Bi-doped Sb2Te3 thermoelectric thin film and preparation method thereof
By using a Bi-doped Sb2Te3 thermoelectric thin film preparation method, the problems of compositional deviation and antisite defects in Sb2Te3 thin films were solved, the Seebeck coefficient and film quality were improved, and efficient thermoelectric performance was achieved.
Patent Information
- Application Number
- CN202610574491.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-04-28
- Publication Date
- 2026-07-10
AI Technical Summary
Existing Sb2Te3 thin film preparation processes suffer from problems such as compositional deviation and antisite defects, resulting in low thermoelectric performance and high preparation costs, making it difficult to simultaneously obtain high Seebeck coefficients and good film quality.
A method for preparing Bi-doped Sb2Te3 thermoelectric thin films was adopted. By heating Sb2Te3 powder and Bi powder in a vacuum chamber and controlling the matching of evaporation rate with substrate temperature, Bi-doped Sb2Te3 thermoelectric thin films were formed, thus optimizing carrier concentration and film quality.
The Bi-doped Sb₂Te₃ thin film exhibited good doping uniformity, with the Seebeck coefficient increasing from 106 μV·K⁻¹ to 173 μV·K⁻¹ and the power factor increasing to 32 μW·cm⁻¹·K⁻², significantly improving compositional consistency and structural uniformity.
Smart Images
Figure CN122373677A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of new energy materials, and in particular to a Bi-doped Sb2Te3 thermoelectric thin film and its preparation method. Background Technology
[0002] Sb₂Te₃ is a typical layered narrow bandgap semiconductor and one of the most representative P-type thermoelectric materials near room temperature. Due to its excellent electrical transport properties, low lattice thermal conductivity, and unique layered crystal structure, Sb₂Te₃ and its solid solution system have long been considered one of the most promising thermoelectric materials in the near-room temperature range.
[0003] However, the overall thermoelectric performance of current Sb₂Te₃ thin films still lags behind that of high-performance bulk materials. The main reason for this is that the thin film preparation process is more prone to problems such as compositional deviation and antisite defects, limiting the improvement of thermoelectric performance. Secondly, existing preparation methods for Sb₂Te₃ thin films often face the problem of both increased processing costs and performance degradation: on the one hand, as the film thickness increases, deposition time, energy consumption, and process control become significantly more difficult, leading to increased preparation costs; on the other hand, with increased film thickness, the film growth process is susceptible to factors such as differences in component volatilization, stress accumulation, and limited surface migration, resulting in compositional inhomogeneity, increased defects, and orientation degradation. All these factors contribute to the lower overall thermoelectric performance of Sb₂Te₃ thin films prepared by current technologies.
[0004] Although optimizing key deposition parameters and heat treatment temperature can effectively improve the crystal quality and electrical transport properties of thin films, their Seebeck coefficient remains low, which restricts further breakthroughs in thermoelectric properties.
[0005] Therefore, existing technologies need to be improved. Summary of the Invention
[0006] In view of the shortcomings of the prior art, the purpose of this invention is to provide a Bi-doped Sb2Te3 thermoelectric thin film and its preparation method, which aims to solve the technical problems of poor doping uniformity and difficulty in simultaneously obtaining high Seebeck coefficient and good film quality when Bi is equivalently doped in Sb2Te3 thermoelectric thin films by traditional preparation methods.
[0007] The technical solution of the present invention is as follows: In a first aspect, the present invention provides a method for preparing a Bi-doped Sb₂Te₃ thermoelectric thin film, comprising the following steps: S1. Take a clean substrate; S2. Spread the raw material evenly in the graphite boat, and place the substrate upside down on top of the graphite boat so that the vertical distance between the substrate and the raw material is 1~50mm. The raw material includes Sb2Te3 powder and Bi-containing powder. S3. Place the graphite boat and substrate as a whole in a vacuum chamber and evacuate the chamber until the pressure is ≤1Pa; S4. Heat the substrate and the raw material to deposit a Bi-doped Sb2Te3 thermoelectric thin film on the substrate surface.
[0008] Optionally, the Bi-containing powder is Bi powder or Bi2Te3 powder.
[0009] Optionally, the mass ratio of the Sb2Te3 powder to the Bi-containing powder is 100:1-33.
[0010] Optionally, the heating temperature of the raw material is 500~600℃; preferably, the heating temperature of the raw material is 550~570℃, such as 550℃, 551℃, 552℃, 553℃, 554℃, 555℃, 556℃, 557℃, 558℃, 559℃, 560℃, 561℃, 562℃, 563℃, 564℃, 565℃, 566℃, 567℃, 568℃, 569℃, and 570℃.
[0011] Optionally, the raw material is heated using a gradient temperature increase, wherein the gradient temperature increase includes: The room temperature is raised to 240°C in 0-2 minutes, the temperature is further raised to 300°C in 2-4 minutes, and the temperature is raised to the target heating temperature in 4-5 minutes.
[0012] Optionally, the heating temperature of the substrate is 200~400℃; preferably, the heating temperature of the substrate is 200~250℃, such as 200℃, 210℃, 220℃, 230℃, 240℃, or 250℃.
