Hydriding and dehydriding behavior of lanthanum silicides

The reactivity of hydrogen towards the lanthanum silicides, La5Si3, LaSi and LaSi2, has been studied by gravimetric and differential thermoanalytical methods. Synthesized silicides and hydrogenated phases have been characterized by X-ray diffraction. The hydrogen interaction is attributed to the lanthanum content of the silicide phase. Whereas LaSi2 does not react with hydrogen over a wide pressure–temperature range, La5Si3 takes up hydrogen even at 100°C. Hydrogenation of La5Si3 leads from a metastable hydride with about one hydrogen atom per lanthanum atom to the decomposition into lanthanum hydride, LaH2+x, and another phase without X-ray pattern. On the contrary, hydrogen release is not complete at temperatures up to 900°C. LaSi reacts reversibly with hydrogen under formation of a ternary hydride phase.