Epitaxial strain-tuned oxygen vacancy formation, reduction behavior, and electronic structure of perovskite SrIrO3

The formation and study of oxygen vacancies are critical for the development of enhanced functional oxides; in the oxygen evolution reaction (OER), oxygen vacancies are proposed to influence the activity and degradation of electrocatalysts. We use thin films of state-of-the-art OER catalyst $\mathrm{SrIr}{\mathrm{O}}₃$ deposited on crystal substrates with varied lattice parameters to demonstrate the effect of epitaxial strain on oxygen vacancy formation. Through in situ x-ray diffraction under elevated temperatures and reducing conditions of 3% ${\mathrm{H}}₂$/balance ${\mathrm{N}}₂$, we show that tensile epitaxial strain makes oxygen vacancy formation more favorable, whereas compressive epitaxial strain has no significant effect compared with an unstrained film. We further use in situ and ex situ x-ray absorption spectroscopy to reveal the effect of strain on the favorability of full reduction of Ir species within $\mathrm{SrIr}{\mathrm{O}}₃$ films from $\mathrm{I}{\mathrm{r}}⁴⁺$ to $\mathrm{I}{\mathrm{r}}⁰$ and on the energy levels of unoccupied electronic states in the out-of-plane direction, respectively. This study adds experimental evidence for the link between strain and oxygen vacancy formation in $5d$ thin film perovskites, for which the discussion has been dominated by theory-based approaches.