Pressure and temperature dependences of the electronic conductivity of boron carbides

The effects of combined hydrostatic pressure (0–25 kbar) and temperature (300–600 K) on the electronic conductivities of the high-temperature semiconductors ${\mathrm{B}}_4$C and ${\mathrm{B}}_9$C were investigated. The conductivities of both materials decrease with pressure. In particular, both the preexponential factor and the activation energy of the conductivities increase with pressure. These results are in semiquantitative agreement with predictions of a model which ascribes electronic transport in these materials to the hopping of small bipolarons between the ${\mathrm{B}}_{11}$C icosahedra of the boron carbides.