A method for preparing Bi2O3 composite SnTe thermoelectric material

Abstract

This invention discloses a method for preparing a Bi2O3 composite SnTe thermoelectric material, belonging to the field of energy conversion. The thermoelectric material, composed of a certain amount of Bi2O3-SnTe, is prepared using a high-temperature solid-state method, high-temperature annealing, and rapid hot-pressing. First, Sn powder and Te powder are weighed according to a stoichiometric ratio. A SnTe sample is prepared using a high-temperature solid-state method, and then thoroughly ground to obtain SnTe powder. Next, Bi2O3 and SnTe powders are mixed uniformly according to a certain molar ratio to obtain a mixed powder. This mixture is then subjected to high-temperature annealing, and finally hot-pressed and sintered using a rapid hot-pressing process to obtain a composite 0~2.5% mol Bi2O3-SnTe thermoelectric material. The sample preparation process of this invention is simple and rapid, and the obtained sample has stable properties and high density. This invention overcomes the shortcomings of traditional SnTe thermoelectric materials, such as low Seebeck coefficient and high thermal conductivity, improving the thermoelectric figure of merit of the material by 36.1% across the entire temperature measurement range.

Description

Technical Field

[0001] This invention relates to a method for preparing a thermoelectric material, specifically a method for preparing a Bi2O3 composite SnTe thermoelectric material, which belongs to the field of energy conversion. Background Technology

[0002] With the continuous development of science and technology, problems such as global warming and the shortage of fossil fuels have emerged one after another. Developing new energy sources is an important guarantee for achieving global sustainable development. Thermoelectric materials, as a new type of energy material, can directly convert heat energy into electrical energy, and have certain advantages in applications such as waste heat recovery and temperature difference refrigeration. Thermoelectric materials are usually measured by their thermoelectric figure of merit (ZT = S). 2 The thermoelectric performance of a material is evaluated by the thermoelectric figure of merit (dT / k), where S is the Seebeck coefficient, d is the electrical conductivity, T is the absolute temperature, and k is the thermal conductivity. The larger the thermoelectric figure of merit, the better the thermoelectric performance of the material.

[0003] SnTe is a typical mid-temperature thermoelectric material with applications in waste heat recovery. Compared to PbTe thermoelectric materials, it has a similar crystal structure and band structure, is an environmentally friendly thermoelectric material without Pb, and is considered a strong candidate to replace PbTe thermoelectric materials. However, due to the intrinsic Sn vacancies, SnTe has an excessively high carrier concentration, resulting in a low Seebeck coefficient, excessively high thermal conductivity, and low ZT value, making it difficult to apply in practice. Therefore, this application employs a high-temperature solid-state method, high-temperature annealing, and rapid hot-pressing process to composite a certain amount of Bi₂O₃ into a SnTe matrix. During the annealing process, Bi substitution at Sn sites is achieved. On the one hand, Bi substitution at Sn sites can effectively regulate the carrier concentration of SnTe, thereby optimizing and controlling the electrical transport performance of SnTe. On the other hand, the second phase introduced by the composite can effectively enhance the scattering of its thermal phonons and reduce the thermal conductivity of SnTe. Finally, the electrical and thermal properties of SnTe are synergistically optimized, resulting in a high-performance SnTe-based thermoelectric material. The composite 1.5% mol Bi₂O₃-SnTe thermoelectric material obtained by this invention has a thermoelectric figure of merit of 0.83 at 823 K, which is 36.1% higher than that of the uncomposite sample.

[0004] To date, there have been no reports on the preparation of SnTe materials using a high-temperature solid-state method, followed by high-temperature annealing, and finally obtaining composite 0 ~ 2.5% mol Bi2O3-SnTe bulk thermoelectric materials via a rapid hot-pressing process. Summary of the Invention

[0005] This invention discloses a method for preparing Bi2O3 composite SnTe thermoelectric materials. Using Sn powder, Te powder, and Bi2O3 powder as raw materials, SnTe material is first prepared by a high-temperature solid-state method, then composited by high-temperature annealing, and finally high-density composite 0-2.5% mol Bi2O3-SnTe bulk thermoelectric materials are obtained at 450-550 ℃ using a rapid hot-pressing process. This method successfully improves the thermoelectric performance of SnTe alone, and the thermoelectric figure of merit of the samples is significantly improved throughout the entire temperature range (323 K-823 K).

