Promoted Hydride\nSubstitution in BaTiO<sub>3</sub> Cubes

We report the synthesis of perovskite oxyhydride BaTiO<sub>3–<i>x</i></sub>H<i><sub>x</sub></i> cubes\n(100–300\nnm) using the topochemical hydride reaction of the hydrothermally\nsynthesized oxide. X-ray and neutron diffraction studies revealed\nthat the anion (hydride/oxide) exchange is greatly improved, leading\nto a maximum hydride content of 0.7, which is higher than previously\nreported, while no reaction is seen for those with oleic acid on their\nsurface. These results indicate that the well-defined {100} facets,\nas well as the absence of organic residues, are crucial for promoting\nhydrogenation. Kissinger analysis on BaTiO<sub>2.3</sub>H<sub>0.7</sub> yielded an activation energy of 165 kJ/mol, much lower than that\nof BaTiO<sub>2.4</sub>H<sub>0.6</sub> (313 kJ/mol). In contrast to\noxides, oxyhydrides with well-defined facets have not been reported\nbefore; thus, this study opens new avenues for the rational synthesis\nof oxyhydride materials with controlled chemical composition and morphology.