Aluminum-doped AgBiSe2 nanomaterials and their preparation method

Abstract

The present invention discloses an aluminum-doped AgBiSe2 nanomaterial and a preparation method thereof. Based on the S-doped AgBiSe2, Al is further doped, and the hydrothermal method is used to synthesize the aluminum-doped AgBiSe2 nanomaterial. In the AgBi 1‑y Al y Se 1.5 S 0.5 nanomaterial of the present invention, the doped S is used to adjust the electronic energy band structure and simultaneously introduce lattice distortion, and the doped Al is used to increase the phonon-phonon scattering in the AgBiSe2 nanomaterial and simultaneously change its crystal phase structure, improve its power factor, and reduce the lattice thermal conductivity, thereby achieving an increase in zT. The power factor reaches 0.34 mW / m / K at 773K 2 , and the thermoelectric figure of merit zT reaches a maximum of 1.02, significantly improving the thermoelectric performance of the AgBiSe2 nanomaterial.

Description

Technical Field

[0001] The present invention belongs to the field of thermoelectric materials and relates to an aluminum (Al)-doped AgBiSe2 nanomaterial and a preparation method thereof. Background Art

[0002] Thermoelectric conversion technology is a green and environmentally friendly technology that can directly convert electrical energy and thermal energy into each other. The energy conversion efficiency of thermoelectric materials is measured by the dimensionless thermoelectric figure of merit zT = (S 2 σ / κ)T = S 2 σT / (κ e +κ l ), where σ, S, S 2 σ, T, κ, κ e and κ l are the electrical conductivity, Seebeck coefficient, power factor, absolute temperature, total thermal conductivity, and electronic and lattice thermal conductivities, respectively. It can be seen that at a certain temperature T, to make the material have high thermoelectric efficiency, it is necessary to make it have a high power factor S 2 σ and a low thermal conductivity κ.

[0003] The AgBiSe2 compound is a typical narrow-band semiconductor with multiple crystal structures and usually exists in three crystal structures: cubic phase, hexagonal phase, and rhombohedral phase. AgBiSe2 synthesized by the solution route exhibits p-type semiconductor behavior, and the zTmax reaches 1.5 (10.1021 / ja308936b) at 700K. As a n-type semiconductor with poor conductivity, the thermoelectric properties of AgBiSe2 can be improved by doping at the Ag position or at the Se position. In Document 1, by doping In at the Ag position, Ag, In, Bi, and Se were loaded into a vacuum melting quartz tube, and the tube was heat-treated in a programmable furnace before being cooled to room temperature at a rate of 60K / h. The temperature was raised to 673K in 14h, then raised to 1123K in 4h, and homogenized for 20h to obtain powder, which was sintered into bulk particles using a spark plasma sintering system, where the zTmax of the product was 0.7 (10.1063 / 1.4963779). In Document 2, by doping Te at the Se position, the raw materials were mixed and pressed into particles, and then heated in a vacuum quartz tube at 500°C for 15 hours, where the zTmax of the product was 0.6 (10.1039 / c7dt04821a). The above methods all adopt the mechanical alloying method, which is relatively cumbersome and costly. Summary of the Invention

[0004] In order to obtain a stable structure of the AgBiSe2 phase and improve its thermoelectric performance, the present invention provides an aluminum-doped AgBiSe2 nanomaterial and a preparation method thereof. The aluminum-doped AgBiSe2 nanomaterial of the present invention is AgBi 1-y Aly Se 1.5 S 0.5 , where y = 0.01 - 0.1.

