A First-principle Study Of Chalcogenide In Thermoelectric Materials

The latest data from the National Bureau of Statistics shows that non-renewable energy sources such as raw coal are still the main energy sources in China.And the pollutants released by these non-renewable energy sources will cause serious air pollution and affect the health of people.Therefore,we need to accelerate the development of renewable and clean energy sources.Thermoelectric materials are one of them,which can directly achieve the conversion between electrical and heat energy.In addition,researchers are more and more enthusiastic about finding new materials and predicting the optimal performance of materials through theoretical calculations,as the supercomputing technology of China gradually ranks among the international advanced level.Many research results show that layered chalcogenides generally have a lower lattice thermal conductivity and excellent electrical transport properties.Therefore,we use the first-principle calculation that based on density functional theory and semi-classical Boltzmann transport theory to study the thermoelectric properties of three-dimensional layered SnS and monolayer AuSe in this paper.The low temperature Pnma phase SnS is an indirect band gap semiconductor with a band gap of 0.878 eV,while its electrical and thermal transport have obvious anisotropy.The calculation results show that the largest ZT_max of both P-and N-type SnS are along the a axis at 750 K,which are 2.21 and 3.13,respectively.However,the experimental ZT_max of P-and N-type SnS is lower than the theoretical value.Because Sn vacancies in SnS make the carrier concentration lower,and the frequently-used method to increase the carrier concentration is elemental doping.Therefore,we use K,Ca,Ga,Ge,As,Se,Br as the substitutional impurity in Sn₃₆S₃₆ with a concentration of 2.7%,judging their respective effects on the electric transport performance of SnS by electronic properties.The results show that the electric transport performance of P-type Sn₃₅KS₃₆ after K replace Sn,Sn₃₅GaS₃₆ after Ga replace Sn and Sn₃₆S₃₅As after As replace of S will be improved compared to the P-type pure phase SnS.At the same time,the electric transport performance of N-type Sn₃₅AsS₃₆ after As replacing Sn and Sn₃₆S₃₅Br after Br replacing S will be improved compared to N-type pure phase SnS.If the theoretical ZT_max can be reached or approached experimentally,the p-n junction thermoelectric devices that made of economical and environmentally friendly SnS will greatly benefit the development of low-power-consumption refrigerators and passive device power supplies.Monolayer AuSe is the first time as a thermoelectric material in this paper,which is an indirect band gap semiconductor with a band gap of 1.75 eV.The molecular dynamics results show that has good thermal stability at 1200 K,and the phonon spectrum results prove its dynamic stability.The electrical and thermal properties of P-and N-type monolayer AuSe are anisotropic,their lattice thermal conductivity is at a medium level in monolayer thermoelectric materials,but higher than that of bulk thermoelectric materials.Generally,it is not suitable for thermoelectric materials,but when the temperature is 1200K,the ZT_max of P-type monolayer AuSe is 1.46 along the a axis,and the ZT_max of N-type monolayer AuSe is 1.75 along the b axis.It shows that the monolayer AuSe can be used as a high-temperature thermoelectric material in some extreme environments.The study also tells us that materials with high lattice thermal conductivity may also be used in the field of thermoelectric materials.