On the Crystal Chemistry of Photochromic Yttrium Oxyhydride

Yttrium oxyhydride exhibits photochromic properties at ambient temperature and pressures. Although oxygen plays an important role in determining the optoelectronic properties of the material, the question remains open regarding the site that it occupies in the crystal structure. In this paper, we address the issue by synchrotron radiation and neutron powder diffraction measurements. We report that the oxide anions occupy tetrahedral sites together with hydride anions in the face-centered cubic structure.