First Principles Theory Design Of Heusler Alloy Thermoelectric Materials

With the development of industry the continuous decrease of natural resources and the effects of global warming,how to effectively utilize the existing resources and recycle the resources becomes very important.Thermoelectric materials can realize the direct transformation between the heat energy and the electrical energy.So,the thermoelectric materials has a good application prospect on waste heat recovery and refrigeration.Therefore,searching for new thermoelectric materials is particularly important.In this paper,the first principles calculation based on density functional theory?DFT?is used to study a series of Heusler alloys concerning their structural,electrical and magnetic properties.In addition,the boltzmann transport theory is uesd to calculate their thermoelectric properties,and predict seven semiconducting thermoelectric Heusler alloys with high power factor at room temperature.The first principle calculation results of series of Heusler alloys Sc₂FeX?X=Si,Ge,Sn and Pb?show that they have clear gap in the two spin direction,showing a semiconductor,two spin states with the same band dispersion,no spin splitting.They have a zero magnetic moment for theirone unit cell,belonging to the nonmagnetic semiconductors with the slater-pauling?SP?rule M_t=Z_t-18.The thermoelectric transport calculation results show that the thermoelectric properties of Sc₂FeX?X=Si,Ge,Sn and Pb?semiconducting thermoelectric materials obtain good thermoelectric properties by electron doping.The maximum thermoelectric power factor atroom temperature 300Kis 48.77(10¹⁴?Wcm^-1K^-2s^-1),47.11(10¹⁴?Wcm^-1K^-2s^-1),49.94(10¹⁴?Wcm^-1K^-2s^-1)and 46.86(10¹⁴?W cm^-1K^-2s^-1)for Sc₂FeSi,Sc₂FeGe,Sc₂FeSn and Sc₂FePb,respectively.The result of electronic structure calculation of Heusler-type alloy Sc₂MnSb shows that it has a spin splitting,but the whole is not magnetic,and has a band gap of 0.04eV,which belongs to nonmagnetic semiconductors.The thermoelectric calculation results show that the high power factor at room temperature is 43.44(10¹⁴?Wcm^-1K^-2s^-1)at the electron doping concentration-2.01×10²⁶m^-3.The results of the first principles and Boltzmann transport theory of the Heusler alloys Ti₂CrGe and Ti₂CrSn indicate that their electronic band structure have spin splitting,the total magnetic moment is zero.They belong to nonmagnetic semiconductors and have good thermoelectric properties.Higher power factor can be obtained by hole doping than by electron doping for both of the two alloys.With the increase of temperature,the Seebeck coefficient in hole and electronic doping decreases with the increase of power factor.At room temperature,the maximum of power factor at300K by hole doping is 51.38(10¹⁴?Wcm^-1K^-2s^-1)for Ti₂CrSn and 47.53(10¹⁴?Wcm^-1K^-2s^-1)for Ti₂CrGe.The calculation results show that the above seven predicted Heusler alloys belong to the candidate thermoelectric materials because that their thermoelectric power factorare close to that of widelycommercial thermoelectric material Bi₂Te₃ with the power factor of 50.00(10¹⁴?Wcm^-1K^-2s^-1)is very similar at room temperature.