Dilatometer based thermal expansion studies have been carried out on the starting oxide mixtures of some of the important relaxor ferroelectric compositions including lead iron niobate, lead magnesium niobate-lead titanate and lead zinc niobate-barium titanate. An anomalous thermal expansion behavior is observed between 550 and 650 degreesC corresponding to the onset of the solid state reaction. Further heating of the reaction mixture resulted in a decrease in the dimension of the sample. From the complementary evidence of DTA, X-ray diffraction (XRD) and scanning electron microscopy (SEM), it is shown that the initiation of solid state reaction results in the restructuring of the reacting grains to form the agglomerates of fine particles of reaction intermediates. This phenomenon is shown to be absent in the barium zinc niobate system where the pyrochlore intermediates do not exist. This novel dilatometric approach has been projected as a possible technique to identify optimum calcination temperatures to produce sinter-active powders in the above oxide system, thereby help in reducing the sintering temperatures. (C) 2003 Elsevier Science Ltd. All rights reserved.