a purity of 99.999%, and seal them in a vacuum quartz tube according to an atomic percentage of 1:1:3:1 (the mass ratio of the metallic silver particles, bismuth particles, tellurium particles, and lead particles with a purity of 99.999% is 53.935:104.49:191.4:103.6). Slowly heat the quartz tube to 1273K over 10 hours and hold it at this temperature for 6 hours to obtain a melt.

[0036] The melt was then cooled to 923K within 2 hours, annealed at this temperature for 48 hours, and then slowly cooled to room temperature for 6 hours to obtain the ingot.

[0037] The obtained ingots were manually ground into fine powder, and then hot-pressed in a graphite mold at 823K with an axial pressure of 50MPa for 7 minutes to form cylindrical blocks with a diameter of 12mm and a thickness of 2.5mm.

[0038] Comparative Example 1 A method for preparing AgBiTe2 includes the following steps: Metallic silver particles, bismuth particles, and tellurium particles, all with a purity of 99.999%, were weighed in an atomic ratio of 1:1:2 and sealed in a vacuum quartz tube. The quartz tube was slowly heated to 1273K over 10 hours and held at this temperature for 6 hours. Then it was cooled to room temperature over 48 hours to obtain AgBiTe2.

[0039] Comparative Example 2 A method for preparing AgBiTe2 includes the following steps: Metallic silver particles, bismuth particles, and tellurium particles, all with a purity of 99.999%, were weighed in an atomic ratio of 1:1:2 and sealed in a vacuum quartz tube. The quartz tube was slowly heated to 1273K over 10 hours and held at this temperature for 6 hours. The resulting product was manually ground into a fine powder and then hot-pressed in a graphite mold at 823K with an axial pressure of 50MPa for 7 minutes to produce cylindrical AgBiTe2 blocks with a diameter of 12mm and a thickness of 2mm~3mm.

[0040] Comparative Example 3 A method for preparing AgBiTe2 includes the following steps: Metallic silver particles, bismuth particles, and tellurium particles, all with a purity of 99.999%, were weighed in an atomic percentage ratio of 1:1:2 and sealed in a vacuum quartz tube. The quartz tube was slowly heated to 1273K over 10 hours, then rapidly cooled and held at 773K for 6 hours, and finally quenched in water to obtain hexagonal AgBiTe2.

[0041] (AgBiTe) prepared in Examples 1-3 2 ) 0.7 (|PbTe|) 0.3 、(AgBiTe 2 ) 0.6 (|PbTe|) 0.4 and (AgBiTe) 2 ) 0.5 (|PbTe|) 0.5 The phase composition of AgBiTe2 prepared in Comparative Examples 1 to 3 was determined by copper... Kα The radiation was analyzed using an X-ray diffractometer (XRD, Rigaku Smartlab). The (AgBiTe) prepared in Examples 1-3... 2 ) 0.7 (|PbTe|) 0.3 、(AgBiTe 2 ) 0.6 (|PbTe|) 0.4 and (AgBiTe) 2 ) 0.5 (|PbTe|) 0.5 Heat flow was measured using a differential scanning calorimeter (DSC404 F3, Netzsch) at a flow rate of 10 K / min under an argon atmosphere. -1 The process was carried out at a certain rate. Examples 1-3 prepared (AgBiTe) 2 ) 0.7 (|PbTe|) 0.3 、(AgBiTe 2 )0.6 (|PbTe|) 0.4 and (AgBiTe) 2 ) 0.5 (|PbTe|) 0.5 The microstructure was observed using a scanning electron microscope (SEM, Zeiss Gemini 360) equipped with a dual-spherical aberration corrector and a Thermo Fisher Spectra 300 microscope (operating voltage 300 kV) equipped with a dual-spherical aberration corrector. Chemical composition was analyzed using energy-dispersive X-ray spectroscopy coupled with SEM and TEM.

[0042] Figure 1 (a) shows that conventional heat treatment failed to stabilize the target cubic phase in AgBiTe2. Both the AgBiTe2 prepared by slow cooling in Comparative Example 1 and the AgBiTe2 prepared by hot pressing in Comparative Example 2 severely decomposed into Ag2Te (PDF#65-1104) and Bi2Te3 (PDF#89-4302). Although the sample prepared by rapid quenching at 773 K in Comparative Example 3 exhibited hexagonal AgBiTe2 characteristics (PDF#18-1173), this phase, accompanied by persistent secondary impurities, failed to maintain high cubic symmetry. These results confirm that the cubic phase of pristine AgBiTe2 is thermodynamically unstable at room temperature and is prone to structural distortion (becoming hexagonal) or phase decomposition.