[0006] This invention is achieved through the following technical solution:

[0007] A method for preparing a Bi2O3 composite SnTe thermoelectric material is characterized by using Sn powder, Te powder, and Bi2O3 powder as raw materials. First, according to the stoichiometric ratio of Sn and Te, Sn powder and Te powder are weighed and ground in a mortar until uniformly dispersed. The ground mixture is then placed into a quartz tube, which is evacuated and sealed at high temperature. After sealing, the quartz tube containing the sample is placed in a pit furnace for a high-temperature solid-state reaction to prepare a SnTe sample. Next, the prepared SnTe sample is ground into powder in a mortar. The required mass of Bi2O3 powder is accurately weighed according to the stoichiometric ratio of 0~2.5% mol Bi2O3-SnTe, mixed with the prepared SnTe powder, and ground again until completely homogeneous. The mixture is then evacuated and sealed at high temperature. After sealing, the quartz tube containing the sample is placed in a pit furnace for high-temperature annealing to prepare the composite 0~2.5% mol... Bi2O3-SnTe samples were then ground uniformly and placed into a graphite mold. High-density composite 0 ~ 2.5% mol Bi2O3-SnTe thermoelectric materials were prepared using a rapid hot pressing process.

[0008] Furthermore, the specific steps of the synthesis method are as follows:

[0009] (1) High-temperature solid-state reaction: Based on the stoichiometric ratio of Sn and Te in SnTe, weigh out the required 2.374 g of Sn powder and 2.552 g of Te powder, mix them evenly in a clean mortar, load the mixed powder into a clean and dry quartz tube, evacuate and seal the tube at high temperature, and place the quartz tube containing the sample into a pit furnace for a high-temperature solid-state reaction to obtain 4.926 g of SnTe sample. The conditions for the high-temperature solid-state reaction are: 0.5 ~ 1.5 o Heating rate increased to 450 °C / min o C, then 1 to 2 o The temperature was continuously increased at a rate of C / min to 950 ~ 1050. o C, keep warm for 8-12 hours, then at 1-2o Cooling rate reduced to 650 °C / min o C, keep warm for 20-26 hours, and finally reduce to 1-2 o The rate of decrease from C / min to room temperature was continuously reduced. The quartz tube used had an inner diameter of 12.5 mm and a wall thickness of 1.2 mm. The vacuum level was maintained at 1*10 during the vacuum sealing process. -1 ~ 5*10 -1 MPa.

[0010] (2) High-temperature annealing treatment: Weigh the SnTe sample obtained in step (1) and grind it into a uniform powder. Weigh 4.500 g of the obtained SnTe powder. Weigh Bi2O3 powder according to the ratio of 0 ~ 2.5% mol Bi2O3-SnTe. Mix the Bi2O3 powder evenly in a mortar. Put the mixed powder into a clean and dry quartz tube, evacuate and seal the tube at high temperature. Put the quartz tube containing the sample into a pit furnace for high-temperature annealing treatment to obtain the desired SnTe sample with 0 ~ 2.5% mol Bi2O3. The conditions for the high-temperature annealing treatment are: 1 ~ 2 o The temperature continued to rise at a rate of C / min to 750. o C, keep warm for 5-9 hours, then at 1-2 o Cool to room temperature at a rate of C / min. For details on the quartz tube used and the vacuum sealing requirements, please refer to step (1).

[0011] (3) Rapid hot pressing sintering process: The composite 0 ~ 2.5% mol Bi2O3-SnTe sample obtained in step (2) is ground in a mortar until completely mixed. Then, the obtained sample powder is loaded into a graphite mold and rapidly hot-pressed and sintered under an axial pressure of 40 ~ 60 MPa and a temperature of 500 ~ 600 °C. o High-density 0-2.5% molBi2O3-SnTe thermoelectric materials were prepared by hot pressing at C for 20-40 min.

