Accelerated formation of barium titanate by solid-state reaction in water vapour atmosphere

Barium titanate (BaTiO3) powders were synthesized from commercially available raw materials (BaCO3 and rutile) without particular mechanochemical processing by solid-state reactions in water vapour atmosphere. The formation rate of BaTiO3 was accelerated by water vapour and single phase of BaTiO3 was obtained by calcination at 700 degrees C for 4 h in water vapour atmosphere, though high temperature (850 degrees C for 2.5 h) was required by calcinations in air to complete the reaction. The formation kinetics followed the Valensi-Carter equation, which suggested that the reaction proceeded by a diffusion controlled process. The apparent activation. energy for the formation of BaTiO3 in air and water vapour atmosphere was estimated to be 361 +/- 20 kJ/mol and 142 +/- 17 kJ/mol, respectively. Water vapour is considered to enhance thermal decomposition of BaCO3 and formation of BaTiO3 by attacking surface Ti-O-Ti bonds in TiO2, increasing partial pressure of Ba(OH)(2), and producing vacancies in the BaTiO3 structure. (C) 2009 Elsevier Ltd. All rights reserved.