Structure Model for Anion-Disordered Photochromic Gadolinium Oxyhydride Thin Films

Rare-earth (RE) oxyhydride thin films prepared by reactive magnetron sputtering followed by air-oxidation show a color-neutral photochromic effect at ambient conditions within a wide composition range (REOxH3-2x where 0.5 <= x < 1.5). Due to the high degree of anion sublattice disorder present in these thin films, the structure models proposed for the related bulk materials are not directly applicable. Instead we use a combination of EXAFS analysis and lattice energy calculations to establish a fcc-based model linking the oxyhydrides to the related binary compounds. The oxide anions are found to occupy predominantly the tetrahedral sites in the fcc structure, which is attributed to electrostatic lattice energy minimization.