A Bi2Te 2.7 Se 0.3 -AgBiSe2 composite thermoelectric material and a preparation method thereof

Abstract

The application provides a Bi2Te 2.7 Se 0.3 The application relates to a AgBiSe2 composite thermoelectric material and a preparation method thereof, and belongs to the technical field of thermoelectric material preparation. The method comprises the following steps: reacting selenium powder, silver nitrate and bismuth chloride to synthesize AgBiSe2 nanoparticles, and then mixing the AgBiSe2 nanoparticles with Bi2Te 2.7 Se 0.3 After grinding, vacuum hot-pressing sintering is carried out to obtain the Bi2Te 2.7 Se 0.3 The application introduces the nano-structured AgBiSe2 prepared by a chemical method as a second phase into a Bi2Te 2.7 Se 0.3 matrix, and the ZT value of the composite material can be obviously improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of thermoelectric material preparation, and particularly relates to a Bi2Te 2.7 Se 0.3 -AgBiSe2 composite thermoelectric material and a preparation method thereof. BACKGROUND

[0002] Bi2Te3-based thermoelectric material is a typical room-temperature thermoelectric material, which is widely used in thermoelectric refrigeration, precision temperature control, waste heat recovery and other fields. In addition, it is a typical narrow-bandgap (~0.13eV) semiconductor, which has the highest power factor known so far. Commercial single crystals are usually obtained by controlled growth through a melting method, and then devices are prepared by mechanical cutting. However, this kind of material has low mechanical properties, high mechanical strength and high processing waste rate, which makes it difficult to miniaturize the device. Therefore, researchers use powder metallurgy and other means to prepare polycrystalline Bi2Te3-based materials to improve its mechanical properties. However, the conversion efficiency of this kind of thermoelectric material is still low, which limits its commercial application. By doping Bi2Te3-based materials, p-type and n-type semiconductor thermoelectric materials of different conductive types are obtained. Bi2Te3-based materials have high thermoelectric conversion efficiency, but their mechanical properties are poor, which limits their commercial application. 2.7 Se 0.3 (BTS) alloy is a known n-type Bi2Te3-based thermoelectric material with excellent performance, but its ZT value is limited due to its high thermal conductivity. SUMMARY

[0003] Therefore, the present application aims to provide a Bi2Te 2.7 Se 0.3 -AgBiSe2 composite thermoelectric material and a preparation method thereof.

[0004] AgBiSe2 is an n-type thermoelectric material with intrinsic low thermal conductivity (thermal conductivity of 0.45W / m K at 300K), and the carrier concentration is about 1018cm -3 . At low temperature (T<393K), it is a hexagonal structure (alpha phase), at medium temperature (393K<T<560K), it is an orthorhombic structure (beta phase), and at high temperature (T>560K), it is a cubic structure (gamma phase). By introducing AgBiSe2 nanoparticles into the BTS matrix, due to the different energy band structures of the composite phase and the matrix, an interface potential barrier is formed in the composite material, which significantly improves the Seebeck coefficient of the material, and further optimizes the power factor. At the same time, the composite phase acts as a phonon scattering center to hinder the movement of phonons and suppress the lattice thermal conductivity.

[0005] In order to achieve the above-mentioned purpose, the present application provides the following technical scheme: a Bi2Te 2.7 Se 0.3A preparation method of AgBiSe2 composite thermoelectric material, comprising the following steps:

[0006] (1) adding selenium powder into ethylenediamine, heating and refluxing in an oil bath at 150℃, magnetically stirring, evaporating ethylenediamine by using residual heat after boiling, and dissolving in ethylene glycol while hot to form selenium anion precursor;

[0007] (2) adding ethylene glycol, silver nitrate, bismuth chloride and glycerol into the selenium anion precursor obtained in step (1), stirring and dissolving, reacting at 180℃ for 6h, collecting the precipitate after cooling to room temperature and performing washing and drying to obtain AgBiSe2 nanoparticles;

[0008] (3) grinding Bi2Te 2.7 Se 0.3 After grinding the matrix, adding the AgBiSe2 nanoparticles obtained in step (2) for grinding, and then performing vacuum hot-press sintering to obtain a dense block.

