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Octahedral tilt relaxation decoupled from lattice parameters in epitaxial perovskite oxide films

Xuhui Xu1,*, Yuta Ishii2, Hidekazu Shimotani3, Yuta Inoue4, Yuto Miyahara4, Kohei Miyazaki4,5, Masao Nakamura1, Daisuke Okuyama6, Hajime Sagayama6,7 et al.

Kakeru Ninomiya8, Maiko Nishibori8, and Yusuke Wakabayashi1,†

  • *Contact author: xu.xuhui.s7@dc.tohoku.ac.jp
  • †Contact author: wakabayashi@tohoku.ac.jp
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Phys. Rev. Materials 10, 103601 – Published 5 October, 2026

DOI: https://doi.org/10.1103/72nx-sczv

Abstract

Epitaxial strain in perovskite oxide thin films is conventionally understood through lattice parameter modulation, characterized by the c/a ratio of the pseudocubic cell. However, internal atomic arrangements such as octahedral tilting can relax independently, a phenomenon that has remained largely unexplored. Here, we demonstrate that electrochemical operation induces internal structural relaxation in epitaxial La0.7Sr0.3CoO3 films while in-plane lattice parameters remain pinned to the substrate. Synchrotron x-ray diffraction reveals that prolonged electrochemical treatment drives the octahedral tilt mode from the as-grown strained configuration toward the bulk structure without conventional lattice parameter changes. This relaxation is enabled by ionic oxygen migration during electrochemical reactions, which reduces energy barriers between structural configurations. Our findings reveal a relaxation pathway in epitaxial oxides that operates independently of conventional lattice parameter relaxation, and demonstrate the importance of monitoring internal atomic arrangements under operating conditions. This establishes electrochemically driven ionic migration as a versatile tool for controlling internal structure in epitaxial oxides, opening opportunities for designing strain-engineered functional materials.

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Phys. Rev. Materials 10, 103601– Published 5 October, 2026
  • Received 30 March 2026
  • Accepted 26 August 2026
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