Heating-rate effect on the BaTiO3 formation by thermal decomposition of metal citrate polymeric precursors

Barium titanate nano-sized powders had been prepared by a slightly modified Pechini method. DTA/TG thermal analysis indicated that thermal decompositi on of the precursor proceeds through four major step processes: (a) dehydra tion reaction, (b) combustion reactions, (c) intermediate phases formation, and (d) decarbonation of the intermediate to give BaTiO3. X-ray diffractom etry (XRD) and Raman spectroscopy results indicated that, depending on the heating-rate, the BaTiO3 formation took place via a predominant solid-state reaction between nano-sized BaCO3 and amorphous TiO2 (TiO2-x) when crystal lized by low heating-rate (1.5 degreesC min(-1)). Although a small amount o f a quasi-amorphous intermediate phase was also present. BaTiO3 crystalliza tion by rapid heating-rate (5 degreesC mini) took place through a quasi-amo rphous intermediate phase formation as the main rate-controlling factor for the crystallization process. Although room temperature XRD results seems t o indicate the formation of pseudo-cubic BaTiO3 as the final reaction produ ct, the Raman spectra indicated as more probable the formation of a mixture of an oxygen-deficient hexagonal and tetragonal BaTiO3 phases rights reser ved below 700 degreesC. Above that temperature, the tetragonal BaTiO3 was t he only phase present. (C) 2001 Elsevier Science B.V. All rights reserved.