Phase transitions of the ferroelectric Na_0.5Bi_0.5TiO₃ by dielectric and internal friction measurements

This work focuses on the high temperature dielectric and mechanical spectroscopic properties of lead free relaxor Sodium Bismuth Titanate (NBT) ceramics, fabricated by conventional ceramic double sintering method. Systematic measurements of dielectric and mechanical properties have been performed as a function of temperature. A sequence of phase transitions has been studied by both dielectric and anelastic measurements. Three internal friction peaks were observed near 350, 200 and 120° C. The 350°C-peak corresponds to a transition associated with the tetragonal (P4bm) to rhombohedral (R3c) phase, and the 200°C-peak is related to the ferroelectric to antiferroelectric phase transition. The 120°C-peak could be ascribed to the interaction between the domain walls and the diffusion of oxygen vacancies in the domains