A[Bi<SUB>3</SUB>Ti<SUB>4</SUB>O<SUB>13</SUB>] and A[Bi<SUB>3</SUB>PbTi<SUB>5</SUB>O<SUB>16</SUB>] (A = K, Cs): new n = 4 and n = 5 members of the layered perovskite series, A[A&#8216;<SUB>n-1</SUB>B<SUB>n</SUB>O<SUB>3n+1</SUB>], and their hydrates

We describe the synthesis and structural characterization of new layered bismuth titanates, A[Bi3Ti4O13] and A[Bi3PbTi5O16] for A = K, Cs, corresponding to n = 4 and 5 members of the Dion-Jacobson series of layered perovskites of the general formula, A[A&#8216;n-1BnO3n+1]. These materials have been prepared by solid state reaction of the constituents containing excess alkali, which is required to suppress the formation of competitive Aurivillius phases. Unlike the isostructural niobates and niobium titanates of the same series, the new phases reported here are spontaneously hydrateda feature which could make them potentially useful as photocatalysts for water splitting reaction. On hydration of the potassium compounds, the c axis expands by ca.2 &#197; and loses its doubling [for example, the tetragonal lattice parameters of K[Bi3Ti4O13] and its dihydrate are respectively a = 3.900(1) &#197;, c = 37.57(2) &#197;; a = 3.885(1) &#197;, c = 20.82(4) &#197;]; surprisingly, the cesium analogues do not show a similar change on hydration