An ag-doped layered selenide semiconductor material and a method for preparing the same

Abstract

This invention relates to the field of semiconductor materials technology, specifically to an Ag-doped layered selenide semiconductor material and its preparation method. The general chemical formula of the Ag-doped layered selenide semiconductor material is Ge. 0.85‑x Ag x Bi 2.21 Se4,x represents the mole fraction of Ag doping, with a value ranging from 0 to x ≤ 0.075, and the Ag-doped layered selenide semiconductor material has a rhombohedral phase crystal structure. This invention utilizes Ge... 0.85 Bi 2.21 Introducing a specific amount of Ag atoms into the Se4 lattice, Ag + Partially replaces Ge 2+ By altering the carrier concentration and scattering mechanism, the absolute value of the Seebeck coefficient significantly increases with increasing temperature in the 300-700 K range, while the electrical conductivity decreases moderately, and the power factor and thermoelectric merit are improved. This material overcomes the limitations of existing Ge... 0.85 Bi 2.21 The Se4 series addresses the issues of low Seebeck coefficient and poor thermoelectric performance, significantly improving thermoelectric conversion efficiency.

Description

Technical Field

[0001] This invention relates to the field of semiconductor materials technology, and in particular to an Ag-doped layered selenide semiconductor material and its preparation method. Background Technology

[0002] Thermoelectric materials, based on the Seebeck effect, can directly convert heat energy into electrical energy, thus attracting significant attention in research areas such as waste heat recovery and green energy. However, their conversion efficiency is often limited by material properties. The conversion efficiency of thermoelectric materials is mainly related to the quantized thermoelectric figure of merit ZT, where ZT = S 2 σT / k, where S is the Seebeck coefficient, T is the absolute temperature, σ is the electrical conductivity, and κ is the thermal conductivity. 2 σ is the power factor (PF), which comprehensively reflects the electrical transport properties, while thermal conductivity is mainly determined by carrier thermal conductivity (κ). e ) and lattice thermal conductivity (κ) L )composition.

[0003] The prior art discloses a ternary layered selenide Ge 0.85 Bi 2.15+x Se4 (0≤x≤0.06) semiconductor materials and their preparation methods have solved the technical problem of obtaining single-phase GeBi2Se4, but in Ge 0.85 Bi 2.21 Se4-based material systems still suffer from drawbacks such as low Seebeck coefficients and poor thermoelectric properties. Therefore, further adjustments to Ge4-based materials using technological means are needed. 0.85 Bi 2.15+x The electrical properties of Se4-based materials are of great significance for promoting their application in fields such as functional materials. Current technologies still require improvement and development. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide an Ag-doped layered selenide semiconductor material and its preparation method, aiming to solve the problems of Ge in the prior art. 0.85 Bi 2.21 The technical problems of Se4 materials, such as low Seebeck coefficient and poor thermoelectric properties.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: An Ag-doped layered selenide semiconductor material, wherein the chemical formula of the Ag-doped layered selenide semiconductor material is Ge. 0.85-x Ag x Bi 2.21 Se4, where x represents the mole fraction of Ag doping, and its value ranges from 0 to x ≤ 0.075, and the Ag-doped layered selenide semiconductor material has a rhombohedral phase crystal structure.

[0006] The Ag-doped layered selenide semiconductor material, wherein the space group of the rhombohedral crystal structure is R-3m.

[0007] The Ag-doped layered selenide semiconductor material, wherein, within a temperature range of 300 K to 700 K, has a conductivity that decreases with increasing temperature and a Seebeck coefficient that increases with increasing temperature.

[0008] In the Ag-doped layered selenide semiconductor material, the value of x is 0.01 < x ≤ 0.075.

[0009] The Ag-doped layered selenide semiconductor material has a layered morphology, and its layer growth direction is crystallographically c-axis oriented.

[0010] A method for preparing Ag-doped layered selenide semiconductor material as described in this invention, comprising the steps of: S1, according to the general chemical formula Ge 0.85-x Ag x Bi 2.21 The molar ratio of Se4 is determined by weighing and mixing raw material powders of Ge, Ag, Bi, and Se to obtain a mixed powder. S2. Place the mixed powder in a quartz tube, evacuate the quartz tube, and then seal it. S3. Heat the vacuum-sealed quartz tube to cause the mixed powder inside to undergo a melting reaction; S4. Anneal the product after the molten reaction to obtain the Ag-doped selenide semiconductor material.

