Hydrogen Ordering and New Polymorph of Layered Perovskite Oxyhydrides: Sr2VO4-xHx

TL;DR

This study synthesizes and characterizes tunable vanadium oxyhydrides Sr2VO4-xHx, revealing hydrogen site preferences, a new orthorhombic phase, and the relationship between anion ordering and V-ligand bonding.

Contribution

It reports the first synthesis of compositionally tunable Sr2VO4-xHx oxyhydrides with detailed structural analysis and a newly discovered hydrogen-ordered orthorhombic phase.

Findings

Hydrogen selectively replaces equatorial oxygen in VO6 layers.

A new orthorhombic phase forms at high hydrogen content.

Anion ordering correlates with V-ligand bonding interactions.

Abstract

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.