Role of entropy in the stability of cobalt titanates

Jacob, K. T. ; Rajitha, G. (2010) Role of entropy in the stability of cobalt titanates The Journal of Chemical Thermodynamics, 42 (7). pp. 879-885. ISSN 0021-9614

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The standard molar Gibbs free energy of formation of Co2TiO4, CoTiO3, and CoTi2O5 as a function of temperature over an extended range (900 to 1675) K was measured using solid-state electrochemical cells incorporating yttria-stabilized zirconia as the electrolyte, with CoO as reference electrode and appropriate working electrodes. For the formation of the three compounds from their component oxides CoO with rock-salt and TiO2 with rutile structure, the Gibbs free energy changes are given by: Δf(ox)(Co2TiO4)±104/(J·mol-1)=-18865-4.108(T/K) Δf(ox)(CoTiO3)±56/(J·mol-1)=-19627+2.542(T/K) Δf(ox)(CoTi2O5)±52/(J·mol-1)=-6223-6.933(T/K) Accurate values for enthalpy and entropy of formation were derived. The compounds Co2TiO4 with spinel structure and CoTi2O5 with pseudo-brookite structure were found to be entropy stabilized. The relatively high entropy of these compounds arises from the mixing of cations on specific crystallographic sites. The stoichiometry of CoTiO3 was confirmed by inert gas fusion analysis for oxygen. Because of partial oxidation of cobalt in air, the composition corresponding to the compound Co2TiO4 falls inside a two-phase field containing the spinel solid solution Co2TiO4–Co3O4 and CoTiO3. The spinel solid solution becomes progressively enriched in Co3O4 with decreasing temperature.

Item Type:Article
Source:Copyright of this article belongs to Elsevier Science.
Keywords:Co2TiO4; CoTiO3; CoTi2O5; Gibbs Free Energy; Enthalpy; Entropy; Thermodynamic Properties; Phase Diagram
ID Code:95067
Deposited On:09 Nov 2012 06:31
Last Modified:09 Nov 2012 06:31

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