High-Pressure Synthesis of Hydrides in Ca-Mg-Ni Systems

Abstract

The high-pressure synthesis of new hydrides of the Ca–Mg–Ni system and crystal structural and thermal analyses have been conducted. The high-pressure synthesis was carried out at 1073 K for 2 h at 5 GPa using a cubic-anvil-type apparatus. An additional hydrogen source was used to stabilize the hydride phases. A series of (Ca_1−xMg_x)₂NiH_δ was found to form solid solutions in the range of x=0–0.4. The crystal structure of the (Ca_1−xMg_x)₂NiH_δ solid solutions was of the CsCl-type. The lattice constant of the CsCl-type phase decreased from 0.35542(2) nm (x=0) to 0.35478(2) nm (x=0.4) with increasing Mg content. For the samples with a Ni-rich composition, in addition to the CsCl-type phase, a Mg₂Ni₃H_3.4 phase was also present at high pressures. The CsCl-type phases were thermally stable at less than 646 ±2 K, regardless of Mg content.