Atomic Structure Analysis of Octahedral Rotations in Strained SrRuO3 Thin Films

Abstract

Physical properties of perovskite oxides are strongly dependent on subtle structural deformation because of the large lattice-electron correlations, therefore it is essential to obtain accurate structural information to understand the underlying mechanism of structure-property relationship. Particularly, perovskite oxide thin films which are subject to the substrate-induced stress present a range of intriguing physical properties.. In this study, we investigated strain effects on SrRuO3 thin films by measuring RuO6 octahedral rotation across the interface using high resolution scanning transmission electron microscopy-annular bright field (STEM-ABF) imaging together with electron diffraction patterns, and the corresponding changes in electronic properties. We compared the crystal structures of SrRuO3 thin films on two substrates, GdScO3 (GSO) and SrTiO3 (STO), which are chosen for inducing tensile/ compressive strain and having the orthorhombic and cubic structure respectively. HRTEM images and their fast Fourier transformed micrographs revealed that the SRO films consisted of different domains, with sustained and released octahedral rotation. High resolution STEM-ABF images of released octahedral rotation region demonstrate less-distorted octahedral rotation patterns both on GSO and STO substrates. Only difference was the interface region. On GSO substrate, including topmost layer of GSO, SRO has somewhat sustained octahedral rotation up to two unit cells, while on STO, there was almost no rotation throughout the whole film. These different results in interface area can be ascribed to the symmetry mismatch effect. Since in both cases, SRO films have mixed structure with no big distinction, electrical property shows similar data. This study demonstrates that the octahedral rotations can be understood the interplay between lattice mismatch and symmetry mismatch.