Preparation And Electrothermal Transport Properties Of SnSe Crystal

Thermoelectric materials can realize the mutual conversion between thermal energy and electric energy by carrier transporting inside material.SnSe,as a kind of thermoelectric material with excellent performance,has attracted wide attention in recent years due to its advantages of environmental friendliness and abundant resources.However,the intrinsic properties of SnSe are still to be studied,such as the low carrier concentration of polycrystalline SnSe and the preferred orientation of the thermoelectric properties of n-type single crystal SnSe.In this paper,SnSe was taken as the research object,SnSe polycrystals were prepared by melting hot pressing method,and SnSe single crystals were prepared by temperature gradient method.Their properties and unusual thermoelectric behavior were discussed.The specific research is as follows:By alloying with AgSbSe₂,it was found that the phase of polycrystalline SnSe changed from Pnma phase to Fm3m phase,and the proportion of Fm3m phase increase with the increase of AgSbSe₂content.In addition,due to the spin-orbit coupling(SOC)effect,the mutual restriction relationship between Seebeck coefficient and electrical conductivity was partially decouple in this experiment,realizing the simultaneous growth of Seebeck coefficient and electrical conductivity,which presented a relatively abnormal experimental phenomenon.After adding AgSbSe₂into the matrix,the carrier concentration of polycrystalline SnSe was also effectively increased,among which the carrier concentration of sample Sn_0.5(AgSb)_0.25Se could reach 4.6×10²⁰cm^-3at room temperature.As the electrical conductivity and Seebeck coefficient increased with the increase of AgSbSe₂content,its maximum power factor at 842 K was as high as?8?Wcm^-1K^-2.Alloying with AgSbSe₂also enhanced the phone scattering in cubic phase polycrystalline SnSe and reduced the lattice thermal conductivity.Finally,the sample Sn_0.4(AgSb)_0.3Se obtained the maximum ZT value of at 842 K,about 0.82.Single crystal SnSe was grown by temperature gradient method.After doping PbBr₂,the intrinsic p-type SnSe was successfully transformed into n-type.Single crystal SnSe showed obvious anisotropy,in general,the ZT value in out-of-plane direction is higher than that in in-plane direction,which is contrary to the preferred orientation of p-type SnSe single crystal.Along the out-of-plane direction,sample SnSe_0.95+2%PbBr₂obtained ZT_max?2.1 at 723 K,while sample SnSe_0.95+1%PbBr₂obtained the largest ZT_ave?1.07 between 300 and 813 K.In addition,we also found that there was abnormal electrical behavior in the out-of-plane direction.When the doping amount of PbBr₂was 3%,the carrier mobility decreased sharply.It is found by XRD and theoretical calculation that this was due to the change of Fermi surface dynamics caused by the change of lattice constant.After adjusting the lattice constant a by doping 1%Ge into sample SnSe_0.95+3%PbBr₂,the carrier mobility returned to the original level,and the ZT_maxof the sample increased from 0.6 to 1.7.