Impact of microscopic bonding on the thermal stability and mechanical property of CaB6: A first-principles investigation

The electronic structures, thermodynamic, and mechanical stabilities of cubic CaB6 were investigated by first-principles technique. The results indicated that CaB6 is thermodynamically and mechanically stable. The calculated formation enthalpy of CaB6 is −299.023kJmol−1, which mainly results from the Ca–B ionic bonds. However, the B–B(I) and B–B(II) covalent bonds are crucial for the good mechanical performance of the compound. By analyzing the extraction of Ca ions from the B6 framework, it can be further identified that B–B (I) and B–B(II) bonds are responsible for the very large C11 and bulk modulus, while the shear deformation behavior of CaB6 is dominant by the B–B(I) bonds. Therefore, CaB6 shows moderate ductility.