阅读说明：本技术 一种PbSe基热电材料的制备方法 (Preparation method of PbSe-based thermoelectric material ) 是由 宋吉明 周宁宁 于 2021-01-07 设计创作，主要内容包括：本发明公开了一种Ag掺杂的PbSe基热电材料的制备方法,属于能源转换技术领域。首先采用水热合成PbSe纳米粒子,随后按一定化学计量比与自制的Ag纳米粒子复合,然后将复合纳米粒子在合适的压力和温度下退火,再结合高频炉加热、热压烧结工艺制备出PbSe-X wt%Ag块体热电材料。本发明制备的PbSe-X wt%Ag热电材料的电导率为5630.86～11099.02 S/m,热导率为0.50～0.70 W/mK,热电最优值为0.46～0.97。该制备方法周期短,操作简便,对设备要求低,而且所得热电材料为p型半导体,制备的PbSe基热电材料在能源转换领域具有潜在的应用价值。(The invention discloses a preparation method of an Ag-doped PbSe-based thermoelectric material, belonging to the technical field of energy conversion. Firstly, hydrothermally synthesizing PbSe nano particles, then compounding the PbSe nano particles with self-made Ag nano particles according to a certain stoichiometric ratio, annealing the composite nano particles at a proper pressure and temperature, and then combining a high-frequency furnace heating and hot-pressing sintering process to prepare the PbSe-X wt% Ag block thermoelectric material. The electric conductivity of the PbSe-X wt% Ag thermoelectric material prepared by the invention is 5630.86-11099.02S/m, the thermal conductivity is 0.50-0.70W/mK, and the thermoelectric optimum value is 0.46-0.97. The preparation method has the advantages of short period, simple and convenient operation and low requirement on equipment, and the prepared PbSe-based thermoelectric material is a p-type semiconductor and has potential application value in the field of energy conversion.)

1. A preparation method of a PbSe-based thermoelectric material is characterized by firstly synthesizing PbSe nano particles by a liquid phase method, then blending the PbSe nano particles with self-made Ag nano particles, annealing, preparing pellets by a hot-pressing sintering process, and obtaining the PbSe-based thermoelectric material, wherein the chemical formula of the thermoelectric material is PbSe-X wt% Ag, wherein X = 1-10, and the specific steps are as follows: preparing PbSe nanoparticles by a hydrothermal method, dissolving 0.1-0.3 g of selenium source and 1.1-1.2 g of lead source in 35-45 ml of ethylene glycol, stirring for 10-60 minutes, transferring the mixture into a stainless steel autoclave with a 50 ml capacity of polytetrafluoroethylene lining, keeping the autoclave at 180-200 ℃ for 6-12 hours, cooling the reaction kettle to room temperature, washing precipitates for 4-6 times by deionized water and ethanol, centrifugally collecting, and vacuum-drying the obtained sample at 60 ℃ for 12 hours to obtain dried PbSe nanoparticles; dispersing 5.2-6.2 g of dry PbSe nanoparticle powder in 50-150 ml of ethanol, then adding 0.06-0.60 g of self-made Ag nanoparticles into the ethanol solution, fully stirring the mixture solution, and then evaporating the dispersing agent in a vacuum atmosphere to obtain the uniformly mixed PbSe-X wt% Ag material.

2. Preparing the pellets by annealing treatment, high-frequency furnace heating and hot-pressing sintering processes: annealing the mixed PbSe-X wt% Ag material for 1-5 h at 450-600 ℃ in a weak reducing atmosphere, then loading the annealed powder into a graphite grinding tool, sealing the upper part and the lower part by carbon rods, wrapping the upper part and the lower part by carbon paper, heating a sample in a glove box by adopting a high-frequency furnace under the axial pressure of 35-65 MPa, and carrying out hot pressing for 10-30 min at 450-550 ℃ to obtain a PbSe-based bulk thermoelectric material with high density and high purity; the PbSe-X wt% Ag composite thermoelectric material obtained by the preparation method has good crystallinity, high density and high purity, the electric conductivity is 5630.86-11099.02S/m, the thermal conductivity is 0.50-0.70W/mK, and the thermoelectric optimum ZT is 0.20-0.97.

