SKUTTERUDITE ANTIMONIDES - QUASI-LINEAR BANDS AND UNUSUAL TRANSPORT

Electronic-structure calculations are reported for IrSb3, CoSb3, and CoAs3 in the skutterudite structure. The band structures show a pseudogap around the Fermi level. The single band, which crosses the pseudogap, touches the conduction-band minimum at the Gamma point in CoAs3 and IrSb3 and almost touches it in CoSb3 due to a different ordering of the conduction bands. The dispersion of this gap-crossing band is quadratic at the Gamma point as expected, but for the antimonides it remarkably crosses over to linear behavior extremely close to the band edge, so that for doping levels as low as 3X10(16) holes/cm(3) the properties are determined by the linear dispersion. This yields interesting transport effects, such as a completely off-diagonal inverse mass tensor and unusual doping dependencies of the hole mobility and Seebeck coefficient. The Seebeck coefficients calculated from the band dispersion are in excellent agreement with experiment.