VIBRATIONAL CONTRIBUTION TO THE SEEBECK COEFFICIENT OF BIPOLARONIC CARRIERS IN BORON CARBIDES

The Seebeck coefficients (thermoelectric powers) of boron carbides are unusual in that they 1. have large values (>200 mu V/K) despite the p resence of high carrier densities (>10(21) cm(-3)) and 2. have tempera ture dependencies that are qualitatively different from these characte rizing common conductors and semiconductors. These novel features have made boron carbides attractive candidates for use in high-temperature thermoelectric energy conversion. Here the origin of the anomalous Se ebeck coefficients of boron carbides is investigated. Attention is foc used on how the interactions between electronic carriers and the latti ce affect the Seebeck coefficient since prior studies indicate that in boron carbides carriers are singlet bipolarons. It is concluded that an especially significant carrier-induced softening of its surrounding s, associated with singlet-bipolaron formation in boron carbides, can account for tile surprising thermoelectric properties of boron carbide s.