Thermoelectric properties of boron compound-doped α-SiC ceramics

The effects of boron compound additive on the thermoelectric properties of alpha-SiC ceramics were studied. Porous SiC ceramics with 57-62% relative density were fabricated by sintering the pressed alpha-SiC powder compacts with B, B4C, and BN at 2000-2100degreesC for 3 h in Ar and/or N-2 atmosphere. The sintered bodies were analyzed by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). Lattice parameter measurements revealed incorporation of a certain amount of added B into the SiC lattice and negligible phase transformation during sintering. The Seebeck coefficient, electrical conductivity and thermal conductivity were measured at 600-900degreesC in Ar and/or vacuum atmosphere. The kind of additives, the amount of addition and sintering atmosphere had significant effects on the thermoelectric properties. On the whole, the excess addition had a harmful influence upon electrical conductivity. The thermoelectric figure of merit of B-doped SiC was lower than that of n-type SiC.