Phase Diagram of the Ferroelectric Perovskite (Na0.5Bi0.5)1-xBaxTiO3 by Anelastic and Dielectric Relaxation Measurements

Anelastic and dielectric relaxation measurements have been carried out on poled and unpoled samples of the ferroelectric perovskite (Na0.5Bi0.5)1-xBaxTiO3 (NBT-xBT), with composition in the range between pure NBT and the morphotropic phase boundary, 0 <= x <= 0.08. The complex elastic compliance spectra contain clear indications of both the rhombohedral/tetragonal and tetragonal/cubic transitions, allowing the determination of the phase diagram, which is difficult to obtain by diffraction techniques due to the very low distortions in both the tetragonal and rhombohedral phases and to the structural disorder in the Na/Bi sublattice. An extensive study is made for concentrations in the region of the morphotropic boundary (x ~ 0.06) in order to find possible signatures of monoclinic phase, as for the case of PbZr1-xTixO3 (PZT). The main features in the anelastic curves are compared with those in the dielectric spectra and are tentatively related to different modes of octahedral rotations and polar cation shifts.