Tuning the structural distortion and visible-light-driven photocatalytic properties of LaCoO3 thin films by epitaxial strain

Abstract Perovskite-type LaCoO3 thin films were deposited on (001) oriented LaSrAlO4, LaAlO3, (LaAlO3)0.3(Sr2AlTaO6)0.7 and SrTiO3 single-crystal substrates, respectively. All the films are epitaxially grown on these substrates with tetragonal distortion of CoO6 octahedrons. Due to different lattice mismatch between the film and substrate, there exists Jahn-Teller-like tetragonal distortion with out-of-plane elongated CoO6 octahedrons for LaCoO3 on LaSrAlO4 or LaAlO3 substrate, but compressed octahedrons for LaCoO3 on (LaAlO3)0.3(Sr2AlTaO6)0.7 or SrTiO3. All the LaCoO3 epitaxial films, with strain-induced larger unit-cell sizes and longer Co O bond lengths compared with those of bulk LaCoO3, exhibit obvious visible-light-driven photocatalytic activity. The photocatalytic ability increases gradually for the LaCoO3 grown on (LaAlO3)0.3(Sr2AlTaO6)0.7, SrTiO3, LaAlO3 and LaSrAlO4, consistent with the increasing order of tetragonal distortion degree for CoO6 octahedrons. It reveals that the photocatalytic performance of the LaCoO3 films is closely related to the stain-induce tetragonal distortion of CoO6 octahedrons. Larger degree of tetragonal distortion can further reduce the crystal field splitting energy of CoO6 octahedrons as well as the band gap, thus enhancing the visible-light-driven photocatalytic ability of LaCoO3. The present study demonstrates that epitaxial strain is an efficient way to controllably tune the structural distortion, electronic structure, and thereby improve the photocatalytic properties of perovskite and perovskite-derived oxides.