[0043] The (AgBiTe) prepared in Examples 1 to 3 respectively 2 ) 0.7 (|PbTe|) 0.3 、(AgBiTe 2 ) 0.6 (|PbTe|) 0.4 and (AgBiTe) 2 ) 0.5 (|PbTe|) 0.5 Overcoming the instability of AgBiTe2, through Figure 1 (b) shows a clear composition-dependent phase evolution, especially for low alloy content ( x= 0.3, (AgBiTe 2 ) 0.7 (|PbTe|) 0.3 The diffraction pattern indicates the presence of a multiphase complex composed of a cubic AgBiTe2 matrix and secondary Bi2Te3 precipitates; it should be noted that small amounts of silver-rich inclusions may also coexist, but their diffraction signals are blurred due to peak overlap. In contrast, increasing the PbTe content to [a specific value]... xA value ≥0.4 can completely suppress these secondary phases, resulting in a pure single-phase rock salt structure (PDF#65-7102). This transformation confirms that sufficient configurational entropy is crucial for reducing Gibbs free energy and stabilizing highly symmetric cubic phases.

[0044] Figure 1 (c) in the figure gives the (AgBiTe) prepared in Example 2 2 ) 0.6 (|PbTe|) 0.4 The composition was analyzed using Rietveld-refined XRD patterns to verify the crystallographic quality of this entropy-stable matrix. Figure 1 As shown in (c), the weighted profile R-factor (Rwp) obtained after refinement is approximately 8.61%, confirming the high purity of the cubic phase (space group). Fm3m Furthermore, the excellent agreement between its observational and computational models confirms the formation of a homogeneous solid solution, and no phase separation was detected.

[0045] Figure 1 (d) in Example 2 shows the preparation of (AgBiTe) 2 ) 0.6 (|PbTe|) 0.4 Temperature-dependent XRD patterns from 300K to 623K. (Source: [Insert source here]) Figure 1 As shown in (d), no secondary phase formation or decomposition was detected throughout the heating process. Notably, all diffraction peaks systematically shifted to lower angles with increasing temperature. This shift corresponds to the continuous lattice expansion driven by anharmonic lattice vibrations, confirming the strong thermal stability of the cubic framework.

[0046] Figure 1 (e) in the figure further confirms (AgBiTe) through DSC curves. 2 ) 0.6 (|PbTe|) 0.4 Phase stability. For example... Figure 1 As shown in (e), the lack of obvious endothermic or exothermic peaks rules out the possibility of a primary structure phase transition. The subtle features observed near 400 K involve edge atom motion or local relaxation within the cation sublattice, rather than the rapid atomic rearrangement typical of macroscopic phase reconstruction.

[0047] Figure 1 (f) in (AgBiTe) 2 ) 0.6 (|PbTe|) 0.4 The components maintained their structural integrity throughout the entire operating temperature range, and their microstructure morphology and elemental distribution were detected using SEM and EDS mapping. For example... Figure 1 From (f) in the text, we can see that (AgBiTe) 2) 0.6 (|PbTe|) 0.4 The polished surface exhibits a dense microstructure. Furthermore, the elemental distribution map shows that silver (Ag), bismuth (Bi), lead (Pb), and tellurium (Te) are uniformly distributed at the micrometer scale, confirming the successful synthesis of an entropy-stable high-quality alloy.

[0048] Electrical conductivity and Seebeck coefficient were simultaneously measured using a commercial system (CTA-3, Cryo-all) in a helium atmosphere ranging from 303 K to 632 K. Thermal conductivity ( κ ) through formula κ=DCp The calculation yielded the result. p ,in D For thermal diffusivity, Cp For specific heat capacity, ρ Density. Thermal diffusivity was determined using laser flash analysis (LFA457, Netzsch). Specific heat capacity was estimated using the Dulong-Pettit law. Density was determined using the Archimedes method. Room temperature Hall coefficient ( RH The Hall carrier concentration was determined by the van der Berg method under a 1.5T reversible magnetic field. nH ) and Hall mobility ( μH ) respectively through formula nH = 1 / (eRH) and μH = σRH Taking into account instrument uncertainty, the estimated experimental errors for electrical conductivity, Seebeck coefficient, and thermal conductivity are approximately 5%, 7%, and 7%, respectively.

