Structure of the high pressure phase gamma-MgH2 by neutron powder diffraction

The high-pressure phase gamma-MgH2 was formed by heating the low-pressure p hase alpha-MgH2 in a multianvil press at 2 GPa pressure to 1070 K for 120 m in and successive rapid quenching. Investigation by X-ray and neutron powde r diffraction on the deuteride at ambient conditions revealed that it cryst allises with the orthorhombic alpha-PbO2 type structure (space group Pbcn, Z = 4, a = 4.5213(3), b = 5.4382(3), c = 4.9337(3) Angstrom (hydride); a = 4.5056(3), b = 5.4212(3), c = 4.9183(3) Angstrom (deuteride) at T = 295 K). The deuterium atoms surround magnesium in a distorted octahedral configura tion with bond distances Mg-D = 1.915(3), 1.943(3) and 2.004(3) Angstrom. T he rutile structure of alpha-MgH2 was re-evaluated. (C) 1999 Elsevier Scien ce S.A. All rights reserved.