Thin films of ferroelectric calcium barium niobate, CaxBa1-xNb2O6, are deposited on MgO(100) substrates by pulsed laser deposition. The microstructure of the films is investigated by means of conventional and high-resolution transmission electron microscopy. The observation of plan-view and cross-sectional samples shows that the films are polycrystalline. The grains orient with their c-axis parallel to the normal of the film surface. Two sets of preferential in-plane crystallographic relationships are determined as < 110 >(CBN)// < 410 >(MgO) and < 100 >(CBN)// < 310 >(MgO). Chemical reactions occur at the interface between the film and the MgO substrate, leading to the formation of two phases, corundum-type Mg4Nb2O9 and pseudobrookite-type Mg5Nb4O15. (c) 2006 Elsevier B.V. All rights reserved.