[0013] Optionally, the deposition time is 10 to 150 seconds, such as 10s, 60s, 110s and 150s.
[0014] Optionally, the preparation method further includes the following step: annealing the Bi-doped Sb2Te3 thermoelectric thin film obtained in S4 at a temperature of 275~350℃ for 0.5~1.5 hours.
[0015] Secondly, the present invention provides a Bi-doped Sb2Te3 thermoelectric thin film, which is prepared by the aforementioned preparation method.
[0016] Beneficial effects: This invention provides a Bi-doped Sb₂Te₃ thermoelectric thin film and its preparation method. This invention effectively incorporates Bi into the Sb₂Te₃ thermoelectric thin film, resulting in not only uniform doping and high film quality, but also effectively optimizing the carrier concentration by increasing the Bi content, thus improving the Seebeck coefficient from 10⁶ μV·K⁻¹. -1 Increased to 173 μV·K -1When Bi₂Te₃-Sb₂Te₃ mixtures were used as raw materials to prepare Bi-doped Sb₂Te₃ films, the compositional inhomogeneity caused by differences in component volatilization was effectively alleviated, and the compositional consistency and structural uniformity of the films were significantly improved. An appropriate amount of Bi₂Te₃ powder optimized the carrier concentration of the film while significantly improving carrier mobility. When 29 wt% of Bi₂Te₃ powder was added, the power factor increased to 32 μW·cm⁻¹ at room temperature. -1 ·K -2 . Attached Figure Description
[0017] Figure 1 This is a process flow diagram for preparing Bi-doped Sb2Te3 thermoelectric thin films according to the present invention.
[0018] Figure 2 The sample element content and X-ray diffraction pattern are shown for samples obtained by mixing Bi powder of different masses. (a) is the content of each element, (b) is the X-ray diffraction pattern, the inset is the magnified (015) peak, and (c) is the lattice constant.
[0019] Figure 3 The above are XPS images of the sample obtained in Example 3, where (a) is about Sb, (b) is about Te, and (c) is about Bi.
[0020] Figure 4 The images show the SEM characterization results of samples prepared by mixing Bi powder with different masses. (a) is the SEM surface morphology image (with 0 wt% Bi added), (b) is the SEM surface morphology image (with 13 wt% Bi added), (c) is the SEM surface morphology image (with 17 wt% Bi added), (d) is the SEM surface morphology image (with 21 wt% Bi added), (e) is the SEM surface morphology image (with 25 wt% Bi added), (f) is the EDS surface scan element distribution map of the sample prepared by adding 21 wt% Bi powder, (g) is the cross-sectional view of the sample prepared by adding 0 wt% Bi powder, (h) is the cross-sectional view of the sample prepared by adding 17 wt% Bi powder, and (i) is the cross-sectional view of the sample prepared by adding 21 wt% Bi powder.
[0021] Figure 5 The images shown are TEM images of the sample obtained in Example 3, where (a) is a low-magnification TEM image, (b) is a high-resolution TEM image corresponding to the green box in (a), (c) is an IFFT image corresponding to the orange dashed box in (b), and (d) is a geometric phase analysis image corresponding to (b).
[0022] Figure 6KPFM analysis of the samples prepared in Example 3 (after mixing with 21 wt% Bi powder) and Example 1 (after mixing with 13 wt% Bi powder) is shown. (a) is the AFM surface morphology of the sample in Example 3, (b) is the surface contact potential diagram of the sample in Example 3, (c) is the surface contact potential diagram line scan of the sample in Example 3, (d) is the AFM surface morphology of the sample in Example 1, (e) is the surface contact potential diagram of the sample in Example 1, and (f) is the surface contact potential diagram line scan of the sample in Example 1.
[0023] Figure 7 The thermoelectric properties of different samples are shown, where (a) is the conductivity of different samples at varying temperatures, (b) is the Seebeck coefficient of different samples at varying temperatures, and (c) is the carrier concentration and mobility at room temperature.
[0024] Figure 8 The X-ray diffraction patterns and lattice constants of the samples obtained in Examples 5-8 and Comparative Example 1 are shown, where (a) is the X-ray diffraction pattern of different samples and (b) is the lattice constant of different samples.
[0025] Figure 9 The SEM surface morphology of the samples obtained in Examples 5-8 is shown, where (a) is the surface of sample B2, (b) is the surface of sample B3, (c) is the surface of sample B4, and (d) is the surface of sample B5.
[0026] Figure 10 The following are EDS scan elemental distribution maps of sample B4, where (a) is the surface EDS scan elemental distribution map of sample B4 (60 μm) and (b) is the cross-sectional EDS scan elemental distribution map of sample B4 (2 μm).
[0027] Figure 11 Here are the XPS plots for sample B4, where (a) is about Te, (b) is about Sb, and (c) is about Bi.
[0028] Figure 12 The images are TEM images of sample B4, where (a) is a TEM image of sample B4, (b) is a low-resolution HAADF image of the yellow rectangular region A in (a), (c)-(f) are elemental distribution maps of the sample in region (b), (g) is a HAADF-STEM image of region B in (b), where (g1) and (g2) represent the IFFT images of regions b1 and b2, respectively, (h) is a HAADF-STEM image of region C in (b), where (h1) and (h2) correspond to its FFT and IFFT distributions, respectively, and (i)-(l) are geometric phase analysis maps of (h).
