Hydrogen-induced phase decomposition of Ba7Al13 and the crystal structure of Ba2AlH7

The hydrogenation characteristics of Ba7Al13 have been studied under a hydrogen pressure of 7 MPa at different temperatures for 5 days. Ba7Al13 reacts with hydrogen to form BaAlH5 and Al between 373 and 553 K. When the temperature is in the range from 553 to 603 K, Ba7Al13 is hydrogenated to Ba2AlH7 and Al. However, further increasing the temperature leads to the hydrogen-induced decomposition of Ba7Al13 into Ba2AlH7 and BaAl4. The crystal structure of Ba2AlD7 was also studied by neutron powder diffraction. Ba2AlD7 is isostructural to Sr2AlD7, crystallizing with a monoclinic structure in space group I2/a. The lattice parameters were determined as a=13.197(3) A, b=10.237(2) A, c=8.509(2) A, β=101.290(9) deg.