Relaxor properties of Ba-based layered perovskites

Ferroelectric materials with Bi-layered structure such as SrBi₂Ta₂O₉ (SBT) and SrBi₂Nb₂O₉ (SBN) are now intensively investigated in view of their applications in non-volatile computer memories and high-temperature piezoelectric transducers. When Sr is substituted with Ba, significant disorder is induced and material exhibits broadening of the phase transition. In this work, BaBi₂Ta₂O₉ (BBT) and Ba₂Bi₂Nb₂O₉ (BBN) ceramics were sintered using mixed oxide route. Dielectric properties were investigated in the temperature range 20-600°C at frequencies 25 Hz to 1 MHz. Strong dispersion of the dielectric permittivity is found indicating relaxor nature of the phase transition. It is shown that the dielectric relaxation in BBN ceramics is different from that of conventional relaxors such as PbMg_1/3Nb_2/3O₃ (PMN). Fitting with Vögel-Fulcher relationship is used to evaluate parameters of the dielectric relaxation such as freezing temperature and attempt frequency.