[0011] The method for preparing the Ag-doped layered selenide semiconductor material includes the following melting reaction: heating a vacuum-sealed quartz tube from room temperature to 900-950°C at a heating rate of 2-5°C / min, holding it at 900-950°C for 12-24 hours, and then quenching and cooling it to room temperature.

[0012] The method for preparing the Ag-doped layered selenide semiconductor material, wherein the annealing treatment includes: heating the quenched and cooled product to 540-560°C at a heating rate of 2-5°C / min, holding it at 540-560°C for 3-5 days, and then cooling it to room temperature in the furnace.

[0013] The method for preparing the Ag-doped layered selenide semiconductor material further includes, after step S4, grinding and sieving the material obtained by annealing to obtain the Ag-doped selenide semiconductor material in powder form.

[0014] The method for preparing the Ag-doped layered selenide semiconductor material further includes: hot-pressing and sintering the powdered Ag-doped selenide semiconductor material to obtain a dense bulk material; the hot-pressing and sintering temperature is 440-460℃, the pressure is 45-55 MPa, and the holding time is 25-35 minutes.

[0015] Beneficial effects: In the Ag-doped selenide semiconductor material and preparation method provided by this invention, through Ge 0.85 Bi 2.21 Introducing a specific amount (0 < x ≤ 0.075) of Ag atoms into the Se4 lattice, while maintaining the rhombohedral (R-3m) layered crystal structure, Ag... + Partially replaces Ge 2+ This method alters the carrier concentration and scattering mechanism of the material, causing the absolute value of the Seebeck coefficient to increase significantly with increasing temperature in the 300-700 K range, while the electrical conductivity decreases moderately, thereby effectively improving the power factor and thermoelectric figure of merit. This material significantly enhances the thermoelectric performance of the original system, and the preparation method is simple and the parameters are controllable, making it suitable for industrial production. Attached Figure Description

[0016] Figure 1 Ge prepared in Example 1 of this application 0.8 Ag 0.05 Bi 2.21 Optical photograph of Se4 material.

[0017] Figure 2 Ge prepared in Example 1 of this application 0.8 Ag 0.05 Bi 2.21 Powder X-ray diffraction pattern of Se4 material.

[0018] Figure 3 Ge prepared in Example 1 of this application 0.8 Ag 0.05 Bi 2.21 Scanning electron microscope image of the microstructure of Se4 material.

[0019] Figure 4 Ge prepared in Example 1 of this application 0.8 Ag 0.05 Bi 2.21 X-ray energy spectrum of Se4 material.

[0020] Figure 5 Ge prepared in Example 1 of this application 0.8 Ag 0.05 Bi 2.21 Atomic resolution structural diagram of Se4 material

[100] projected along the direction.

[0021] Figure 6 Ge prepared in Example 2 of this application 0.825 Ag 0.025 Bi 2.21 Powder X-ray diffraction pattern of Se4 material.

[0022] Figure 7 Ge prepared in Example 2 of this application 0.825 Ag 0.025 Bi 2.21 X-ray energy spectrum of Se4 material.

[0023] Figure 8 Ge prepared in Example 3 of this application 0.775 Ag 0.075 Bi 2.21 Powder X-ray diffraction pattern of Se4 material.

[0024] Figure 9 Ge prepared in Example 3 of this application 0.775 Ag 0.075 Bi 2.21 X-ray energy spectrum of Se4 material.

[0025] Figure 10 Ge prepared for Comparative Example 1 of this application 0.75 Ag 0.1 Bi 2.21 Scanning electron microscope backscattered electron image of Se4 material.

[0026] Figure 11 Ge prepared for Comparative Example 2 of this application 0.85 Bi 2.21 Powder X-ray diffraction pattern of Se4 material.

[0027] Figure 12 The graphs show the Seebeck coefficient of the materials in Examples 1, 2, 3 and Comparative Example 2 of this application as a function of temperature.

[0028] Figure 13 The graphs show the changes in electrical conductivity of the materials in Examples 1, 2, 3 and Comparative Example 2 of this application as a function of temperature.

[0029] Figure 14 The above are comparative graphs showing the thermoelectric figure of merit of the materials in Examples 1, 2, 3 and Comparative Example 2 of this application as a function of temperature. Detailed Implementation

[0030] This invention provides an Ag-doped layered selenide semiconductor material and its preparation method. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0031] This invention provides an Ag-doped layered selenide semiconductor material, wherein the general chemical formula of the Ag-doped layered selenide semiconductor material is Ge. 0.85-x Ag x Bi 2.21 Se4, where x represents the mole fraction of Ag doping, and its value ranges from 0 to x ≤ 0.075, and the Ag-doped layered selenide semiconductor material has a rhombohedral phase crystal structure.

