Ab initiostudy of thermoelectric transport properties of pure and doped quaternary compounds

Recent experiments on thermoelectric characterization of doped quaternary compounds of sattanite or kesterite-type Cu₂ZnSnSe₄, Cu₂ZnSnS₄, and Cu₂CdSnSe₄, show promise for their use as bulk thermoelectrics. In this paper we present and discuss the energetic, electronic, and transport properties of several tetrahedrally bonded quaternary compounds Cu₂QSnX₄, where Q=Zn,Cd; X=S,Se,Te and their alloyed/doped structures, Cu doped at Q sites and M doped (M=Al,Ga,In) at Sn sites, for elucidating their thermoelectric performance. In our calculations, using density-functional theory and Boltzmann transport equations, we determine Seebeck coefficients, conductivities, power factors, a simple measure ``maximum'' $ZT$ for each compound at experimentally amenable doping levels. Based on the electronic-structure and transport property calculations, we conclude that the base compounds and several doped compounds show similar potential as thermoelectric materials to the experimentally characterized one.