Pressure-induced structural change from hexagonal to fcc metal lattice in scandium trihydride

We synthesized scandium hydrides by hydrogenation of a scandium foil with hydrogen fluid under high pressure at ambient temperature. Scandium dihydride (ScH2) and trihydride (ScH3) were prepared near 4 and 5 GPa, respectively. The hydrogenation process and pressure-induced ScH3 were investigated by synchrotron radiation X-ray diffraction measurements up to 54.7 GPa. A structural transition from structural chances in ScH3 hexagonal to the fcc lattice began at 30 GPa and was completed at 46 GPa via an intermediate state similar to those reported for other hexagonal trihydrides. The intermediate state was not interpreted in terms of a coexisting state for the low-pressure hexagonal and the high-pressure fcc, structures. The onset transition pressure of ScH3 supported the previously proposed relation that the hexagonal-fcc transition pressure is inversely proportional to the ionic radius of the trihydride. (C) 2007 Elsevier B.V. All rights reserved.