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Measurement of Gibbs energy of formation of LaGaO3 using a composition-graded solid electrolyte

Published online by Cambridge University Press:  31 January 2011

K. Thomas Jacob ,
Niladri Dasgupta ,
Helfried Näfe  and
Fritz Aldinger
K. Thomas Jacob*
Affiliation:
Department of Metallurgy and Materials Research Center, Indian Institute of Science, Bangalore 560 012, India
Niladri Dasgupta
Affiliation:
Ceramic Technology Institute, Bharat Heavy Electricals Limited, Bangalore 560 012, India
Helfried Näfe
Affiliation:
Max-Planck-Institut für Metallforschung, Heisenbergstrasse 5, D-70569 Stuttgart, Germany
Fritz Aldinger
Affiliation:
Max-Planck-Institut für Metallforschung, Heisenbergstrasse 5, D-70569 Stuttgart, Germany
*
a)Address all correspondence to this author.katob@metalrg.iisc.ernet.in
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Abstract

A composition-graded solid electrolyte (LaF3)y · (CaF2)1-y was used for the measurement of the standard Gibbs energy of formation of LaGaO3 from its component oxides. An equimolar mixture of CaO and CaF2 was employed as the reference electrode. The composition of the working electrode depended on temperature. A three-phase mixture of LaGaO3 + Ga2O3 + LaF3 was used in the temperature range from 910 to 1010 K, while a mixture of LaGaO3 + Ga2O3 + LaO1-xF1+2x was employed from 1010 to 1170 K. Both the reference and working electrodes were placed under pure oxygen gas. Because of the high activity of LaF3 at the working electrode, there was significant diffusion of LaF3 into CaF2. The composition-graded electrolyte was designed to minimize the electrode–electrolyte interaction. The concentration of LaF3 varied across the solid electrolyte; from y = 0 near the reference electrode to a maximum value y = 0.32 at the working electrode. For the correct interpretation of the electromotive force at T > 1010 K, it was necessary to use thermodynamic properties of the lanthanum oxyfluoride solid solution. The standard Gibbs energy of formation of LaGaO3 from its component oxides according to the reaction, ½La2O3 (A-rare earth) + ½Ga2O3 (b) → LaGaO3 (rhombohedral) can be represented by the equation: δGo f,(ox) /J mol -1 = –46 230 + 7.75 T/K (±1500).

Type
Articles
Information
Journal of Materials Research , Volume 15 , Issue 12 , December 2000 , pp. 2836 - 2843
Copyright
Copyright © Materials Research Society 2000

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References

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