[0029] Figure 13The thermoelectric properties of samples B1, B2, B3, B4, and B5 are given, where (a) is the conductivity at varying temperatures, (b) is the Seebeck coefficient at varying temperatures, and (c) is the carrier concentration and mobility at room temperature. Detailed Implementation
[0030] This invention provides a Bi-doped Sb₂Te₃ thermoelectric thin film 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. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
[0031] This embodiment provides a method for preparing a Bi-doped Sb₂Te₃ thermoelectric thin film, such as... Figure 1 As shown, it includes the following steps: S1. Take a clean substrate; S2. Spread the raw material evenly in the graphite boat, and place the substrate upside down on top of the graphite boat so that the vertical distance between the substrate and the raw material is 1~50mm. The raw material includes Sb2Te3 powder and Bi-containing powder. S3. Place the graphite boat and substrate as a whole in a vacuum chamber and evacuate the chamber until the pressure is ≤1Pa; S4. Heat the substrate and the raw material to deposit a Bi-doped Sb2Te3 thermoelectric thin film on the substrate surface.
[0032] Specifically, this embodiment utilizes the thermal evaporation of raw materials to grow the material on a hot substrate at close range. The substrate used in this invention can be a graphite substrate or a silicon substrate. A clean substrate typically requires sequential immersion in pure water, alcohol, and acetone, followed by ultrasonication for 20 minutes. The distance between the substrate and the raw material is 1-50 mm (preferably 10-30 mm). If the distance is too large, the mean free path of the vapor molecules increases, reducing the flux reaching the substrate, resulting in a slow deposition rate, easy oxidation of the film, and poor crystallinity. If the distance is too small, the thermal radiation from the evaporation source will directly "bake" the substrate, causing temperature runaway, forming granular polycrystalline particles, increasing the complexity of phonon scattering, making it difficult to achieve a uniform nanosheet structure, and ultimately making it difficult to obtain low thermal conductivity. The raw materials include Sb₂Te₃ powder and Bi-containing powder. Specifically, a powder premixing method is used for doping: high-purity Sb₂Te₃ powder and different masses of Bi-containing powder (such as high-purity Bi powder) are thoroughly ground as raw materials, then evenly spread in a mold using a sieve, and then subsequent steps are performed. This invention effectively improves the thermoelectric properties of Sb2Te3 thin films by introducing Bi as a dopant: Bi can achieve equivalent substitution for Sb sites, thereby adjusting the intrinsically high hole concentration to a range closer to the optimal range, which can effectively improve the Seebeck coefficient of Sb2Te3 thin films. Essentially, this reflects the rebalancing of carrier contributions and the suppression of the adverse effects on bipolar transport.
[0033] In some embodiments, the Bi-containing powder is Bi powder or Bi2Te3 powder.
[0034] In some embodiments, the mass ratio of the Sb₂Te₃ powder to the Bi-containing powder is 100:1-33. When the Bi-containing powder is Bi powder, the mass ratio of the Sb₂Te₃ powder to the Bi-containing powder is 100:1-25 (e.g., 100:1, 100:13, 100:17, 100:21, 100:25). When the Bi-containing powder is Bi₂Te₃ powder, the mass ratio of the Sb₂Te₃ powder to the Bi-containing powder is 100:1-33 (e.g., 100:1, 100:16, 100:22, 100:29, 100:33).
[0035] In some embodiments, the heating temperature of the raw material is 500~600℃; preferably, the heating temperature of the raw material is 550~570℃, such as 550℃, 551℃, 552℃, 553℃, 554℃, 555℃, 556℃, 557℃, 558℃, 559℃, 560℃, 561℃, 562℃, 563℃, 564℃, 565℃, 566℃, 567℃, 568℃, 569℃, and 570℃.
[0036] In some embodiments, the heating of the raw material employs a gradient temperature increase, which includes: Raise the room temperature to 200-250℃ within 0-2 minutes, for example, 200℃, 210℃, 220℃, 230℃, 240℃, 250℃; continue to raise the temperature to 300-400℃ within 2-4 minutes, for example, 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, 360℃, 370℃, 380℃, 390℃, 400℃; and raise the temperature to the target heating temperature within 4-5 minutes.
[0037] In some embodiments, the heating temperature of the substrate is 200~400°C; preferably, the heating temperature of the substrate is 200~250°C, such as 200°C, 210°C, 220°C, 230°C, 240°C, or 250°C.
[0038] The key to this embodiment lies in controlling the matching between the "evaporation rate" and the "substrate temperature" to form a thin film with a regular atomic arrangement and an appropriate number of point defects inside.
[0039] In some implementations, the deposition time is 10 to 150 seconds, such as 10s, 60s, 110s, and 150s.
[0040] In some embodiments, the preparation method further includes the following step: annealing the Bi-doped Sb2Te3 thermoelectric thin film obtained in S4 at a temperature of 275~350°C (e.g., 275°C, 300°C, 300°C, 325°C and 350°C) for 0.5~1.5 hours (e.g. 0.5 hours, 1 hour and 1.5 hours).
