Structural studies of epitaxial BaTiO3 film deposited on MgO-buffered r-plane cut sapphire

The microstructure of epitaxial BaTiO3 thin films on MgO-buffered r-plane cut sapphire substrates was investigated by means of transmission electron microscopy. The BaTiO3 (BTO) films exhibit orientation relationships with the MgO (MO) buffer layer and the r-plane cut sapphire (AO) substrates of [1 0 0](BrO)\ \ [1 0 0](MO)\ \ [1 1 2 0](AO) and (0 1 0)(BrO)\ vertical bar>(*) over bar * (0 1 0)(MO)\ vertical bar>(*) over bar * (1 1 0 2)(AO) Following these relationships, the (0 0 1)(BTO) and the (0 0 1)(MO) planes make an angle of several degrees with the (1 1 0 2)(AO) plane, the surface plane of the substrate. A MgAl2 O-4 spinel reaction layer appears at the interface between the MgO buffer layer and the sapphire substrates for the films deposited at high temperature. In thick films (800nm) cracks penetrating the whole film thickness are developed by the tensile stress induced by the difference in thermal expansion between the him and the substrate. An anisotropic distribution of planar defects such as {111} stacking faults and microtwins is observed in the BaTiO3 film. This anisotropy can be explained by the application of the thermal stress to the BaTiO3 film with its [0 0 1] axis deviating by a small angle from the normal of the substrate surface. (C) 2000 Published by Elsevier Science B.V.