Phase transition and elastic properties of BeO under pressure from first-principles calculations

We have performed first-principles calculations to investigate the phase transition and elastic proper-ties of Beryllium oxide (BeO) within the framework of density functional theory. The elastic constants, shear modulus, bulk modulus and its pressure derivative are all calculated for three polymorphs of BeO: wurtzite (WZ), zincblende (ZB) and rocksalt (RS). These properties at equilibrium phase agree well with the available theoretical and experimental values. Based on the enthalpy criterion, we have found that the WZ to RS structural phase transition occurs at 106 GPa, and there is no phase transition between the WZ and the ZB phases with the pressure up to 200 GPa. Especially, we studied the pressure dependence of elastic properties of these three phases for the first time. It was shown that, for the WZ structure, C-11, C-12, C-13, and C-33 were sensitive to pressure in the range of 0-200 GPa, while C-44 remains almost invariant. The similar phenomenon of C-11, C-12 and C-44 for the ZB structure was found. Differing from the WZ and ZB structures, the elastic constant C-12 and C-44 as a function of pressure had a crossover point at 138 GPa for the RS structure. The band structure is also investigated at 0 and 106 GPa for WZ structure. Under the influence of pressure, we have found that the WZ-BeO has transformed to indirect gap semiconductor. (C) 2009 Elsevier B.V. All rights reserved.