Raman scattering study of α-MgH2 and γ-MgH2

Two modifications of MgH2 have been studied by Raman spectroscopy: α-MgH2 with the P42/mnm space group and γ-MgH2 with the Pbcn space group. The latter was prepared from α-MgH2 by exposing it to a pressure of 5.6 GPa at 470 °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 α-MgH2 in the range 1470–1790 cm−1 was identified as the B2g phonon mode. A Raman spectrum of γ-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 1Ag (186 cm−1), 3B3g (509 cm−1), 2Ag (660 cm−1) and 3B1g (706 cm−1) phonon modes.

► A sample with a mass ratio of γ/(γ+α)>0.85 of the γ and α polymorphic phases of MgH2 is prepared under high pressure.
► Raman spectra of the γ and α polymorphs of MgH2 are measured at room temperature.
► Raman spectra of both polymorphs are computed using a DFT method.
► All intense peaks in the experimental Raman spectra of both polymorphs are assigned to the phonon modes.