[0012] (4) The thermal diffusivity of the sample obtained in step (3) was measured by a German Netzsch LFA467 thermal conductivity meter, and its thermal conductivity was calculated by combining the thermal conductivity formula; its electrical conductivity and Seebeck coefficient were obtained by measuring relevant parameters by a German LSR-3 and calculated. The 0 ~ 2.5% mol Bi2O3-SnTe thermoelectric material obtained by the above preparation method has good crystallinity and high density, electrical conductivity of 66400 ~ 110000 S / m, Seebeck coefficient of 130 ~ 166 μV / K, thermal conductivity of 1.891 ~ 2.266 W / mK, and ZT value of 0.61 ~ 0.83.

[0013] (5) This invention prepares 0~2.5% mol Bi2O3-SnTe thermoelectric materials through a high-temperature solid-state reaction method, high-temperature annealing treatment, and rapid hot-pressing sintering process. It has the following advantages: First, compared with traditional chemical methods, this process is simple and quick to prepare samples, can obtain a large number of samples at once, and the samples are stable and can be scaled up proportionally. Second, the composite of 0~2.5% mol Bi2O3 in SnTe can simultaneously have beneficial effects on the electrical and thermal transport processes of the material. By adjusting the carrier concentration, the Seebeck coefficient is increased, and the second phase introduced by the composite enhances the phonon scattering process to reduce the thermal conductivity of the material, thus synergistically optimizing the thermoelectric performance of the material. Third, the samples obtained using this process have high density and good repeatability. Attached Figure Description

[0014] Figure 1 X-ray diffraction (XRD) patterns of 0, 1, 1.5, and 2.5% mol Bi₂O₃-SnTe powder samples;

[0015] Figure 2 The image shows a scanning electron microscope (SEM) image of the fracture surface of the bulk obtained after hot pressing and sintering of 1.5% mol Bi2O3-SnTe sample.

[0016] Figure 3 The thermal conductivity-temperature curves are for Examples 1, 2, 3 and 4 of this invention.

[0017] Figure 4 The conductivity-temperature curves are for Examples 1, 2, 3 and 4 of this invention.

[0018] Figure 5 Seebeck coefficient-temperature curves for Examples 1, 2, 3 and 4 of this invention;

[0019] Figure 6 The thermoelectric figure of merit-temperature curves are for Examples 1, 2, 3 and 4 of this invention. Detailed Implementation

[0020] The present invention will be specifically described below with reference to the embodiments:

[0021] Example 1

[0022] Bi2O3 did not participate in the preparation of the composite SnTe thermoelectric material. The specific preparation process is as follows:

[0023] (1) High-temperature solid-state reaction: First, according to the stoichiometric ratio of Sn and Te in SnTe, weigh 2.374 g of Sn powder and 2.552 g of Te powder, pour them into a clean and dry mortar and mix them evenly. Then, put them into a quartz tube and seal the tube under vacuum. Evacuate the tube to 3*10-1 The pressure was increased to MPa, and the vacuum process lasted for 15 minutes. After the tube was sealed and cooled, it was placed in a well furnace for high-temperature solid-phase reaction to obtain the required 4.926 g SnTe sample.

[0024] (2) High-temperature annealing treatment: Grind the SnTe sample obtained in step (1) into a uniform powder, weigh 4.500 g of the SnTe powder and put it into a clean and dry quartz tube, vacuum and seal the tube at high temperature, and put the quartz tube containing the sample into a pit furnace for high-temperature annealing treatment to obtain the desired SnTe sample.

[0025] (3) Rapid hot pressing sintering process: The SnTe sample obtained in step (2) is placed in a mortar and ground thoroughly until uniform. Then, the powder is loaded into a graphite mold with an inner diameter of 13 mm and subjected to an axial pressure of 50 MPa and a temperature of 500°C. o The sample was kept at a temperature of C for 30 minutes. After the temperature was maintained, the heating source was turned off and the pressure was reduced. The SnTe thermoelectric material was obtained after the sample was completely cooled.

