A[Bi3Ti4O13] and A[Bi3PbTi5O16] (A = K, Cs): New n=4 and n=5 members of the layered perovskite series, A[A ' n-1B nO3n+1], and their hydrates

We describe the synthesis and structural characterization of new layered bi smuth titanates, A[Bi3Ti4O13] and A[Bi3PbTi5O16]for A = K, Cs, correspondin g to n = 4 and 5 members of the Dion-Jacobson series of layered perovskites of the general formula, A[A'n-1BnO3n+1]. These materials have been prepare d by solid state reaction of the constituents containing excess alkali, whi ch 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 hydrated-a feature which c ould make them potentially useful as photocatalysts for water splitting rea ction. On hydration of the potassium compounds, the c axis expands by ca. 2 Angstrom and loses its doubling [for example, the tetragonal lattice param eters of K[Bi3Ti4O13] and its dihydrate are respectively a = 3900(1)Angstro m c 37.57(2) Angstrom; a 3.885(1) Angstrom, c = 20.82(4) Angstrom]; surpris ingly, the cesium analogues do not show a similar change on hydration.