Rare earth doped SnTe material with high Seebeck coefficient and special microstructure

Abstract

The invention relates to the technical field of thermoelectric material preparation, and particularly discloses a rare earth doped SnTe material with a high Seebeck coefficient and a special microstructure, which is prepared by the following steps: S1, in a glove box in an inert gas atmosphere, weighing Sn, Te, Cu and Ce according to a preset stoichiometric ratio, and mixing to obtain a mixed raw material; s2, performing sealing treatment on the mixed raw material to obtain a sealing assembly; s3, treating the sealing assembly to obtain a cast ingot; s4, the cast ingot is ground into powder in the inert gas atmosphere, and raw material powder is obtained; s5, the raw material powder is subjected to spark plasma sintering treatment, and a sintered body is obtained; s6, cutting the sintered body to obtain a sample; the rare earth doped SnTe material with a high Seebeck coefficient and a special microstructure is prepared through collaborative doping of Ce and Cu, collaborative optimization of electrical performance improvement and thermal performance reduction is achieved, the thermoelectric figure of merit ZT is finally improved, and the material has better energy conversion efficiency and application potential in the thermoelectric conversion field.

Description

Technical Field

[0001] This invention belongs to the field of thermoelectric material preparation technology, specifically relating to a rare earth-doped SnTe material with a high Seebeck coefficient and a special microstructure. Background Technology

[0002] Thermoelectric materials, as functional materials capable of directly converting heat energy into electrical energy, have significant application value in fields such as industrial waste heat recovery, waste heat power generation, and solid-state refrigeration. Their core performance is measured by the thermoelectric figure of merit ZT (ZT = S²σT / κ, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature, and κ is the total thermal conductivity). A higher ZT value indicates higher energy conversion efficiency. SnTe, due to its abundant raw material reserves, low cost, and suitable band structure, is considered one of the most promising mid-temperature thermoelectric materials and has become a research hotspot in recent years.

[0003] However, the thermoelectric properties of pure SnTe have significant limitations, restricting its practical applications. On the one hand, intrinsic defects in pure SnTe (such as Sn vacancies) lead to excessively high carrier concentrations, resulting in a low Seebeck coefficient, which in turn limits the improvement of the power factor. On the other hand, its high lattice thermal conductivity, mainly due to weak phonon scattering in the lattice, leads to significant heat loss, ultimately making it difficult for the ZT value of pure SnTe to meet the requirements for efficient thermoelectric conversion.

[0004] To improve the thermoelectric properties of SnTe, existing technologies often employ strategies such as element doping, solid solution formation, or microstructure control. However, these approaches still have several shortcomings: First, single-element doping makes it difficult to simultaneously optimize both electrical and thermal transport properties. For example, while some doping elements can increase the Seebeck coefficient, they can significantly reduce electrical conductivity, or vice versa. Second, research on rare-earth element doping in SnTe is relatively scarce, and existing doping processes often result in low solid solubility of rare-earth elements in the crystal lattice, or even the formation of impurity phases, which disrupts the crystal structure stability of SnTe and degrades the material's properties. Third, existing preparation methods (such as traditional melt-annealing or ordinary sintering processes) cannot precisely control the microstructure of the material (such as lattice distortion, grain size, and defect density), leading to uneven distribution of doping elements and coarse grains. This makes it difficult to effectively enhance phonon scattering to reduce lattice thermal conductivity, and also makes it difficult to stably maintain the balance between carrier concentration and mobility required for a high Seebeck coefficient.

[0005] To address this issue, this application proposes a rare-earth-doped SnTe material with a high Seebeck coefficient and a unique microstructure. Summary of the Invention

[0006] The purpose of this invention is to provide a rare earth-doped SnTe material with a high Seebeck coefficient and a special microstructure to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A rare-earth-doped SnTe material with a high Seebeck coefficient and a special microstructure is prepared by the following steps:

[0009] S1. In a glove box with an inert gas atmosphere, Sn, Te, Cu and Ce are weighed and mixed according to a preset stoichiometric ratio to obtain a mixed raw material;

[0010] S2. Transfer the mixed raw materials to a graphite crucible, then place the graphite crucible inside a quartz glass tube, and seal the quartz glass tube to obtain a sealing assembly.

