The factors influencing crystallization of layered-perovskite lanthanum substituted bismuth titanate, starting from an aqueous metal-chelate precursor-gel, were identified by means of statistically designed experiments. To ensure experimental economy and efficiency in spite of the large number of factors possibly affecting the phase purity, a fractional factorial design was chosen. The calcination atmosphere turned out to be the most important to avoid the formation of the Sillenite secondary phase, Bi12TiO20. In order to study its impact on phase purity thoroughly an extensive number of ambient compositions were tested. These tests showed that dry air is the optimal composition. Precursor stoichiometry and gas flow rate during heat treatment also significantly influenced the formation of Bi12TiO20. Furthermore, the precursor stoichiometry and cooling rate as well as the calcination atmosphere and crystallization time turned out to interact. (C) 2003 Elsevier Ltd. All rights reserved.