[0049] Figure 2 (a) shows the (AgBiTe) prepared in Examples 1 to 3 respectively. 2 ) 0.7 (|PbTe|) 0.3 、(AgBiTe 2 ) 0.6 (|PbTe|) 0.4 and (AgBiTe) 2 ) 0.5 (|PbTe|) 0.5 Temperature-dependent conductivity. The transport behavior exhibits different dependencies on phase composition. Example 1 prepared (AgBiTe) 2 ) 0.7 (|PbTe|) 0.3 The multiphase sample exhibited the highest conductivity, which decreased monotonically with temperature, a characteristic of degenerate semiconductor transport, likely dominated primarily by the highly conductive secondary phase. In contrast, single-phase solid solutions ( x =0.4, x =0.5, which is the (AgBiTe) prepared in Example 2.2 ) 0.6 (|PbTe|) 0.4 and the (AgBiTe) prepared in Example 3 2 ) 0.5 (|PbTe|) 0.5 The cubic samples prepared in Examples 1-3 exhibit significantly lower electrical conductivity values ​​due to enhanced alloy scattering. Notably, the conductivity of these cubic samples shows a non-monotonic trend: it initially increases with increasing temperature, then decreases at higher temperatures. This transition indicates a competition between thermally activated carrier generation and phonon scattering suppression.

[0050] Figure 2 (b) shows the (AgBiTe) prepared in Examples 1 to 3 respectively. 2 ) 0.7 (|PbTe|) 0.3 、(AgBiTe 2 ) 0.6 (|PbTe|) 0.4 and (AgBiTe) 2 ) 0.5 (|PbTe|) 0.5 The temperature-dependent Seebeck coefficient. A negative Seebeck coefficient confirms n-type conductivity, indicating that electrons are the dominant charge carriers. Specifically, the (AgBiTe) prepared in Example 2... 2 ) 0.6 (|PbTe|) 0.4 It exhibits approximately 80 μV K at room temperature -1 The Seebeck coefficient increases to approximately 111 μVK at 632 K. -1 .

[0051] Figure 2 (c) in the figure shows the (AgBiTe) prepared in Examples 1 to 3 respectively. 2 ) 0.7 (|PbTe|) 0.3 、(AgBiTe 2 ) 0.6 (|PbTe|) 0.4 and (AgBiTe) 2 ) 0.5 (|PbTe|) 0.5 The temperature dependence test results of the power factor. Among them, the multiphase sample prepared in Example 1 (AgBiTe) 2 ) 0.7 (|PbTe|) 0.3 It exhibits the highest power factor (approximately 7.1 µW cm⁻¹) at 632 K. -1 K 2This is primarily due to its high metallic conductivity. In contrast, single-phase... x Example 2 prepared (AgBiTe) with a concentration of 0.4 2 ) 0.6 (|PbTe|) 0.4 The sample exhibits competitiveness in the low-temperature range, with its enhanced Seebeck coefficient compensating for the decrease in conductivity.

[0052] Figure 2 (d) in the figure shows the (AgBiTe) prepared in Examples 1 to 3 respectively. 2 ) 0.7 (|PbTe|) 0.3 、(AgBiTe 2 ) 0.6 (|PbTe|) 0.4 and (AgBiTe) 2 ) 0.5 (|PbTe|) 0.5 The total thermal conductivity. (From) Figure 2 As can be seen from (d) in the figure, the multiphase sample (AgBiTe) 2 ) 0.7 (|PbTe|) 0.3 It exhibits the highest thermal conductivity across the entire temperature range. This is primarily attributed to the significant electronic thermal conductivity resulting from its high electrical conductivity, and the potential presence of a secondary phase with high thermal conductivity. In contrast, single-phase solid solutions ( x =0.4 and x =0.5 of (AgBiTe) 2 ) 0.6 (|PbTe|) 0.4 and (AgBiTe) 2 ) 0.5 (|PbTe|) 0.5 The thermal conductivity of is much lower. K Lattice thermal conductivity ( K L = K - K e This is obtained by subtracting the electron contribution. This is achieved through the Wiedemann-Franz law (…). K e = LσT )(See Figure 6 ), of which the Lorentz number ( L The unit is 10 -8 WΩ K -2 )pass L The value is estimated using 1.5 + exp(-|S| / 116).

[0053] For multiphase preparation of (AgBiTe) 2 )0.7 (|PbTe|) 0.3 In the sample, the coexistence of multiple phases renders the standard single-phase Cp and L approximately ineffective; therefore... Figure 2 In (e), only single-phase solid solutions (x≥0.4) are considered. As shown in (e) of the figure, K L In (AgBiTe) 2 ) 0.5 (|PbTe|) 0.5 Initially decreasing, but exhibiting a characteristic rebound at high temperatures, indicating the presence of significant bipolar heat transport. In contrast, (AgBiTe) 2 ) 0.6 (|PbTe|) 0.4 It maintains a stable plateau in the high-temperature region, reaching approximately 0.31 W / m² at 579 K. -1 K -1 The lowest value.

