Large enhancement of boron carbides' seebeck coefficients through vibrational softening

We report measurements of the Seebeck coefficients of boron carbides having compositions B12+xC3-x, 0.15 < x < 1.7, from 6 to 900 K. These Seebeck coefficients are large, approximate to 200 mu V/K at 300 K, despite boron carbides having high carrier densities, approximate to 10(21) cm(-3). The Seebeck coefficients also have unusual temperature dependencies and depend only weakly on carrier density. These exceptional properties can arise from boron carbides' bipolaronic holes substantially softening the vibrational modes with which they interact.