LARGE ENHANCEMENT OF BORON CARBIDES SEEBECK COEFFICIENTS THROUGH VIBRATIONAL SOFTENING

We report measurements of the Seebeck coefficients of boron carbides h aving compositions B12+xC3-x, 0.15 < x < 1.7, from 6 to 900 K. These S eebeck coefficients are large, approximate to 200 mu V/K at 300 K, des pite boron carbides having high carrier densities, approximate to 10(2 1) cm(-3). The Seebeck coefficients also have unusual temperature depe ndencies and depend only weakly on carrier density. These exceptional properties can arise from boron carbides' bipolaronic holes substantia lly softening the vibrational modes with which they interact.