[0054] Figure 2 (f) shows the (AgBiTe) prepared in Examples 1 to 3, respectively. 2 ) 0.7 (|PbTe|) 0.3 、(AgBiTe 2 ) 0.6 (|PbTe|) 0.4 and (AgBiTe) 2 ) 0.5 (|PbTe|) 0.5 temperature dependence zT All samples showed an increase with increasing temperature. zT Trend. Among them, the (AgBiTe) prepared in Example 2... 2 ) 0.6 (|PbTe|) 0.4 It reaches a peak value of approximately 0.42 at 632K. zT .

[0055] Determining the entropy-stable cubic phase (AgBiTe) 2 ) 0.6 (|PbTe|) 0.4 After establishing an optimal robust matrix, we introduced Cd to further adjust the carrier concentration and enhance electrical transport properties, specifically preparing (AgBi1- y Cd y Te2) 0.6 (|PbTe|) 0.4 ( y (0.04~0.08) as shown in Examples 4~6.

[0056] Example 4 A type of (AgBi)0.96 Cd 0.04 Te 2 ) 0.6 (|PbTe|) 0.4 The preparation method of [the substance] specifically includes the following steps: Weigh out metallic silver particles, bismuth particles, tellurium particles, lead particles, and cadmium particles, all with a purity of 99.999%, and seal them in a vacuum quartz tube at an atomic ratio of 75:72:200:50:3 (mass ratio of metallic silver particles, bismuth particles, tellurium particles, lead particles, and cadmium particles, all with a purity of 99.999%, is 64.722:120.372:20416:82.88:2.698). Slowly heat the quartz tube to 1273K over 10 hours and hold it at this temperature for 6 hours to obtain a melt.

[0057] The melt was then cooled to 923K within 2 hours, annealed at this temperature for 48 hours, and then slowly cooled to room temperature for 6 hours to obtain the ingot.

[0058] The obtained ingots were manually ground into fine powder, and then hot-pressed in an 823K graphite mold at an axial pressure of 50MPa for 7 minutes to form cylindrical blocks with a diameter of 12mm and a thickness of 2mm~3mm.

[0059] Example 5 A type of (AgBi) 0.94 Cd 0.06 Te 2 ) 0.6 (|PbTe|) 0.4 The preparation method of [the substance] specifically includes the following steps: Weigh out metallic silver particles, bismuth particles, tellurium particles, lead particles, and cadmium particles, all with a purity of 99.999%, and seal them in a vacuum quartz tube at an atomic ratio of 150:141:400:100:9 (mass ratio of metallic silver particles, bismuth particles, tellurium particles, lead particles, and cadmium particles, all with a purity of 99.999%, is 64.722:117.865:204.16:82.88:4.047). Slowly heat the quartz tube to 1273K over 10 hours and hold it at this temperature for 6 hours to obtain a melt.

[0060] The melt was then cooled to 923K within 2 hours, annealed at this temperature for 48 hours, and then slowly cooled to room temperature for 6 hours to obtain the ingot.

[0061] The obtained ingots were manually ground into fine powder, and then hot-pressed in an 823K graphite mold at an axial pressure of 50MPa for 7 minutes to form cylindrical blocks with a diameter of 12mm and a thickness of 2mm~3mm.

[0062] Example 6 A type of (AgBi) 0.92 Cd 0.08 Te 2 ) 0.6 (|PbTe|) 0.4 The preparation method of [the substance] specifically includes the following steps: Weigh out metallic silver particles, bismuth particles, tellurium particles, lead particles, and cadmium particles, all with a purity of 99.999%, and seal them in a vacuum quartz tube at an atomic ratio of 75:69:200:50:6 (the mass ratio of the metallic silver particles, bismuth particles, tellurium particles, lead particles, and cadmium particles with a purity of 99.999% is 64.722:115.357:204.16:82.88:5.396). Slowly heat the quartz tube to 1273K over 10 hours and hold it at this temperature for 6 hours to obtain a melt.

[0063] The melt was then cooled to 923K within 2 hours, annealed at this temperature for 48 hours, and then slowly cooled to room temperature for 6 hours to obtain the ingot.

[0064] The obtained ingots were manually ground into fine powder, and then hot-pressed in an 823K graphite mold at an axial pressure of 50MPa for 7 minutes to form cylindrical blocks with a diameter of 12mm and a thickness of 2mm~3mm.

