Electric-field-induced and spontaneous relaxor-ferroelectric phase transitions in (Na1/2Bi1/2)1-xBaxTiO3

Complex dielectric susceptibility was used to investigate the relaxor properties and the ferroelectric phase transitions in (Na1/2Bi1/2)(1-x)BaxTiO3 (0 <= x <= 0.08) ceramics. XRD was used to characterize the ground states of poled and unpoled samples. Dielectric susceptibility vs. temperature studies allowed to obtain the relaxor properties and to identify the electric field-induced phase transitions in the morphotropic phase boundary (MPB) compositions (0.06 < x < 0.08) and the spontaneous relaxor-ferroelectric phase transitions in the rhombohedral compositions (x < 0.06). The frequency dispersion of the dielectric maximum at Tm was observed for all compositions, although of decreased extension for lower x. The relaxor properties have been analysed with Vogel-Fulcher law. The activation energy and attempt frequency for the MPB compositions are similar to those of classical relaxors like Pb(Mg1/3Nb2/3)O-3, while for rhombohedral compositions, they are similar to relaxor ferroelectrics with spontaneous relaxor-ferroelectric phase transitions, like Pb(Sc1/2Nb1/2)O-3. A relationship has been found between the relaxor dispersion degree and the hysteresis of the ferroelectric transition.