[0005] The aluminum-doped AgBiSe2 nanomaterial of the present invention is synthesized by a hydrothermal method and is sintered by spark plasma sintering. The powder sample is pressed into a bulk material with good density. The specific steps are as follows:

[0006] Mix aluminum chloride hexahydrate, silver nitrate, and bismuth nitrate pentahydrate evenly according to the molar ratio of silver nitrate: bismuth nitrate pentahydrate: selenium powder: N,N'-diphenylthiourea: aluminum chloride hexahydrate of 10:8.5:15:10:0.1 - 1. Add the mixed solution of oleylamine, oleic acid, and octadecene, evacuate, introduce N2 for protection, heat to 170 - 180 °C, and sequentially add the diphenyl ether solution of N,N'-diphenylthiourea and the octadecene dispersion of selenium powder. Keep the temperature for reaction. After the reaction is completed, cool to room temperature, take out the product, centrifuge and wash to remove impurities, dry in vacuum, and finally perform spark plasma sintering to obtain the bulk aluminum-doped AgBiSe2 nanomaterial.

[0007] Preferably, the molar ratio of silver nitrate: bismuth nitrate pentahydrate: selenium powder: N,N'-diphenylthiourea: aluminum chloride hexahydrate is 10:8.5:15:10:0.5.

[0008] Preferably, in the diphenyl ether solution of N,N'-diphenylthiourea, the concentration of N,N'-diphenylthiourea is 0.22 mol / L.

[0009] Preferably, in the octadecene dispersion of selenium powder, the concentration of selenium powder is 1 mol / L.

[0010] Preferably, in the mixed solution of oleylamine, oleic acid, and octadecene, the volume ratio of oleylamine: oleic acid: octadecene is 1:1:7.

[0011] Preferably, the reaction time for keeping the temperature is 30 - 60 min.

[0012] Preferably, the centrifugation conditions are 6000 - 10000 r / min and the centrifugation time is 3 - 8 min.

[0013] Preferably, the washing method is to wash twice with absolute ethanol first, and then wash twice with a mixture of cyclohexane and absolute ethanol.

[0014] Preferably, the vacuum drying temperature is 50 - 70 °C and the drying time is 6 - 10 h.

[0015] Preferably, the sintering temperature of the spark plasma sintering is 300 - 350 °C, the holding time is 5 - 10 min, and the sintering pressure is 40 - 50 MPa.

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

[0017] (1) The present invention synthesizes aluminum-doped AgBiSe2 material by hydrothermal method. The synthesis process is simple and time-consuming is short. And the spark plasma sintering technology is adopted, which has the characteristic of sintering during the pressurization process. Compared with the forming technologies such as hot pressing, the required temperature is lower, and the mechanical properties and density of the sample are better, improving the production efficiency and reducing the synthesis energy consumption;

[0018] (2) The present invention dopes S to adjust the electronic energy band structure and simultaneously introduces lattice distortion. Further doping with Al increases the phonon-phonon scattering in the AgBiSe2 nanomaterial and simultaneously changes its crystal phase structure. When y = 0, 0.01, 0.1, a stable cubic structure of AgBi 1-y Al y Se 2-x S x ; can be obtained at room temperature; when y = 0.03, 0.05, 0.07, a stable hexagonal structure of AgBi 1-y Al y Se 2-x S x can be obtained at room temperature. By doping aluminum into the AgBiSe2 material, three thermoelectric parameters are regulated, significantly improving the electrical conductivity σ (from 62.06 S cm -1 of the undoped sample to 146.80 S cm -1 of the sample doped with 5% aluminum, the same below). The power factor PF shows a large increase (from 0.2 mW / m / K 2 to 0.34 mW / m / K 2 ), and the thermal conductivity κ decreases slightly (from 0.31 W / m / K to 0.26 W / m / K), comprehensively improving the thermoelectric figure of merit; BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a graph showing the relationship between the electrical conductivity (σ) and temperature change of AgBi 1-y Al y Se 1.5 S 0.5 (y = 0, 0.01, 0.03, 0.05, 0.07, 0.1) samples in each embodiment and comparative example.

[0020] Figure 2 is a graph showing the relationship between the Seebeck coefficient (S) and temperature change of AgBi 1-y Al y Se 1.5 S 0.5 (y = 0, 0.01, 0.03, 0.05, 0.07, 0.1) samples in each embodiment and comparative example.

