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International audience; Perovskite oxyhydride SrVO2H (V3+, d2) is a Mott insulator with a strong two-dimensional correlation due to anion ordering. In this study, we attempted electron doping by aliovalent substitution. Although Sr1-xLaxVO3 thin films (x ≤ 0.4) on a SrTiO3 substrate were topochemically reduced using CaH2, vanadium of the reduced films retained the trivalent state. Combined with the results of secondary ion mass spectroscopy, we conclude that Sr1-xLaxVO2+xH1-x is obtained, where the apical oxygen site is partially replaced by hydride anions. First-principles theoretical calculations highlight the role played by compressive biaxial strain in stabilizing the charge-compensated Sr1-xLaxVO2+xH1-x phase, rather than the electron-doped Sr1-xLaxVO2H. The present study demonstrates that topochemical reactions combined with substrate strain provide various opportunities to widen the compositional space in mixed-anion compounds. ©

SrVO2H, obtained by a topochemical reaction of SrVO3 perovskite using CaH2, is an anion-ordered phase with hydride anions exclusively at the apical site. In this study, we conducted a CaH2 reduction of SrVO3 thin films epitaxially grown on KTaO3 (KTO) substrates. When reacted at 530 &deg, C for 12 h, we observed an intermediate phase characterized by a smaller tetragonality of c/a = 0.96 (vs. c/a = 0.93 for SrVO2H), while a longer reaction of 24 h resulted in the known phase of SrVO2H. This fact suggests that the intermediate phase is a metastable state stabilized by applying tensile strain from the KTO substrate (1.4%). In addition, secondary ion mass spectrometry (SIMS) revealed that the intermediate phase has a hydrogen content close to that of SrVO2H, suggesting a partially disordered anion arrangement. Such kinetic trapping of an intermediate state by biaxial epitaxial strain not only helps to acquire a new state of matter but also advances our understanding of topochemical reaction processes in extended solids.

Perovskite oxides can host various anion-vacancy orders, which greatly change their properties, but the order pattern is still difficult to manipulate. Separately, lattice strain between thin film oxides and a substrate induces improved functions and novel states of matter, while little attention has been paid to changes in chemical composition. Here we combine these two aspects to achieve strain-induced creation and switching of anion-vacancy patterns in perovskite films. Epitaxial SrVO3 films are topochemically converted to anion-deficient oxynitrides by ammonia treatment, where the direction or periodicity of defect planes is altered depending on the substrate employed, unlike the known change in crystal orientation. First-principles calculations verified its biaxial strain effect. Like oxide heterostructures, the oxynitride has a superlattice of insulating and metallic blocks. Given the abundance of perovskite families, this study provides new opportunities to design superlattices by chemically modifying simple perovskite oxides with tunable anion-vacancy patterns through epitaxial lattice strain., Using strain to control oxynitride properties. 京都大学プレスリリース. 2020-12-01., 原子空孔の配列を制御する新手法の発見. 京都大学プレスリリース. 2020-12-02.