Oxygen octahedral distortions in compressively strained SrRuO3 epitaxial thin films.

We carried out the synchrotron X-ray diffraction measurements and investigated the oxygen octahedral distortions in compressively strained SrRuO₃ epitaxial thin films on NdGaO₃ substrates. We observed half-order Bragg reflections originating from the RuO₆ octahedral distortions accommodated in the compressively strained films. Our structural analysis shows that the RuO₆ octahedra are elongated along the out-of-plane direction and are rotated in the out-of-phase manner only about the out-of-plane direction. The RuO₆ rotation angle γ_rot is 10.9° ± 1.2°, which is larger than that in the bulk SrRuO₃. The results indicate that the substrate-induced compressive strain enhances the out-of-plane rotations while strongly suppressing the in-plane rotations. In fact, the half-order Bragg reflections arising from the octahedral rotations about the in-plane direction are found to be weak and broad, implying that the in-plane rotations exist only in the interface region, not in the entire film. This indicates that while the in-plane octahedral rotation propagates through the interfacial octahedral connections into the film, its propagation decays within the interface region because of the compressive strain. Our results indicate that both the substrate-induced strain and the interfacial octahedral connection play important roles in determining the octahedral distortions accommodated in the strained SrRuO₃ films. [ABSTRACT FROM AUTHOR]