[0011] S3. The sealing assembly is placed in a heating device and subjected to heating, heat preservation, cooling and annealing treatments to obtain an ingot;

[0012] S4. Grind the ingot into powder under an inert gas atmosphere to obtain raw material powder;

[0013] S5. The raw material powder is placed in a graphite mold and subjected to spark plasma sintering treatment to obtain a sintered body;

[0014] S6. The sintered body is cut and processed to obtain a rare earth-doped SnTe material sample for electrical performance testing.

[0015] Preferably, in step S1, the preset stoichiometric ratio is Sn. 1-x Ce x Cu 0.1 Te 1.05 Where x = 0.01, 0.02, 0.03, 0.04; the purity of Sn, Te, Cu and Ce is 99.99%.

[0016] Preferably, in step S1, the inert gas atmosphere is an argon atmosphere.

[0017] Preferably, in step S2, the sealing process is performed using an oxyhydrogen flame gun to seal the tube.

[0018] Preferably, in step S3, the heating device is a muffle furnace;

[0019] The specific process of heating, holding, cooling and annealing is as follows: heating from room temperature to 1273K over 10 hours, holding at 1273K for 10 hours, cooling down to 923K over 8 hours, annealing at 923K for 24 hours, and then slowly cooling to room temperature.

[0020] Preferably, in step S4, the grinding is carried out in a glove box under an argon atmosphere.

[0021] Preferably, in step S5, the inner diameter of the graphite mold is 12.7 mm;

[0022] The process parameters for the spark plasma sintering treatment are as follows: under an axial pressure of 50 MPa, the temperature is raised from room temperature to 573 K in 5 minutes, then raised to 853 K in 3 minutes, and held for 5 minutes.

[0023] Preferably, in step S6, the cutting process processes the sintered body into a long strip shape.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] (1) From the perspective of crystal structure, the doping of Ce and Cu in this invention does not change the original crystal structure of SnTe. It only forms a stable solid solution by regulating the lattice constant, which not only ensures the structural integrity of the matrix material, but also realizes the effective occupancy of doped atoms in the lattice, providing a structural basis for the directional regulation of material properties. In terms of electrical transport performance, doping can achieve synergistic optimization of Seebeck coefficient and conductivity by regulating carrier concentration and mobility. The introduction of Ce can effectively regulate the transport behavior of carriers by replacing defects or energy level structures formed by lattice sites, so that the material can maintain a high power factor over a wide temperature range and improve the power output capability.

[0026] (2) In terms of thermal transport performance, the mass difference and ionic radius mismatch between Ce and Sn can significantly enhance phonon-impurity scattering and effectively suppress lattice thermal conductivity. Simultaneously, the decoupling and regulation of electrical and thermal transport reduces the total thermal conductivity, decreasing heat loss during thermoelectric conversion and creating conditions for improving energy conversion efficiency. From the perspective of comprehensive thermoelectric performance, the synergistic doping of Ce and Cu achieves synergistic optimization of improved electrical performance (power factor) and reduced thermal performance (thermal conductivity), ultimately improving the thermoelectric figure of merit (ZT) and giving the material superior energy conversion efficiency and application potential in the thermoelectric conversion field. This doping regulation strategy provides a reference for the performance optimization of other thermoelectric materials, namely, achieving precise regulation of electrical and thermal transport performance through multi-element synergistic doping, balancing the material's electrical output and heat loss, thereby improving overall functional characteristics. Attached Figure Description

[0027] Figure 1 This is a flowchart of a method for preparing rare-earth-doped SnTe materials with high Seebeck coefficient and special microstructure according to the present invention;

[0028] Figure 2 Sn of the present invention1-x Ce x Cu 0.1 Te 1.05 X-ray diffraction (XRD) pattern of the sample at room temperature after sintering;