[0041] This embodiment also provides a Bi-doped Sb2Te3 thermoelectric thin film, which is prepared by the aforementioned preparation method.
[0042] It should be noted that the Bi-doped Sb₂Te₃ thermoelectric thin film obtained in this embodiment is Bi x Sb 2-x Te 3+y , where x is 0-0.6 and y is 0-0.5.
[0043] The present invention will be further described below with reference to specific embodiments.
[0044] The raw material heating in the following examples uses the following gradient heating: the room temperature is raised to 240°C in 0-2 minutes, the temperature is further raised to 300°C in 2-4 minutes, and the temperature is raised to 560°C in 4-5 minutes.
[0045] Example 1 A method for preparing a Bi-doped Sb₂Te₃ thermoelectric thin film includes the following steps: S1. Take a clean graphite substrate; S2. Spread the raw material evenly in the graphite boat, and place the substrate upside down on top of the graphite boat so that the vertical distance between the substrate and the Sb2Te3 powder is 20mm; the raw material includes Sb2Te3 powder and Bi powder in a mass ratio of 100:13. S3. Place the graphite boat and substrate as a whole in a vacuum chamber and evacuate the chamber until the pressure is ≤1Pa; S4. Heat the substrate to 200°C and heat the raw material to deposit a Bi-doped Sb2Te3 thermoelectric thin film on the substrate surface.
[0046] Example 2 A method for preparing a Bi-doped Sb₂Te₃ thermoelectric thin film includes the following steps: S1. Take a clean graphite substrate; S2. Spread the raw material evenly in the graphite boat, and place the substrate upside down on top of the graphite boat so that the vertical distance between the substrate and the Sb2Te3 powder is 20mm; the raw material includes Sb2Te3 powder and Bi powder in a mass ratio of 100:17. S3. Place the graphite boat and substrate as a whole in a vacuum chamber and evacuate the chamber until the pressure is ≤1Pa; S4. Heat the substrate to 200°C and heat the raw material to deposit a Bi-doped Sb2Te3 thermoelectric thin film on the substrate surface.
[0047] Example 3 A method for preparing a Bi-doped Sb₂Te₃ thermoelectric thin film includes the following steps: S1. Take a clean graphite substrate; S2. Spread the raw material evenly in the graphite boat, and place the substrate upside down on top of the graphite boat so that the vertical distance between the substrate and the Sb2Te3 powder is 20mm; the raw material includes Sb2Te3 powder and Bi powder in a mass ratio of 100:21. S3. Place the graphite boat and substrate as a whole in a vacuum chamber and evacuate the chamber until the pressure is ≤1Pa; S4. Heat the substrate to 200°C and heat the raw material to deposit a Bi-doped Sb2Te3 thermoelectric thin film on the substrate surface.
[0048] Example 4 A method for preparing a Bi-doped Sb₂Te₃ thermoelectric thin film includes the following steps: S1. Take a clean graphite substrate; S2. Spread the raw material evenly in the graphite boat, and place the substrate upside down on top of the graphite boat so that the vertical distance between the substrate and the Sb2Te3 powder is 20mm; the raw material includes Sb2Te3 powder and Bi powder in a mass ratio of 100:25. S3. Place the graphite boat and substrate as a whole in a vacuum chamber and evacuate the chamber until the pressure is ≤1Pa; S4. Heat the substrate to 200°C and heat the raw material to deposit a Bi-doped Sb2Te3 thermoelectric thin film on the substrate surface.
[0049] Comparative Example 1 A method for preparing an Sb₂Te₃ thermoelectric thin film includes the following steps: S1. Take a clean graphite substrate; S2. Spread the raw material evenly in the graphite boat, and place the substrate upside down on top of the graphite boat so that the vertical distance between the substrate and the Sb2Te3 powder is 20mm; the raw material is Sb2Te3 powder. S3. Place the graphite boat and substrate as a whole in a vacuum chamber and evacuate the chamber until the pressure is ≤1 Pa; S4. Heat the substrate to 200°C and heat the raw material to deposit a Bi-doped Sb2Te3 thermoelectric thin film on the substrate surface.
[0050] The thermoelectric thin films obtained in Examples 1-4 and Comparative Example 1 were subjected to EDS testing, and the results are as follows: Figure 2As shown, the Bi content in the film gradually increases with increasing Bi powder mass. EDS quantitative analysis yielded five groups of samples with different Bi doping contents: 0 at.%, 3.51 at.%, 6.74 at.%, 8.34 at.%, and 9.88 at.%, respectively. The Te content remained relatively constant at 60.00 at.%, while the Sb content gradually decreased. The phase structure of the samples mixed with different masses of Bi powder was characterized, and the results are shown below. Figure 2 As shown in (b), the main diffraction peaks of all samples can be matched with the Sb2Te3 standard card (PDF#15-0874), and no peaks of the second phase appear. Furthermore, the position of the (015) crystal plane diffraction peak shifts slightly to a lower angle with increasing Bi powder mass. The change in lattice constant value obtained through refinement is shown in Figure (b). Figure 2 As shown in (c), the lattice constants a / b and c increase nearly linearly with the increase of Bi powder mass. This is because Bi... 3+ The ionic radius is 1.55 Å, compared to Sb 3+ The ionic radius (1.45 Å) is large. The shift in diffraction peaks and the increase in lattice parameters further prove that Bi was successfully incorporated into the Sb2Te3 lattice, causing certain lattice distortions, which may affect the thermoelectric properties of the Sb2Te3 thin film.
