Sc₃B_0.75C₃, a novel scandium boron carbide

A Sc-based boron carbide, Sc₃B_0.75C₃, containing linear C-B-C chains and isolated C atoms has been synthesized by a solid-state chemical reaction route. The crystal structure was determined using the X-ray powder diffraction technique and can be assigned to represent a new structure type of rare-earth boron carbides. The tetragonal crystal structure (a = 3.3315(3) angstroms, c = 7.6737(1) angstroms, P4/mmm (No.123)) is built up from chains of [Sc₁₀] polyhedra parallel to the c-axis and contains linear C-B-C chains. The linear C-B-C chains exhibit a short B-C bond length of 1.417(1) angstroms. Both the X-ray powder diffraction data and high-resolution transmission electron microscopy analysis suggest the possible presence of a B vacancy and site disorder in the C-B-C chain-end sites.