Phase stability and mechanical properties of rhenium borides by first-principles calculations

The phase stability and elastic properties of Re-B system were systematically investigated by use of the density functional theory. The formation enthalpies are negative for Re(3)B, Re(7)B(3), Re(2)B, ReB, Re(2)B(3), and ReB(2), indicating that they are thermodynamically stable. Re(7)B(3), Re(2)B, ReB, Re(2)B(3), and ReB(2) are mechanically stable. Combining the study of enthalpy and pressure relationship with the convex hull, it was found that the ground state phases are Re(3)B, Re(7)B(3), and ReB(2) at zero pressure, in agreement with the experimental observations. At the pressure of 90 GPa, Re(3)B, and ReB(2) are the most stable phases.