[0065] In determining the entropy-stable cubic phase (AgBiTe) 2 ) 0.6 (PbTe) 0.4 After establishing the optimal robust matrix, we introduce Cd to further modulate the carrier concentration and enhance the electrical transport performance. Figure 7 It shows (AgBi) 0.96 Cd 0.04 Te 2 ) 0.6 (|PbTe|) 0.4 、(AgBi 0.94 Cd 0.06 Te 2 ) 0.6 (|PbTe|) 0.4 、(AgBi 0.92 Cd 0.08 Te 2 ) 0.6 (|PbTe|) 0.4 and the (AgBiTe) prepared in Example 2 2 ) 0.6 (|PbTe|) 0.4 The room temperature XRD pattern. All observed diffraction peaks conform to the cubic structure of rock salt. At y=0.06 (AgBi 0.94 Cd 0.06 Te 2 )0.6 (|PbTe|) 0.4 The presence of a CdTe secondary impurity phase indicates that Cd exists in (AgBiTe) 2 ) 0.6 (|PbTe|) 0.4 The maximum solubility in it is less than 6 at%.

[0066] Figure 3 The (AgBi) prepared in Examples 4 to 6 0.96 Cd 0.04 Te 2 ) 0.6 (|PbTe|) 0.4 、(AgBi 0.94 Cd 0.06 Te 2 ) 0.6 (|PbTe|) 0.4 、(AgBi 0.92 Cd 0.08 Te 2 ) 0.6 (|PbTe|) 0.4 Compared with the (AgBiTe) prepared in Example 2 2 ) 0.6 (|PbTe|) 0.4 Temperature-dependent thermoelectric properties diagram. (See diagram for example.) Figure 3 As shown in (a), the Hall carrier concentration at room temperature exhibits a non-monotonic change: the (AgBi) prepared at y=0.06 0.94 Cd 0.06 Te 2 ) 0.6 (|PbTe|) 0.4 It reached its peak value, and then (AgBi) was prepared at y=0.08. 0.92 Cd 0.08 Te 2 ) 0.6 (|PbTe|) 0.4 The carrier concentration decreased. However, crucially, the carrier concentration of all Cd-doped samples remained significantly higher than that of the undoped matrix (AgBiTe) prepared in Example 2. 2 ) 0.6 (|PbTe|) 0.4 This sustained enhancement provides strong evidence that Cd doping primarily functions as a donor mechanism. This anomaly is attributed to the inherent cation disorder of the high-entropy rock salt lattice, where Cd atoms may occupy Ag sites or interstitial positions, thus donating electrons and offsetting nominal acceptor substitution. (AgBi) prepared at higher doping levels (y=0.08) 0.92 Cd 0.08 Te 2 ) 0.6(|PbTe|) 0.4 The observed slight decrease indicates the onset of site competition or self-compensation, which partially offsets but does not negate the overall donor effect. Despite the increase in carrier concentration, conductivity still exhibits a systematic decrease, such as... Figure 3 As shown in (b) above. This decoupling stems from a severe suppression of carrier mobility. Figure 3 As shown in (a) of Example 2, the undoped matrix (AgBiTe) was prepared. 2 ) 0.6 (|PbTe|) 0.4 Carrier mobility increased from approximately 51.4 cm⁻¹ 2 V -1 s -1 It dropped sharply to about 9.8cm 2 V -1 s -1 (AgBi) 0.94 Cd 0.06 Te 2 ) 0.6 (|PbTe|) 0.4 This degradation confirms that the incorporation of Cd introduces significant mass and strain fluctuations, which exacerbate alloy scattering and suppress carrier mobility more significantly than the increase in carrier concentration.

[0067] Figure 3 (c) The (AgBi) prepared in Examples 4 to 6 0.96 Cd 0.04 Te 2 ) 0.6 (|PbTe|) 0.4 、(AgBi 0.94 Cd 0.06 Te 2 ) 0.6 (|PbTe|) 0.4 、(AgBi 0.92 Cd 0.08 Te 2 ) 0.6 (|PbTe|) 0.4 and the (AgBiTe) prepared in Example 2 2 ) 0.6 (|PbTe|) 0.4 The temperature-dependent Seebeck coefficient. Negative Seebeck coefficient values ​​across the entire temperature range confirm n-type conductivity. Notably, the Seebeck coefficient increases anomalously with increasing Cd content, especially for (AgBi) prepared at y=0.06. 0.94 Cd 0.06 Te 2 ) 0.6 (|PbTe|) 0.4The peak value is reached. Considering the simultaneous increase in carrier concentration mentioned above, this enhancement of the Seebeck coefficient strongly suggests a significant increase in the effective mass (m*) at the density of states. This inference is supported by the Pisarenko plot (e.g., Figure 3 (d) in the figure was quantitatively verified, in which the experimental data of the Cd-doped sample were compared with those of the original sample ((AgBiTe)). 2 ) 0.6 (|PbTe|) 0.4 The theoretical curve deviates significantly upward from the sample. Calculated based on the single parabolic band (SPB) model, m* increases from approximately 0.49me (y=0, (AgBiTe)). 2 ) 0.6 (|PbTe|) 0.4 The value rose sharply to approximately 1.62 me (y=0.06, (AgBi)). 0.94 Cd 0.06 Te 2 ) 0.6 (|PbTe|) 0.4 The peak value of (AgBi) was then obtained at y=0.08. 0.92 Cd 0.08 Te 2 ) 0.6 (|PbTe|) 0.4 The effective mass decreased to approximately 1.20 me. This significant increase in effective mass likely indicates a change in the band structure, specifically band flattening or convergence caused by Cd incorporation.