[0029] Figure 3 Sn, as an embodiment of the present invention 0.97 Ce 0.03 Cu 0.1 Te 1.05 SEM images of the samples and corresponding EDS analysis plots;

[0030] Figure 4 Sn, as an embodiment of the present invention 0.97 Ce 0.03 Cu 0.1 Te 1.05 FESEM images and corresponding EDS analysis plots of the samples;

[0031] Figure 5 Sn, as an embodiment of the present invention 0.97 Ce 0.03 Cu 0.1 Te 1.05 FESEM images and corresponding EDS analysis plots of the samples;

[0032] Figure 6 Sn of the present invention 1-x Ce x Cu 0.1 Te 1.05 The Seebeck coefficient (S) of the sample varies with temperature.

[0033] Figure 7 Sn of the present invention 1-x Ce x Cu 0.1 Te 1.05 A bar chart comparing the Seebeck coefficient (S) of the sample with that of other element-doped SnTe-based materials at 823 K.

[0034] Figure 8 Sn of the present invention 1-x Ce x Cu 0.1 Te 1.05 Curves showing the variation of total thermal conductivity (K) and lattice thermal conductivity (Kl) of the sample with temperature; Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0036] Example 1:

[0037] Please see Figure 1 As shown, a rare-earth-doped SnTe material with a high Seebeck coefficient and a special microstructure is presented:

[0038] Experimental materials and equipment:

[0039] The reagents required for the experiment are shown in Table 1 below:

[0040] Table 1

[0041] Reagent Name (Chemical Formula) purity Manufacturers Tellurium (Te) 99.99% Tianjin Lassvet Chemical Trading Co., Ltd. Tin (Sn) 99.99% Shanghai McLean Biochemical Technology Co., Ltd. Copper (Cu) 99.99% Beijing Innocare Technology Co., Ltd. Cerium (Ce) 99.99% Shanghai Titan Technology Co., Ltd.

[0042] The experimental instruments and equipment used in the experiment are shown in Table 2 below:

[0043] Table 2

[0044] name model Manufacturers glove box Super Michael Vacuum tube sealing machine system MRVS-3003 Wuhan Bailibo Muffle stove (box type) KSL-1200X Hefei Kejing Spark plasma sintering furnace KCE-FCT HPD 10 German FCT Electrical performance testing system CTA-3S Beijing KRIOU Laser thermal conductivity meter Netzsch LFA-457 Netzsch, Germany Hall effect measurement system Lake Shore 8400 Quantum Design, USA X-ray diffraction instrument Rigaku Ultima VI JapanRigaku Scanning electron microscope MIRA LMS Czech Republic TESCAN Transmission electron microscope FEI Talos F200X US FEI Electron probe JXA-8530F PLUS JapanJEOL

[0045] The specific preparation method of rare earth-doped SnTe materials is as follows:

[0046] First, in a glove box protected by an argon atmosphere, Sn (99.99%), Te (99.99%), Cu (99.99%), and Ce (99.99%) were reacted according to the chemical formula Sn 1-x Ce x Cu 0.1 Te 1.05 The mixture (x=0.01, 0.02, 0.03, 0.04) was weighed, transferred to a graphite crucible, thoroughly mixed, and then placed in a high-strength quartz glass tube. The tube was then flame-sealed using an oxyhydrogen flame torch. After sealing, it was placed in a muffle furnace and heated from room temperature to 1273 K over 10 hours, held at 1273 K for 10 hours, and then slowly cooled (8 hours) to 923 K. Annealing was performed at 923 K for 24 hours, followed by slow cooling to room temperature. The test tube was removed, broken, and the molten ingot was extracted. The ingot was ground into powder in a glove box and then subjected to spark plasma sintering (SPS) in a graphite mold with an inner diameter of 12.7 mm. The sintering process was as follows: under an axial pressure of 50 MPa, the temperature was increased from room temperature to 573 K over 5 minutes, then increased to 853 K over 3 minutes, and held for 5 minutes. After cooling, the sample was removed, and the resulting disc sample was cut into strips for electrical performance testing.