[0032] Due to Ag + Ions and Ge 2+ Due to differences in ion valence states and ionic radii, this invention effectively modulates the carrier concentration and carrier scattering mechanism in the material by introducing Ag atoms to partially replace Ge atoms. While maintaining the original layered structure, it significantly improves the absolute value of the Seebeck coefficient. This results in the absolute value of the Seebeck coefficient increasing with temperature in the 300-700 K temperature range, while the electrical conductivity decreases moderately with increasing temperature, thereby optimizing the power factor and ultimately improving the thermoelectric figure of merit (ZT) of the material. This solves the problem of Ge... 0.85 Bi 2.21 Se4-based materials suffer from low Seebeck coefficients and poor thermoelectric properties.

[0033] In some embodiments, the space group of the rhombohedral phase crystal structure is R-3m. In this embodiment, the R-3m space group assignment indicates that the material possesses a specific atomic arrangement symmetry, which is the crystallographic basis for maintaining the layered structure and stable thermoelectric properties of the material. Through X-ray diffraction analysis and indexing the diffraction pattern, it can be determined that all diffraction peaks belong to the R-3m space group. For example, the (00l) series peaks (l=3, 6, 9…) appearing in the diffraction pattern are typical characteristics of the layered structure in the R-3m space group. Combined with subsequent atomic resolution structural images (such as…), Figure 5 As shown in the figure, the layered atomic arrangement stacked along the c-axis can be clearly observed, further confirming the R-3m space group structure.

[0034] In some implementations, to achieve better electrical performance modulation while ensuring the formation of a single-phase solid solution, x satisfies 0.01 < x ≤ 0.075. When the x value is too low, the Ag doping effect may not be significant; when the x value exceeds 0.075 (e.g., x = 0.1), it easily leads to the precipitation of a second phase, disrupting the single-phase nature of the material and thus affecting the stability and repeatability of thermoelectric properties. Within the range of 0.01 < x ≤ 0.075, Ag atoms can be effectively incorporated into Ge. 0.85 Bi 2.21 A stable solid solution is formed in the Se4 lattice. For example, when x is 0.025, Ag atoms are uniformly distributed at an appropriate concentration, effectively regulating carrier concentration without causing excessive lattice distortion or phase separation. By designing a value of 0.01 < x ≤ 0.075, the material's structural uniformity and performance stability are ensured, allowing the regulatory effect of Ag doping to be fully utilized. To further balance the Seebeck coefficient and conductivity within the range of 0.01 < x ≤ 0.075 to obtain more balanced and superior thermoelectric performance, x satisfies 0.02 ≤ x ≤ 0.06. Within this narrower range, the amount of Ag doping can more finely regulate carrier behavior, resulting in a higher power factor. For example, when x is 0.05, the introduction of Ag places the carrier concentration in an ideal range, ensuring a high baseline conductivity while significantly improving the Seebeck coefficient, thereby maximizing the power factor.

[0035] In some embodiments, a method for preparing Ag-doped layered selenide semiconductor material as described in this invention is also provided, comprising the steps of: S1, according to the general chemical formula Ge 0.85-x Ag x Bi 2.21 The molar ratio of Se4 is determined by weighing and mixing raw material powders of Ge, Ag, Bi, and Se to obtain a mixed powder. In this step, the mass purity of all raw material powders is preferably not less than 99.99%. The mixing can be done by hand grinding and mixing in an agate mortar for 10-20 minutes, or by mixing in a three-dimensional mixer for 1-2 hours to ensure that each component is evenly distributed. S2. Place the mixed powder in a quartz tube, evacuate the quartz tube, and seal it. This step aims to remove air and moisture to prevent oxidation or side reactions of the raw materials during subsequent high-temperature processes. To ensure sufficient vacuum within the quartz tube to effectively prevent oxidation and avoid rupture during encapsulation, step S2 involves evacuating to a vacuum level ≤1 Pa. Specifically, connect the quartz tube containing the mixed powder to a molecular pump unit and evacuate until the pressure gauge reads 5 × 10⁻⁶ Pa. -3 Below Pa, the quartz tube is then sealed under vacuum using an oxyhydrogen flame or a propane torch. These steps create an oxygen-free environment for the subsequent high-temperature reaction, ensuring the purity of the product and the smooth progress of the reaction.