[0068] Figure 3 (e) in the middle gives (AgBi) 0.96 Cd 0.04 Te 2 ) 0.6 (|PbTe|) 0.4 、(AgBi 0.94 Cd 0.06 Te 2 ) 0.6 (|PbTe|) 0.4 、(AgBi 0.92 Cd 0.08 Te 2 ) 0.6 (|PbTe|) 0.4 and (AgBiTe) 2 ) 0.6 (|PbTe|) 0.4 Temperature-dependent power factor test plot. Despite the suppressed conductivity, the significant increase in the Seebeck coefficient compensates for the mobility loss and dominates the transport behavior. Therefore, a composition with y=0.06 achieves approximately 6.24 μW / cm² at 632 K. -1 K -2The maximum power factor. Figure 3 In (f) of Example 2, the (AgBiTe 2 ) 0.6 (|PbTe|) 0.4 and those of (AgBi 0.96 Cd 0.04 Te 2 ) 0.6 (|PbTe|) 0.4 , (AgBi 0.94 Cd 0.06 Te 2 ) 0.6 (|PbTe|) 0.4 , (AgBi 0.92 Cd 0.08 Te 2 ) 0.6 (|PbTe|) 0.4 and AgBiTe 2 ) 0.6 (|PbTe|) 0.4 and those of (AgBiTe 2 ) 0.7 (SnTe) 0.3-6% Br in the temperature range of 303K - 632K. The (AgBi 0.94 Cd 0.06 Te 2 ) 0.6 (|PbTe|) 0.4 with y = 0.06 shows an average power factor of about 4.6 μWcm -1 K -2 , which is about 26.8% higher than that of the previously reported n-type (AgBiTe 2 ) 0.7 (SnTe) 0.3-6% Br. These results indicate that moderate Cd doping effectively improves the overall electrical properties of the AgBiTe2 - <PbTe< / PbTe solid solution system.

[0069] Figure 4 The (AgBi 0.96 Cd 0.04 Te 2 ) 0.6 (|PbTe|) 0.4 , (AgBi 0.94 Cd 0.06 Te 2 ) 0.6 (|PbTe|) 0.4 , (AgBi 0.92Cd 0.08 Te 2 ) 0.6 (|PbTe|) 0.4 Compared with the (AgBiTe) prepared in Example 2 2 ) 0.6 (|PbTe|) 0.4 Thermodynamics and ZT Value, of which Figure 4 (a) shows the preparation of (AgBi) in Examples 4-6 respectively. 0.96 Cd 0.04 Te 2 ) 0.6 (|PbTe|) 0.4 、(AgBi 0.94 Cd 0.06 Te 2 ) 0.6 (|PbTe|) 0.4 、(AgBi 0.92 Cd 0.08 Te 2 ) 0.6 (|PbTe|) 0.4 and the (AgBiTe) prepared in Example 2 2 ) 0.6 (|PbTe|) 0.4 Temperature-dependent thermal conductivity. (AgBi) 0.96 Cd 0.04 Te 2 ) 0.6 (|PbTe|) 0.4 、(AgBi 0.94 Cd 0.06 Te 2 ) 0.6 (|PbTe|) 0.4 、(AgBi 0.92 Cd 0.08 Te 2 ) 0.6 (|PbTe|) 0.4 and (AgBiTe) 2 ) 0.6 (|PbTe|) 0.4 The thermal conductivity of all samples initially decreased to approximately 476 K, then rebounded at higher temperatures, likely due to the onset of bipolar thermal transport. In contrast, the lattice thermal conductivity of all samples exhibited a monotonically decreasing trend with temperature, such as... Figure 4 As shown in (b) above. Notably, the lattice thermal conductivity reaches an ultra-low 0.31 W / m² at 632 K. -1 K -1The relatively low lattice thermal conductivity is attributed to the atomic disorder within the cubic structure and the coexistence of multiple microstructures.

