Thermal Transport And Thermoelectric Properties Of ?-? Group Graphene-like Materials And Mercury Chalcogenides Based On First-principle Calculations

The social turmoil caused by the world energy shortage and the environmental pollution caused by the burning of fossil fuels are becoming more and more serious.As a result,people try to explore clean,pollution-free and sustainable energy.The field of the thermal transport and the thermoelectricity have attracted widespread attention because of the capacity for thermoelectric devices to be able to achieve the direct conversion of thermal energy to electrical energy.In this paper,based on first-principles calculations combined with Boltzmann transport equation(BTE),the thermal transport properties of II-VI group graphene-like materials(BeO,MgO,CaO,SrS and SrSe)and the thermal transport and thermoelectric performances of mercury chalcogenides were systematically investigatedIn this paper,on the one hand,we confirmed the thermal transport properties of 5?-? group graphene-like materials(BeO,MgO,CaO,SrS and SrSe).The lattice thermal conductivity of 118.68,42.48,11.13,3.33 and 3.09 W/mK are obtained at 300 K in BeO,MgO,CaO,SrS and SrSe,respectively,which is much lower than that of graphene.Strikingly,the lattice thermal conductivity of SrS and SrSe is lower than most two-dimensional materials.Further analyses revealed that lower phonon group velocity of SrS and SrSe caused by larger atomic mass reduced the lattice thermal conductivity,and strong anharmonicity and more available phonon scattering channels enhanced phonon anharmonic scattering resulting in lower lattice thermal conductivity.By means of the relationship between lattice thermal conductivity and phonon mean-free path and nanowires width,the size dependence of lattice thermal conductivity is investigated as well,which provides a theoretical basis for the design of thermoelectric nanostructuresOn the other hand,the thermal transport and thermoelectric properties of mercury chalcogenides(HgX,X=o,s,Se,Te)are introduced.Remarkably,the calculated lattice thermal conductivity of-the a-HgO and a-HgS at room temperature are fairly low,about 0.6 W/mK,which is about 30%of the value for the typical thermoelectric material PbTe.Meanwhile,the value of power factors S~2o for a-HgS is relatively high,which,as a result,leads to a good thermoelectric performance,with the thermoelectric figure of merit ZT exceeding 1.28.However,due to the lower S~2o of a-HgO,its ZT value is only 0.58.In addition,for?-HgS,?-HgSe and?-HgTe,their lattice thermal conductivity is higher than that of PbTe at room temperature,thus limiting their thermoelectric applications.