New substitutions and novel derivatives of the Aurivillius phases, Bi5TiNbWO15 and Bi4Ti3O12

We investigated isomorphous substitution of several metal atoms in the Aurivillius structures, Bi5TiNbWO15 and Bi(4)Ti3O(12), in an effort to understand structure-property correlations. Our investigations have led to the synthesis of new derivatives, Bi(4)LnTiMWO(15) (Ln = La, Pr; M = Nb, Ta), as well as Bi4PbNb2WO15 and Bi3LaPbNb2WO15, that largely retain the Aurivillins (n = 1) + (n = 2) intergrowth structure of the parent oxide Bi5TiNbWO15, but characteristically tend toward a centrosymmetric/tetragonal structure for the Ln-substituted derivatives. On the other hand, coupled substitution, 2Ti(IV) -> M-v + Fe-III in Bi4Ti3O12, yields new Aurivillius phases, Bi4Ti3-2xNbxFexO12 (x = 0.25, 0.50) and Bi4Ti3-2xTaxFexO12 (x = 0.25) that retain the orthorhombic noncentrosymmetric structure of the parent Bi4Ti3O12. Two new members of this family, Bi2Sr2Nb2RuO12 and Bi2SrNaNb2RuO12 that are analogous to Bi2Sr2Nb2TiO12, possessing tetragonal (I4/mmm) Aurivillius structure have also been synthesized. (c) 2006 Elsevier Ltd. All rights reserved.