Effect of mechanical milling on solid state formation of BaTiO3 from BaCO3-TiO2 (rutile) mixtures

Barium metatitanate (BaTiO3) is widely used because of its high dielectric constant, ferroelectric properties and positive temperature coefficient of electrical resistivity. The present work reports the results obtained in the set up of a preparation method of BaTiO3 by milling and annealing mixtures of BaCO3 and TiO2 (rutile). High energy milling of a BaCO3-TiO2 (rutile) equimolecular mixture resulted in a noticeable temperature drop of the temperature where the reaction can occur. The formation of single phase BaTiO3 was confirmed by thermogravimetric analysis (TGA) (both alone and coupled with Fourier transform infrared spectroscopy (FT-IR) evolved gas analysis), by differential scanning calorimetry (DSC) and X-ray powder diffractometry (XRPD). The formation of phases like Ba2TiO4 (orthotitanate), which are known to be detrimental for BaTiO3 end performances, has only been revealed as an intermediate minor phase that disappears by annealing at temperatures as low as 750 degreesC. At such temperatures the crystal size of the product is 400 Angstrom. BaTiO3 formation occurs either by a slow heating (2 K/min) of the milled mixture or by a rapid heating followed by an isothermal annealing of 12 h. (C) 2001 Elsevier Science B.V. All rights reserved.