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

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 °C via the transient growth of an interfacial phase, the γ phase, with lattice parameters intermediate between those of the α (dilute solid solution) and β (concentrated hydride) phases. The γ phase forms to partially accommodate the 24% change in unit cell volume between the α and β phases during hydriding and dehydriding. The α, γ and β phases coexist at the nanoscopic level.

Research highlights▶ Very carefully controlled study of hydride formation in LaNi5 via crystallography. ▶ Much more gamma phase formed transiently than in Joubert et al.’s work. ▶ Demonstration that the gamma phase is a necessary intermediate in hydride formation. ▶ Demonstration that the alpha, beta and gamma phases coexist nanoscopically.