Exploring Multi-Anion Chemistry in Yttrium Oxyhydrides: Solid-State NMR Studies and DFT Calculations

Rare earth oxyhydrides REOxH(3–2x), with RE = Y, Sc, or Gd and a cationic FCC lattice, are reversibly photochromic in nature. It is known that structural details anion (O2–:H–) composition dictate the efficiency of behavior. The mechanism behind photochromism is, however, not yet understood. In this study, we use 1H, 2H, 17O, 89Y solid-state NMR spectroscopy density functional theory (DFT) calculations to study various yttrium, hydrogen, oxygen local environments, oxidation states, hydride ion dynamics. DFT models YOxH(3–2x) both anion-ordered anion-disordered sublattices constructed for range compositions show good correlation experimental parameters. Two-dimensional 17O–1H 89Y–1H experiments reveal heterogeneities samples, which appear consist hydride-rich (x ≈ 0.25) hydride-poor domains 1) rather than single homogeneous mixing. compositional variation (as indicated by different x values YOxH(3–2x)) determined comparing static 1H line widths calculated 1H–1H dipolar couplings yttrium oxyhydride models. 1D 17O MAS spectrum demonstrates presence small percentage hydroxide (OH–) ions. modeling indicates reaction between protons hydroxides hydrides form molecular hydrogen (H+ + H– → H2). mobile component that, based on finding, attributed trapped H2 lattice.