On the dynamical conductivity in icosahedral boron-rich solids

Abstract

The FIR spectra of boron-rich solids measured down to 10 cm-1 exhibit strongly increasing reflectivities towards lower frequencies. These spectra are well described when a superposition of Drude-type and hopping-type dynamical conductivity is assumed. The corresponding fits were simultaneously made for the real and the imaginary part of the dielectric function to achieve unambiguous parameters. The results obtained can be described consistently, for example, with DC conductivity measurements, and moreover in the case of β-rhombohedral boron, with the known energy band scheme. The bipolaren hopping model of the electronic transport in boron carbide is proved to be inappropriate.