Alternating covalent-ionic and metallic bonding in perovskite borides studied usingab initiomethods

Abstract

Using ab initio calculations, we have studied 20 boron-based perovskites ($R{M}_3\mathrm{B}$, where $R$ and $M$ are rare earth and $4d$ metals, respectively). We show that the coupling between $M\text{−}R$ and $M\text{−}\mathrm{B}$ layers in $R{M}_3\mathrm{B}$ can be switched from predominantly covalent-ionic to metallic in character by varying the population of the $Md$ shells. Based on the electron density distribution resemblance to the so-called MAX phases [Sun et al., Phys. Rev. B 70, 092102 (2004)], it is reasonable to assume that alternating covalent-ionic and metallic bonding in these compounds may give rise to similar properties as observed for MAX phases.