[0021] Figure 3 For AgBi in each example and comparative example 1-y Al y Se 1.5 S 0.5 (y = 0, 0.01, 0.03, 0.05, 0.07, 0.1) Relationship diagram of the power factor (S 2 σ) of the samples versus temperature change.

[0022] Figure 4 For AgBi in each example and comparative example 1-y Al y Se 1.5 S 0.5 (y = 0, 0.01, 0.03, 0.05, 0.07, 0.1) Relationship diagram of the thermal conductivity (κ) of the samples versus temperature change.

[0023] Figure 5 For AgBi in each example and comparative example 1-y Al y Se 1.5 S 0.5 (y = 0, 0.01, 0.03, 0.05, 0.07, 0.1) Relationship diagram of the thermoelectric figure of merit (zT) of the samples versus temperature change.

[0024] Figure 6 For AgBi in each example 1-y Al y Se 1.5 S 0.5 (y = 0, 0.01, 0.03, 0.05, 0.07, 0.1) XRD change diagram of the samples. Detailed implementation manners

[0025] The present invention will be further described in detail below in conjunction with examples and drawings.

[0026] Example 1

[0027] Dissolve 10 mmol of N,N'-diphenylthiourea in 45 ml of diphenyl ether at 145 °C to obtain a diphenyl ether solution of N,N'-diphenylthiourea; ultrasonically disperse 15 mmol of selenium powder in 15 mL of octadecene to obtain an octadecene dispersion of selenium powder; weigh 0.1 mmol of aluminum chloride hexahydrate, 10 mmol of silver nitrate, and 8.5 mmol of bismuth nitrate pentahydrate into a three-necked flask, and add 10 ml of oleylamine, 10 ml of oleic acid, and 70 ml of octadecene mixed solution; heat the three-necked flask, evacuate, and introduce N2 for protection. Then heat the mixed solution to 180 °C, sequentially add the diphenyl ether solution of N,N'-diphenylthiourea and the octadecene dispersion of selenium powder, and keep warm for 30 min; after the reaction is completed, cool to room temperature, take out the product, centrifuge at 10000 r / min for 3 min, wash twice with absolute ethanol, wash twice with a mixture of cyclohexane and absolute ethanol for impurity removal, and then vacuum dry at 60 °C for 10 h. Sinter the dried product by spark plasma sintering, with a sintering temperature of 350 °C, a holding time of 10 min, and a sintering pressure of 40 MPa to obtain AgBi 0.99 Al 0.01 Se 1.5 S 0.5 bulk material.

[0028] Example 2

[0029] Dissolve 10 mmol of N,N'-diphenylthiourea in 45 ml of diphenyl ether at 145 °C to obtain a diphenyl ether solution of N,N'-diphenylthiourea; ultrasonically disperse 15 mmol of selenium powder in 15 mL of octadecene to obtain an octadecene dispersion of selenium powder; weigh 0.3 mmol of aluminum chloride hexahydrate, 10 mmol of silver nitrate, and 8.5 mmol of bismuth nitrate pentahydrate into a three-necked flask, and add 10 ml of oleylamine, 10 ml of oleic acid, and 70 ml of octadecene mixed solution; heat the three-necked flask, evacuate, and introduce N2 for protection. Then heat the mixed solution to 180 °C, sequentially add the diphenyl ether solution of N,N'-diphenylthiourea and the octadecene dispersion of selenium powder, and keep warm for 30 min; after the reaction is completed, cool to room temperature, take out the product, centrifuge at 10000 r / min for 3 min, wash twice with absolute ethanol, wash twice with a mixture of cyclohexane and absolute ethanol for impurity removal, and then vacuum dry at 60 °C for 10 h. Sinter the dried product by spark plasma sintering, with a sintering temperature of 350 °C, a holding time of 10 min, and a sintering pressure of 40 MPa to obtain AgBi 0.97 Al 0.03 Se 1.5 S 0.5 bulk material.