[0036] S3. The vacuum-sealed quartz tube is heated to cause the mixed powder inside to melt; the high temperature causes Ge, Ag, Bi and Se elements to diffuse into each other and undergo chemical reactions to form a homogeneous melt. S4. Anneal the product after the molten reaction to obtain the Ag-doped selenide semiconductor material. The annealing process helps to eliminate the internal stress generated by high-temperature quenching, promotes atomic rearrangement, and enables the material to be fully homogenized and stabilized at the metastable phase line temperature, ultimately obtaining a single-phase, well-crystallized target material.

[0037] In this embodiment, to control the reaction rate, ensure the raw materials are fully melted and react uniformly, and avoid pressure imbalance inside and outside the quartz tube or violent volatilization of selenium due to excessively rapid heating, step S3 includes the following melting reaction: heating the vacuum-sealed quartz tube from room temperature to 900-950°C at a heating rate of 2-5°C / min, holding it at 900-950°C for 12-24 hours, and then quenching and cooling it to room temperature. For example, the quartz tube is placed vertically in a single-temperature zone muffle furnace, heated to 920°C at a rate of 3°C / min, and held at this temperature for 18 hours. After the holding period, the quartz tube is quickly removed from the furnace and quenched in cold water to rapidly solidify the high-temperature melt, forming a metastable alloy ingot. These steps achieve complete melting and preliminary alloying of the raw materials, and quenching yields a homogeneous intermediate product, laying the foundation for subsequent annealing.

[0038] In this embodiment, to transform the metastable ingot obtained by high-temperature quenching into a thermodynamically stable target crystalline phase, and to eliminate internal stress and improve crystal quality, step S4 includes the annealing treatment comprising: heating the quenched and cooled product to 540-560°C at a heating rate of 2-5°C / min, holding it at 540-560°C for 3-5 days, and then furnace cooling to room temperature. For example, the quenched quartz tube (containing the ingot) is placed back into a muffle furnace, heated to 550°C at a rate of 4°C / min, and held at this temperature for 4 days; after the holding period, the heating power is turned off, and the furnace body and the sample are allowed to cool slowly to room temperature together (i.e., furnace cooling). This long-term low-temperature annealing process is to obtain a single-phase Ge with a good layered structure. 0.85-x Ag x Bi 2.21 The key to Se4 materials lies in the annealing process, which promotes atomic diffusion and orderly arrangement, ultimately yielding Ag-doped selenide semiconductor materials with a complete crystal structure and a single phase.

[0039] In some embodiments, to obtain a powder material that is easy to characterize or use as a precursor, after step S4, the annealed material is further ground and sieved to obtain the Ag-doped selenide semiconductor material in powder form. Specifically, the annealed block material is taken out of the quartz tube, thoroughly ground in an agate mortar, and then sieved using a standard sieve (such as a 100-mesh or 200-mesh sieve), and the powder passing through the sieve is collected. This powder can be used for structural characterization such as X-ray diffraction (XRD) and scanning electron microscopy (SEM). Standardized powder samples can be obtained through the above steps, facilitating batch analysis and initial performance screening of the material.

[0040] In some embodiments, to process the powder material into a high-density bulk suitable for performance testing and device integration, the method further includes: hot-pressing the Ag-doped selenide semiconductor material in powder form to obtain a dense bulk; the hot-pressing sintering temperature is 440-460°C, the pressure is 45-55 MPa, and the holding time is 25-35 minutes. For example, sieved powder is placed into a graphite mold with an inner diameter of 10 mm and then placed in a rapid hot-pressing sintering furnace. Under an argon protective atmosphere, the temperature is increased to 450°C at a rate of 50°C / min, while a uniaxial pressure of 50 MPa is applied, and the temperature is held at 450°C and 50 MPa for 30 minutes. After the holding time, the pressure is released and the furnace is cooled to room temperature. This hot-pressing process is carried out at a relatively low temperature (below the material's melting point but above its recrystallization temperature) and high pressure, achieving tight bonding between powder particles through plastic flow and diffusion creep mechanisms, greatly reducing porosity and improving the density and electrical conductivity of the bulk material. Through the above technical solution, this embodiment realizes the preparation of high-performance dense bulk materials from powder, which is a key step for materials to move towards practical applications.