[0051] To analyze the chemical valence of each element within the sample, XPS characterization was performed on Example 3 (the sample prepared after adding 21 wt% Bi powder). The results are as follows: Figure 3 As shown. The Sb 3d electron orbital has a binding energy of 528.78 eV (3d... 5 / 2 ) and 538.18eV (3d 3 / 2 A peak appears at (), corresponding to Sb 3+ The presence of a weak Sb–O composition only on the high binding energy side indicates slight surface oxidation due to minimal air exposure; the Te 3d electron orbitals have a binding energy of 572.58 eV (3d... 5 / 2 ) and 582.98 eV (3d 3 / 2 A peak appears at (), corresponding to Te 2- Valence state; Bi4f electron orbitals at a binding energy of 157.78 eV (4f 7 / 2 ) and 163.08 eV (4f 5 / 2 A peak appears at (), corresponding to Bi. 3+ Price state.
[0052] Figure 4 SEM characterization results of samples prepared by mixing with different masses of Bi powder are shown. From the surface... Figure 4As can be seen in (a)-(e), with the increase of Bi powder mass, the film gradually refines and becomes more uniform from relatively coarse lamellar grains, and the overall structure evolves from loose stacking to a denser lamellar interlacing structure. The EDS surface distribution of the sample prepared after adding 21 wt% Bi powder is shown in (a)-(e). Figure 4 (f) shows that Sb, Te, and Bi are uniformly distributed over a large scale, with no obvious enrichment or phase separation regions, indicating that Bi doping has good compositional uniformity at the micrometer scale. More noteworthy is the significant change in cross-sectional morphology: the undoped sample ( Figure 4 In the middle (g) content, the main grains are relatively large, nearly vertically penetrating columnar grains, with relatively loose intergranular bonding and noticeable gaps and discontinuous interfaces in some areas; while at higher Bi contents ( Figure 4 (h) and Figure 4 In the middle (i), the cross-section shows a certain angle of tilted layer stacking, the layer units are thinner, the overlap is more complete, and the overall film is more compact.
[0053] Figure 5 TEM image of the sample prepared in Example 3 (with 21 wt% Bi powder added), wherein Figure 5 (a) is a low-magnification TEM image of the sample prepared after mixing with 21 wt% Bi powder. It can be seen that the sample has complete overall crystallization and no macroscopic phase separation. Figure 5 (b) is Figure 5 In the high-resolution TEM image of the area corresponding to the green box in (a), the lattice fringes on both sides of the interface are clearly visible and continuous. The interplanar spacings were measured to be 0.394 nm and 0.321 nm, respectively, corresponding to the (009) and (015) crystal planes of Sb₂Te₃. Further magnification... Figure 4 (b) The orange dashed box area (e.g.) Figure 5 In (c), variations in stripe contrast and periodicity are visible in localized areas (marked by red circles). This corresponds to local perturbations in the interlayer stacking sequence, possibly originating from changes in interlayer coupling caused by Bi doping. The lattice strain distribution results are based on geometric phase analysis (GPA). Figure 5 As shown in (d), there is a significant local compressive strain field in the Bi-doped region, which is caused by lattice distortion due to the substitution of Sb sites by Bi atoms. This micro-strain characteristic is consistent with the trend of small-angle shift of diffraction peaks in XRD.
[0054] To further reveal the differences in potential distribution near grain boundaries in samples prepared by mixing different masses of Bi powder, typical regions were characterized using Kelvin probe force microscopy (KPFM). Surface morphology and contact potential difference distribution were simultaneously acquired, and line scan analysis was performed along selected grain boundaries. The results are as follows: Figure 6 As shown. The KPFM results for the sample prepared in Example 3 (after mixing with 21wt% Bi powder) are as follows. Figure 6 As shown in (a)-(c), the average potential difference near the selected grain boundaries is 20.14 mV; in contrast, the CPD distribution of the sample prepared in Example 1 (after mixing with 13 wt% Bi powder) is more gradual, as shown in the KPFM results. Figure 6 As shown in (d)-(f), the average potential difference obtained by line scanning near the selected grain boundaries is 16.58 mV. This result indicates that increasing the mass of Bi powder exacerbates the non-uniformity of the local potential near the grain boundaries on the sample surface, which may lead to more significant charge bending or charge accumulation effects at the grain boundaries.
