Relaxor-like behaviour of thin ferroelectric films with imperfect crystal structure

Structural aspects of phase transitions in thin ferroelectric films of (Ba,Sr)TiO3 and PbTiO3 were studied by XRD and Raman spectroscopy, with respect to crystal structure perfection. With decreasing crystal structure perfection, numerically estimated by the microstrain value, films acquired features typical of ferroelectrics-relaxors: instead of abrupt phase transition characteristic of bulk material and firms where perfect structure, imperfect films demonstrated smeared transition to a macroscopically cubic phase with some film micro-volumes remained polar far above the transition temperature. It is proposed that relaxer-like features are determined by the relationship between the degree of distortion of the crystal lattice in the polar phase and by the crystal structure imperfection, respectively.