High-pressure synthesis of hydrides in Ca-Mg-Ni systems

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 2h 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 less than 646 ±2 K, regardless of Mg content.