Strain stabilized metal-insulator transition in epitaxial thin films of metallic oxide CaRuO₃

We report the observation of both metallic and semiconducting behavior in epitaxial thin films of the metallic oxide CaRuO₃ deposited under identical conditions. X-ray diffraction studies showed that while semiconducting films with enlarged unit cells were obtained on single-crystal (100) SrTiO₃ substrates, metallic films with lattice parameters close to the bulk material grew on (100) LaAlO₃ substrates and poor crystalline quality SrTiO₃ substrates. It is believed that a strain induced substitution of the small Ru⁴⁺ cations by the larger Ca²⁺ cations occurs, breaking the conduction pathway within the three-dimensional network of the RuO₆ octahedra and leading to a metal-insulator transition. This unique phenomenon, which is not observed in bulk material, can be significant in technologically important epitaxial perovskite oxide heterostructures.