| With the depletion of fossil fuels and the environmental problems caused by the great industrial development,energy and environmental problems have become increasingly serious and urgent.Therefore,renewable clean energy sources such as hydropower,wind power and solar power have attracted much attention,and related research increases rapidly.In addition,the secondary use of large amounts of waste heat generated by the daily activities of industry and human beings has also drawn increasing attention.Thermoelectric materials are a class of energy materials that can directly convert thermal energy into electrical energy or convert electrical energy into thermal energy,these characteristics make thermoelectric materials have inherent advantages in the secondary utilization of waste heat and the reduction of Freon used in the traditional refrigeration process.However,the current conversion efficiency of thermoelectric materials is low,and the high cost of production has become a negative factor restricting their development.Lead telluride is currently recognized as the best thermoelectric material in the middle temperature zone,scientists have never stopped their research in it.Lead telluride is selected as the research object in this paper,and a relatively economic and mass-produced hydrothermal/solvothermal method is chosen as the preparation method.The addition of Ag and S is to prepare a PbTe-based composite to improve the thermoelectric properties.The morphology and crystal structure have a great influence on the thermoelectric properties of PbTe.Funnel-like PbTe binary materials were prepared by hydrothermal method and the effect of surfactant and temperature on the morphology and structure was discussed.The optimal reaction temperature is 160 ?.PbTe-Pb S Powder was prepared by a two-step method and the powder materials with different compositions(S content)were prepared by changing the concentration of reductant(the amount of thioacetamide).The bulk material is prepared by cold pressing-annealing process,the optimum annealing temperature is 390 ?.The electrical conductivity after annealing is significantly higher than that before annealing,the highest conductivity before annealing is 1.208 S/cm for PbTe binary material,the highest value after annealing is 23.942 S/cm for the PbTe S composites with a sulfur source ratio of 2:1.Generally the thermal conductivities of composites are lower than that of PbTe in the range of test temperatures.PbTe S composite with 1:2 feed ratio is low in the whole range of test temperatures,The composite with 1:1 material ratio gets the lowest thermal conductivity at 420 K as 0.9013 W/m·K.Ag-doped PbTe-Pb S composite is prepared by a hydrothermal-solvothermal twostep method.The effects of alkali concentration and reactant concentration on the doping process are investigated.The optimal alkali concentration is 4 mol/L and the optimal reactant concentration is 0.167 mol/L,and Ag PbTe S composite powders with different silver content are prepared.The prepared Ag PbTe S powder material is cold pressed then annealed to obtain bulk material.The highest electrical conductivity and maxium Seebeck coefficient are respectively 39.54 S/cm at 660 K and 400 ?V·K-1 at room temperature when the silver doping ratio is x=0.04,then the maxium PF is 30.45×10-5 W·m-1·K-2 with the same silver doping ratio at 480 K.The maxium value of ZT is 0.368 at 480 K when the Ag doping ratio is 0.04. |
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