Chemical synthesis of nanoscale Aurivillius ceramics, Bi2A2TiM2O12 (A = Ca, Sr, Ba and M = Nb, Ta)

A group of three-layered Aurivillius compounds with composition Bi2A2TiM2O12, where A = Ca, Sr, Ba and M = Nb and Ta, have been synthesized as nanoscale powders using two variants of the complex polymerization method. A new modified method is presented that yields single phase powders using reaction temperatures as low as 700 °C and accommodates a wide range of chemical substitutions. The resulting crystallites have dimensions below 100 nm and surface area ~10 m2/g. In situ analysis of the decomposition of the polymeric precursor shows that the polymer yields a three-phase mixture consisting of Bi2A2TiM2O12 and the metastable δ- and β-polymorphs of Bi2O3 upon heating under flowing air. Full kinetics analysis of a 2-step solid state synthesis method was used to demonstrate that the crystallization of δ Bi2O3 in the sol–gel method greatly accelerates the conversion to the Aurivillius phase. The fluorite structure of δ Bi2O3 is the same as that of the [Bi2O2]2+ layer in the Aurivillius phase, facilitating rapid and low-temperature crystallization of the Aurivillius phase from the δ Bi2O3 template.