[0030] Example 3

[0031] Dissolve 10 mmol of N,N'-diphenylthiourea in 45 ml of diphenyl ether at 145 °C to obtain a diphenyl ether solution of N,N'-diphenylthiourea; ultrasonically disperse 15 mmol of selenium powder in 15 mL of octadecene to obtain an octadecene dispersion of selenium powder; weigh 0.5 mmol of aluminum chloride hexahydrate, 10 mmol of silver nitrate, and 8.5 mmol of bismuth nitrate pentahydrate into a three-necked flask, and add 10 ml of oleylamine, 10 ml of oleic acid, and 70 ml of octadecene mixed solution; heat the three-necked flask, evacuate, and introduce N2 for protection. Then heat the mixed solution to 180 °C, and successively add the diphenyl ether solution of N,N'-diphenylthiourea and the octadecene dispersion of selenium powder, and keep warm for 30 min; after the reaction is completed, cool to room temperature, take out the product, centrifuge at 10000 r / min for 3 min, wash twice with absolute ethanol, wash twice with a mixture of cyclohexane and absolute ethanol for impurity removal, and then vacuum dry at 60 °C for 10 h. Perform spark plasma sintering on the dried product, with a sintering temperature of 350 °C, a holding time of 10 min, and a sintering pressure of 40 MPa to obtain AgBi 0.95 Al 0.05 Se 1.5 S 0.5 bulk material.

[0032] Example 4

[0033] Dissolve 10 mmol of N,N'-diphenylthiourea in 45 ml of diphenyl ether at 145 °C to obtain a diphenyl ether solution of N,N'-diphenylthiourea; ultrasonically disperse 15 mmol of selenium powder in 15 mL of octadecene to obtain an octadecene dispersion of selenium powder; weigh 0.7 mmol of aluminum chloride hexahydrate, 10 mmol of silver nitrate, and 8.5 mmol of bismuth nitrate pentahydrate into a three-necked flask, and add 10 ml of oleylamine, 10 ml of oleic acid, and 70 ml of octadecene mixed solution; heat the three-necked flask, evacuate, and introduce N2 for protection. Then heat the mixed solution to 180 °C, and successively add the diphenyl ether solution of N,N'-diphenylthiourea and the octadecene dispersion of selenium powder, and keep warm for 30 min; after the reaction is completed, cool to room temperature, take out the product, centrifuge at 10000 r / min for 3 min, wash twice with absolute ethanol, wash twice with a mixture of cyclohexane and absolute ethanol for impurity removal, and then vacuum dry at 60 °C for 10 h. Perform spark plasma sintering on the dried product, with a sintering temperature of 350 °C, a holding time of 10 min, and a sintering pressure of 40 MPa to obtain AgBi 0.93 Al 0.07 Se 1.5 S 0.5 bulk material.

[0034] Example 5

[0035] Dissolve 10 mmol of N,N'-diphenylthiourea in 45 ml of diphenyl ether at 145 °C to obtain a diphenyl ether solution of N,N'-diphenylthiourea; ultrasonically disperse 15 mmol of selenium powder in 15 mL of octadecene to obtain an octadecene dispersion of selenium powder; weigh 1.0 mmol of aluminum chloride hexahydrate, 10 mmol of silver nitrate, and 8.5 mmol of bismuth nitrate pentahydrate into a three-necked flask, and add a mixed solution of 10 ml of oleylamine, 10 ml of oleic acid, and 70 ml of octadecene; heat the three-necked flask, evacuate, and introduce N2 for protection. Then heat the mixed solution to 180 °C, and successively add the diphenyl ether solution of N,N'-diphenylthiourea and the octadecene dispersion of selenium powder, and keep warm for 30 min; after the reaction is completed, cool to room temperature, take out the product, centrifuge at 10000 r / min for 3 min, wash twice with absolute ethanol, wash twice with a mixture of cyclohexane and absolute ethanol for impurity removal, and then dry in vacuum at 60 °C for 10 h. Sinter the dried product by spark plasma sintering, with a sintering temperature of 350 °C, a holding time of 10 min, and a sintering pressure of 40 MPa to obtain AgBi 0.9 Al 0.1 Se 1.5 S 0.5 bulk material.