[0009] Preferably, the ratio of selenium powder to ethylenediamine in step (1) is 3mmol:30-80ml.

[0010] Preferably, the molar ratio of selenium powder, silver nitrate and bismuth chloride is 3:6:6.

[0011] Preferably, the washing in step (2) is washing with distilled water and anhydrous ethanol respectively.

[0012] Preferably, the doping amount of AgBiSe2 nanoparticles in step (3) is 0.1-0.5wt% of the obtained block, more preferably 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, and most preferably 0.2wt%.

[0013] Preferably, the vacuum hot-press sintering condition in step (3) is temperature of 523-673K, time of 0.5-2h, and pressure of 20-500MPa.

[0014] Preferably, the grinding time in step (3) is 20-30min.

[0015] The application further provides a Bi2Te 2.7 Se 0.3 -AgBiSe2 composite thermoelectric material prepared by the preparation method.

[0016] Beneficial technical effects:

[0017] The application can optimize the electrical performance of the composite material by energy filtering effect and reduce the lattice thermal conductivity by strong scattering of phonons at the phase interface between the AgBiSe2 nanoparticles and the matrix, thereby improving the thermoelectric figure of merit of the composite system. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 XRD diffraction pattern of AgBiSe2 prepared in Example 1, and the inset is the XRD diffraction pattern of the composite sample (1) and the un-composited Bi2Te 2.7 Se 0.3 (2) XRD pattern obtained at a scanning speed of 2° / min slow scan;

[0019] Figure 2 XRD diffraction pattern of Bi2Te 2.7 Se 0.3 Se and the composite sample obtained in Examples 1-5; 2.7 Se 0.3 XRD diffraction pattern of the composite sample of AgBiSe2;

[0020] Figure 3 TE-SEM pattern of BTS, AgBiSe2, Bi2Te 2.7 Se 0.3 AgBiSe2; wherein, (a) cross-section FE-SEM scanning pattern of BTS, (b) cross-section FE-SEM scanning pattern of the Bi2Te 2.7 Se 0.3 0.5wt% AgBiSe2 composite material, (c) FE-SEM micrograph of AgBiSe2 particles, and (d) particle size of AgBiSe2 in (c);

[0021] Figure 4 Cross-section FE-SEM scanning pattern and energy spectrum analysis pattern of the Bi2Te 2.7 Se 0.3 0.5wt% AgBiSe2 composite material; wherein, (a) cross-section FE-SEM scanning pattern of the Bi2Te 2.7 Se 0.3 0.5wt% AgBiSe2 composite material, (b)-(f) energy spectrum analysis pattern of the element distribution of Bi, Te, Se and Ag;

[0022] Figure 5 Cross-section FE-SEM scanning pattern of the Bi2Te 2.7 Se 0.3 Se and the composite sample obtained in Examples 1-5;

[0023] Figure 6 Bi2Te 2.7 Se 0.3 Scattering parameter λ of the composite samples of Examples 1-5 as a function of AgBiSe2 content (at 300 K);

[0024] Figure 7 Bi2Te 2.7 Se 0.3 Power factor PF of the composite samples of Examples 1-5 as a function of temperature;

[0025] Figure 8 Bi2Te 2.7 Se 0.3 Thermal performance of the composite samples of Examples 1-5 as a function of temperature (a) κ;

[0026] Figure 9 Bi2Te 2.7 Se 0.3 ZT value of the composite samples of Examples 1-5 as a function of temperature. DETAILED DESCRIPTION

[0027] In order to better understand the present application, the following further illustrates the content of the present application in conjunction with the examples, but the content of the present application is not limited only to the following examples.