[0047] Specifically, the sample densities are shown in Table 3 below:

[0048] Table 3

[0049] sample <![CDATA[Test density (g cm -3 )]]> Relative density (%) SnTe 6.276 97.38 x=0.01 6.265 97.21 x=0.02 6.266 97.22 x=0.03 6.276 97.38 x=0.04 6.279 97.42

[0050] Specifically, the above samples were characterized and tested as follows:

[0051] 1. X-ray diffraction (XRD) analysis:

[0052] (1) Sample preparation: Take the round sample after spark plasma sintering, grind it into powder in an agate mortar (particle size ≤10μm), and remove large particles by passing it through a 200-mesh sieve;

[0053] (2) Testing instruments: X-ray diffractometer (such as Bruker D8 Advance);

[0054] (3) Test conditions: Cu target Kα radiation (λ=0.15406nm), tube voltage 40kV, tube current 40mA; scanning range 2θ=20°~80°, step size 0.02°, scanning speed 2° / min; test at room temperature, sample placed in quartz sample holder;

[0055] (4) Data analysis: The phase composition was analyzed by comparing the diffraction peaks with the SnTe standard card using MDIJade software; the lattice constant was calculated and the peak position shift was analyzed by combining the Bragg equation (2dsinθ=λ);

[0056] like Figure 2 As shown, XRD analysis revealed that the diffraction peaks of all samples matched the SnTe standard card (PDF#46-1210), indicating the absence of impurities; this suggests that Ce and Cu doping did not alter the crystal structure of SnTe. Furthermore, with increasing x, the diffraction peaks shifted to lower angles compared to the SnTe standard card, indicating an increase in lattice constants. When Ce substitutes for Sn sites in the lattice, it increases the lattice constant, which is also related to the Ce ionic radius. 3+ (1.03Å) is greater than Sn 2+（ The result is consistent with 0.93 Å. According to the Bragg equation (2dsinθ=λ), an increase in the lattice constant d leads to a decrease in the diffraction angle θ (a leftward shift of the peak), confirming that Cu and Ce elements have been successfully doped into the SnTe lattice.

[0057] 2. Scanning electron microscopy (SEM) testing and elemental distribution analysis (EDS):

[0058] like Figure 3 As shown, to further verify the distribution of Cu and Ce elements in SnTe, the SnTe after SPS sintering was subjected to further analysis. 0.97 Ce0.03 Cu 0.1 Te 1.05 The free fracture surface of the sample was vacuum-plated with platinum and tested using scanning electron microscopy (SEM) and elemental distribution analysis (EDS). The Sn content in the sample... 0.97 Ce 0.03 Cu 0.1 Te 1.05 In the analysis, Sn, Te, Cu, and Ce elements are uniformly distributed on the free fracture surface, indicating that Cu and Ce elements successfully entered SnTe and formed a stable solid solution, which is consistent with the XRD results.

[0059] like Figure 4 and Figure 5 As shown, in order to further understand the internal microstructure of the sample, Sn... 0.97 Ce 0.03 Cu 0.1 Te 1.05 The free fracture surface of the sample was characterized by field emission scanning electron microscopy (FESEM). As shown in the figure, a large number of nano-islands with a size of approximately 100-250 nm were observed to form in situ at the grain boundaries of the SnTe matrix under high-magnification scanning electron microscopy. EDS analysis showed that these nano-islands should be Cu2Te. However, in a Sn... 0.97 Ce 0.03 Cu 0.1 Te 1.05 Numerous nanospheres, approximately 100-250 nm in size, were observed to form in situ at the grain boundaries of the sample during its free fracture surface. EDS analysis revealed that these nanospheres are likely composed of Cu and Cu₂Te.

[0060] 3. Seebeck coefficient (S) test:

[0061] (1) Sample preparation: Fix the electrodes at both ends of the long strip sample (approximately 3mm×3mm×10mm in size) with silver paste and place it on the sample stage protected by inert gas;

[0062] (2) Testing instruments: Electrical performance testing system (such as CTA-3S);

[0063] (3) Test conditions:

[0064] Temperature range: 300K~900K, heating rate 5K / min, holding time at each temperature point for 10min;

[0065] Atmosphere: Argon (99.99% purity) protection, flow rate 20 mL / min;

[0066] Seebeck coefficient: The steady-state temperature difference method was used, with a temperature difference of 5-10K applied across the two ends of the sample, and the ratio of thermoelectric potential difference to temperature difference was recorded.

