Relaxor behavior of bismuth layer-structured ferroelectric ceramic with m=2

In this paper, the crystal structure, dielectric and ferroelectric studies of PbBi2Nb2O9 and Pb0.8Ba0.2Bi2Nb2O9 ceramics are reported. X-ray structural studies along with Rietveld refinement confirmed it to be an m = 2 member of the Aurivillius family of oxides and the refined lattice parameters are calculated. The orthorhombic distortion decreases with increasing dopant radius. The decrease of the orthorhombic distortion further causes a decrease of the Curie temperature. It can be inferred that substitution of Pb by the larger cation Ba2+ would lead to a lower thermal energy for phase transition. Broad dielectric maxima, which shift to higher temperature with increasing frequency, and the value of the relaxation parameter gamma which is above I (estimated from the linear fit of the modified Curie-Weiss law with other empirical parameters Delta T-m, Delta T-relax) indicate the relaxor nature for PBBN ceramics. Well-developed P-E hysteresis loops are obtained from PBBN samples. The Pr values are improved to 10.5 mu C/cm(2) at 423 K when Ba2+ is introduced into the PBN-based ceramic. (C) 2008 Elsevier Ltd. All rights reserved.