[0028] Example 1

[0029] (1) Preparation of selenium anion precursor

[0030] 0.2369 g (3 mmol) of elemental selenium powder was weighed, 50 mL of ethylenediamine was added, and the mixture was heated to reflux in an oil bath at 150°C with magnetic stirring. After boiling, the ethylenediamine was evaporated using residual heat, and the selenium anion precursor was dissolved in 10 mL of ethylene glycol while hot.

[0031] (2) Preparation of AgBiSe2 nanoparticles

[0032] The above-prepared selenium anion precursor was added to a 70 mL volume autoclave lined with polytetrafluoroethylene, and 10 mL of ethylene glycol, 1.0192 g (6 mmol) of silver nitrate, 1.892 g (6 mmol) of bismuth chloride, and 30 mL of glycerol were sequentially added. The particles were fully dispersed in the solvent by magnetic stirring. Then the reaction kettle was sealed and placed in an oven set at 180°C for 6 h. After cooling to room temperature, the AgBiSe2 nanoparticles were obtained by washing with distilled water and anhydrous ethanol to remove impurities and drying.

[0033] The obtained AgBiSe2 nanoparticles were characterized by XRD, as shown in Figure 1As shown, the results show that, in addition to a small amount of diffraction intensity weak diffraction peaks, the rest of the characteristic diffraction peaks can be well matched with AgBiSe2 phase (JCPDS #74-0842), indicating that AgBiSe2 nanoparticles are successfully synthesized.

[0034] (3) Bi2Te 2.7 Se 0.3 Preparation of AgBiSe2 composite samples

[0035] The BTS ingot was ground into powder with a mortar for 30 min, and the grinding force was ensured to be uniform and the same each time. The AgBiSe2 nanoparticles were mixed with the BTS powder obtained by grinding at a doping amount of 0.1wt%, and then transferred into a mortar for fine grinding for 20 min to obtain a relatively fine and uniform composite powder. The powder was loaded into a tungsten carbide mold with an inner diameter of 13 mm, and vacuum hot-pressed sintering was performed at 623 K and a pressure of 250 Mpa for 1 hour to obtain a dense block, which was recorded as Bi2Te 2.7 Se 0.3 -0.1wt% AgBiSe2.

[0036] Example 2

[0037] The same as Example 1, except that the AgBiSe2 nanoparticles were mixed with the BTS powder obtained by grinding at a doping amount of 0.2wt%, which was recorded as Bi2Te 2.7 Se 0.3 -0.2wt% AgBiSe2.

[0038] Example 3

[0039] The same as Example 1, except that the AgBiSe2 nanoparticles were mixed with the BTS powder obtained by grinding at a doping amount of 0.3wt%, which was recorded as Bi2Te 2.7 Se 0.3 -0.3wt% AgBiSe2.

[0040] Example 4

[0041] The same as Example 1, except that the AgBiSe2 nanoparticles were mixed with the BTS powder obtained by grinding at a doping amount of 0.4wt%, which was recorded as Bi2Te 2.7 Se 0.3 -0.4wt% AgBiSe2.

[0042] Example 5

[0043] The same as Example 1, except that the AgBiSe2 nanoparticles were mixed with the BTS powder obtained by grinding at a doping amount of 0.5wt%, which was recorded as Bi2Te 2.7 Se0.3 -0.5wt% AgBiSe2.

