1Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China
2University of Washington, Seattle, WA 98195-2120, USA
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DOI:
10.7502/j.issn.1674-3962.2015.01.04
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Abstract:
Complex doping is one of the challenging problems to be understood in doping and the associated structure tuning in materials science. Here we investigate the single-impurity-induced complex doping behaviors of group 13 elements Ga or In in caged skutterudite CoSb3 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 predominantly form the dual-site 2GaVF-GaSb defects and substitute for Sb only at very high Fermi levels or electron concentrations. 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 fully charge-compensated dual-site defects (2InVF-InSb and 4InVF-2InSb) 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 visibly 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.