[0070] Figure 4 (c) in the middle gives (AgBi) 0.96 Cd 0.04 Te 2 ) 0.6 (|PbTe|) 0.4 、(AgBi 0.94 Cd 0.06 Te 2 ) 0.6 (|PbTe|) 0.4 、(AgBi 0.92 Cd 0.08 Te 2 ) 0.6 (|PbTe|) 0.4 and (AgBiTe) 2 ) 0.6 (|PbTe|) 0.4 and Ag 0.8 Na 0.94 Sb 0.6 Bi 0.4 Te 2 and (AgBiTe) 2 ) 0.7 (SnTe) 0.3-6% Br zT The test results were passed. Figure 4 From (c), we can know that the compound (AgBi) 0.94 Cd 0.06 Te 2 ) 0.6 (|PbTe|) 0.4 It reaches a peak value of approximately 0.51 at 632K. zT This exceeds the previously reported Ag 0.8 Na 0.94 Sb 0.6 Bi 0.4 Te 2 and (AgBiTe) 2 ) 0.7 (SnTe) 0.3-6% Br. That is... zT It increases with increasing temperature, reaching a peak of 0.51 at 632K, which is higher than the value reported in the literature.

[0071] Figure 4 The average values ​​of typical silver-based IV-VI2 thermoelectric materials at (d) 303K and 632K are shown in the figure. zT Value comparison result graph, through Figure 4As shown in (d), although p-type AgSbTe2 alloys currently exhibit superior peak performance within this material family, the development of efficient n-type counterparts remains challenging due to phase instability and carrier optimization. As illustrated below, our work achieves a competitive breakthrough in a limited n-type AgSbTe2-based system, significantly outperforming the current leading n-type (AgBiTe) alloys. 2 ) 0.7 (SnTe) 0.3-6% These results highlight the effectiveness of entropy engineering in stable cubic phases and emphasize Cd doping as an efficient strategy for decoupling electron-phonon transport in AgBiTe2-based thermoelectric materials, where p-type alloys include Ag. 1.02 Sb 0.96 Ge 0.02 Te 2 AgSb 0.973 Cd 0.017 Se 2 、(AgBi 0.99 Cd 0.01 Te 2 ) 0.6 (SnTe) 0.4 n-type alloys include (AgBiTe) 2 ) 0.7 (SnTe)0.3-6%Br, (AgBiTe) 2 ) 0.7 (SnTe)0.3-1%Br and (AgBi) 0.94 Cd 0.06 Te 2 ) 0.6 (|PbTe|) 0.4 .

[0072] To elucidate the structural origin of the ultra-low thermal conductivity, we performed a comprehensive microstructure characterization using scanning transmission electron microscopy (STEM). Figure 5 (a) shows the optimized sample (AgBi) 0.94 Cd 0.06 Te 2 ) 0.6 (|PbTe|) 0.4 Low-magnification STEM images. The corresponding selected area electron diffraction (SAED) pattern (inset) further confirms the high crystallinity of the rock salt cubic matrix, consistent with the XRD results. High-angle annular dark-field (HAADF) STEM images along the

[100] crystal axis (e.g.) Figure 5 (b) clearly shows the presence of edge dislocations (see HAADF-STEM images of more dislocations). Figure 8 The Burgers vector was determined as follows: Complete Burgers circuits of dislocations and inserted half-planes. The symbol indicates ⊥ (as shown in (b) of Figure 5 and (c) of Figure 5 ). Geometric phase analysis (GPA) (inset in (c) of Figure 5 ) further confirms that edge dislocations generate a significant strain field in the lattice. In addition, HAADF images combined with energy spectrum analysis (in (d) of Figure 5 and (e) of Figure 5 ) identify Cd-enriched nano-precipitates and CdTe nano-precipitates embedded in the matrix. These precipitates may be due to Cd supersaturation, promoting the formation of CdTe and elemental Cd inclusions in the entropy-stabilized matrix. Therefore, these layered structures act as effective phonon scatterers, significantly suppressing the lattice thermal conductivity.

