High-pressure synthesis of novel hydride in Mg-M systems (M = Li, Pd)

Phases present and thermal stability of synthesized new compounds in the Mg-Li-H and Mg-Pd systems by preparing under a high pressure were studied. In the Mg-Li-H system, a new hydride with a tentative composition Mg ₂LiH₅ is synthesized by exposing a mixture of MgH ₂ and LiH to pressures of 2-5 GPa at 973 K for 4 h. The hydride has a cubic structure with the lattice parameter of 0.4219 nm. In the Mg-Pd system, a new intermetallic compound Mg-20 at.% Pd was synthesized at 1073 K and a pressure exceeding 2 GPa. This phase had a bcc structure with a=1.4053(1) nm and it transformed into a low-symmetry phase on heating above 663 K. Moreover, hydrogenation of the compound at 650 K for 3 days under hydrogen pressure of 9 MPa, changed into MgH₂ and new hydride Mg₂PdH_x with fcc structure similar to that of Mg₂PdC_x [D. Noréus, B. Bogdanović, U. Wilczok, J. Less-Common Met. 169 (1991) 369-373]. The new hydride dehydrogenated at 586 K that is about 100 K lower than MgH₂.