[0067] Electrical conductivity: The resistance of the sample at different temperatures was measured using the four-probe method, and the resistance was calculated in combination with the sample dimensions (cross-sectional area and length) (σ=L / (R・S), where L is the electrode spacing, R is the resistance, and S is the cross-sectional area).

[0068] (4) Data recording: Real-time acquisition of S value (μV / K) at each temperature point.

[0069] The results are as follows Figure 6 As shown, the Seebeck coefficient (S) of all samples increases with increasing temperature, exhibiting highly degenerate p-type semiconductor characteristics. It also increases with increasing Ce doping. When the Ce doping amount reaches a certain level (x=0.04), the Seebeck coefficient decreases with increasing doping amount. Among the doped samples, the S value is highest at x=0.03, approaching 180 μV / K at 823 K, followed by x=0.04, while x=0.01 and x=0.02 are lower, all higher than undoped SnTe.

[0070] (5) Data comparison: Seebeck coefficients (S) of SnTe-based materials doped with different elements were collected in recent years.

[0071] like Figure 7 As shown, at a temperature of 823 K, Cu-Ce co-doping has the most significant effect on improving the Seebeck coefficient of SnTe-based materials. Cu and Ce have a significant effect on regulating the carrier concentration and optimizing the band structure of SnTe-based thermoelectric materials, providing an effective doping strategy for optimizing the thermoelectric performance of SnTe-based thermoelectric materials.

[0072] 4. Thermal conductivity (K) test:

[0073] (1) Sample preparation: Take a circular sample with a diameter of 10 mm and a thickness of 2 mm (a sintered body obtained after spark plasma sintering), polish the surface to Ra≤0.5μm, and spray it with dry graphite spray.

[0074] (2) Testing instruments:

[0075] Laser thermal conductivity meter (e.g., Netzsch LFA467): measures thermal diffusivity (α);

[0076] Electronic densitometer: The sample density (ρ) is measured using the Archimedes water displacement method;

[0077] (3) Test conditions:

[0078] Temperature range: 300K~900K, argon atmosphere (flow rate 10mL / min).

[0079] Thermal diffusivity: Laser pulse energy 5J, 3 tests were conducted at each temperature point and the average value was taken;

[0080] Specific heat capacity (Cp): calibrated using a standard sample (Pyroceram 9606), calculated as Cp = Cpstandard × (ρstandard × αstandard) / (ρ × α);

[0081] (4) Calculation of total thermal conductivity: calculated according to K=α×ρ×Cp;

[0082] (5) Calculation of electronic thermal conductivity (Ke) and lattice thermal conductivity (KI):

[0083] Ke = L × σ × T (L is the Lorentz constant, taken as 2.45 × 10⁻⁶) -8 W・Ω / K²; T is absolute temperature);

[0084] KI = K - Ke.

[0085] like Figure 8 As shown, the total thermal conductivity (κ) of all samples decreases with increasing Ce concentration, and the total thermal conductivity of all doped samples is lower than that of the intrinsic SnTe sample. This is because the special microstructures (nano-islands and nanospheres) generated by the large amount of Cu2Te and Cu alloying enhance phonon scattering at different frequencies, resulting in a significant decrease in lattice thermal conductivity. As the temperature increases, phonon scattering intensifies, κ decreases, and therefore the overall κ decreases with temperature.

[0086] As can be seen from the crystal structure perspective, the doping of Ce and Cu does not change the original crystal structure of SnTe. It only forms a stable solid solution by regulating the lattice constant, which not only ensures the structural integrity of the matrix material, but also realizes the effective occupancy of doped atoms in the lattice, providing a structural basis for the directional regulation of material properties.

