Novel high-pressure phases of AlN: A first-principles study

Four novel AlN phases with low density and high hardness are predicted by using a evolutionary methodology on structural search. All four phases are thermodynamically more favourable than the rock salt structure of AlN at ambient pressure and will be transformed to rock salt AlN at certain pressure. All these phases are mechanically and dynamically stable by checking the independent elastic constants and phonon dispersion spectra. The calculated mechanical properties reveal that the proposed AlN phases are hard, and the Vickers hardness of the AlN phases ranges from 13.2 GPa to 15.2 GPa. The calculated band structures of the novel AlN phases reveal that these AlN phases possess semiconductive properties with wide direct band gaps at G points, and the gaps range from 3.627 eV to 3.927 eV. (C) 2016 Published by Elsevier B.V.