Microwave Synthesis And Thermoelectric Properties Of CoSb₃-based Skutterudites Compounds

The thermoelectric material is a clean and environmentally friendly functional material.Thermoelectric materials can convert heat to electricity or electricity to heat based on the Seebeck or Peltier.Low-grade heat sources such as natural temperature difference and waste heat from thermal power plants can be used for power generation and cooling.The skutterudite material is a kind of medium temperature thermoelectric material with great development prospects.Among many skutterudite compounds,CoSb₃-based compounds are of the most interest to researchers due to their good electrical transport property,relative low price and large element abundance.However,the high lattice thermal conductivity would results in a low dimensionless thermoelectric fifigure of merit.The preparation procedures of skutterudite bulks usually includes high pressure or melting synthesis of compound ingot,quenching and annealing of the resulting ingot,and subsequently sintered via spark plasma sintering technique?SPS?.Material preparation cycle is long,equipment is complex,and long-term annealing results in excessive grain growth,and the lattice thermal conductivity is high.Different from the traditional method,the microwave rapid heating method was used in the experiment.Green SiC was chosen as the absorbing material and the heating time was 4.5 minutes.Microwave relies on dielectric loss material to couple with the radiation to realize rapid heating,demonstrating many advantages on material synthesis when contrasted to conventional heating ways,such as greatly shortening the synthesis time and improving the microstructure.The thermoelectric properties of CoSb₃-based skutterudite can be improved via doping process.For unfilled CoSb₃,it has been found that Te substitution is effective in improving the electrical transport properties through affecting the carrier concentration,whereas substituting Se for Sb is effective in reducing the hermal conductivity because of the chemical disorder associated with mass and volume fluctuations.In this dissertation,substituting Se and Te for Sb of CoSb₃-based skutterudite.Formation of ternary and multicomponent solid solution alloys.Strengthen material electronegativity.The carrier concentration is greatly increased.And then reduce its resistivity.Atomic mass and volume fluctuations due to replacement elements.The material produces lattice defects,and enhanced phonon and electron scattering.The lattice thermal conductivity is greatly reduced.CoSb_3-xTe_x?x=0,0.05,0.1,0.2,0.3?Te-doped samples were prepared.Compared with the blank sample?CoSb₃?,the carrier concentration increased by about 1,000 times.Reducing material resistivity.When x=0.3,the lowest resistivity is6.19??·m.Effectively increase mass and volume fluctuations.It results in strong electron-phonon scattering,which reduces the thermal conductivity of the material lattice.The thermal conductivity of x=0.05 is 2.099Wm^-1K^-1.The dimensionless thermoelectric fifigure of merit of CoSb_2.95Te_0.05 is the largest.The maximum is 1.06at 764K.With Se_0.1-doped as invariant.The samples of Co₄Sb_12-0.1-xTe_xSe_0.1?x=0.2,0.3,0.4,0.5,0.6?and Co₄Sb_12-x-yTe_xSe_y?x=0,y=0;x=0.5,y=0.2;x=0.5,y=0.1?were prepared.Single doping is compared with double doping.To explore the doping effect of Te and Se.Exploring Solution Limit.The highest dimensionless thermoelectric fifigure of merit of Te _0.4Se _0.1 sample is 0.8133 at 773K.The dimensionless thermoelectric fifigure of merit of Co₄Sb_11.4Te_0.5Se_0.1 sample reaches 0.775 at 773K.The dimensionless thermoelectric fifigure of merit of Co₄Sb_11.3Te_0.5Se_0.2 is only 0.58at 773K because of its solution limit.