Crystal structure and ferroelectric properties of mixed bismuth layer-structured Bi7Ti4+x/2Nb1-xWx/2O21 ceramics

The effects of Ti and W substitutions for Nb on the ferroelectric properties and the crystal structure of Bi7Ti4+x/2Nb1-xWx/2O21 ceramics were investigated in this study. From the XRPD patterns, no impurity phase was observed in the composition range from 0 to 1. The solid solutions have orthorhombic symmetry, with 12cm space group. The curve representing the relationship between composition x and remanent polarization (P,) passes through a maximum at approximately x = 0.75; therefore, the maximum P-r value of 12.4 mu C/cm(2) was obtained for this composition. The variation in the structural distortion of oxygen octahedra in the pseudo-perovskite block showed the same tendency as that of the P-r values. On the other hand, the coercive field (E-c) of the samples at the composition range from 0 to 1 remained the approximately constant value of 90 kV/cm. Moreover, the Curie temperature (T,) of the samples was decreased from 840 to 715 degrees C by the increase of the structural distortion of the pseudo-perovskite block, which was caused by the Ti and W substitutions for Nb. (c) 2006 Elsevier B.V. All rights reserved.