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

Structural aspects of phase transitions in thin ferroelectric films of (Ba, Sr)TiO 3 and PbTiO 3 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 films 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 relaxor-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.