The role of lattice misfit strains in the deposition of epitaxial (Ba1− y Sr y )Ti0.5Nb0.5O3 films

Epitaxial (001)-oriented films of the metallic oxide (Ba1− y Sr y )Ti0.5Nb0.5O3, with y=0, 0.4, 0.5 and 0.6, are deposited onto (001) MgAl2O4 substrates using the pulsed laser deposition technique. The strontium for barium substitution gives rise to a decrease in the lattice constant, without altering the conductivity of the film. X-ray diffraction measurements show a significant number of [111], [011] and [221] misoriented grains that are not present for the y=0.6 composition. Transmission electron microscopy images of the film–substrate interface obtained for the y=0.6 composition show a sharp interface with flawless epitaxy. We attribute the improvements to a decrease in the lattice misfit strain made possible through the superior lattice match to the substrate obtained through strontium substitution.