Photochromic oxygen-containing yttrium hydride has been synthesized using atwo step process. The process consists of an initial sputter deposition ofoxygen-free yttrium hydride YH$_mathrm{x}$, followed by a controlled reactionwith air that causes incorporation of oxygen into the material. An in-situstudy of the YH$_mathrm{x}$ as it reacted with oxygen was made possible byapplying an aluminium capping layer with a low but non-zero oxygen permeabilityprior to air exposure. During the reaction, the visual appearance of theYH$_mathrm{x}$ went from dark and opaque to transparent and yellowish. Thistransition was accredited incorporation of oxygen into the material, as shownthrough analysis with energy dispersive x-ray spectroscopy (EDS) and x-rayphotoemission spectroscopy (XPS). Grazing incidence x-ray diffraction (GIXRD)studies revealed an fcc structure both before and after oxygen exposure, with alattice parameter that increased from 5.2 {AA} to 5.4 {AA} during thereaction. With the lattice parameter in the oxygen free YH$_mathrm{x}$ beingequal to that reported earlier for YH$_mathrm{2}$, our findings suggest thatthe non-reacted YH$_mathrm{x}$ in this study is in-fact YH$_mathrm{2}$.
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