Study On Doping Optimization Of Thermoelectric Performance And Mechanism Of Silver Selenide

Thermoelectric materials can directly realize the mutual conversion of thermal energy and electric energy based on the thermoelectric effect,which can use thermal energy for thermoelectric power generation and electric energy to achieve solid-state cooling(heating),and thermoelectric devices are easy to be miniaturized and flexible,and have no noise during operation.The advantages of non-polluting and strong stability are getting more and more attention.At present,the near-room temperature thermoelectric materials that can be used commercially are mainly bismuth telluride(Bi₂Te₃)based materials,but Te has disadvantages such as expensive,scarce resources,and high toxicity.The study found that silver selenide is a cost-effective near-room temperature thermoelectric material,which is expected to replace Bi₂Te₃-based thermoelectric materials.In the existing research,the synthesis of silver selenide mainly adopts tube sealing smelting or ball milling reaction and long time heat treatment with high temperature.The experiment cycle is long and the energy consumption is large;the research on the synthesis of silver selenide by wet chemical method is often synthesized by introducing the doping of external elements.The experimental steps are more complicated,and the doping process is more difficult to control;the room temperature thermoelectric figure of merit value(ZT)of the silver selenide bulk material is still not high enough.Therefore,this thesis has carried out the following research to address the above issues:(1)Silver selenide powders with different molar ratios of silver to selenium(n(AgNO₃)/n(Se))are synthesized by the solvothermal method at a lower temperature,and then the bulk silver selenide is directly synthesized by spark plasma sintering.The experimental method decreases energy remand and is easy to operate.(2)By adjusting n(AgNO₃)/n(Se),the carrier transport characteristics of the silver selenide bulk and the thermoelectric performance are optimized.The room temperature ZT value of the bulk silver selenide with n(AgNO₃)/n(Se)of 2.0:1 is the largest,about 0.74,and the maximum ZT value of silver selenide bulk with n(AgNO₃)/n(Se)of 1.9:1 is about1.08 within the test temperature range(average ZT value is about 0.83).The thermoelectric performance of the silver selenide bulk are optimized by adjusting the sintering temperature.When the sintering temperature is 573 K,the silver selenide bulk with n(AgNO₃)/n(Se)of 2.0:1 has the largest room temperature ZT value,which is about 0.78;The output performance of the silver selenide bulk(n(AgNO₃)/n(Se)with 2.0:1)has been verified by theoretical simulation and experimental testing of thermoelectric power generation devices,and the results show that the experimentally synthesized silver selenide bulk is expected to replace the N-type Bi₂Te₃-based thermoelectric material.(3)The electrical and thermal performance of the silver selenide bulk are optimized by the vacuum sealing tube melt doping heteroatom S/Te.The power factor of the doping silver selenide bulk increases,the total thermal conductivity decreases,and the ZT value is improved.The ZT value of the bulk silver selenide doping with 3% S is the largest at room temperature,about 0.70,and its maximum ZT value in the test temperature range is about0.81.The ZT value of the silver selenide bulk with 2%Te doping is the largest at room temperature,which is about 0.78,and its maximum ZT value in the test temperature range is about 1.07.(4)The electrical performance of silver selenide bulk are optimized by doping rare earth element Y.While the carrier concentration is basically unchanged,the carrier mobility is greatly increased,and the power factor is improved.Besides,the ZT value of silver selenide bulk with 6%Y doping is the largest at room temperature,which is about 0.68.