Interface reaction between PbTiO₃ epitaxial thin films and La-doped SrTiO₃ (001) substrates through edge dislocations induced by 90° domain formation

Abstract

The interface structure change between PbTiO₃ (PTO) thin films with various thickness grown on La-doped SrTiO₃(001) (La:STO) single crystal substrates by chemical solution deposition method was elucidated by (scanning) transmission electron microscopy ((S)TEM). The films were comprised of perovskite single phase and cube-on-cube orientation relationship with the substrate. STEM images revealed that the twin deformation precedes the nucleation of edge dislocations away from the coherent interface between the film and the substrate. Diffusion of Pb ions into the substrate was also observed through edge dislocations away from the interface. Edge dislocations climbs downward into the substrate with further diffusion of Pb ions increasing the film thickness. This phenomenon was not observed in the PTO film deposited on the non-doped STO substrate. Therefore, lattice defects in the La:STO substrate. the misfit dislocation induced by 90° domain formation as well as similar ionic radius between Pb and Sr ions appeared to facilitate the local interdiffusion of the constituent elements between the film and the substrate.