Raman scattering study of α-MgH2 and γ-MgH2

Two modifications of MgH2 have been studied by Raman spectroscopy: alpha-MgH2 with the P4(2)/mnm space group and gamma-MgH2 with the Pbcn space group. The latter was prepared from alpha-MgH2 by exposing it to a pressure of 5.6 GPa at 470 degrees C for 1.5 h. A comparison of the experimental spectra with ab-initio calculations allowed identification of a few phonon modes. A broad feature in the Raman spectrum of alpha-MgH2 in the range 1470-1790 cm(-1) was identified as the B-2g phonon mode. A Raman spectrum of gamma-MgH2 consists of five discernible peaks at 186 cm(-1), 313 cm(-1), 509 cm(-1), 660 cm(-1), 706 cm(-1) and of three broad features in the regions 890-980 cm(-1), 1010-1220 cm(-1) and 1240-1430 cm(-1). The peaks are identified as the 1A(g) (186 cm(-1)), 3B(3g) (509 cm(-1)), 2A(g) (660 cm(-1)) and 3B(1g) (706 cm(-1)) phonon modes. (C) 2012 Elsevier Ltd. All rights reserved.