Compositionally tunable vanadium oxyhydrides Sr2VO4-xHx (x = 0 - 1) without considerable anion vacancy were synthesized by high-pressure solid state reaction. The crystal structures and their properties were characterized by powder neutron diffraction, synchrotron X-ray diffraction, thermal desorption spectroscopy, and first-principles density functional theory (DFT) calculations. The hydrogen anions selectively replaced equatorial oxygen sites in the VO6 layers via statistical substitution of hydrogen in the low x region (x < 0.2). A new orthorhombic phase (Immm) with an almost entirely hydrogen-ordered structure formed from the K2NiF4-type tetragonal phase with x > 0.7. Based on the DFT calculations, the degree of oxygen/hydrogen anion ordering is strongly correlated with the bonding interaction between vanadium and the ligands.
@article{arxiv.1405.3011,
title = {Hydrogen Ordering and New Polymorph of Layered Perovskite Oxyhydrides: Sr2VO4-xHx},
author = {Joonho Bang and Satoru Matsuishi and Haruhiro Hiraka and Fumika Fujisaki and Toshiya Otomo and Sachiko Maki and Jun-ichi Yamaura and Reiji Kumai and Youichi Murakami and Hideo Hosono},
journal= {arXiv preprint arXiv:1405.3011},
year = {2014}
}