Electrical and Structural Properties of Lattice-Mismatched Calcium Manganese Oxide Thin Films

Electron-doped CaMnO$_{3-\delta}$ thin films are of interest for use in renewable energy applications because of their oxygen stoichiometry. We have investigated the properties of CaMnO$_{3-\delta}$ films epitaxially grown by pulsed laser deposition on LaAlO$_{3}$ and SrTiO$_{3}$ substrates,both of which have larger in-plane lattice parameters than CaMnO$_{3-\delta}$. This lattice-mismatch leads to bi-axial tensile strain in the thin films. We have characterized the thickness dependence of structural and electrical properties of these films using high resolution x-ray diffraction and temperature-dependent electrical resistivity measurements. We found that the thickness dependence is characteristically different from what has been preciously observed for hole-doped manganite thin films. Our results suggest that the electrical and structural properties of CaMnO$_{3-\delta}$ are related to a coupling between the tensile strain and the oxygen deficiency in the thin films.