[0026] Example 2

[0027] The preparation process of 1% Bi2O3 composite SnTe thermoelectric material is as follows:

[0028] (1) High-temperature solid-state reaction: The preparation process is the same as that in Example 1 (1);

[0029] (2) High temperature annealing treatment: Weigh the SnTe sample obtained in step (1) and grind it into a uniform powder. Weigh 4.500 g of SnTe powder and weigh 0.085 g of Bi2O3 powder according to the 1% mol Bi2O3-SnTe composite ratio. Mix it evenly in a mortar and then prepare it in the same way as in Example 1 (2). Finally, SnTe sample with 1% mol Bi2O3 composite is obtained.

[0030] (3) Rapid hot pressing sintering process: The preparation process is the same as that in Example 1 (3).

[0031] Example 3

[0032] The preparation process of 1.5% mol Bi2O3 composite SnTe thermoelectric material is as follows:

[0033] (1) High-temperature solid-state reaction: The preparation process is the same as that in Example 1 (1);

[0034] (2) High-temperature annealing treatment: Grind the SnTe sample obtained in step (1) into a uniform powder, weigh 4.500 g of SnTe powder, and weigh 0.128 g of Bi2O3 powder according to the ratio of 1.5% mol Bi2O3-SnTe. Mix them evenly in a mortar. The subsequent preparation is the same as in (2) of Example 1. Finally, SnTe sample with 1.5% mol Bi2O3 composite is obtained.

[0035] (3) Rapid hot pressing sintering process: The preparation process is the same as that in Example 1 (3).

[0036] Example 4

[0037] The preparation process of 2.5% mol Bi2O3 composite SnTe thermoelectric material is as follows:

[0038] (1) High-temperature solid-state reaction: The preparation process is the same as that in Example 1 (1);

[0039] (2) High-temperature annealing treatment: Grind the SnTe sample obtained in step (1) into a uniform powder, weigh 4.500 g of the SnTe powder, and weigh 0.213 g of Bi2O3 powder according to the ratio of 2.5% mol Bi2O3-SnTe. Mix them evenly in a mortar. The subsequent preparation is the same as in (2) of Example 1. Finally, SnTe sample with 2.5% mol Bi2O3 composite is obtained.

[0040] (3) Rapid hot pressing sintering process: The preparation process is the same as that in Example 1 (3).

[0041] Example 5

[0042] The phase composition, thermal diffusivity, resistivity, and Seebeck coefficient of the samples obtained in Examples 1, 2, 3, and 4 were tested: The samples were first cut into circular and cylindrical shapes using a Shenyang Kejing STX-202A diamond wire cutter, followed by thermoelectric performance testing. X-ray diffraction patterns (…) Figure 1 As can be seen, the diffraction peaks in the spectra of 0, 1, 1.5, and 2.5% mol Bi2O3-SnTe samples are characteristic diffraction peaks of SnTe. The positions of the diffraction peaks are completely consistent with the standard card of SnTe (PDF# 46-1210), indicating a cubic crystal system and good crystallinity. Only the sample with composite 2.5% mol Bi2O3-SnTe showed a diffraction peak of the (110) crystal plane of the secondary phase SnO2 (PDF# 41-1445). No obvious secondary phase diffraction peaks were observed in the other composite samples. Figure 2The SEM image of the fresh fracture surface of the 1.5% mol Bi₂O₃-SnTe bulk sample clearly shows the high density of the 1.5% mol Bi₂O₃-SnTe bulk sample. Figure 3 As shown, the thermal conductivity of all samples decreased with increasing temperature throughout the entire temperature range (323 K ~ 823 K). Furthermore, after a certain amount of Bi₂O₃ was incorporated into the SnTe sample, the thermal conductivity also showed a gradual decreasing trend with increasing in the amount of Bi₂O₃ incorporated. At 823 K, the thermal conductivity of the 1.5% mol Bi₂O₃-SnTe sample was 1.955 W / m K. Figure 4 As shown, the conductivity of all samples decreased with increasing temperature throughout the entire temperature range (323 K ~ 823 K). Furthermore, after a certain amount of Bi₂O₃ was incorporated into the SnTe sample, the conductivity also showed a gradual decreasing trend with increasing incorporation amount. At 823 K, the conductivity of the 1.5% mol Bi₂O₃-SnTe sample was 71500 S / m. Figure 5 As shown, the Seebeck coefficient of all samples increases with increasing temperature, and the Seebeck coefficient of all Bi₂O₃-composite SnTe samples is higher than that of the uncomposite original SnTe samples. At a temperature of 823 K, the Seebeck coefficient of the 1.5% mol Bi₂O₃-SnTe sample is 166 μV / K. Figure 6 As shown, the thermoelectric figure of merit of all samples increased with increasing temperature throughout the entire temperature range (323 K ~ 823 K), and the thermoelectric figure of merit of all SnTe samples with composite Bi2O3 was higher than that of the uncomposite original SnTe samples. At a temperature of 823 K, the thermoelectric figure of merit of the 1.5% mol Bi2O3-SnTe sample was 0.83.

