Mechanism of the α-to-β phase transformation in the LaNi5–H2 system

Abstract

High-energy synchrotron in situ X-ray powder diffraction has been used to elucidate the mechanism of the hydriding phase transformation in a LaNi5 model hydrogen storage intermetallic in real time. The transformation proceeds at 10 àvia the transient growth of an interfacial phase, the ? phase, with lattice parameters intermediate between those of the a (dilute solid solution) and ߠ(concentrated hydride) phases. The ? phase forms to partially accommodate the 24% change in unit cell volume between the a and ߠphases during hydriding and dehydriding. The a, ? and ߠphases coexist at the nanoscopic level.