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Properties of perovskite oxides can be changed by manipulating anion-vacancy order patterns, but they are difficult to control. Here the authors show strain-induced creation and switching of anion vacancies in perovskite films in which the direction or periodicity of anion-vacancy planes is altered depending on the substrate employed.

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 °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.

We report the topochemical protonation of rutile oxides Rh0.5V0.5O2 and Cr0.5V0.5O2 by low-temperature hydrogen gas treatment. After the treatment, nonmagnetic V5+ (d0) ions were selectively reduced to +3.5 (d1.5) for HxRh0.5V0.5O2 (x ~ 0.75) and +4 (d¹) for HxCr0.5V0.5O2 (x ~ 0.5). HxRh0.5V0.5O2 with nonmagnetic Rh3+ ions has weak magnetic interactions with a spin glass transition at Tf = 6 K. In contrast, protonation of Cr0.5V0.5O2 with Cr3+ (d³) enhances antiferromagnetic interactions with the Weiss temperature of θ = -199(1) K. However, the spin glass transition temperature is still low (Tf = 10 K), indicating competing interactions, in which a frustration factor of 20 is the largest among rutile compounds. Topochemical protonation can be a useful method for extending the family of magnetic oxides. [ABSTRACT FROM AUTHOR]