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 −299.023 kJ mol−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.