Pressure induced phase transformation of REH3

High-pressure X-ray diffraction studies of the number of rare earth trihydrides (REH3) have been carried out in a diamond anvil cell up to 30 GPa at room temperature. This includes the fan-Lily of rare earth trihydrides that possess hexagonal structure at ambient conditions. A reversible structural phase transformation from the hexagonal to cubic phase has been observed for the Sm, Gd, Er, Ho and luthetium trihydrides. The same type of phase transition has been found also for yttrium trihydride. The lattice parameters of the new cubic phases and the volume changes at transition points were determined for the all compounds investigated. The parameters of the equation of state for all the hexagonal and cubic phases have been determined in the pressure range up to 30 GPa. The role of H-H repulsive interaction as a probable promoter of the transition and a systematics of transition are discussed. (C) 2006 Elsevier B.V. All rights reserved.