Novel superhard polymorphs of Be3N2 predicted by first-principles

We have performed extensively crystal structure prediction on Be3N2 to uncover two novel superhard polymorphs with rhombohedral (R3m) and hexagonal (P-3m1) symmetries, which are energetically much superior to previously proposed gamma-Be3N2 and stable against decomposition into a mixture of 3Be + N-2. The calculated Vickers hardness for the two predicted phases is beyond 50 GPa, exceeding that of well-known superhard materials B6O. Thermodynamic study suggests that the P-3m1 phase becomes most stable above 118 GPa. (C) 2010 Elsevier B.V. All rights reserved.