Observation of phase transitions in hydrogenated Yttrium films via normalized infrared emissivity

The direct observation of a sequence of phase transitions during hydrogenation of Y thin films has been realized through the use of in situ isothermal infrared emissivity measurements. The formation of different phases, α-Y(H), YH2 and YH3, has been identified based on the observation of changes in the slope of the normalized IR emissivity vs. time curve during hydrogen loading. The presence of α-Y(H), YH2 and YH3 was confirmed by ex situ X-ray diffraction, transmission electron microscopy, and prompt gamma activation analysis. Transmission electron microscopy further demonstrated epitaxial orientation relationships between the Al2O3 substrate, Ti buffer layer, the as-deposited Y film, as well as its hydrides. These results clearly demonstrate the power of IR emissivity imaging to monitor, in real time, the formation of hydride phases of both metallic and insulating character near the surface of a thin-film sample.