Enhanced non-classical electrostriction in strained tetragonal ceria

Electrostriction is the upsurge of strain under an electric field in any dielectric material. Oxygen-defective metal oxides, such as acceptor-doped ceria, exhibit high electrostriction 10^-17 m²V^-2 values, which can be further enhanced via interface engineering at the nanoscale. This effect in ceria is "non-classical" as it arises from an intricate relation between defect-induced polarisation and local elastic distortion in the lattice. Here, we investigate the impact of mismatch strain when epitaxial Gd-doped CeO₂ thin films are grown on various single-crystal substrates. We demonstrate that varying the compressive and tensile strain can fine-tune the electromechanical response. The electrostriction coefficients achieve a large M₁₁ ≈ 3.6·10^-15 m²V^-2 in lattices of in-plane compressed films, i.e., a positive tetragonality (c/a-1 > 0), with stress above 3 GPa at the film/substrate interface. Chemical and structural analysis suggests that the high electrostriction stems from anisotropic distortions in the local lattice strain, which lead to constructively oriented elastic dipoles and Ce³⁺ electronic defects.