[0041] The present invention will be further explained and illustrated below through specific embodiments: Example 1 A method for preparing an Ag-doped layered selenide semiconductor material, comprising: Step 1, Ingredient Preparation and Packaging: Using germanium powder (99.99% purity), bismuth powder (99.99% purity), selenium powder (99.99% purity), and silver powder (99.99% purity) as raw materials, for the chemical formula Ge... 0.8 Ag 0.05 Bi 2.21 Se4 was prepared by weighing and mixing germanium powder, silver powder, bismuth powder and selenium powder in a molar ratio of 0.8:0.05:2.21:4 in a quartz tube, evacuating the vacuum to ≤1 Pa, and then sealing the quartz tube containing the sample using a flame sealing device.

[0042] Step 2, High-temperature melting and sintering: The vacuum-sealed quartz tube is placed vertically in a single-temperature zone pit furnace with the quartz tube near the thermocouple. The temperature is increased from room temperature to 950°C at a rate of 5°C / min and held at this temperature for 12 hours. After the holding period, the tube is quenched and cooled to room temperature.

[0043] Step 3, Material Annealing: The product obtained after the molten reaction in Step 2 is heated to 550℃±10℃ at a heating rate of 5℃ / min and held at this temperature for 4 days; then cooled to room temperature in the furnace, and then the material is taken out from the quartz tube.

[0044] Step 4: Grind the annealed ingot thoroughly into a fine powder in an agate mortar and pass it through a 100-mesh stainless steel sieve. Weigh an appropriate amount of powder and place it into a graphite mold (10 mm inner diameter), then perform hot-press sintering in a rapid hot-pressing furnace. The sintering process is as follows: heat to 450°C at a heating rate of 100°C / min, hold for 30 minutes, and apply and maintain a uniaxial pressure of 50 MPa during the holding stage. After sintering, cool to room temperature with the furnace, demold to obtain a dense cylindrical sample for subsequent performance testing.

[0045] The morphology, chemical composition, and structure of the sample prepared in Example 1 were analyzed and characterized by optical microscopy, X-ray diffraction, scanning electron microscopy, X-ray energy dispersive spectroscopy, and transmission electron microscopy. Specific characterization results are as follows: Figures 1 to 5 As shown. Among them, the powder X-ray diffraction pattern was analyzed (…). Figure 2 ) and X-ray energy spectrum ( Figure 4 The material obtained under these conditions was determined to be a single-phase material, and its chemical composition was Ge. 0.8 Ag 0.05 Bi 2.21 Se4; by indexing its X-ray diffraction pattern ( Figure 2 ), and obtained microscopic morphology images using scanning electron microscopy (SEM). Figure 3 The diffraction peak was determined to be Ge. 0.85 Bi 2.21 The (00l) crystal plane of the Se4 crystal structure indicates that this material exhibits a layered morphology in its macroscopic structure, with the lamellar growth direction aligned with the crystallographic c-axis. Furthermore, high-angle annular dark-field images obtained using electron microscopy (…) Figure 5 This further demonstrates that the obtained material has a distinct layered structure, and its crystal structure is similar to that of Ge. 0.85 Bi 2.21 The structure is consistent with Se4.

[0046] A systematic study of the thermoelectric properties of the material in this embodiment revealed that Ge 0.8 Ag 0.05 Bi 2.21The electrical conductivity of Se4 gradually decreases with increasing temperature. At 300 K, its conductivity is 4.8 × 10⁻⁶. 4 S m -1 Its conductivity at 700K is 3.3 × 10⁻⁶. 4 S m -1 The Seebeck coefficient increases significantly with increasing temperature, reaching -57.6 μV at 300 K. K -1 Its Seebeck coefficient at 700K is -125.5μV. K -1 The negative sign indicates that the material is still n-type conductive, but its absolute value is significantly increased compared to the undoped sample (Comparative Example 2), indicating that Ag doping effectively suppresses the electron concentration. Calculations show that the material achieves a thermoelectric figure of merit (ZT) of 0.47 at 700 K.

[0047] Example 2 A method for preparing an Ag-doped layered selenide semiconductor material, comprising: Step 1, Ingredient Preparation and Packaging: Using germanium powder (99.99% purity), bismuth powder (99.99% purity), selenium powder (99.99% purity), and silver powder (99.99% purity) as raw materials, for the chemical formula Ge... 0.825 Ag 0.025 Bi 2.21 Se4 was prepared by weighing and mixing germanium powder, silver powder, bismuth powder and selenium powder in a molar ratio of 0.825:0.025:2.21:4 in a quartz tube, evacuating the tube to ≤1 Pa, and then sealing the quartz tube containing the sample using a flame sealing device.

