Substrate deformation induced by epitaxial La_0.8MnO_3-δ thin films

Abstract
A thin film of lacunar lanthanum manganites La_0.8MnO_3-δ has been epitaxially grown by injection chemical vapour deposition on a MgO (100) substrate. Transmission electronic microscopy and X-ray diffraction measurements were carried out on films before and after a thermal treatment at 700°C in air for 3 hours. Structural transformations were observed as a consequence of the annealing treatment : the as-deposited film which is almost single-phased, transforms into a mixing of two phases, and Mn octahedra become more regular, with significant increases of Mn-O-Mn bond angles close to 180°. The surprising feature developed in this paper concerns the MgO / La_0.8MnO_3-δ interface : a substrate deformation induced by the epitaxial film has been evidenced : MgO exhibits domains about 400 A thick from the interface with a cubic Fd3 lattice and a cell parameter twice this of normal MgO.