CVD Synthesis and Thermoelectric Properties of Boron Carbide

Abstract

Dense polycrystals of boron carbide with various compositions were synthesized by a thermal CVD method using a reaction in the BCl3-CH4-H2 system. Results of electrical conductivity and thermoelectric power measurements indicated that the thermoelectric power-factor increased with increasing boron content from B4C to B13C2 and stayed practically unchanged for further boron-rich compositions within the single-phase region. This result was slightly different from those in the previous reports in which hot-pressed samples were employed for measurements. Thermally activated hopping of small polarons was confirmed to be a dominant conduction mechanism at high temperatures, but it was pointed out that more detailed investigation would be needed to specify their hopping sites. A strong effect of microstructure on the thermoelectric properties, especially Seebeck coefficient, of B4C was also found.