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Mechanism of $BaTiO_3$, formation through gel-to crystallite conversions

Kutty, TRN and Padmini, P (1995) Mechanism of $BaTiO_3$, formation through gel-to crystallite conversions. In: Materials Chemistry and Physics, 39 (3). pp. 200-208.

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Abstract

The wet chemical synthesis of $BaTiO_3$, through gel-to-crystallite conversions involves the reaction of coarse $TiO_2.xH_2O$ (10<x<120) gels, free of anionic contaminants, with $Ba(OH)_2$, solutions under refluxing conditions at $T\leq 100^o C$, giving rise to nanosized crystallites. The paper focuses on the mechanism of formation of $BaTi0_3$. The reaction kinetics were monitored for various temperatures and concentrations and were found to be strongly dependent on $Ba(OH)_2$, concentration. Two regions of concentration could be detected: below 0.15 M $Ba(OH)_2$, polytitanates are formed, whereas at higher concentrations, i.e., greater than 0.15 M, perovskite phase is stabilised. Analyses of the kinetic data were carried out using various kinetic models used for heterogeneous reactions. Under higher concentrations of $Ba(OH)_2$ a bulk diffusional process dominates, accompanied by the collapse of the gel and a large decrease in volume. The present results also indicate the general features of gel-to-crystallite conversions, involving instability of the metal hydroxide gel brought about by the upset of ionic pressure in the gel, as a result of faster migration of $Ba^{2+}$ ions through the solvent cavities within the gel framework. It is proposed that with increasing pH within the gel, de-olation of the bridging groups such as Ti-OH-Ti and Ti-O-Ti takes place, followed by oxolation, leading to the formation of corner-sharing $TiO_6$ octahedra that are charge-compensated by $Ba^{2+}$ ions.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to Elsevier.
Keywords: Metal hydroxide gels;Perovskites;Diffusion;Liesegang rings
Department/Centre: Division of Chemical Sciences > Materials Research Centre
Date Deposited: 15 Mar 2007
Last Modified: 19 Sep 2010 04:35
URI: http://eprints.iisc.ernet.in/id/eprint/9780

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