Technical Field

The invention belongs to the technical field of material preparation and energy conversion, and particularly relates to a method for preparing a p-type PbSe nano composite material by combining annealing and hot pressing, wherein the material has excellent thermoelectric property.

Background

The thermoelectric material is a material capable of realizing interconversion of heat energy and electric energy, and can be used for thermoelectric refrigeration and thermoelectric power generation. Thermoelectric devices assembled with p-type and n-type semiconductor thermoelectric materialsThe part has the advantages of high stability, small volume, long service life, environmental protection and the like, thereby having wide application prospect in the fields of sensors, refrigeration, waste heat recycling, aerospace and the like. However, the performance of thermoelectric materials is usually measured by the thermoelectric figure of merit, ZT = S²Sigma T/k, wherein S is Seebeck coefficient, sigma is electric conductivity, T is absolute temperature, and k is thermal conductivity. The power factor of the material is PF = S²And sigma. Therefore, excellent thermoelectric materials require a high Seebeck coefficient, high electrical conductivity, and low thermal conductivity at the same time. Harmonizing the relationship between the parameters is important for improving the finally determined ZT value and realizing the conversion efficiency of the thermoelectric material.

Lead selenide (PbSe) is considered to be an excellent functional material because of its unique optical and electrical properties. The potential applications of PbSe in the fields of photoresistors, photocatalysis, infrared detectors, solar cells, etc. have been widely explored over the last 20 years. The intrinsic PbSe material is an n-type semiconductor, and the PbSe carrier species can be changed by compounding or doping to be converted into a p-type semiconductor. Compared with a large-scale block material, the nano composite material has the characteristics of multiple components, small size, high-density crystal boundary, phase boundary, lattice defect and the like, can effectively reduce the heat conductivity coefficient of the material and increase the phonon scattering of the material, and the composition and structural characteristics usually have synergistic effect on improving the thermoelectric property of the material. Considering that PbSe is a narrow-band-gap semiconductor material with stable physical and chemical properties, PbSe is taken as a matrix in the application, and Ag nanoparticles are doped in PbSe nanoparticles by using a doping technology to improve the thermoelectric properties of a sample; firstly synthesizing PbSe and Ag nano particles by adopting a liquid phase method, then annealing precursor powder of the thermoelectric material, then preparing a block PbSe-X wt% Ag thermoelectric material with high density by combining a high-frequency furnace heating and hot-pressing sintering process, and finally testing the electric conduction and heat conduction properties of the prepared PbSe-based thermoelectric material. The results show that the ZT of the PbSe-based thermoelectric material doped with 5 wt% Ag is 0.97 at 723K, which is 8.8 times that of the undoped PbSe, and is higher than the ZT value of most p-type thermoelectric materials at the temperature.

The prepared composite material is characterized by adopting the technologies of a Scanning Electron Microscope (SEM), an X-ray powder diffractometer (XRD), a high-resolution transmission electron microscope (HRTEM) and the like. The preparation method is simple and easy to operate, the raw materials are cheap and have low toxicity compared with PbTe-based materials, and meanwhile, the p-type PbSe composite material can be quickly obtained by the method. At present, no report is available for preparing p-type PbSe-based thermoelectric materials by doping PbSe nanoparticles with blended Ag nanoparticles.

Disclosure of Invention

The invention relates to a preparation method of a p-type PbSe-based thermoelectric material. The material has simple preparation method, good repeatability and easy mass synthesis. The nano composite material prepared by the invention has higher electrical conductivity, higher Seebeck coefficient and reduced thermal conductivity, the silver nano particles and the lead selenide nano crystals are mixed by a solution method, and finally the p-type composite material is prepared by hot pressing.

The invention is realized by the following technical scheme:

a preparation method of Ag nano particle doped PbSe thermoelectric material is characterized in that PbSe nano particles and Ag nano particles are used as raw materials. Weighing a proper amount of PbSe and self-made Ag nanoparticles according to a chemical general formula of PbSe-X wt% Ag, wherein X is the mass ratio of Ag nanoparticles to PbSe nanoparticles, and the range of X = 1-10, uniformly mixing the PbSe and the self-made Ag nanoparticles in an agate mortar, and fully grinding to obtain a ground mixed sample; then putting the mixture into an alumina crucible, putting the alumina crucible into a tubular furnace, vacuumizing the tubular furnace, and annealing the tubular furnace in a flowing weak reducing atmosphere to obtain Ag-doped lead selenide precursor powder; and then, filling the powder into a graphite grinding tool, and heating and hot-pressing sintering the graphite grinding tool by a high-frequency furnace to prepare the PbSe-X wt% Ag block thermoelectric material with good crystallinity and high purity.