[0055] Figure 7 The thermoelectric properties of Sb₂Te₃ thin film samples with different Bi contents were investigated. As the mass of added Bi powder increased from 0 wt% to 25 wt%, the room temperature conductivity of the film increased from 1313 S·cm. -1 Gradually decreased to 548 S·cm -1 (like Figure 7 As shown in (a), the Seebeck coefficient is 106 μV·K. -1 Gradually rising to 173 μV·K -1 (like Figure 7 (As shown in (b)). The synergistic changes in the aforementioned electrical transport properties mainly stem from the effective regulation of carrier concentration by Bi doping. Figure 7 As shown in (c), the carrier concentration ranges from 10.6 × 10⁻⁶. 19 cm -3 Gradually decreased to 2.95×10 19 cm -3 The migration rate was 77.25 cm. 2 ·V -1 ·s -1 Increased to approximately 116.28cm 2 ·V -1 ·s -1 This phenomenon can be attributed to the following mechanism: in the Sb₂Te₃ system, Sb Te Antisite defects are the main source of high carrier concentration. Because the electronegativity and ionic radius differences between Bi and Te are greater than those between Sb and Te, the substitution of Sb sites by Bi atoms significantly suppresses Sb... Te The formation of antisite defects effectively optimizes the carrier concentration. The decrease in carrier concentration is the direct cause of the decrease in conductivity and the increase in the Seebeck coefficient. Therefore, appropriate Bi doping can optimize the carrier concentration and effectively improve the Seebeck coefficient, providing an effective way to optimize the thermoelectric properties of Sb₂Te₃-based materials.
[0056] Example 5 A method for preparing a Bi-doped Sb₂Te₃ thermoelectric thin film includes the following steps: S1. Take a clean graphite substrate; S2. Spread the raw material evenly in the graphite boat, and place the substrate upside down on top of the graphite boat so that the vertical distance between the substrate and the Sb2Te3 powder is 20mm; the raw material includes Sb2Te3 powder and Bi2Te3 powder in a mass ratio of 100:16 wt%. S3. Place the graphite boat and substrate as a whole in a vacuum chamber and evacuate the chamber until the pressure is ≤1Pa; S4. Heat the substrate to 200°C and heat the raw material to deposit a Bi-doped Sb2Te3 thermoelectric thin film on the substrate surface.
[0057] Example 6 A method for preparing a Bi-doped Sb₂Te₃ thermoelectric thin film includes the following steps: S1. Take a clean graphite substrate; S2. Spread the raw material evenly in the graphite boat, and place the substrate upside down on top of the graphite boat so that the vertical distance between the substrate and the Sb2Te3 powder is 20mm; the raw material includes Sb2Te3 powder and Bi2Te3 powder in a mass ratio of 100:22wt%. S3. Place the graphite boat and substrate as a whole in a vacuum chamber and evacuate the chamber until the pressure is ≤1Pa; S4. Heat the substrate to 200°C and heat the raw material to deposit a Bi-doped Sb2Te3 thermoelectric thin film on the substrate surface.
[0058] Example 7 A method for preparing a Bi-doped Sb₂Te₃ thermoelectric thin film includes the following steps: S1. Take a clean graphite substrate; S2. Spread the raw material evenly in the graphite boat, and place the substrate upside down on top of the graphite boat so that the vertical distance between the substrate and the Sb2Te3 powder is 20mm; the raw material includes Sb2Te3 powder and Bi2Te3 powder in a mass ratio of 100:29wt%. S3. Place the graphite boat and substrate as a whole in a vacuum chamber and evacuate the chamber until the pressure is ≤1Pa; S4. Heat the substrate to 200°C and heat the raw material to deposit a Bi-doped Sb2Te3 thermoelectric thin film on the substrate surface.
[0059] Example 8 A method for preparing a Bi-doped Sb₂Te₃ thermoelectric thin film includes the following steps: S1. Take a clean graphite substrate; S2. Spread the raw material evenly in the graphite boat, and place the substrate upside down on top of the graphite boat so that the vertical distance between the substrate and the Sb2Te3 powder is 20mm; the raw material includes Sb2Te3 powder and Bi2Te3 powder in a mass ratio of 100:33wt%. S3. Place the graphite boat and substrate as a whole in a vacuum chamber and evacuate the chamber until the pressure is ≤1Pa; S4. Heat the substrate to 200°C and heat the raw material to deposit a Bi-doped Sb2Te3 thermoelectric thin film on the substrate surface.
[0060] For ease of description, the samples obtained by adding different masses of Bi2Te3 powder (0wt%, 16wt%, 22wt%, 29wt%, and 33wt%, respectively) are numbered B1, B2, B3, B4, and B5, respectively. Among them, B1 is Comparative Example 1 (the control sample without Bi2Te3). Figure 8 The XRD patterns and lattice parameter variations of samples prepared by mixing Bi₂Te₃ powders of different masses are shown. Figure 8 As shown in (a), the diffraction peak positions of samples B1-B5 are consistent with those of the standard card Sb2Te3 (PDF#15-0874), with the characteristic crystal plane diffraction peaks of (015), (110), and (205) clearly visible in each sample. There are some differences in diffraction peak intensity among different samples, but the peak shape and position are generally consistent, and no significant new diffraction peaks were observed. Detailed data on the material's crystal structure can be obtained through XRD pattern characterization and refinement. By comparing with the standard crystal structure, the lattice constants a, b, and c were obtained. Figure 8 In Figure (b), the lattice parameters of samples B1-B5 change. With the increase of Bi2Te3, the a / b ratio in the lattice increases monotonically from 4.26 Å to 4.30 Å, and the c ratio gradually increases from 30.44 Å to 30.61 Å.