[0036] Comparative Example 1

[0037] Dissolve 10 mmol of N,N'-diphenylthiourea in 45 ml of diphenyl ether at 145 °C to obtain a diphenyl ether solution of N,N'-diphenylthiourea; ultrasonically disperse 15 mmol of selenium powder in 15 mL of octadecene to obtain an octadecene dispersion of selenium powder; weigh 10 mmol of silver nitrate and 8.5 mmol of bismuth nitrate pentahydrate into a three-necked flask, and add a mixed solution of 10 ml of oleylamine, 10 ml of oleic acid, and 70 ml of octadecene; heat the three-necked flask, evacuate, and introduce N2 for protection. Then heat the mixed solution to 180 °C, and successively add the diphenyl ether solution of N,N'-diphenylthiourea and the octadecene dispersion of selenium powder, and keep warm for 30 min; after the reaction is completed, cool to room temperature, take out the product, centrifuge at 10000 r / min for 3 min, wash twice with absolute ethanol, wash twice with a mixture of cyclohexane and absolute ethanol for impurity removal, and then dry in vacuum at 60 °C for 10 h. Sinter the dried product by spark plasma sintering, with a sintering temperature of 350 °C, a holding time of 10 min, and a sintering pressure of 40 MPa to obtain AgBiSe 1.5 S 0.5 bulk material.

[0038] Table 1

[0039]

[0040] Figure 1 for AgBi in each example and comparative example1-y Al y Se 1.5 S 0.5 (y = 0, 0.01, 0.03, 0.05, 0.07, 0.1) Relationship diagram of the conductivity (σ) of the samples versus temperature change. It can be seen that the conductivity of the undoped aluminum AgBiSe2 material prepared in Comparative Example 1 is relatively low, only 62.06 S cm at 773 K -1 , which is significantly lower than the conductivities of Examples 1 - 5, which are 71.76 S cm -1 , 105.74 S cm -1 , 146.80 S cm -1 , 222.55 S cm -1 , 41.04 S cm -1 . When the aluminum doping is 0.05, a relatively high conductivity of 146.80 S cm is achieved at 773 K -1 , indicating that the doping of aluminum elements can significantly improve the conductivity of the material, with an increase amplitude of up to 136%.

[0041] Figure 2 For AgBi in each example and comparative example 1-y Al y Se 1.5 S 0.5 (y = 0, 0.01, 0.03, 0.05, 0.07, 0.1) Relationship diagram of the Seebeck coefficient (S) of the samples versus temperature change. At 773 K, Examples 1 - 5 and Comparative Example 1 are -209.11 uV / K, -157.61 uV / K, -151.35 uV / K, -112.46 uV / K, -216.89 uV / K, -187.67 uV / K respectively. Since the Seebeck coefficient and conductivity restrict each other, the Seebeck coefficient of the AgBiSe2 material after aluminum element doping decreases slightly, but the decrease amplitude is small.

[0042] Figure 3 For AgBi in each example and comparative example 1-y Al y Se 1.5 S 0.5 (y = 0, 0.01, 0.03, 0.05, 0.07, 0.1) Relationship diagram of the power factor (S 2 σ) of the samples versus temperature change. At 773 K, Examples 1 - 5 and Comparative Example 1 are 0.31 mW / m / K 2 , 0.26 mW / m / K 2 , 0.34 mW / m / K 2 , 0.28 mW / m / K 2 , 0.19 mW / m / K2 、0.20 mW / m / K 2 It can be seen that compared with the undoped AgBiSe2 material, the power factor of the AgBiSe2 material after aluminum doping has increased significantly, with an increase of 70%.

[0043] Figure 4 For AgBi in each example and comparative example 1-y Al y Se 1.5 S 0.5 (y = 0, 0.01, 0.03, 0.05, 0.07, 0.1) Relationship diagram of the thermal conductivity (κ) of the samples with temperature change. At 773K, for Examples 1-5 and Comparative Example 1, they are 0.34 mW / m / K, 0.36 mW / m / K, 0.26 mW / m / K, 0.47 mW / m / K, 0.26 mW / m / K, 0.31 mW / m / K respectively. It can be found that the thermal conductivity of the AgBiSe2 sample after aluminum doping has decreased slightly, with a decrease of 20%.