[0087] In terms of electrical transport properties, doping can achieve synergistic optimization of Seebeck coefficient and electrical conductivity by controlling carrier concentration and mobility. The introduction of Ce can effectively regulate carrier transport behavior by replacing defects or energy level structures formed by lattice sites, enabling the material to maintain a high power factor over a wide temperature range and improve its power output capability.

[0088] In terms of thermal transport properties, the mass difference and ionic radius mismatch between Ce and Sn will cause lattice distortion. The large number of nano-islands and nanospheres generated in situ can significantly enhance phonon scattering and effectively suppress lattice thermal conductivity.

[0089] From the perspective of comprehensive thermoelectric performance, a SnTe material with a high Seebeck coefficient and a special microstructure was prepared by synergistic doping of Ce and Cu. This achieved synergistic optimization of improved electrical performance (power factor) and reduced thermal performance (thermal conductivity), ultimately increasing the thermoelectric figure of merit (ZT) and giving the material superior energy conversion efficiency and application potential in the thermoelectric conversion field. This doping control strategy provides a reference for the performance optimization of other thermoelectric materials, namely, achieving precise control of electrical and thermal transport properties through multi-element synergistic doping, balancing the material's electrical energy output and heat loss, thereby improving overall functional characteristics.

[0090] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A rare-earth doped SnTe material with high Seebeck coefficient and special microstructure, characterized in that, The preparation steps of the material are as follows: S1. In a glove box in an inert gas atmosphere, Sn, Te, Cu and Ce are weighed and mixed according to a preset stoichiometric ratio to obtain mixed raw materials; S2. The mixed raw materials are transferred to a graphite crucible, and the graphite crucible is placed in a quartz glass tube, and the quartz glass tube is sealed to obtain a sealed assembly; S3. The sealed assembly is placed in a heating device, and is subjected to temperature rising, temperature keeping, temperature falling and annealing treatment to obtain an ingot; S4. The ingot is ground into powder under an inert gas atmosphere to obtain raw material powder; S5. The raw material powder is placed in a graphite mold, and is subjected to discharge plasma sintering treatment to obtain a sintered body; S6. The sintered body is cut and processed to obtain a rare earth doped SnTe material sample for electrical performance test.

2. The rare earth doped SnTe material with high Seebeck coefficient and special microstructure according to claim 1, characterized in that, In step S1, the preset stoichiometric ratio is Sn 1-x Ce x Cu 0.1 Te 1.05 wherein x = 0.01, 0.02, 0.03, 0.04; the purity of Sn, Te, Cu and Ce is 99.99%.

3. The rare earth doped SnTe material with high Seebeck coefficient and special microstructure according to claim 1, characterized in that, In step S1, the inert gas atmosphere is an argon atmosphere.

4. The rare earth doped SnTe material with high Seebeck coefficient and special microstructure according to claim 1, characterized in that, In step S2, the sealing treatment is flame sealing of the tube by using a hydrogen-oxygen flame gun.

5. The rare earth doped SnTe material with high Seebeck coefficient and special microstructure according to claim 1, characterized in that, In step S3, the heating device is a muffle furnace. The specific process of the temperature rising, temperature keeping, temperature falling and annealing treatment is as follows: from room temperature to 1273K for 10h, keeping at 1273K for 10h, then falling to 923K for 8h, annealing at 923K for 24h, and then slowly cooling to room temperature.

6. The rare earth doped SnTe material with high Seebeck coefficient and special microstructure according to claim 1, characterized in that, In step S4, the grinding is carried out in a glove box under an argon atmosphere.

7. The rare earth doped SnTe material with high Seebeck coefficient and special microstructure according to claim 1, characterized in that, In step S5, the inner diameter of the graphite mold is 12.7mm. The process parameters of the discharge plasma sintering treatment are as follows: under an axial pressure of 50MPa, from room temperature to 573K for 5min, then to 853K for 3min, and keeping for 5min.

8. The rare earth doped SnTe material with high Seebeck coefficient and special microstructure according to claim 1, characterized in that, In step S6, the cutting and processing is to process the sintered body into a long strip.

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