[0061] Figure 9 Images (a)-(d) show the SEM surface morphology of Bi-Sb-Te thin film samples prepared by mixing Bi2Te3 powders of different masses. Figure 9 As shown, with the increase of Bi2Te3 introduction, the film surface maintained continuous coverage, but the grain size and uniformity showed a trend of first improving and then fluctuating. Sample B2 had a wider grain size distribution, with localized coarse grain protrusions leading to larger surface undulations; in sample B3, the proportion of coarse grains decreased, and their size tended to be more concentrated; sample B4 had the most uniform grain distribution and denser packing, with the best morphological consistency; when the Bi2Te3 mass further increased, sample B5 showed a certain degree of re-coarsening and localized agglomeration, and the surface undulations increased again. Figure 9 (d)). This morphological evolution is consistent with the trend shown by XRD that the thin film retains the Sb2Te3 main phase and the lattice parameter increases with increasing doping.
[0062] Figure 10 Figure (a) shows the EDS surface distribution (60 μm) of sample B4. The three elements Te, Sb, and Bi are uniformly distributed in the film, with no obvious enriched or missing regions, indicating that the overall composition of the film has good macroscopic uniformity under this doping condition. In addition, combined with morphological observation, the grains are relatively densely packed, reflecting the synergistic optimization of the film in terms of composition and structure. Figure 10 (b) is the EDS surface distribution diagram (2μm) of the corresponding cross section. The results show that the signal distribution of Bi, Sb and Te is continuous along the thickness direction of the film, with no obvious layered enrichment or phase separation, which further confirms that the film has good compositional uniformity in the cross section direction.
[0063] XPS analysis further confirmed the chemical valence states of each element in sample B4, as shown in the results. Figure 11 As shown, the 3d orbital of Sb exhibits a pair of spin-orbit splitting peaks at 538.36 eV and 528.94 eV, representing the spin-orbit splitting peaks of Sb, respectively. 3+ 3D 3 / 2 With 3D 5 / 2 The orbital energy levels indicate that Sb is primarily in a Sb-Te bonded environment. 3+ The morphology exists; the 3d orbitals of Te have distinct characteristic peaks at 583.17 eV and 572.78 eV, corresponding to Te, respectively. 2- 3D 3 / 2 With 3D 5 / 2 Orbital energy levels; the 4f orbital of Bi exhibits distinct characteristic peaks at 163.17 eV and 157.89 eV, corresponding to Bi4f and Bi4f, respectively. 3+ 4f 5 / 2 With 4f 7 / 2 The orbital energy levels indicate that Bi is incorporated into the Sb₂Te₃ lattice structure in the +3 valence state. Furthermore, small amounts of weak oxide components, attributed to Sb₂O₃, TeO₂, and Bi₂O₃, were also discernible in the high-resolution spectra of Sb, Te, and Bi, respectively. The appearance of these oxygen-containing peaks is mainly related to the surface-sensitive characteristics of XPS testing. Due to the relatively large thickness of the thin film samples and the short etching time in this study, the ion etching process could not completely remove the natural oxide layer on and near the sample surface; therefore, certain oxide signals were still detected during the test. Considering the relatively weak intensity of each oxide peak, it can be determined that these oxygen-containing components mainly originate from residual oxidation on the surface, rather than significant oxidation occurring within the thin film.
[0064] To further characterize the microstructure of the thin film, transmission electron microscopy (TEM) was used to analyze sample B4. Figure 12 As shown in (a), the cross-sectional TEM results show that the film grows continuously on the substrate surface; Figure 12 (b) is Figure 12The low-resolution HAADF image corresponding to region A in (a) is shown below. The EDS element surface scan of this region is shown below. Figure 12 As shown in (c)-(f), the constituent elements Bi, Sb and Te of the sample are uniformly distributed in the thin film, and no obvious impurity phase enrichment region or large-scale clusters were observed. Figure 12 (g) is Figure 12 The HAADF-STEM image of region B marked in (b) is shown. Regions b1 and b2 are selected for analysis, and insets (g1) and (g2) correspond to the fast inverse Fourier transform (IFFT) images of b1 and b2, respectively. The lattice spacing of region b1 is d1 = 0.238 nm, corresponding to the (1010) crystal plane of Sb2Te3; the lattice spacing of region b2 is d2 = 0.317 nm, corresponding to the (015) crystal plane of Sb2Te3. Figure 12 HAADF-STEM image of region C marked in (b) as follows Figure 12 As shown in (h), the corresponding inset is a Fourier transform (FFT) image. Figure 12 (h1) and Fast Inverse Fourier Transform (IFFT) images ( Figure 12 (h2)). The geometric phase analysis (GPA) results based on this HAADF-STEM image are as follows: Figure 12 As shown in (i)-(l), respectively, xx , yy , xy With D xy The spatial distribution and color distribution reflect the variation characteristics of local lattice strain in different directions of the thin film, indicating that there is a certain degree of local strain and distortion distribution in the thin film.