[0048] Step 2, High-temperature melting and firing: The vacuum-sealed quartz tube is placed vertically in a single-temperature zone pit furnace with the quartz tube near the thermocouple. The temperature is increased from room temperature to 950°C at a rate of 5°C / min. The temperature is held at this temperature for 12 hours. After the holding period, the tube is quenched and cooled to room temperature.

[0049] Step 3, Material Annealing: The product obtained after the molten reaction in Step 2 is heated to 550 ℃±10℃ at a heating rate of 5 ℃ / min and held at this temperature for 3 days; then cooled to room temperature in the furnace and the material is taken out from the quartz tube.

[0050] The prepared material was analyzed using X-ray diffraction and X-ray energy dispersive spectroscopy, and the results are as follows: Figure 6 and Figure 7 As shown, the XRD pattern reveals a rhombohedral phase structure with no impurity peaks; EDS spectroscopy confirms its chemical composition as Ge. 0.825 Ag 0.025 Bi 2.21 Se4.

[0051] A systematic study of the thermoelectric properties of the material in this embodiment revealed that Ge 0.825 Ag 0.025 Bi 2.21 The electrical conductivity of Se4 gradually decreases with increasing temperature. At 300 K, its conductivity is 4.4 × 10⁻⁶. 4 S m -1 Its conductivity at 700K is 2.9 × 10⁻⁶. 4 S m -1 The Seebeck coefficient increases significantly with increasing temperature, reaching -52.8 μV at 300 K. K -1 Its Seebeck coefficient at 700K is -119.6μV. K -1 Calculations show that the thermoelectric figure of merit (ZT) of this material at 700 K is 0.36.

[0052] Example 3 A method for preparing an Ag-doped layered selenide semiconductor material, comprising: Step 1, Ingredient Preparation and Packaging: Using germanium powder (99.99% purity), bismuth powder (99.99% purity), selenium powder (99.99% purity), and silver powder (99.99% purity) as raw materials, for the chemical formula Ge... 0.775 Ag 0.075 Bi 2.21 Se4 was prepared by weighing and mixing germanium powder, silver powder, bismuth powder and selenium powder in a molar ratio of 0.775:0.075:2.21:4 in a quartz tube, evacuating the tube to ≤1 Pa, and then sealing the quartz tube containing the sample using a flame sealing device.

[0053] Step 2, High-temperature melting and firing: The vacuum-sealed quartz tube is placed vertically in a single-temperature zone pit furnace with the quartz tube near the thermocouple. The temperature is increased from room temperature to 950°C at a rate of 5°C / min. The temperature is held at this temperature for 12 hours. After the holding period, the tube is quenched and cooled to room temperature.

[0054] Step 3, Material Annealing: The product obtained after the molten reaction in Step 2 is heated to 550 ℃±10℃ at a heating rate of 5 ℃ / min and held at this temperature for 3 days; then cooled to room temperature in the furnace and the material is taken out from the quartz tube.

[0055] The prepared material was analyzed using X-ray diffraction and X-ray energy dispersive spectroscopy, and the results are as follows: Figure 8 and Figure 9 As shown, the XRD pattern reveals a pure rhombohedral phase structure with no impurity peaks; EDS spectroscopy confirms its chemical composition as Ge. 0.775Ag 0.075 Bi 2.21 Se4.

[0056] A systematic study of the thermoelectric properties of the material in this embodiment revealed that Ge 0.775 Ag 0.075 Bi 2.21 The electrical conductivity of Se4 gradually decreases with increasing temperature. At 300 K, its conductivity is 3.8 × 10⁻⁶. 4 S m -1 Its conductivity at 700K is 2.6 × 10⁻⁶. 4 S m -1 The Seebeck coefficient increases significantly with increasing temperature, reaching -53.7 μV at 300 K. K -1 Its Seebeck coefficient at 700K is -125.1μV. K -1 Calculations show that the thermoelectric figure of merit (ZT) of this material at 700 K is 0.36.