Claims

1. A method for preparing a Bi2O3 composite SnTe thermoelectric material, characterized in that, Using Sn powder, Te powder, and Bi₂O₃ powder as raw materials, a 0–2.5% mol Bi₂O₃-SnTe thermoelectric material was prepared through high-temperature solid-state reaction, high-temperature annealing, and rapid hot-pressing sintering. The specific steps are as follows: a. High-temperature solid-state reaction: According to the stoichiometric ratio of Sn and Te in SnTe, 2.374 g of Sn powder and 2.552 g of Te powder were weighed and mixed evenly in a clean mortar. The mixed powder was then loaded into a clean and dry quartz tube, vacuumed, and sealed at high temperature. The quartz tube containing the sample was placed in a pit furnace for high-temperature solid-state reaction to obtain 4.926 g of SnTe sample; b. High-temperature annealing: The SnTe sample obtained in step a was ground into a uniform powder. 4.500 g of SnTe powder was weighed and annealed according to the 0–2.5% mol Bi₂O₃-SnTe sintering process. The Bi2O3-SnTe ratio is as follows: Weigh Bi2O3 powder, mix it evenly in a mortar, load the mixed powder into a clean and dry quartz tube, evacuate and seal the tube at high temperature, and place the quartz tube containing the mixed sample into a pit furnace for high-temperature annealing to obtain the desired composite 0-2.5% mol Bi2O3 SnTe sample; c. Rapid hot pressing sintering process: Place the composite 0-2.5% mol Bi2O3-SnTe sample obtained in step b into a mortar and grind it thoroughly until completely mixed. Then, load the obtained sample powder into a graphite mold and rapidly hot press and sinter to obtain a high-density 0-2.5% mol Bi2O3-SnTe thermoelectric material.

2. The preparation method of Bi2O3 composite SnTe thermoelectric material as described in claim 1, wherein the high-temperature solid-state reaction is characterized by: heating to 450°C at a rate of 0.5-1.5°C / min, then continuously heating to 950-1050°C at a rate of 1-2°C / min, holding at that temperature for 8-12 hours, then cooling to 650°C at a rate of 1-2°C / min, holding at that temperature for 20-26 hours, and finally continuously cooling to room temperature at a rate of 1-2°C / min.

3. The preparation method of Bi2O3 composite SnTe thermoelectric material as described in claim 1, wherein the annealing treatment is characterized by: heating to 750°C at a rate of 1-2°C / min, holding at that temperature for 5-9 hours, and then cooling to room temperature at a rate of 1-2°C / min.

4. The preparation method of Bi2O3 composite SnTe thermoelectric material as described in claim 1, wherein the rapid hot pressing sintering process is characterized by: hot pressing for 20 to 40 minutes under an axial pressure of 40 to 60 MPa and an environment of 500 to 600 °C.

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