Further, the synthesis method comprises the following specific steps:

(1) preparation of PbSe nanoparticles: the PbSe nano-particles are prepared by a hydrothermal method. 0.1-0.3 g of selenium source and 1.1-1.2 g of lead source are dissolved in 35-45 ml of ethylene glycol. Stirring for 10-60 minutes, transferring the mixture into a stainless steel autoclave with a 50 ml capacity of a polytetrafluoroethylene lining, keeping the autoclave at 180-200 ℃ for 6-12 hours, then cooling the reaction kettle to room temperature, washing precipitates for 4-6 times by deionized water and ethanol, centrifuging and collecting, and vacuum-drying the obtained sample at 60 ℃ for 12 hours to obtain the dried PbSe nanoparticles.

(2) Blending of PbSe and Ag nanoparticles: in order to fully mix the PbSe nanoparticles and the homemade Ag nanoparticles, 5.2-6.2 g of dry PbSe nanoparticle powder is dispersed in 50-150 ml of ethanol, then 0.06-0.60 g of homemade Ag nanoparticles are added into the ethanol solution, and the mixture solution is fully stirred. Then evaporating the dispersant under vacuum atmosphere to obtain the uniformly mixed PbSe-X wt% Ag material.

(3) Preparing the pellets by annealing treatment, high-frequency furnace heating and hot-pressing sintering processes: annealing the mixed powder for 1-5 h at 450-600 ℃ in a weak reducing atmosphere, then putting the annealed powder into a graphite grinding tool, sealing the upper part and the lower part by using carbon rods, wrapping the powder by using carbon paper, heating a sample in a glove box by using a high-frequency furnace under the axial pressure of 35-65 MPa, and carrying out hot pressing for 10-30 min at 450-550 ℃ to obtain the PbSe-based bulk thermoelectric material with high density and high purity.

(4) The PbSe-X wt% Ag composite thermoelectric material obtained by the preparation method has good crystallinity, high density and high purity, the electric conductivity is 5630.86-11099.02S/m, the thermal conductivity is 0.50-0.70W/mK, and the thermoelectric optimum ZT is 0.20-0.97. The thermal conductivity of the material is measured by a Netzsch LFA-467 laser flash method thermal conductivity instrument (Germany Chi-resistant company); the conductivity and the Seebeck coefficient of the material are measured on a Germany LSR-3 Seebeck coefficient/resistance tester to obtain related parameters, and the thermoelectric optimum value ZT is determined by a formula ZT = S²And sigma T/k is obtained through calculation.

The reactant selenium source is selenium powder

The reactant lead source is lead acetate trihydrate

The reaction solvent is distilled water self-made by a laboratory and glycol purchased from Chinese medicines

The reaction vessel is a purchased high-pressure reaction kettle.

FIG. 1 is an X-ray diffraction pattern (XRD) of the resulting hot-pressed sample

FIG. 2 is a Scanning Electron Micrograph (SEM) of the resulting thermocompressed sample

FIG. 3 is a High Resolution Transmission Electron Micrograph (HRTEM) of the resulting hot pressed sample

FIG. 4 is a graph of thermal conductivity data of the obtained hot-pressed sample at different temperatures

FIG. 5 is a graph of conductivity and Seebeck coefficient data for the resulting hot pressed samples at different temperatures

FIG. 6 shows the thermoelectric optima (ZT) of the resulting hot-pressed samples at different temperatures

The specific implementation mode is as follows:

the invention is illustrated in detail below with reference to the examples:

example 1:

the preparation of the PbSe-based thermoelectric material doped with Ag with X = 3% comprises the following specific preparation process

