Synthesis and structural studies of lanthanide substituted bismuth-titanium pyrochlores

Abstract

The identity of the pyrochlore phase seen during the synthesis of ferroelectric Bi(4-x)Ln(x)Ti(3)O(12) Aurivillius oxides is shown to be Bi(2/3)Ln(4/3)Ti(2)O(7). This pyrochlore is only stable for Ln(3+) = Sm3+ or smaller. For larger lanthanides the layered Aurivillius oxide is favoured. The presence of six-fold disorder, associated with the Bi 6s(2) lone pair electrons, is believed to stabilise the unexpected stoichiometry of this oxide. Precise structures, obtained by Rietveld refinement from synchrotron X-ray diffraction data, of three examples Ln(3+) = Eu, Ho and Yb are presented. © 2009, Elsevier Ltd.