Synthesis of (Bi,La)4Ti3O12 by a new aqueous solution-gel route

A new aqueous solution-gel route for the synthesis of ferroelectric lanthanum substituted bismuth titanate was developed, based on aqueous Bi3+- and La3+-citrate solutions and an aqueous peroxocitrato-Ti(IV) solution. A homogeneous, amorphous precursor gel was prepared by evaporation of the BLT precursor solution. The homogeneity was maintained throughout the entire thermo-oxidative decomposition of the gel, as shown by TEM measurements on freestanding thin films. This molecular scale mixing and high degree of homogeneity led to the direct crystallization of the Aurivillius phase from the amorphous phase. As a consequence the crystallization temperature was as low as 525 °C, which was shown by a high temperature X-ray diffraction study of the stoichiometric precursor. The addition of an excess of Bi3+ decreased the crystallization temperature, but also introduced a Bi2O3 secondary phase.