Influence of the Hydride Content on the Local Structure of a Perovskite Oxyhydride BaTiO_3–xH_x

Abstract

The local structure of BaTiO 3 perovskite has been investigated for studying phase transitions by several groups. While it has been shown that H − doping into BaTiO 3 changes its long-range average crystal symmetry from tetragonal to cubic, factors contributing to the structural change have not been fully understood. In this work, we investigated the dependence of the local structure of BaTiO 3−x H x on the doped H − amount by means of Raman and X-ray absorption finestructure (XAFS) spectroscopy measurements. The x value of BaTiO 3−x H x could vary in the range of 0−0.5 by changing the amount of the CaH 2 precursor in the topochemical synthesis of BaTiO 3−x H x . Raman spectroscopy indicated that the cubic phase is induced in the initial tetragonal phase when the doped H − amount was relatively large (x ≥ 0.2). On the other hand, XAFS measurements revealed that the symmetry of the TiO 6 octahedral in BaTiO 3−x H x is strongly affected by the doped H − amount. The local distortion of the Ti [111] displacement is relaxed with an increase of H − , causing the tetragonal-to-cubic structural change.

Significant Roles of Surface Hydrides in Enhancing the Performance of Cu/BaTiO2.8H0.2 Catalyst for CO2 Hydrogenation to Methanol

“…Inductively coupled plasma (ICP) results for both catalysts showed similar Cu weight loading (12.1 wt % in Cu/BaTiO 3 and 13.9 wt % in Cu/BaTiO 2.8 H 0.2 ). Powder XRD (Figure S1) showed that partial replacement of oxygen anions by hydrides did not change the bulk structure of the support, consistent with previous XRD studies [8a,c, 9] . Inelastic neutron scattering characterization (Figure S2), which is extremely sensitive to H species, showed peaks at ~922 and ~1065 cm −1 , indicating the formation of bulk hydride [10] .…”

“…To determine the stoichiometry of hydrides in the oxyhydride catalyst, thermogravimetric analysis (TGA) in air was performed (Figure S3). About 1.2 % weight increase was observed and caused by the abstraction of H − and the oxidation of the oxyhydride support [9,11] while no weight increase was observed on BaTiO 3 . The composition of the oxyhydride support was estimated to be BaTiO 2.8 H 0.2 .…”