[0057] Comparative Example 1 A method for preparing an Ag-doped layered selenide semiconductor material, comprising: Step 1, Ingredient Preparation and Packaging: Using germanium powder (99.99% purity), bismuth powder (99.99% purity), selenium powder (99.99% purity), and silver powder (99.99% purity) as raw materials, for the chemical formula Ge... 0.75 Ag 0.1 Bi 2.21 Se4 was prepared by weighing and mixing germanium powder, silver powder, bismuth powder and selenium powder in a molar ratio of 0.75:0.1:2.21:4 in a quartz tube, evacuating the vacuum to ≤1 Pa, and then sealing the quartz tube containing the sample using a flame sealing device. Step 2, High-temperature melting and firing: The vacuum-sealed quartz tube is placed vertically in a single-temperature zone pit furnace, with the quartz tube near the thermocouple. The temperature is increased from room temperature to 950°C at a rate of 5°C / min, and held at this temperature for 12 hours. Step 3, Material Annealing: The product obtained after the molten reaction in Step 2 is cooled to 550℃±10℃ at a cooling rate of 5℃ / min and held at this temperature for 3 days; then cooled to room temperature in the furnace and the material is taken out from the quartz tube.

[0058] For the material prepared in Comparative Example 1, the morphology, chemical composition, and structure of the obtained material were analyzed and characterized by optical microscopy, X-ray diffraction, scanning electron microscopy, and X-ray energy dispersive spectroscopy. Although the main diffraction peaks in the XRD pattern (not shown) still correspond to the rhombohedral phase and no obvious impurity phase peaks appeared, observations using the backscattered electron (BSE) mode of the scanning electron microscope (e.g., Figure 10 As shown in the image, numerous bright white and dark black regions are clearly visible in the matrix. Combined with EDS analysis, the bright white regions are the matrix phase, and the dark black regions are the Ge-rich phase. This indicates that when the Ag doping concentration exceeds 0.075%, the solid solubility limit is breached, and Ag cannot fully enter the Ge sites, leading to the precipitation of some atoms in the system as a second phase. The presence of the second phase introduces complex interfaces, strain, and scattering centers, masking or interfering with the intrinsic doping effects, thereby severely damaging the material's homogeneity and electrical transport properties.

[0059] Comparative Example 2 A method for preparing a selenide semiconductor material, comprising: Step 1, Ingredient Preparation and Packaging: Using germanium powder (99.99% purity), bismuth powder (99.99% purity), and selenium powder (99.99% purity) as raw materials, for the chemical formula Ge... 0.85 Bi 2.21 Se4 was prepared by weighing and mixing germanium powder, bismuth powder and selenium powder in a molar ratio of 0.85:2.21:4 in a quartz tube, evacuating to ≤1 Pa, and then sealing the quartz tube containing the sample using a flame sealing device. Step 2, High-temperature melting and sintering: The vacuum-sealed quartz tube is placed vertically in a single-temperature zone pit furnace with the quartz tube near the thermocouple. The temperature is increased from room temperature to 950°C at a rate of 5°C / min and held at this temperature for 12 hours. After the holding period, the tube is quenched and cooled to room temperature.

[0060] Step 3, Material Annealing: The product obtained after the molten reaction in Step 2 is heated to 550℃±10℃ at a heating rate of 5℃ / min and held at this temperature for 3 days; then cooled to room temperature in the furnace, and then the material is taken out from the quartz tube.

[0061] The chemical composition of the material prepared in Comparative Example 2 was analyzed and characterized by X-ray diffraction, and the results are as follows: Figure 11 As shown, this proves that it is a single-phase material.

[0062] A systematic study of the thermoelectric properties of the material in Comparative Example 2 revealed that Ge 0.85 Bi 2.21 The electrical conductivity of Se4 gradually decreases with increasing temperature. At room temperature, its electrical conductivity is 6.8 × 10⁻⁶. 4 S m -1Its conductivity at 700K is 3.8 × 10⁻⁶. 4 S m -1 The Seebeck coefficient increases significantly with increasing temperature, reaching -28.7 μV at room temperature. K -1 Its Seebeck coefficient at 700K is -93.3 μV. K -1 Calculations show that the ZT value of this material is only 0.32 at 700 K.

[0063] The thermoelectric performance data from Examples 1-3 and Comparative Examples 1-2 show that when the Ag doping amount x is in the range of 0 < x ≤ 0.075 (as in Examples 1, 2, and 3), the obtained materials are all single-phase. Figure 2 , 6 (as shown in Figure 8), and its Seebeck coefficient absolute value is significantly improved compared to the undoped Comparative Example 2 material (e.g., Figure 12 As shown), while the conductivity remains on the same order of magnitude (e.g. Figure 13 As shown), this significantly improves the power factor and the final thermoelectric figure of merit (ZT) (e.g. Figure 14 (As shown), the reason lies in the appropriate amount of Ag + Replace Ge 0.85 Bi 2.21 Ge in Se4 2+ This introduces additional hole carriers and alters the band structure and carrier scattering mechanism, thereby significantly improving the Seebeck coefficient without excessively sacrificing conductivity. In Comparative Example 1, when x = 0.1 exceeds the range of this application, a second phase appears in the material (such as...). Figure 10 As shown in the figure, the destruction of the single-phase nature leads to uncontrollable performance, demonstrating the importance of the range x≤0.075 in the claims of this application for obtaining stable, high-performance single-phase materials.

