THE INFLUENCE OF THE PRECURSOR COMPOSITION ON THE PECULIARITIES OF THE BARIUM TITANATE FORMATION

Abstract

In the process of obtaining barium titanate by the Pechini method, a connection between the conditions of complexes precipitation and the nature of their thermal decomposition was established. X-ray phase analysis of thermally decomposed precursors showed that the formation of a single-phase system based on barium titanate can be achieved in the range of Ba/Ti ratio 0.96-1.01 at high reagent concentration and low solution pH during the precursor deposition process. On the basis of thermogravimetric analysis, a possible mechanism of precursor decomposition and its composition is assumed. It is shown that the number of hydroxide groups in the structure affects the crystallization mechanism, total mass loss, and the amount of water adsorbed on the surface. In particular, samples obtained at low solution pH have a minimal amount of hydroxyl groups and decompose according to a typical four-step mechanism of thermal decomposition of barium titanyl oxalate. Other samples contain hydro and carbo groups, which leads to an increase in the final decomposition temperature above 770 °C and a multistage decomposition process due to the difference in the activation energy of the nucleation of different phases. This, in turn, may determine the dominance of the nucleation process over the growth and nucleation of smaller crystallites, compared to the product of pure oxalate decomposition. On the one hand, the high content of chloride ions at the lowest pH promotes the crystallization of the product and the formation of additional nucleation centers from the phase of amorphous titanium dioxide. On the other hand, the formation of smaller crystallites occurs due to the absence of significant particle collisions in conditions of low concentration of the solution. On the basis of thermogravimetric analysis, it is shown that at high concentration, barium titanyl oxalate decomposes mainly by the mechanism of formation of intermediate oxycarbonates, and not barium carbonate and titanium dioxide. Thus, the optimization of the precursor precipitation parameters and the study of the barium titanate formation mechanism allow for better regulation of the composition and crystallite size of the final product.