Ferroelectric phase transition characteristics of Nb-doped bismuth layered ceramics prepared by solid-solid reaction

Ferroelectric ceramics of Bi3.25La0.75Ti3(1-y)Nb3yO12, BLTNy (y = 0.0, 0.03, 0.09, 0.15, 0.21) were synthesized using the solid-solid reaction method. The effects of Nb doping on the ferroelectric properties of BLTNy ceramics were studied using dielectric constant and P (polarization) - E (electric field) measurements. Ferroelectricity was observed in the composition with y = 0.0 - 0.21 at room temperature. The maximum remanent polarization, Pr = 28 μC/cm2 was achieved in the composition of y = 0.09. The phase transition temperature (Tm) decreased with increasing Nb-contents. The relaxor ferroelectric phase transition behavior was appreciably observed in the composition of y ≥ 0.09. The relaxor behavior is confirmed by frequency and temperature dependent dielectric behavior. For y ≥ 0.09, Tm was observed to increase with increasing measuring frequency, which means that the ferroelectric phase transition of BLTNy changed from a normal (y < 0.09) to a relaxor (y ≥ 0.09) ferroelectric phase transition with increasing Nb contents. This relaxor ferroelectric phase transition was found to satisfy the Vogel-Fulcher law rather than the Arrhenius law.