Ytterbium-doped tin selenide thermoelectric material and method of making

Abstract

The application discloses a ytterbium-doped tin selenide thermoelectric material and a preparation method thereof. The method is to synthesize ytterbium-doped tin selenide powder material by a solvothermal method, and to sinter the sample into a block by using a large current to heat in a pressurization process by using a discharge plasma sintering technology; the plasma generated by the pulse current and the pressurization in the sintering process are favorable for reducing the sintering temperature of the powder, and meanwhile, the characteristics of low voltage and high current can enable the powder to be rapidly sintered and densified. The method is simple, time-consuming is short, and a small amount of heavy rare earth element ytterbium is doped, so that the power factor of the material is improved by 60% at 823K, the thermoelectric figure of merit zT reaches 1.1, and the thermoelectric performance of the tin selenide material is obviously improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of thermoelectric materials, and relates to a ytterbium-doped tin selenide thermoelectric material and a preparation method thereof. BACKGROUND

[0002] Thermoelectric materials can realize direct conversion between heat and electricity, and are considered as an important means to solve the environmental pollution and energy shortage caused by excessive dependence on fossil fuels. Thermoelectric materials have the advantages of small volume, no pollution and no mechanical movement, and have a relatively broad application prospect in the fields of waste heat recovery, semiconductor refrigeration, biological medicine and the like. However, the thermoelectric materials have problems of high preparation cost, weak thermoelectric performance, weak material mechanical performance and difficulty in large-scale use. Therefore, simplifying the production steps and improving the material mechanical performance and thermoelectric performance are a major focus of thermoelectric material research.

[0003] The power generation efficiency of thermoelectric materials is determined by the thermoelectric figure of merit zT of the materials, zT=(S 2 σ / κ)T. At a certain temperature, the larger the Seebeck coefficient (S) of the material, the higher the electrical conductivity (σ) and the lower the thermal conductivity (κ), the better the thermoelectric performance of the material. However, these parameters are mutually restricted, and it is difficult to realize the independent control of a certain parameter. Research has found that when the carrier concentration of the material is 10 19 ~ 10 21 cm -3 , the best electrical transport performance (S 2 σ) can be obtained, and the thermal transport performance will not be significantly increased.

[0004] Tin selenide (SnSe) is a typical layered material, and the mineral resources of its synthesis raw materials Sn and Se are abundant, which greatly reduces the synthesis cost. SnSe has a relatively low lattice thermal conductivity and a high thermoelectric application value, but its low carrier concentration and low power factor limit its development. At present, the main ways to optimize the performance of polycrystalline SnSe thermoelectric materials are as follows: (1) doping, optimizing the carrier concentration and changing the state density effective mass, so as to obtain a higher power factor, for example, Rhyee et al. improved the room-temperature carrier concentration of SnSe material from 2.6×10 17 cm -3 to 6.2×10 18 cm -3while retaining a large Seebeck coefficient, with a maximum zT of 1.6 at 823 K (10.1021 / acs.chemmater.7b01612); (2) optimizing the lattice thermal conductivity of the material through nanostructuring and phonon engineering, for example, Serrano et al. significantly enhanced the phonon scattering of the material by introducing GeSe nanoparticles into SnSe, which reduced the lattice thermal conductivity of the sample to only 0.35 Wm -1 K -1 (10.1016 / j.jmat.2021.03.016). SUMMARY

[0005] In order to overcome the defects of high preparation cost of thermoelectric materials and weak mechanical properties of materials, the present application provides a kind of doped ytterbium tin selenide thermoelectric material and its preparation method.The method is to synthesize polycrystalline tin selenide thermoelectric material by solvothermal method, and to press the powder sample into a block material with good density by using spark plasma sintering.

[0006] The technical scheme adopted by the present application is as follows:

[0007] The preparation method of the doped ytterbium tin selenide thermoelectric material is to synthesize polycrystalline tin selenide thermoelectric material by solvothermal method, and to press the powder sample into a block material with good density by using spark plasma sintering, and the specific steps are as follows:

[0008] Step 1, according to the molar ratio of stannous chloride dihydrate, selenium dioxide and ytterbium chloride hexahydrate of 0.97-0.99:1:0.01-0.03, stannous chloride dihydrate, selenium dioxide and ytterbium chloride hexahydrate are added to ethylene glycol, and sodium hydroxide is added, stirred until mixed uniformly, and solvent thermal reaction is carried out at 200-250℃. After the reaction is completed, cool to room temperature, take out the product, centrifugal wash to remove impurities, vacuum drying, get doped ytterbium tin selenide (Sn 1-x Yb x Se) powder, wherein the ratio of ethylene glycol and sodium hydroxide is 70-90:80-100, mL:mmol;

[0009] Step 2, the powder is subjected to spark plasma sintering (SPS) to obtain a doped ytterbium tin selenide block.

[0010] Preferably, in step 1, the molar ratio of stannous chloride dihydrate, selenium dioxide and ytterbium chloride hexahydrate is 0.98:1:0.02.

[0011] Preferably, in step 1, the solvent thermal reaction time is 34-38 hours.