[0044] The XRD patterns of the composite materials obtained from different amounts of AgBiSe2nanoparticles in Examples 1-5 were characterized, and the results are shown in Figure 2 As can be seen, the XRD patterns of the Bi2Te 2.7 Se 0.3 / χ(AgBiSe2)(χ=0.1wt.%, 0.2wt.%, 0.3wt.%, 0.4wt.% and 0.5wt.%) composite samples at room temperature are basically consistent with the XRD patterns of the matrix Bi2Te 2.7 Se 0.3 , and the orientation factor does not change significantly with the increase of the composite amount, indicating that the texture of the sample does not change significantly before and after the composite. In addition, since the specific gravity of AgBiSe2in the Bi2Te 2.7 Se 0.3 / (AgBiSe2) composite sample is small, no diffraction peak of AgBiSe2is found in the rapid scanning diffraction pattern, but from the slow scanning pattern (scanning rate is 2 / min), the (104) diffraction peak of AgBiSe2at 2θ=30.8° can be observed (as shown in the Figure 1 insert in Fig. Figure 1 The XRD pattern of the Bi2Te 2.7 Se 0.3 / 0.5wt.% AgBiSe2composite sample), indicating that it exists in the hot-pressed bulk of the composite sample. At the same time, the FE-SEM observation results also confirm that AgBiSe2exists in the composite bulk.

[0045] Figure 3 (a) gives the FE-SEM image of the fracture surface of the BTS matrix, from which it can be seen that the BTS matrix grain size is tens of microns and has a layered structure. Figure 3 (b) gives the fracture surface scanning image of the BTS / 0.5wt.% AgBiSe2composite sample, and compared with (a), it can be found that there are nanoscale small particles with a size of about 30-90nm at the fracture surface, which is consistent with the size of AgBiSe2particles in Figure 3 (c). In order to further characterize the nanoscale small particles, Figure 3 (d) gives the particle size distribution of the AgBiSe2particle size, and the results show that the small particles are consistent with the size of AgBiSe2phase particles, indicating that the small particles are AgBiSe2nanoparticles. In addition, the results of the element distribution scanning image (EDS) are also very consistent with the above XRD and SEM analysis results. From Figure 4(b) - (c) Elemental mapping images show that in the yellow region, the content of elements Bi (Te) / Se is small and element Ag is in the aggregated state, indicating that the yellow dot is actually an AgBiSe2 particle, which is consistent with the XRD test results. These results show that the BTS / AgBiSe2 nanocomposite sample is successfully prepared.

[0046] Test Example: Performance Test

[0047] 1. Bi2Te 2.7 Se 0.3 - Analysis of the electrical properties of AgBiSe2 composite thermoelectric materials

[0048] Figure 5 The Bi2Te 2.7 Se 0.3 / χ(AgBiSe2) (χ = 0, 0.1, 0.2, 0.3, 0.4 and 0.5 wt.%) samples. It can be clearly seen that the electrical conductivity of the Bi2Te 2.7 Se 0.3 / χ(AgBiSe2) sample monotonically decreases with increasing temperature in the entire temperature range tested, indicating that all materials have degenerate semiconductor transport behavior. It can also be seen that the composite AgBiSe2 does not change the electrical transport behavior of Bi2Te 2.7 Se 0.3 in the entire temperature range. However, it can be clearly seen from the figure that the electrical conductivity σ decreases with increasing AgBiSe2 content at room temperature. As χ increases from 0 wt.% to 0.1 wt.%, 0.2 wt.%, 0.3 wt.%, 0.4 wt.% and 0.5 wt.%, the electrical conductivity σ decreases from 1101.8 S cm -1 to 1010.9 S cm -1 , 983.0 S cm -1 , 897.3 S cm -1 , 843.4 S cm -1 and 782.5 S cm -1 .

