ICT2014 Abstracts

The doping behaviors of group 13 elements Ga and In in caged skutterudite CoSb₃ are studied through a combination of ab initio total-energy calculations and thermodynamics. Formation energies of void filling, Sb-substitution, and complex dual-site occupancy defects with different charge states, and their dependence on chemical potentials of species are considered. Our results show that Ga atoms dominantly form the dual-site 2Ga_VF-Ga_Sb defects and substitute for Sb only at very high Fermi level or electron concentration. Indium atoms, on the other hand, can play multiple roles in skutterudites, including filling in the crystalline voids, substituting for Sb atoms, or forming dual-site occupancy, among which the full charge-compensated dual-site defects (2In_VF-In_Sb and 4In_VF-2In_Sb) are dominant. The total defect concentrations are studied by using overall charge neutrality under the grand canonical ensemble. The concentration ratio of impurities at void-filling sites and that at Sb-substitution sites for Ga-doped CoSb₃ is very close to be 2:1, while this value obviously deviates from 2:1 for In-doped CoSb₃. The 2:1 ratio of Ga-doping in CoSb₃ causes low electron concentration (~2*10¹⁹cm^-3) and makes the doped system a semiconductor. The underlying physics of the doping behavior for group 13 elements in CoSb₃ is also analyzed.