Monoclinic boron carbide crystals

Abstract

The X-ray diffraction (XRD) study of boron carbide obtained by self-propagating high-temperature synthesis reveals monoclinic single crystals. This is in contradiction with the literature data that boron carbide crystals are hexagonal. According to the XRD data, hexagonal and monoclinic crystals of boron carbide have almost identical structures. The article considers one of the possible reasons for the occurrence of monoclinic boron carbide crystals: the crystal symmetry reduction is due to distortions in structural units (icosahedra and/or triatomic groups). This induces the appearance of reflections that should be extinguished in hexagonal crystals. To check this hypothesis, theoretical XRD patterns of hypothetical boron carbide crystals with distorted units are calculated. The calculation results confirm our hypothesis.