[0049] As is known, when two semiconductors (here Bi2Te 2.7 Se 0.3When AgBiSe2 comes into contact with each other, the difference in chemical potential between the two semiconductors creates an interfacial potential (barrier) in a heterojunction (nn-type). This interfacial potential will cause different levels of scattering for charge carriers of different energies: the higher the energy of the charge carrier, the weaker the scattering (conversely, the lower the energy of the charge carrier, the stronger the scattering), i.e., energy-dependent scattering (EDCS), or energy filtering effect (EFE). Due to the energy filtering effect, more high-energy charge carriers participate in transport, leading to an enhanced Seebeck coefficient. On the other hand, the energy filtering effect is closely related to the scattering parameter λ; the larger the value of λ, the stronger the energy filtering effect. Typically, the scattering parameter λ satisfies the relationship: τ(E)=τ0E λ-1 / 2 (Here, τ is the carrier relaxation time, τ0 is a constant independent of energy, and E is the carrier energy.) From this relationship, it can be seen that as λ increases, the carrier energy E increases, and the relaxation time τ increases (i.e., the scattering is weaker). Figure 6 As shown, when the AgBiSe2 content increases from 0 to 0.1, 0.2, 0.3, 0.4, and 0.5 wt.%, the λ value increases from 0 to 0.3, 0.27, 0.33, 0.29, and 0.25, respectively. This indicates that an energy filtering effect (EFE) is generated in the system due to the scattering of the BTS / AgBiSe2 interface potential, and this effect is enhanced with increasing AgBiSe2 content. In the BTS / χ(AgBiSe2) composite system, although the conductivity decreases, the enhanced EFE leads to a significant increase in the thermoelectric potential in the low-temperature region, ultimately resulting in a higher power factor (PF = σS) for all samples. 2 In the low-temperature region, they are all larger than unrecombined BTS, such as Figure 7 As shown. In particular, the sample with χ = 0.2 wt.% at 320 K showed a PF increase of ~21.9% compared to BST (the matrix PF was 27.9 μW / cm² at 320 K). -1 K -2 ).

[0050] 2.Bi2Te 2.7 Se 0.3 Thermal performance analysis of AgBiSe2 composite thermoelectric materials

[0051] Figure 8 The sample Bi2Te was revealed 2.7 Se 0.3The dependence of the total thermal conductivity (κ) of / χ(AgBiSe2) (χ=0, 0.1, 0.2, 0.3, 0.4 and 0.5 wt.%) on temperature shows that the total thermal conductivity of the samples initially decreases with increasing temperature; then, due to the bipolar effect, κ increases with further increases in temperature. Furthermore, the κ value decreases with increasing AgBiSe2 composite content at low composite concentrations, and then increases with further increases in composite content. For example, when χ increases from 0 to 0.1, 0.2, 0.3, 0.4 and 0.5 wt.%, the total thermal conductivity at 300 K decreases from 1.40 to 1.17, 1.10, 1.02, 1.22 and 1.28 W / m², respectively. -1 K -1 The sample with χ = 0.3 wt.% exhibits a minimum total thermal conductivity κ at 300 K. min =1.02W m -1 K -1 Compared to the matrix BTS (1.40Wm) -1 K -1 The thermal conductivity was reduced by approximately 27%. Therefore, introducing AgBiSe2 into the BTS matrix advantageously reduced the thermal conductivity of the composite sample (χ>0), resulting in a lower overall thermal conductivity than the uncomposite BTS matrix.

[0052] 3.Bi2Te 2.7 Se 0.3 Thermoelectric Performance Analysis of AgBiSe2 Composite Thermoelectric Materials

[0053] Figure 9 Bi2Te was revealed 2.7 Se 0.3 The thermoelectric properties of the / χ(AgBiSe2) series of composite samples (χ=0, 0.1, 0.2, 0.3, 0.4 and 0.5 wt.%) dependent on temperature show that the AgBiSe2 composites did not change the variation of ZT values, and the thermoelectric properties of all composite samples exhibited similar temperature behavior to the matrix BTS. Firstly, the ZT curves increased with increasing temperature at low temperatures, reaching a maximum around 370 K, and then gradually decreased with increasing measurement temperature. Furthermore, the thermoelectric properties of all composite samples were greater than those of the matrix Bi2Te. 2.7 Se 0.3 The thermoelectric properties of the nanocomposite increased with increasing composite content at 373 K as χ increased from 0 to 0.1 and 0.2 wt.%. However, with further increases in composite content, the thermoelectric properties decreased. Therefore, when 0.2 wt.% AgBiSe2 is introduced into the Bi2Te matrix, the thermoelectric properties of the nanocomposite increase with increasing composite content. 2.7 Se 0.3The composite sample formed in the middle obtained the highest ZT value 1.08 at 373K, which increased by about 56.5% than that of the un-composite BTS (0.69).

