Electrical conductivity of boron carbide from ∼5 to ∼2100 K in the whole homogeneity range

Though controversially discussed, understanding of the electronic properties of B4.3C, carbon-rich limit of the homogeneity range has meanwhile reached an advanced degree. In contrast, the knowledge on more boron-rich boron carbides has remained small. As a contribution for closing this gap, we present a study of the electrical conductivity from ∼5 to ∼2100 K. Numerous samples covering the whole homogeneity range came from various sources and were differently prepared, thus allowing to separate intrinsic effects from those of impurities, density and preparation method. We show that at low temperature, the electrical conductivity meets formally Mott's law of variable-range hopping. However, its parameters are incompatible with experimental results and need redefinition. At high temperatures, the electrical conductivity is thermally activated. The activation energies yield the energetical position of gap states above the valence band, which are related to intrinsic defects in the structure depending on the actual chemical composition.