[0012] Preferably, in step 1, the washing is carried out with deionized water and anhydrous ethanol for two times respectively.

[0013] Preferably, in step 1, the centrifugal condition is 6000-10000r / min for 3-8min.

[0014] Preferably, in step 1, the vacuum drying temperature is 50-70℃, and the drying time is 10-14h.

[0015] Preferably, in step 2, the sintering temperature of the spark plasma sintering is 600-650℃, the holding time is 10-20min, and the sintering pressure is 40-50MPa. In the specific embodiment of the present application, the sintering temperature is 650℃, the holding time is 15min, and the sintering pressure is 50MPa.

[0016] Compared with the prior art, the present application has the following advantages:

[0017] (1) The present application uses a solvothermal method to synthesize tin selenide material in one step, and the synthesis process is simple and time-saving. The spark plasma sintering technology has the characteristics of sintering in the pressurization process, and compared with the temperature required by the hot pressing forming technology, the sample has better mechanical properties and densification, which improves the production efficiency and reduces the synthesis energy consumption, and is suitable for industrial application.

[0018] (2) The present application dopes ytterbium to tin selenide material, and controls three thermoelectric parameters, which greatly improves the electrical conductivity σ, the Seebeck coefficient presents a small decrease, and the thermal conductivity κ decreases slightly, so as to ultimately achieve the purpose of improving the thermoelectric conversion efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The electrical conductivity (σ) of Sn 1-x Yb x Se (x=0, 0.01, 0.02 and 0.03) samples versus temperature.

[0020] Figure 2 The electrical conductivity (σ) of Sn 1-x Yb x Seebeck coefficient (S) of Sn

[0021] Figure 3 The electrical conductivity (σ) of Sn 1-x Yb x Power factor (S 2 σ) of Sn

[0022] Figure 4 The electrical conductivity (σ) of Sn1-x Yb x The relationship between thermal conductivity (κ) and temperature for Se samples (x = 0, 0.01, 0.02 and 0.03).

[0023] Figure 5 Sn in each embodiment and comparative example 1-x Yb x The thermoelectric figure of merit (zT) of Se samples (x = 0, 0.01, 0.02 and 0.03) is related to temperature change. Detailed Implementation

[0024] The present invention will now be described in further detail with reference to the embodiments and accompanying drawings.

[0025] Example 1

[0026] 19.8 mmol of stannous chloride dihydrate, 20 mmol of selenium dioxide, and 0.2 mmol of ytterbium chloride hexahydrate were added to 80 mL of ethylene glycol, along with 90 mmol of sodium hydroxide. The mixture was stirred at room temperature for 10 minutes and then sealed in a hydrothermal reactor. A solvothermal reaction was carried out at 230 °C for 36 hours. After the reaction, the reactor was cooled to room temperature, and the product was removed and washed twice each with deionized water and anhydrous ethanol. The product was centrifuged at 8000 r / min for 5 minutes, and then vacuum dried at 60 °C for 12 hours. The sample was then removed, ground into powder, and placed in a specially made graphite mold with an inner diameter of 10 mm for discharge plasma sintering at 650 °C for 15 minutes and a sintering pressure of 50 MPa. Thermoelectric performance tests were conducted perpendicular to the sintering pressure direction.

[0027] Example 2

[0028] 19.6 mmol of stannous chloride dihydrate, 20 mmol of selenium dioxide, and 0.4 mmol of ytterbium chloride hexahydrate were added to 80 mL of ethylene glycol, along with 90 mmol of sodium hydroxide. The mixture was stirred at room temperature for 10 minutes and then sealed in a hydrothermal reactor. A solvothermal reaction was carried out at 230 °C for 36 hours. After the reaction, the reactor was cooled to room temperature, and the product was removed and washed twice each with deionized water and anhydrous ethanol. The product was centrifuged at 8000 r / min for 5 minutes, and then vacuum dried at 60 °C for 12 hours. The sample was then removed, ground into powder, and placed in a specially made graphite mold with an inner diameter of 10 mm for discharge plasma sintering at 650 °C for 15 minutes and a sintering pressure of 50 MPa. Thermoelectric performance tests were conducted perpendicular to the sintering pressure direction.

[0029] Example 3

[0030] 19.4 mmol of stannous chloride dihydrate and 20 mmol of selenium dioxide were added into 80 mL of ethylene glycol, and 90 mmol of sodium hydroxide was added. After stirring at room temperature for 10 minutes, the autoclave was sealed. The solvothermal reaction was carried out at 230°C for 36 hours. After the reaction, the product was taken out, washed with deionized water and anhydrous ethanol twice, centrifuged at 8000 r / min for 5 min, and then vacuum dried at 60°C for 12 h. The sample was ground into powder and placed in a special graphite mold with an inner diameter of 10 mm, and spark plasma sintering was carried out at a sintering temperature of 650°C, a holding time of 15 min, and a sintering pressure of 50 MPa. The thermoelectric performance was tested in the direction perpendicular to the sintering pressure direction.

