High-pressure synthesis of novel hydride in Mg-Ni (-H) system

A novel hydride was synthesized in Mg-Ni-H system by high pressure technique using a cubic-anvil-type apparatus. Crystal structure, thermal stability and hydrogen content of the hydride were studied. The novel hydride with a composition of MgNi₂H_y was synthesized at 973 K for 2 h under the pressure of more than 2GPa, and was found to exhibit the body-centered tetragonal structure (space group 14/mmm, No. 139) with lattice parameters of a = 0.327(3) nm, c = 0.878(9) nm. Moreover, this hydride could be synthesized from each starting material, such as MgNi₂ high pressure phase, MgNi₂ (C36) and mixture of MgH₂-x mol% Ni (x = 65-70). Its hydrogen content was estimated to be 2.23 mass% from fusion analysis and corresponding chemical formula was found to be MgNi₂H _3.2. This hydride was decomposed into MgNi₂ (C36) over 460 K. and has solubility of Ni content and thermal stability of the novel hydride was decreased with increasing Ni content.