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Transition metal oxides are of particular importance in condensed matter physics due to their wide variety of physical properties. Transition metal cations therein play a major role in determining their physical properties; anions, on the other hand, have been regarded as subsidiary constituents. However, mixed-anion strategy – a control of materials properties through multiple anions – have recently attracted increasing attention. Although employing anion degrees of freedom is a fascinating idea, a crucial problem is that the anion configuration in crystal is hard to control while it can drastically change materials properties.
We investigate a text-book mixed-anion compound SrVO₂H using first-principles calculation, to theoretically pin down the factors that stabilize its anion ordering [1]. We find that the trans preference by the characteristic crystal field in the VO₄H₂ octahedron in addition to a coherent shrinkage along the V-H-V direction, taking place when such direction is consistent among neighboring hydrogens, stabilize the anion ordering observed in experiment. Our study gives an important clue for controlling the anion ordering in transition metal oxyhydrides.

[1] M. Ochi and K. Kuroki, Phys. Rev. B 102, 134108 (2020).