[0064] The performance of the samples in Example 1, Example 2, Example 3, and Comparative Example 2 was further compared, including the Seebeck coefficient (e.g., Figure 12 As shown), conductivity (e.g.) Figure 13 (as shown) and thermoelectric figure of merit (e.g.) Figure 14 As shown), compared to the original sample without Ag doping, Ge 0.8 Ag 0.05 Bi 2.21 The Seebeck coefficient and thermoelectric figure of merit of the Se4 sample were significantly improved (the thermoelectric figure of merit increased from 0.32 in the undoped sample to 0.47 in the doped sample at 700 K), demonstrating the effectiveness of Ag doping in regulating the thermoelectric properties of this type of semiconductor material.

[0065] It is understood that those skilled in the art can make equivalent substitutions or modifications to the technical solution and inventive concept of the present invention, and all such substitutions or modifications should fall within the protection scope of the appended claims.

Claims

1. An Ag-doped layered selenide semiconductor material, characterized in that, The general chemical formula of the Ag-doped layered selenide semiconductor material is Ge. 0.85-x Ag x Bi 2.21 Se4, where x represents the mole fraction of Ag doping, and its value ranges from 0 to x ≤ 0.075, and the Ag-doped layered selenide semiconductor material has a rhombohedral phase crystal structure.

2. The Ag-doped layered selenide semiconductor material according to claim 1, characterized in that, The space group of the rhombohedral phase crystal structure is R-3m.

3. The Ag-doped layered selenide semiconductor material according to claim 1, characterized in that, In the temperature range of 300 K to 700 K, the conductivity of the Ag-doped layered selenide semiconductor material decreases with increasing temperature, while the absolute value of its Seebeck coefficient increases with increasing temperature.

4. The Ag-doped layered selenide semiconductor material according to claim 1, characterized in that, The value of x is 0.01 < x ≤ 0.

075.

5. The Ag-doped layered selenide semiconductor material according to claim 1, characterized in that, The Ag-doped layered selenide semiconductor material has a layered morphology, and its layer growth direction is crystallographically c-axis oriented.

6. A method for preparing the Ag-doped layered selenide semiconductor material as described in any one of claims 1-5, characterized in that, Including the following steps: S1, according to the general chemical formula Ge 0.85-x Ag x Bi 2.21 The molar ratio of Se4 (0 < x ≤ 0.075) is determined by weighing and mixing raw material powders of Ge, Ag, Bi, and Se to obtain a mixed powder. S2. Place the mixed powder in a quartz tube, evacuate the quartz tube, and then seal it. S3. Heat the vacuum-sealed quartz tube to cause the mixed powder inside to undergo a melting reaction; S4. Anneal the product after the molten reaction to obtain the Ag-doped selenide semiconductor material.

7. The method for preparing the Ag-doped layered selenide semiconductor material according to claim 6, characterized in that, The melting reaction includes: heating the vacuum-sealed quartz tube from room temperature to 900-950°C at a heating rate of 2-5°C / min, holding it at 900-950°C for 12-24 hours, and then quenching and cooling it to room temperature.

8. The method for preparing the Ag-doped layered selenide semiconductor material according to claim 7, characterized in that, The annealing process includes: heating the quenched and cooled product to 540-560℃ at a heating rate of 2-5℃ / min, holding it at 540-560℃ for 3-5 days, and then cooling it to room temperature in the furnace.

9. The method for preparing the Ag-doped layered selenide semiconductor material according to any one of claims 6-8, characterized in that, After step S4, the material obtained by annealing is further ground and sieved to obtain the Ag-doped selenide semiconductor material in powder form.

10. The method for preparing the Ag-doped layered selenide semiconductor material according to claim 9, characterized in that, Also includes: The Ag-doped selenide semiconductor material in powder form is hot-pressed and sintered to obtain a dense bulk material; the hot-pressing and sintering temperature is 440-460℃, the pressure is 45-55 MPa, and the holding time is 25-35 minutes.

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