Selective Hydride Occupation in BaVO_3–xH_x (0.3 ≤ x ≤ 0.8) with Face- and Corner-Shared Octahedra

Abstract

A growing number of transition metal oxyhydrides have recently been reported, but they are all confined to perovskite-related structures with corner-shared octahedra. Using high pressure synthesis, we have obtained vanadium oxyhydrides BaVO 3−x H x (0.3 ≤ x ≤ 0.8) with a 6H-type hexagonal layer structure consisting of faceshared as well as corner-shared octahedra. Synchrotron X-ray and neutron diffraction measurements revealed that, in BaVO 2.7 H 0.3 , H − anions are located selectively at the face-shared sites, as supported by DFT calculations, while BaVO 2.2 H 0.8 contains H − anions at both sites though the face-shared preference is partially retained. The selective hydride occupation for BaVO 2.7 H 0.3 appears to suppress electron hopping along the c axis, making this material a quasi-two-dimensional metal characterized by anomalous temperature dependence of the electrical resistivity and strong antiferromagnetic fluctuations. In contrast, the anion disordered BaVO 3−x H x in hexagonal (x ≈ 0.8) and cubic (x ≈ 0.9) forms exhibits a semiconducting behavior. This study offers a wide opportunity to develop transition metal oxyhydrides having various polyhedral linkages, along with site preference of H/O anions, aimed at finding interesting phenomena.

High-Pressure and High-Temperature Synthesis of Anion-Disordered Vanadium Perovskite Oxyhydrides

“…Mass spectroscopy measurement of the compounds with x = 0.05, 0.1, and 0.2 upon heating under an He gas flow revealed a significant amount of H 2 being released at 250–650 °C, further confirming the cubic phase is oxyhydride (Figure S3). A similar H 2 release behavior has been seen in other perovskite oxyhydrides. ,,, Note that the sample for x = 0.1 and 0.2 does not contain VH 2 impurity.…”

Engineering Polar Oxynitrides: Hexagonal Perovskite BaWON2

“…The distortion in the WO 3 N 3 octahedra is enhanced by SOJT effect—also affecting the WN 6 octahedra—and by the higher covalency of the W−N bond compared to W−O bond. The preferred occupation of the more electronegative O atom at face‐shared positions may be understood considering the weaker bonding for these sites, with W‐ X ‐W angles ≈90°, compared with corner‐shared sites, with W‐ X ‐W angles ≈180° . The spontaneous polarization, calculated from the coordinates and formal electrical charges of all atoms, is ≈17.7 μC cm −2 , parallel to the c axis.…”

A Partial Anion Disorder in SrVO2H Induced by Biaxial Tensile Strain

“…Hydride anions at the apical sites function as "π-blocker" ligands [9], making this oxyhydride a quasi-two-dimensional Mott insulator [10]. A partial trans-preference has been proposed for the 6H-type perovskite BaVO 3−x H x (0.5 < x < 0.9) where the d-electron count, n, is 1.5 < n < 1.9 [11].…”