Synthesis And Thermoelectric Transport Regulation Of CoSbS-based Thermoelectric Materials

Thermoelectric conversion technology based on thermoelectric materials can use the temperature difference to drive the directional movement of carriers to generate current.This static and stable power generation mode has broad application prospects in metallurgy,thermal power plant,automobile,and other scenarios where a large amount of waste heat is generated.At present,most thermoelectric materials used for thermoelectric power generation have high conversion efficiency only in the high-temperature range above 750K,and most of the components of these materials have the disadvantages of being highly toxic,expensive,and low reserves,which limits the wide application of these materials.Recently,chalcogenides with abundant and inexpensive constituent elements have been widely studied for their potential thermoelectric properties,with CoSb S being favored for their potential applications in mesothermal zones.However,the high resistivity and thermal conductivity of CoSb S limit the improvement of thermoelectric properties.In this paper,CoSb S was prepared by vacuum melting and annealing combined with spark plasma sintering.CoSb S was doped with Se and Sn at the Sb position,Se at Sb and S position,Ni doping at the Co position and Sn doping at Sb position.The influence of the above doping on the thermoelectric transport performance of CoSb S-based compounds was investigated,and the thermoelectric transport mechanism was analyzed.Through the above work,the thermoelectric transport performance of CoSb S-based compounds is significantly improved,which provides a valuable reference for the further development of this kind of materials.The research content and results of this paper mainly include the following:The study of CoSb_1-xSe_xS compounds doped with Se at the Sb site shows that Se doping can effectively modulate the band gap and impurity activation energy of CoSb S,thus increasing the carrier concentration and power factor.Due to the mass fluctuation and strain field fluctuation induced by Se doping,the thermal conductivity of CoSb S is severely inhibited.The maximum z T value of CoSb_0.9Se_0.1S at 823 K is 0.22,which is about twice that of CoSb S.Moreover,the average z T value of the CoSb_1-xSe_xS solid solution in this study is higher than that of the CoSb S_1-xSe_x prepared by the same method.It has shown that constructing Se _Sbanti-stie defects in CoSb S is an effective way to optimize their thermoelectric properties.In CoSb_1-xS_1-xSe_2x（x=0～0.2）series samples,the thermoelectric properties of CoSb S can be significantly improved by doping Se with Sb and S sites simultaneously.The double doping of Sb and S sites not only increases the carrier concentration of CoSb S but also increases the Fermi level,which induces more energy valleys to participate in electric transport and increases the effective mass of carriers.PF of CoSb_0.8S_0.8Se_0.4 is superior to other samples,reaching 11.4m Wm^-1K^-2,which is 60%higher than that of CoSb S(6.8m Wm^-1K^-2).In terms of thermal conductivity,CoSb_1-xS_1-xSe_2x has lower thermal conductivity,especially low-temperature thermal conductivity,due to the difference in mass and atomic radius between Se and S after Se is introduced into S position.Finally,the optimal z T value of the material is 0.3,which is 100%higher than that of the undoped CoSb S（0.15）and 36%higher than that of the CoSb_1-xSe_xS（0.22）.At the same time,owing to the greatly reduced resistivity and low-temperature thermal conductivity,the average z T value of the material is significantly higher than that of single doping Se at Sb or S sites.In CoSb_1-xM_xS（M=Sn,Pb,Ge;x=0.05）series samples,the doping of different elements in the same family has a great influence on the thermal and electrical transport properties of CoSb S.After replacing Sb with three different elements,the thermal conductivity of CoSb S decreases.However,Sn,which has the closest atomic mass and radius to Sb,makes the largest contribution to thermal conductivity.Compared with CoSb S,the thermal conductivity of Sn-doped samples decreased by 65%at room temperature.In terms of electric transport,the resistivity of CoSb_0.95Ge_0.05S increases sharply from 0 to 470K after introducing the metal-like element Ge into Sb,which is nearly tenfold higher than that of CoSb S at room temperature.In terms of z T value,the three doping methods are not better than CoSb S,but the low thermal conductivity of CoSb_0.95Sn_0.05S shows the potential to improve the thermoelectric properties,Ni_yCo_1-ySb_1-xSn_xS（y=0,0.06;x=0,0.025,0.05）series samples were further prepared.It is hoped that Ni doping can increase the carrier concentration and overcome the shortcomings of poor electrical transport of Sn-doped samples.After Ni doping,Ni_yCo_1-ySb_1-xSn_xS（y=0.06;x=0.025,0.05）,maintaining the low thermal conductivity of Sn doping,the resistivity is significantly decreased and the power factor is increased.The maximum z T value reaches 0.52,which is one of the best results in CoSb S system.