Crystal structure and cyclic properties of hydrogen absorption–desorption in Pr2MgNi9

Abstract We investigated the crystal structure and cyclic hydrogen absorption–desorption properties of Pr 2 MgNi 9 . The structural model is based on the PuNi 3 -type structure; the Mg atom is assumed to substitute for the Pr site in an MgZn 2 -type cell. The refined lattice parameters were determined from X-ray diffraction. A wide plateau region was observed in the P – C (pressure composition) isotherm at 298 K. The maximum hydrogen capacity reached 1.12 H/M (1.62 mass%) under a hydrogen pressure of 2.0 MPa. After 1000 hydrogen absorption–desorption cycles, the hydrogen capacity was superior to that of LaNi 5 (82%). Anisotropic lattice strain occurred in the hydriding process. The anisotropic peak-broadening vector was determined to be . The calculated anisotropic lattice strains of the initial cycle and after 1000 cycles were far smaller than those of LaNi 5 .