IR-Active Phonons of Boron and Boron Carbide

Abstract

The possible IR- and Raman-active phonons of a-boron.β-boron, and boron carbide have been obtained by group theoretical methods. Reflectivity and absorption measurements in the spectral range from 10 to 1450 cm−1 and a classical dispersion analysis yield the entire spectra of the anisotropic optical constants in the lattice vibration range of β-boron and beyond. From the reflectivity spectrum of boron carbide the resonance frequencies of the phonons and estimated values of their other characteristic values have been derived. The absorption spectrum of amorphous boron has been included in the discussion. — Certain frequency ranges can be attributed to vibrations of the icosahedra split in the crystal field. Single vibrations with Eǁc displaced to higher frequencies are attributted to the central atoms in the unit cells of β-boron and boron carbide. The phonon shift depending on temperature can be described by the Grüneisen shift. Three- and four-phonon processes are necessary to describe the temperature dependent damping constants of the lattice vibrations. © 1979, Walter de Gruyter. All rights reserved.