[0073] We successfully stabilized the thermodynamically fragile cubic phase of AgBiTe2 over a wide temperature range (303 K - 632 K) through PbTe alloying entropy engineering. Systematic structural and transport characterizations determined that the (AgBiTe 2 ) 0.6 (PbTe) 0.4 composition serves as the optimal matrix, which strikes a balance between the high crystal symmetry of electron transport and the strong lattice disorder of phonon scattering, while effectively suppressing the detrimental bipolar thermal transport observed in materials with higher PbTe content. Based on this n-type matrix, we used Cd doping to decouple the electron-phonon transport properties. Contrary to nominal acceptor substitution, due to the cationic disorder inherent in the high-entropy lattice, Cd mainly acts as a donor. Meanwhile, the band structure change induced by Cd doping increases the effective mass of the density of states, thus significantly enhancing the Seebeck coefficient. In addition, microstructure analysis shows that the incorporation of cadmium exceeds its solubility limit, promoting the formation of Cd-rich nano-precipitates and dense dislocations. These layered defects interact with the entropy-driven atomic disorder, significantly enhancing the phonon scattering effect, thereby minimizing the lattice heat

[0074] conductivity. Therefore, a peak of approximately 0.51 was achieved at 632 K zT , which is about 143% higher than the existing state-of-the-art n-type AgBiTe2-based alloys. This study highlights the potential of entropy engineering in expanding the stability limit of I-V-VI2 semiconductors and emphasizes the key role of defect engineering in optimizing complex high-entropy thermoelectric materials.

[0075] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these changes and modifications.

Claims

1. A cubic phase AgBiTe2 thermoelectric material, characterized in that, The cubic AgBiTe2 thermoelectric material is an AgBiTe2-based thermoelectric material optimized by entropy-mediated structural stabilization combined with carrier optimization, and its chemical formula is (AgBi1- y Cd y Te2) 1-x (|PbTe|) x , x It is 0.3~0.

5. y The value is 0.04~0.

08.

2. The cubic AgBiTe2 thermoelectric material according to claim 1, characterized in that, The chemical formula of the cubic AgBiTe2 thermoelectric material is (AgBi1- y Cd y Te2) 1-x (|PbTe|) x ,and x The values ​​are 0.3, 0.4, and 0.

5. y The values ​​are 0.04, 0.06, and 0.

05.

3. The cubic AgBiTe2 thermoelectric material according to claim 2, characterized in that, The chemical formula of the cubic AgBiTe2 thermoelectric material is (AgBi 0.94 Cd 0.06 Te 2 ) 0.6 (|PbTe|) 0.4 .

4. The cubic AgBiTe2 thermoelectric material according to claim 3, characterized in that, The chemical formula is (AgBi) 0.94 Cd 0.06 Te 2 ) 0.6 (|PbTe|) 0.4 The cubic AgBiTe2 thermoelectric material achieved a 0.31 W / m² output in a helium atmosphere at 303 K–632 K. -1 K -1 The ultra-low lattice thermal conductivity and peak value of 0.51 zT .

5. The method for preparing the cubic AgBiTe2 thermoelectric material according to any one of claims 1 to 4, characterized in that, Includes the following steps: High-purity metallic silver particles, bismuth particles, tellurium particles, lead particles, and cadmium particles are weighed and mixed, then vacuum-sealed and heated to melt to obtain a melt. The melt is cooled to 913K~933K and annealed at this temperature for 45h~50h; after annealing, it is slowly cooled to room temperature to obtain ingots. After grinding the ingots into fine powder, they are hot-pressed into cubic phase AgBiTe2 thermoelectric material blocks.

6. The method for preparing the cubic AgBiTe2 thermoelectric material according to claim 5, characterized in that, The purity of the silver particles, bismuth particles, tellurium particles, lead particles, and cadmium particles is 99.999%.

7. The method for preparing the cubic AgBiTe2 thermoelectric material according to claim 5, characterized in that, The mass ratio of the silver particles, bismuth particles, tellurium particles, lead particles, and cadmium particles is 64.772:115.357~120.372:204.16:82.88:2.698~5.

396.

8. The method for preparing the cubic AgBiTe2 thermoelectric material according to claim 5, characterized in that, The step of heating the metallic silver particles, bismuth particles, tellurium particles, lead particles, and cadmium particles to melt to obtain a melt is as follows: the metallic particles, bismuth particles, tellurium particles, lead particles, and cadmium particles placed in a sealed vacuum environment are heated to 1273K within 10 hours and held at this temperature for 6 hours to obtain a melt.

9. The method for preparing the cubic AgBiTe2 thermoelectric material according to claim 3, characterized in that, The hot pressing temperature of the ingot is 823K, the axial pressure of the hot pressing is 50MPa, and the hot pressing time is 7min to obtain a cylindrical block with a diameter of 12mm and a thickness of 2mm~3mm.

10. The application of the cubic phase AgBiTe2 thermoelectric material according to claim 1 in thermoelectric power generation devices.

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