First-principles Study Of Half-heusler Alloy Thermoelectric Materials

The rapid development of the current industry has caused urgent problems such as energy consumption and environmental pollution.The Seebeck effect discovered in 1821and the Peltier effect discovered in 1834 provide a theoretical basis for the study of thermoelectric conversion technology.Thermoelectric equipment can directly convert thermal energy into electrical energy,and vice versa.In principle,these devices can use any heat source,including solar and waste heat.Therefore,for the field of materials science,thermoelectric materials play a key role in the development of sustainable energy-saving technologies.In this paper,the first-principles calculation method is used to calculate the thermoelectric transport properties of half-Heusler materials.First,the calculation results show that the electronic structure of ScCoSe exhibits a narrow band-gap semiconducting properties.The density of states at the top of the valence band is mainly contributed by Co atoms,and the density of states near the bottom of the conduction band is mainly contributed by Sc atoms.The curve of thermoelectric transport parameters with temperature shows that the highest ZT value of 0.75 is obtained in the eigenstate.The change of thermoelectric transport parameters with chemical potential indicates that it is a p-type semiconductor with a maximum ZT value of 0.77.Then,we substituted the M site with two atoms of Ti,Zr,Hf and Sb atom with P atom in MCoSb half-Heusler compounds to obtain Ti_0.5Zr_0.5Co Sb_0.5P_0.5,Ti_0.5Hf_0.5CoSb_0.5P_0.5,and Zr_0.5Hf_0.5Co Sb_0.5P_0.5.Then,we systematically studied the electronic structure and thermoelectric transport properties of the three compounds by using density functional theory and the semiclassical Boltzmann transport equation.In contrast to their parent compound MCoSb（M=Ti,Zr,Hf）,the substituted compounds retained the properties of indirect bandgap semiconductivity.The lattice thermal conductivity of these three compounds was lower than that of their corresponding parent materials.The thermoelectric figure of merit of the three compounds Ti_0.5Zr_0.5Co Sb_0.5P_0.5,Ti_0.5Hf_0.5Co Sb_0.5P_0.5,and Zr_0.5Hf_0.5Co Sb_0.5P_0.5are 0.86,0.84,and 0.85,respectively,at carrier concentrations of 10²⁰cm^-3and 10²¹cm^-3and temperatures of 900-1500K,which are significantly higher than those of the corresponding parent compounds.Therefore,they are candidates for thermoelectric materials in the 900-1500K temperature range.In addition,we conducted a first-principles study on the electronic structure and thermoelectric properties of TaXGa（X=Ni,Pt）,and then compared the electronic structure and thermoelectric transport properties with and without applied strain,both of which have maintained the semiconducting properties of these two materials.The power factor of Ta Ni Ga increases with tensile strain,and the lattice thermal conductivity decreases.The power factor of TaPtGa increases with compressive strain,but the lattice thermal conductivity also increases.We obtained a ZT value of 0.67 for TaNiGa under 6%strain and a ZT value of 0.80 for TaPtGa under-6%strain.