Dissolving 0.020 g of selenium powder and 1.138 g of lead acetate trihydrate in 42 ml of ethylene glycol, stirring for 30 minutes, transferring the mixture into a 50 ml of stainless steel autoclave lined with polytetrafluoroethylene, keeping the autoclave at 180 ℃ for 12 hours, washing the obtained sample powder with deionized water and ethanol for 6 times, centrifuging and collecting, and vacuum-drying the sample at 60 ℃ for 12 hours; weighing 6.0 g of PbSe and 0.18 g of Ag according to the mass ratio of PbSe to Ag, uniformly mixing the PbSe and the Ag in an agate mortar, fully grinding to obtain a ground mixed sample, then putting the mixed sample into an alumina crucible, putting the alumina crucible into a tubular furnace, vacuumizing, and heating to 450 DEG^oC, annealing for 2 hours in a flowing weak reducing atmosphere to obtain Ag-doped PbSe precursor powder, namely a PbSe-3 wt% Ag thermoelectric material raw material; and (3) filling the PbSe-3 wt% Ag powder into a graphite grinding tool with the inner diameter of 12.7 mm, sealing the upper part and the lower part by using carbon rods, wrapping the upper part and the lower part by using carbon paper, carrying out hot pressing for 20 min in an environment with axial pressure of 55 MPa and the temperature of 500 ℃, then, starting to cool, relieve pressure and close a hot pressing instrument, naturally cooling a sample, and obtaining the PbSe-3 wt% Ag thermoelectric material.

Example 2: the preparation of the Ag-doped PbSe thermoelectric material with X = 5 wt% comprises the following specific preparation process

Weighing 6.0 g of PbSe and 0.30 g of Ag according to the mass ratio of PbSe to Ag, uniformly mixing the PbSe and the Ag in an agate mortar, and fully grinding to obtain a ground mixed sample. The other steps are the same as in example 1.

Example 3: the preparation of the Ag-doped PbSe thermoelectric material with X = 7 wt% comprises the following specific preparation process

Weighing 6.0 g of PbSe and 0.42 g of Ag according to the mass ratio of PbSe to Ag, uniformly mixing the PbSe and the Ag in an agate mortar, and fully grinding to obtain a ground mixed sample. The other steps are the same as in example 1.

Example 4: thermoelectric performance test of PbSe-based composite material

The samples of example 1, example 2 and example 3 were subjected to phase test, thermal conductivity and conductivity test, and thermoelectric property characterization was performed after cutting into pieces using a wire saw for Shenyang Kejing type STX-202A diamond. The test was performed by hot pressing a sample of bulk PbSe-X wt% Ag (X =3, 5, 7). As can be seen from the X-ray diffraction pattern (figure 1), the phase mainly existing in the sample is the characteristic diffraction peak of PbSe (PDF # 06-0354), and Ag also exists in the sample₂Se (PDF #24-1041), and visible Ag nanoparticles generate secondary-phase Ag after heat treatment₂And (5) Se. FIG. 2 is an SEM image of a PbSe-5 wt% Ag bulk thermoelectric material, where small-sized secondary phases can be seen, as indicated by the circles in the figure. FIG. 3 is a HRTEM image of a PbSe-5 wt% Ag bulk thermoelectric material, observing significant Ag in the PbSe matrix₂Grain boundaries of the Se secondary phase. FIG. 4 is a graph of thermal conductivity of samples with different doping ratios, and it can be seen from the graph that after the samples are compounded with Ag nanoparticles, the thermal conductivity thereof gradually decreases with the increase of temperature, and at a temperature of 723K, the thermal conductivity of the sample PbSe-5 wt% Ag is 0.70W/mK. FIGS. 5a and 5b are graphs showing the change of the electrical conductivity and Seebeck coefficient with temperature of samples with different doping ratios, as shown in the graph, after the samples are doped with Ag nanoparticles, the electrical conductivity of the samples with three doping ratios is firstly increased and then decreased with the increase of the temperature, the Seebeck coefficient generally shows an increasing trend, and at the temperature of 723K, the electrical conductivity of the sample PbSe-5 wt% Ag is 11099.02S/m, and the Seebeck coefficient is 290.70 muV/K. FIG. 6 is a graph of thermoelectric optima ZT versus temperature of various groups of samples, and it can be found that PbSe-5 wt% Ag bulk thermoelectric material has the best performancePreferably, the ZT value is 0.97.