[0044] Figure 5 For AgBi in each example and comparative example 1-y Al y Se 1.5 S 0.5 (y = 0, 0.01, 0.03, 0.05, 0.07, 0.1) Relationship diagram of the thermoelectric figure of merit (zT) of the samples with temperature change. At 773K, for Examples 1-5 and Comparative Example 1, they are 0.70, 0.57, 1.02, 0.46, 0.58, 0.50 respectively. It can be seen that when the aluminum content is 0.5, the highest zT of 1.02 is reached at 773K. Compared with the undoped AgBiSe2 sample, the thermoelectric performance has been improved by about 100%.

[0045] Figure 6 For AgBi in each example and comparative example 1-y Al y Se 1.5 S 0.5 (y = 0, 0.01, 0.03, 0.05, 0.07, 0.1) XRD change diagram of the samples. When the y value is 0, 0.01, 0.1, a stable cubic structure of AgBi 1- y Al y Se 1.5 S 0.5 can be obtained at room temperature. When the y value is 0.03, 0.05, 0.07, a stable hexagonal structure of AgBi 1- y Al y Se 1.5 S0.5 。

Claims

1. Preparation method of aluminum-doped AgBiSe2 nanomaterial, characterized in that, The specific steps are as follows: According to the molar ratio of silver nitrate, bismuth nitrate pentahydrate, selenium powder, N,N'-diphenylthiourea and aluminum chloride hexahydrate being 10:8.5:15:10:0.1 - 1, mix aluminum chloride hexahydrate, silver nitrate and bismuth nitrate pentahydrate evenly, add the mixed solution of oleylamine, oleic acid and octadecene, evacuate the air, introduce N2 for protection, heat to 170 - 180 °C, successively add the diphenyl ether solution of N,N'-diphenylthiourea and the octadecene dispersion of selenium powder, keep the temperature for reaction. After the reaction is completed, cool to room temperature, take out the product, centrifuge and wash to remove impurities, dry in vacuum, and finally carry out spark plasma sintering to obtain the bulk aluminum-doped AgBiSe2 nanomaterial AgBi 1- y Al y Se 1.5 S 0.5 , where y = 0.01 - 0.

1.

2. The preparation method according to claim 1, wherein The molar ratio of silver nitrate, bismuth nitrate pentahydrate, selenium powder, N,N'-diphenylthiourea and aluminum chloride hexahydrate is 10:8.5:15:10:0.

5.

3. The preparation method according to claim 1, wherein In the diphenyl ether solution of N,N'-diphenylthiourea, the concentration of N,N'-diphenylthiourea is 0.22 mol / L; in the octadecene dispersion of selenium powder, the concentration of selenium powder is 1 mol / L.

4. The preparation method according to claim 1, characterized in that, In the mixed solution of oleylamine, oleic acid and octadecene, the volume ratio of oleylamine, oleic acid and octadecene is 1:1:

7.

5. The preparation method according to claim 1, characterized in that, The holding reaction time is 30 - 60 min.

6. The preparation method according to claim 1, characterized in that, The centrifugation conditions are 6000 - 10000 r / min and the centrifugation time is 3 - 8 min.

7. The preparation method according to claim 1, characterized in that The washing method is to wash twice with absolute ethanol first, and then wash twice with a mixture of cyclohexane and absolute ethanol.

8. The preparation method according to claim 1, characterized in that, The vacuum drying temperature is 50 - 70 °C and the drying time is 6 - 10 h.

9. The preparation method according to claim 1, characterized in that, The sintering temperature of the spark plasma sintering is 300 - 350 °C, the holding time is 5 - 10 min, and the sintering pressure is 40 - 50 MPa.

10. An aluminum-doped AgBiSe2 nanomaterial prepared by the preparation method according to any one of claims 1 - 9.

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