[0031] Comparative Example 1

[0032] 19.4 mmol of stannous chloride dihydrate and 20 mmol of selenium dioxide were added into 80 mL of ethylene glycol, and 90 mmol of sodium hydroxide was added. After stirring at room temperature for 10 minutes, the autoclave was sealed. The solvothermal reaction was carried out at 230°C for 36 hours. After the reaction, the product was taken out, washed with deionized water and anhydrous ethanol twice, centrifuged at 8000 r / min for 5 min, and then vacuum dried at 60°C for 12 h. The sample was ground into powder and placed in a special graphite mold with an inner diameter of 10 mm, and spark plasma sintering was carried out at a sintering temperature of 650°C, a holding time of 15 min, and a sintering pressure of 50 MPa. The thermoelectric performance was tested in the direction perpendicular to the sintering pressure direction.

[0033] Table 1

[0034]

[0035] Figure 1 The Seebeck coefficient of the Sn 1-x Yb x The relationship between the conductivity (σ) of the Yb-doped SnSe (x = 0, 0.01, 0.02, and 0.03) samples and temperature is shown in the graph. It can be seen that the conductivity of the undoped SnSe material prepared in Comparative Example 1 is low, only 35.55 S cm -1 at 823K, which is significantly lower than that of the examples. When the Yb doping amount is 0.02, a higher conductivity of 78.07 S cm -1 at 823K is achieved, indicating that Yb element doping can significantly improve the conductivity of the material.

[0036] The Seebeck coefficient of each example and comparative example was tested, and the results are shown in Figure 2 . From Figure 2It can be seen that the Seebeck coefficient of the SnSe material doped with Yb decreases slightly, but the decrease is small.

[0037] Figure 3 The SnSe materials in the embodiments and the comparative examples 1-x Yb x The power factor (S2σ) of the SnSe (x=0, 0.01, 0.02 and 0.03) samples versus temperature can be seen from the figure that the power factor of the SnSe material doped with Yb increases obviously compared with the undoped SnSe material. When the Yb content is 0.02, the power factor of the SnSe sample at 823 K is 1.6 times that of the undoped SnSe sample. 2 σ) with temperature, it can be seen that the power factor of the SnSe material doped with Yb increases obviously compared with the undoped SnSe material. When the Yb content is 0.02, the power factor of the SnSe sample at 823 K is 1.6 times that of the undoped SnSe sample.

[0038] Figure 4 The SnSe materials in the embodiments and the comparative examples 1-x Yb x The thermal conductivity (κ) of the SnSe (x=0, 0.01, 0.02 and 0.03) samples versus temperature can be seen from the figure that the thermal conductivity of the SnSe material doped with Yb decreases slightly.

[0039] Figure 5 The SnSe materials in the embodiments and the comparative examples 1-x Yb x The thermoelectric figure of merit (zT) of the SnSe (x=0, 0.01, 0.02 and 0.03) samples versus temperature can be seen from the figure that when the Yb content is 0.02, the highest zT of 1.1 is reached at 823 K, and the thermoelectric performance is improved by about 100% compared with the undoped SnSe sample.

Claims

1. A method of producing a doped ytterbium tin selenide thermoelectric material, characterized by, The specific steps are as follows: Step 1, according to the molar ratio of stannous chloride dihydrate, selenium dioxide, and ytterbium chloride hexahydrate of 0.97-0.99:1:0.01-0.03, stannous chloride dihydrate, selenium dioxide, and ytterbium chloride hexahydrate are added to ethylene glycol, and sodium hydroxide is added, stirred until mixed uniformly, and then subjected to a solvothermal reaction at 200-250°C. After the reaction is completed, the product is cooled to room temperature, removed, centrifuged, washed to remove impurities, and vacuum dried to obtain ytterbium-doped tin selenide powder, wherein the ratio of ethylene glycol and sodium hydroxide is 70-90:80-100, mL:mmol; Step 2, the powder is subjected to discharge plasma sintering to obtain ytterbium-doped tin selenide bulk.

2. The production method according to claim 1, characterized by, In step 1, the molar ratio of stannous chloride dihydrate, selenium dioxide, and ytterbium chloride hexahydrate is 0.98:1:0.

02.

3. The preparation method according to claim 1, characterized in that, In step 1, the solvothermal reaction time is 34-38 hours.

4. The production method according to claim 1, characterized by, In step 1, the washing is performed twice using deionized water and anhydrous ethanol.

5. The preparation method according to claim 1, characterized in that, In step 1, the centrifugation conditions are 6000-10000 r / min for 3-8 min.

6. The method of claim 1, wherein, In step 1, the vacuum drying temperature is 50-70°C, and the drying time is 10-14 h.

7. The preparation method according to claim 1, characterized in that, In step 2, the sintering temperature of discharge plasma sintering is 600-650°C, the holding time is 10-20 min, and the sintering pressure is 40-50 MPa.

8. The method of claim 1, wherein, In step 2, the sintering temperature of discharge plasma sintering is 650°C, the holding time is 15 min, and the sintering pressure is 50 MPa.

9. The ytterbium-doped tin selenide thermoelectric material prepared by the preparation method of any one of claims 1-8.

Images