Study On The Thermoelectric Properties And Microstructure Of P-type SnTe Based Thermoelectric Materials

Environmental pollution and energy dilemma are two key problems the world facing today.Developing renewable energy and improving energy utilization efficiency have become the inevitable choice of the future society.Thermoelectric materials are widely used in the field of thermoelectric power generation(refrigeration)with realizing the mutual conversion between heat and electricity.However,the low energy conversion efficiency limits its market application,so improving thermoelectric performance has become an urgent matter to be solved.In the medium temperature range,Pb Te has good thermoelectric properties,but it can not be used on a large scale due to the toxicity of lead.Therefore,environmental friendly SnTe has become a substitute for Pb Te and enters the historical stage of thermoelectric materials.It has similar energy band structure and crystal structure to Pb Te,and is considered to be a thermoelectric material with great application potential.However,due to the large intrinsic vacancy concentration and narrow band gap,the intrinsic thermoelectric performance of SnTe can be enhanced by optimizing its electro-thermal transport characteristics.In this paper,SnTe based thermoelectric material was studied as the research object,optimizing the electric and thermal transport capacity through the carrier engineering,energy band engineering and phonon engineering,then analyzing the electric and thermal transport mechanism.The main research contents of this paper are as follows:(1)SnTe thermoelectric materials were successfully synthesized by melting method combined with spark plasma sintering.By replacing the lattice position of Te with the double doping of Se and Br elements,the dispersion distribution of nano-Sn Se phase in the matrix was observed by TEM,thus increasing phonon scattering and obtaining low thermal conductivity,Finally,the peak value of z T of Sn_1.03Se_0.12Te_0.87Br_0.01is?0.75 at 823 K.(2)The effect of Ag element on the thermoelectric properties of SnTe based alloy was studied by replacing the lattice position of Sn with Ag element.According to XRD and EPMA analysis,the impurity phase of Sn and Ag₂Te is formed in the matrix,which increases the phonon scattering leads to lattice thermal conductivity a decreased.According to the DET calculation,Ag doping reduces the energy difference between light and heavy bands leads to band convergence effect,so the power factor is significantly enhanced.Finally,the z T value of Sn_0.94Ag_0.09Te is?0.9 at 873 K.(3)Based on the optimization of energy band structure with Ag doping,the thermoelectric properties of Sn_0.94Ag_0.09Te are optimized by La element doping.La doping optimizing the carrier concentration and energy band structure,and introduces large size lanthanum telluride precipitates and dislocations as phonon scattering centers,which significantly reduces the lattice thermal conductivity.As a result,a substantial thermoelectric performance enhancement up to z T?1.0 at 873 K is obtained for the sample Sn_0.94Ag_0.09La_0.05Te,which is twice that of the pristine SnTe.(4)Based on the optimization of energy band structure with Ag doping,the thermal conductivity is optimized by doping Y element.The co-doping of Y and Ag can significantly increase the band gap and band degeneracy,and significantly enhance phonon scattering by constructing defects such as second phase,dislocation and grain boundary,so as to synergically optimize the performance of electrothermal transport.we describe the synergy effect on the modulation of band structure and microstructural defects of SnTe by Ag and Y codoping,in Sn_0.94Ag_0.09Y_0.05Te sample was obtained an increased power factor?2485?W m^-1K^-2,an extremely low lattice thermal conductivity of?0.48 W m^-1K^-1,and a peak z T as high as?1.2 at 873 K.