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

Abstract

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 MgNi2Hy 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. © 2006 The Japan Institute of Metals.