[0054] The above experimental results show that: introducing appropriate amount of AgBiSe2 nanoparticles can achieve the purpose of synergistic regulation of power factor and lattice thermal conductivity. Among them, for the composite sample of χ=0.2wt.%, due to the energy filtering effect at the interface, the thermoelectric potential increases by 15.6% at 300K, so that the power factor reaches 34.1μw cm -1 K -2 at 320K, which increases by about 22.2% than that of the power factor (27.9μw cm -1 K -2 ) of the matrix BTS; and the strong phonon scattering caused by the dispersed nanoparticles and the phase interface makes the lattice thermal conductivity decrease by about 36.9% at 373K. Due to the increase of the thermoelectric potential and the decrease of the lattice thermal conductivity, for the composite sample of χ=0.2wt.%, its thermoelectric figure of merit reaches the maximum value ZT max =1.08 at 373K, which increases by about 56.5% than that of the matrix Bi2Te 2.7 Se 0.3 (0.69). The research results show that by introducing appropriate amount of AgBiSe2 nanoparticles in the matrix Bi2Te 2.7 Se 0.3 , not only the electrical properties of the composite material can be optimized by using the energy filtering effect, but also the lattice thermal conductivity can be reduced by using the strong scattering of phonons caused by AgBiSe2 nanoparticles and the phase interface between the nanoparticles and the matrix, which synergistically regulates and improves the thermoelectric figure of merit of the composite system.

[0055] The above only is the preferred embodiment of the present application, it should be pointed out that, for the ordinary skilled in the art, without departing from the principles of the present application, can also make a number of improvements and refinements, these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A Bi2Te 2.7 Se 0.3 The preparation method of AgBiSe2 composite thermoelectric material is characterized by... Includes the following steps: (1) Add selenium powder to ethylenediamine, heat and reflux in an oil bath at 150 °C, stir magnetically, and after boiling, use residual heat to evaporate the ethylenediamine and dissolve it in ethylene glycol while hot to form a selenium anion precursor. (2) Ethylene glycol, silver nitrate, bismuth chloride and glycerol were added to the selenium anion precursor obtained in step (1), stirred and dissolved, reacted at 180°C for 6 h, and the precipitate was collected after cooling to room temperature and washed and dried to obtain AgBiSe2 nanoparticles. Bi2Te 2.7 Se 0.3 After the matrix is ​​ground, AgBiSe2 nanoparticles obtained in step (2) are added and ground, and then vacuum hot pressing sintering is performed to obtain a dense bulk. The amount of AgBiSe2 nanoparticles in step (3) is 0.1-0.5 wt% of the obtained bulk material.

2. The preparation method according to claim 1, characterized in that, The ratio of selenium powder to ethylenediamine in step (1) is 3 mmol: 30-80 ml.

3. The preparation method according to claim 1, characterized in that, The molar ratio of selenium powder, silver nitrate and bismuth chloride is 3:6:

6.

4. The preparation method according to claim 1, characterized in that, The washing in step (2) involves washing with distilled water and anhydrous ethanol, respectively.

5. The preparation method according to claim 1, characterized in that, The vacuum hot pressing sintering conditions in step (3) are: temperature of 523-673 K, time of 0.5-2 h, and pressure of 20-500 MPa.

6. The preparation method according to claim 1, characterized in that, The grinding time in step (3) is 20-30 min.

7. The Bi₂Te prepared by the preparation method according to any one of claims 1-6 2.7 Se 0.3 -AgBiSe2 composite thermoelectric material.

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