Structural studies of five layer aurivillius oxides:: A2Bi4Ti5O18 (A = Ca, Sr, Ba and Pb)

The room temperature structures of the five layer Aurivillius phases A(2)Bi(4)Ti(5)O(18) (A = Ca, Sr, Ba and Pb) have been refined from powder neutron diffraction data using the Rietveld method. The structures consist of [Bi2O2](2+) layers interleaved with perovskite-like [A(2)Bi(2)Ti(5)O(16)](2-) blocks. The structures were refined in the orthorhombic space group B2eh (SG. No. 41), Z = 4, and the unit cell parameters of the oxides are a 5.4251(2), b = 5.4034(1), c = 48.486(1); a = 5.4650(2), b = 5.4625(3), c = 48.852(1); a = 5.4988(3), b = 5.4980(4), c = 50.352(1); a 5.4701(2), b = 5.4577(2), c = 49.643(1) for A = Ca, Sr, Ba and Pb, respectively. The structural features of the compounds were found similar to n = 2-4 layers bismuth oxides. The strain caused by mismatch of cell parameter requirements for the [Bi2O2](2+) layers and perovskite-like [A(2)BiTi(5)O(16)](2-) blocks were relieved by tilting of the TiO6 octahedra. Variable temperature synchrotron X-ray studies for Ca and Ph compounds showed that the orthorhombic structure persisted up to 675 and 475 K, respectively. Raman spectra of the compounds are also presented. Crown Copyright (C) 2004 Published by Elsevier Inc. All rights reserved.