Study On The Thermoelectric Performance And Microstructure Of Nano-structured SnSe Materials Regulated By Synthesis Process

Thermoelectric modules interconvert between heat and electricity without emitting toxic gases,provide a promising solution for the current energy crisis.Though the single crystal SnSe realizes the ultrahigh thermoelectric performance of ZT=2.6 in the b-axis direction,the poor machinability and the long production cycle of single SnSe limits its application.Developing polycrystalline SnSe with excellent thermoelectric performance are great desired due to facile processing,machinability and scale-up applications.We designed a hydrothermal method with high magnetic field and optimized process paramters to prepare nano-structured SnSe to enhance thermoelectric performance by multiple strategies of energy filtering effects and strain field fluctuation.The main contents of research results are follows:1.Polycrystalline nano-structured SnSe were prepared by high magnetic field assisted hydrothermal synthesis and spark plasma sintering.The magnetic field provided an extra energy to grain nucleate,which provided a tendency of small grain,improved the energy filtering effect to achieve a high Seebeck coefficient,resulted to a high power factor.Furthermore,the sample synthesized under the high magnetic field existed a high density of dislocation and stacking faults.The dislocation and stacking faults induced the strain filed fluctuation to shorten phonon relaxation time,which resulted to a low lattice thermal conductivity.As a result,the Cd,Pb co-doped SnSe prepared by magnetic field assisted hydrothermal method achieved a high ZT～1.88at 873 K due to its high power factor（PF）and ultralow lattice thermal conductivity.2.Cd,Pb co-doped SnSe was synthesized by hydrothermal method and spark plasma sintering.We used different parameters of sythensis processing to improve thermoelectric performance by regulating microstructure.The enhanced power factor of Cd,Pb Co-doped Polycrystalline SnSe resulted from enhanced electrical conductivity by optimizing carrier concentration.The existence of smaller grain,Nanoprecipitates and point defects in polycrystalline SnSe with Cd,Pb doping strengthed the phonon scattering to reduce the lattice thermal conductivity,which were regulated by process parameters.Benefits from the enhanced power factor and low thermal conductivity,the figure of merit of Sn_0.965Cd_0.025Pb_0.01Se at 873K was 1.47.