Synthesis of new hydrides with cubic structures in Mg-Ca-Ni systems by using high pressure

Phases and thermal stability of new hydrides synthesized by using under a high pressure of 5 GPa in Ca-Mg-Ni-H systems were studied. The high-pressure synthesis was carried out at 1073 K-1223 K for 2h under 5 GPa by using an anvil-type apparatus. A series of (Ca_1-xMg_x)₂NiH_δ was found to form solid solution in the range of x = 0-0.4. This hydride decomposed around 646 K regardless of Mg content. In CaH₂-X%MgH₂ systems, hydrides with BCC structure were obtained in the range of X = 50-67. Lattice constant of the BCC phase decreased from 0.4032(9)nm (X = 50) to 0.3988(3)nm (X = 67) with increasing Mg content. The decomposed temperature of the BCC phase increased from 650 K (X = 50) to 673 K (X = 67) with increasing Mg content, in other words, with decreasing the lattice constant of BCC phase.