Synthesis And Thermoelectric Properties Of SnTe Based Materials

Nowadays,environmental pollution and energy crisis are becoming more and more serious.It has been widely recognized that finding clean and new energy to replace non-renewable fossil energy is of great importance to the sustainable development of human beings.Thermoelectric materials can realize the direct conversion of heat and electric energy through the movement of their internal carriers,which is widely concerned in the field of clean power generation and refrigeration.Through the unremitting efforts of researchers and the successful implementation of many practical strategies,some excellent thermoelectric materials have been discovered and developed.For example,materials such as PbTe family,SnSe family and Co Sb₃ skutterudites are all thermoelectric materials with high performance in the middle temperature region.Among them,PbTe has achieved very high thermoelectric properties in the medium temperature region due to its high symmetry crystal structure and high energy band degeneracy.However,the practical application of PbTe is greatly limited due to the fact that PbTe contains highly toxic Pbelement.Therefore,it is of great significance to find a substitute for PbTe for thermoelectric materials with excellent properties.Because of the similar crystal structure and band structure to those of PbTe,SnTe have received extensive attention for thermoelectric application.In this study,we focus on SnTe-based thermoelectric materials and synthesized Cu-doped SnTe samples and Sb,Mn co-doped SnTe samples by using traditional solid-state reaction and melt spining methods.Then,we studied the special microstructure of SnTe caused by melt spinning and Sb doping,and discussed the effects of Cu,Sb and Mn on the thermoelectric properties of SnTe.The main contents of this study are as follows:1.SnTe·xCu samples were prepared by the conventional melting reaction combined with hot pressing sintering.The introduction of Cu atom may fill the Snvacancy or form interstitial point defects in SnTe.Due to the large difference in ion radius and mass between Cu¹⁺ion and Sn²⁺ion,coupled with the effect of intercalation atoms,Cu doping can introduce strong stress field fluctuations and mass field fluctuations in SnTe,thus greatly enhancing phonon scattering and reducing lattice thermal conductivity.The total thermal conductivity and lattice thermal conductivity of the sample with doping x=0.04at 873 K decrease to?1.8 W m^-1 K^-1 and?1 W m^-1 K^-1,respectively.At the same time,Cu doping still maintains the high electrical transport performance of SnTe.Finally,the SnTe·0.04Cu sample obtained a highest z T value?0.8 at 873 K.2.We synthesized Sn_1-xSb_xTe samples via melt spinning(MS)followed by hot pressing.By comparing the lattice thermal conductivity of SnTe samples prepared by conventional melting reaction with that by melt melt spinning,we find that MS not only has higher preparation efficiency,but also can obviously refine the grain size and effectively reduces the lattice thermal conductivity of SnTe sample.In addition,through the characterization of the microstructure of the melt-spun ribbons and sintered samples,we found that during the rapid preparation process,Sb precipitates from inside the grain to divide the grain into several subgrains and refine the grain size.These Sb precipitates can still be observed at the grain boundaries of the bulk samples.Meanwhile,high-density dislocations are also observed in the sintered samples,which proves that the special microstructure can be introduced in Sn_1-xSb_xTe by MS.The special microstructure enhances the phonon scattering and optimizes the heat transport performance effectively.The lattice thermal conductivity at room temperature of the sample Sn_0.84Sb_0.16Te decreases to?0.55 W m^-1 K^-1.In addition,Sb doping also reduces the carrier concentration of SnTe and optimizes the electrical transport performance.At817 K,the thermoelectric properties of the sample Sn_0.84Sb_0.16Te reach the peak z T of?1.27,which is about 110%higher than that of the undoped SnTe.This study proves the advantage of MS as a method for rapid preparation of SnTe based materials in practical application.3.In this study,a series of Sb,Mn co-doped SnTe samples were synthesized by MS.On the basis of keeping the special microstructure introduced by Sb doping,further doping Mn in Sn_0.84Sb_0.16Te effectively regulates the band structure,resulting in the convergence of the light and heavy valence bands.We proved the band tuning of SnTe by Mn solution by calculating the band structure based on DFT.The band degeneracy improved the Seebeck coefficient in the whole temperature range.At room temperature,the Seebeck coefficient of Sn_0.72Sb_0.16Mn_0.12Te reaches?97?V K^-1,which is 145%higher than that of the sample doped with Sb alone.The ZT_ave reaches?0.89 over300-873 K,which is 340%higher than that of the undoped SnTe.This study confirmed the effectiveness of the strategy of combining defect engineering and energy band engineering to optimize the thermoelectric properties of SnTe based materials.