The synthesis and structure of triple layered Bi(2)Ln(2)Ti(3)O(12) Aurivillius phases (Ln = La, Pr, Nd and Sm), prepared from K(2)Ln(2)Ti(3)O(10) Ruddlesden-Popper precursors, has been investigated. These materials adopt a body centred tetragonal structure (space group I4/mmm, with unit cell parameters a similar to 3.8 Angstrom and c similar to 33 Angstrom) comprising a regular intergrowth of [Bi2O2](2+) fluorite-type and [Ln(2)Ti(3)O(10)](2-) perovskite-type layers. A significant degree of cation disorder is present in the Bi(2)Ln(2)Ti(3)O(12) system, involving the cross-substitution of Ln/Bi cations onto the Bi/Ln sites in the fluorite- and perovskite-type layers, respectively. As the size of the lanthanide cation is reduced, Bi/Ln disorder is significantly suppressed due to the effect of bond length mismatch in the perovskite-type layer in the crystal structure of Bi(2)Ln(2)Ti(3)O(12). This offers a potential strategy for the chemical control of cation disorder in the Bi(2)Ln(2)Ti(3)O(12) system. (C) 2003 Elsevier Science Ltd. All rights reserved.