[0065] The thermoelectric transport properties of B1-B5 thin films were characterized, and the results are as follows: Figure 13 As shown. Figure 13 Conductivity of all samples in (a) σ The conductivity decreased monotonically with increasing temperature. At room temperature, the conductivity first increased and then decreased with increasing Bi2Te3 powder content; sample B2 had the highest conductivity, with a value of 1741 S·cm. -1 The conductivity first increased and then decreased with increasing Bi2Te3 content, with sample B5 exhibiting the lowest conductivity at 1043 S·cm. -1 This indicates that an appropriate amount of Bi2Te3 is beneficial to improving electrical conductivity. Figure 13Figure (b) shows the Seebeck coefficient as a function of temperature. The Seebeck coefficient of the samples gradually increases with the increase of Bi2Te3 powder. At room temperature, the Seebeck coefficients of samples B1, B2, B3, B4, and B5 are 106 μV·K. -1 112 μV·K -1 138 μV·K -1 151 μV·K -1 165μV·K -1 Among them, sample B5 has the highest Seebeck coefficient in the series of samples; Figure 13 Figure (c) shows the carrier concentration. n With mobility μ The relationship between the amount of Bi2Te3 introduced and the amount of Bi2Te3 introduced, where n The concentration of compounds introduced continuously decreases with increasing amount, which is related to the fact that the introduction of compound sources regulates the intrinsic defect balance and suppresses acceptor defects. μ The pattern showed an initial increase followed by a decrease, with the maximum value of 171 cm⁻¹ observed in sample B3. 2 ·V -1 ·s -1 This indicates that with appropriate doping, the reduction of defect scattering and the improvement of crystal quality play a dominant role; while further increasing Bi2Te3 will introduce local strain and grain boundary scattering, thereby limiting carrier transport.
[0066] In summary, this invention provides a Bi-doped Sb₂Te₃ thermoelectric thin film and its preparation method. This invention effectively incorporates Bi into the Sb₂Te₃ thermoelectric thin film, resulting in not only uniform doping and high film quality, but also effectively optimizing the carrier concentration by increasing the Bi content, thus improving the Seebeck coefficient from 10⁶ μV·K⁻¹. -1 Increased to 173 μV·K -1 When Bi₂Te₃-Sb₂Te₃ mixtures were used as raw materials to prepare Bi-doped Sb₂Te₃ films, the compositional inhomogeneity caused by differences in component volatilization was effectively alleviated, and the compositional consistency and structural uniformity of the films were significantly improved. An appropriate amount of Bi₂Te₃ powder optimized the carrier concentration of the film while significantly improving carrier mobility. When 29 wt% Bi₂Te₃ powder was added, the power factor was increased to 32 μW·cm⁻¹ at room temperature. -1 ·K -2 .
[0067] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.
Claims
1. A method for preparing a Bi-doped Sb₂Te₃ thermoelectric thin film, characterized in that, Includes the following steps: S1. Take a clean substrate; S2. Spread the raw material evenly in the graphite boat, and place the substrate upside down on top of the graphite boat so that the vertical distance between the substrate and the raw material is 1~50mm. The raw material includes Sb2Te3 powder and Bi-containing powder. S3. Place the graphite boat and substrate as a whole in a vacuum chamber and evacuate the chamber until the pressure is ≤1Pa; S4. Heat the substrate and the raw material to deposit a Bi-doped Sb2Te3 thermoelectric thin film on the substrate surface.
2. The method for preparing a Bi-doped Sb₂Te₃ thermoelectric thin film according to claim 1, characterized in that, The Bi-containing powder is either Bi powder or Bi2Te3 powder.
3. The method for preparing a Bi-doped Sb₂Te₃ thermoelectric thin film according to claim 1, characterized in that, The mass ratio of Sb2Te3 powder to Bi-containing powder is 100:1-33.
4. The method for preparing a Bi-doped Sb₂Te₃ thermoelectric thin film according to claim 2, characterized in that, When the Bi-containing powder is Bi powder, the mass ratio of the Sb2Te3 powder to the Bi-containing powder is 100:1-25.
5. The method for preparing a Bi-doped Sb₂Te₃ thermoelectric thin film according to claim 2, characterized in that, When the Bi-containing powder is Bi2Te3 powder, the mass ratio of the Sb2Te3 powder to the Bi-containing powder is 100:1-33.
6. The method for preparing a Bi-doped Sb₂Te₃ thermoelectric thin film according to claim 1, characterized in that, The heating temperature of the raw materials is 500~600℃.
7. The method for preparing a Bi-doped Sb₂Te₃ thermoelectric thin film according to claim 1, characterized in that, The raw materials are heated using a gradient temperature increase, which includes: The room temperature was raised to 240°C in 0-2 minutes, the temperature was further raised to 300°C in 2-4 minutes, and the temperature was raised to the target heating temperature in 4-5 minutes.
8. The method for preparing a Bi-doped Sb₂Te₃ thermoelectric thin film according to claim 1, characterized in that, The substrate is heated to a temperature of 200~400℃.
9. The method for preparing a Bi-doped Sb₂Te₃ thermoelectric thin film according to claim 1, characterized in that, The preparation method also includes the following steps: annealing the Bi-doped Sb2Te3 thermoelectric thin film obtained in S4 at a temperature of 275~350℃ for 0.5~1.5 hours.
10. A Bi-doped Sb₂Te₃ thermoelectric thin film, characterized in that, Prepared by the preparation method described in any one of claims 1-9.