Phase formation and hydrogen ordering in yttrium-hydrogen system

Phase transformations in epitaxial yttrium films grown on (0001) _TI//(0001)_AL2O3 Ti-buffered sapphire substrates and hydrogenated for 10 min were characterized using transmission electron microscopy. After hydrogen charging, dense twin lamellae form during a(Y(H))-to-β(YH₂) phase transition with twin boundaries predominately parallel to the interface between Y and a substrate. High densities of Shockley partial dislocations are present at the twin boundaries, their glides during phase transformation are responsible for the formation of twin lamellae. Electron diffraction from YH₂ phase shows superlattice reflections, which suggests a new type of ordering on octahedral interstitial sites.