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 ${\mathrm{CaRuO}}_{\mathrm{3}}$ deposited under identical conditions. X-ray diffraction studies showed that while semiconducting films with enlarged unit cells were obtained on single-crystal (100) ${\mathrm{SrTiO}}_{\mathrm{3}}$ substrates, metallic films with lattice parameters close to the bulk material grew on (100) ${\mathrm{LaAlO}}_{\mathrm{3}}$ substrates and poor crystalline quality ${\mathrm{SrTiO}}_{\mathrm{3}}$ substrates. It is believed that a strain induced substitution of the small ${\mathrm{Ru}}^{\mathrm{4+}}$ cations by the larger ${\mathrm{Ca}}^{\mathrm{2+}}$ cations occurs, breaking the conduction pathway within the three-dimensional network of the ${\mathrm{RuO}}_{\mathrm{6}}$ 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.