Compressibility Behavior of CoxB: Experiment and Computation

Structural stability studies on Co2B and Co3B are performed using Mao-Bell type diamond anvil cell. The tetragonal structure of Co2B and the orthorhombic structure of Co3B are stable up to 41 and 43 GPa, respectively. The bulk modulus obtained from high-pressure XRD experiments is 282 +/- 21 GPa and 254 +/- 10 GPa for Co2B and Co3B, respectively, which reasonably agrees with the computed value. The first principle calculations are carried out to understand the elastic and mechanical properties of CoxB (x: 1, 2, and 3). Adding B into Co enhances the elastic and mechanical properties marginally up to Co2B. Whereas in CoB, a significant increase in the elastic and mechanical properties was observed. The electronic density of states of CoB reveals the presence of a pseudo gap at Fermi energy leading to higher bulk modulus among the cobalt borides. Bader charge analysis shows a transfer of charge from Co to B. The valence charge variation indicates the strengthening of B-B bonds at the expense of Co-Co bonds leading to enhanced elastic properties.