Rietveld analysis and dielectric properties of Bi2WO6-Bi4Ti3O12 ferroelectric system

The crystal structures were analyzed by the Rietveld method in the system composed of Bi2WO6(BW) and Bi4Ti3O12(BIT), both belong to the bismuth layer-structured ferroelectrics with m (number of oxygen octahedra in the perovskite layer) of 1 and 3, respectively. The relation between the ferroelectric phase transitions and the structure were investigated in terms of lattice distortion. It was demonstrated that the sintered ceramics with the composition of the molar ratio of BW:BIT = 1:1 have the same structure as compounds with m = 2, whose chemical composition can be expressed by Bi3Ti1.5W0.5O9, and that Bi3Ti1.5W0.5O9 and BIT (BW:BIT = 1:3) compose a regular intergrowth compound with m = 2 - 3. Dielectric measurements revealed that the intergrowth compound shows two dielectric anomalies, which would correspond to each ferroelectric phase transition of the constituent oxide. Compared with the Curie temperature (T-c) of the constituent oxides, the T-c of the intergrowth compound shifted toward a lower temperature, which might be caused by a decrease in lattice distortion in the perovskite layers induced by the constitution of the intergrowth structure. (C) 2001 Elsevier Science Led. Al rights reserved.