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Abstract
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.
Highlights
Mixed-anion compounds have been attracting a great deal of attention due to their potential applications such as photocatalysts, anionic conductors, and thermoelectric materials [1]
The present study demonstrates that an intermediate tetragonal phase appears when the SrVO3 film on the KTO substrate reacts with CaH2 in a short period of time (12 h), and its composition is roughly given by SrVO2 H
X-ray diffraction (XRD) and secondary ion mass spectrometry (SIMS) results show that this intermediate phase is less anisotropic with c/a = 0.96
Summary
Mixed-anion compounds have been attracting a great deal of attention due to their potential applications such as photocatalysts, anionic conductors, and thermoelectric materials [1]. The perovskite oxynitrides AMO2 N (e.g., SrNbO2 N, SrTaO2 N [2], and BaTaO2 N [3]) are composed of only cis-MO4 N2 octahedra, which occurs in order to maximize more covalent M dπ –N pπ bonds [2]. This local constraint gives rise to correlated disorder with various types of zigzag –M–N–M–N– chains assembled within the perovskite framework [4], as originally stated by Pauling for the structure of ice [5]. The vanadium oxyhydride SrVO2 H (V3+ ; d2 ) (Figure 1b), prepared by topochemical hydride reduction of perovskite
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