High-pressure synthesis of hydrides of Ca-TM systems (TM = Mn, Fe, Co and Ni)

New hydrides of Ca-TM-H systems (TM = Mn, Fe, Co and Ni) have been explored by using a high-pressure technique. The high-pressure of up to 5 Gpa was yielded by cubic-anvil-type apparatus. All the samples of Ca-TM-H systems (TM = Mn, Fe and Co) prepared at 1073 K under 5 GPa were found to be mixtures of the raw materials. However, for the Ca-Ni-H system. a new hydride with a chemical composition of CaH2-33 at%Ni was prepared at 1223 K under 5 GPa. The color of the hydride was reddish brown. As an additional hydrogen source was used during the synthesis, the color changed into black. The new hydride prepared with additional hydrogen was found to have the CsCl-type structure. The lattice parameter was a = 0.35542(2) nm.