Mechanical properties of icosahedral boron carbide explained from first principles

An exhaustive study of the neutral structural defects of icosahedral B ₄C has been performed with the density functional theory. Vacancies have been determined to be boron vacancies in the C-B-C chains. Their presence is shown to yield a discontinuous variation of crystal volume upon increasing pressure, when the formation of a C-C bond occurs in the chains. The dynamical failure of shocked B₄C is attributed to the formation of these C-C bonds.