Theoretical Study On The Thermoelectric Properties Of Mg-based And Pb-based Solid Solutions

As a new type of energy material,thermoelectric materials have attracted much attention in recent years.Thermoelectric materials can realize the mutual conversion of thermal energy and electric energy without relying on other media,and also can convert thermal energy into available electric energy derectly.In this work,we systematically studied the crystal structure,electronic structure,and thermoelectric properties of the disordered solid solution structure of Mg2GexSn1-x(x=0.25,0.5,0.75)and PbSxTe1-x(x=0.25,0.5,0.75)based on the first-principles and semi-classical Boltzmann transport theory.The main results are as follows:(1)Based on the special quasi-random structure(SQS)method,the Mg2GexSn1-x(x=0.25,0.5,0.75)disordered solid solution structure containing 24 atoms were constructed,and the bandgap values of 0.35 eV-0.44 eV were obtained under the three ratios and then the electronic structure and thermoelectric properties of the system were studied.The results show that the n-type Mg2Ge0.5Sn0.5 has the highest ZT value of 2.45 with the carrier concentration of 3.28 × 1019 cm-3 at 800 K,which is mainly due to the high power factor and low lattice thermal conductivity.The lower lattice thermal conductivity may result from its high density and low optical mode speed.(2)Based on the SQS method,the PbSxTe1-x(x=0.25,0.5,0.75)disordered solid solution structure containing 32 atoms were constructed.The results show that the bandgap of PbSxTe1-x(x=0.25,0.5,0.75)decreases with the increase of x.Compared with the thermoelectric properties of pure binary PbTe and PbS,the thermoelectric properties of PbSxTe1-xsolid solution have been greatly improved.The effective carrier mass of p-type PbSxTe1-x solid solution is greater than that of n-type solid solution,which leads to a higher value of Seebeck coefficient for p-type PbSxTe1-x The ZT value of the p-type PbS0.75Te0.25 solid solution is 1.67 with the carrier concentration of 2.57× 1019cm-3 at 800 K.For the n-type PbS0.5Te0.5 solid solution,the maximum ZT value reaches to 1.30.