Lanthanum oxyfluoride: structure, stability, and ionic conductivity

Jacob, Kallarackel T. ; Saji, Viswanathan S. ; Waseda, Yoshio (2006) Lanthanum oxyfluoride: structure, stability, and ionic conductivity International Journal of Applied Ceramic Technology, 3 (4). pp. 312-321. ISSN 1546-542X

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Official URL: http://onlinelibrary.wiley.com/doi/10.1111/j.1744-...

Related URL: http://dx.doi.org/10.1111/j.1744-7402.2006.02086.x

Abstract

Structure and phase transition of LaO1−xF1+2x, prepared by solid-state reaction of La2O3 and LaF3, was investigated by X-ray powder diffraction and differential scanning calorimetry for both positive and negative values of the nonstoichiometric parameter x. The electrical conductivity was investigated as a function of temperature and oxygen partial pressure using AC impedance spectroscopy. Fluoride ion was identified as the migrating species in LaOF by coulometric titration and transport number determined by Tubandt technique and EMF measurements. Activation energy for conduction in LaOF was 58.5 (±0.8) kJ/mol. Conductivity increased with increasing fluorine concentration in the oxyfluoride phase, suggesting that interstitial fluoride ions are more mobile than vacancies. Although the values of ionic conductivity of cubic LaOF are lower, the oxygen partial pressure range for predominantly ionic conduction is larger than that for the commonly used stabilized-zirconia electrolytes. Thermodynamic analysis shows that the oxyfluoride is stable in atmospheres containing diatomic oxygen. However, the oxyfluoride phase can degrade with time at high temperatures in atmospheres containing water vapor, because of the higher stability of HF compared with H2O.

Item Type:Article
Source:Copyright of this article belongs to John Wiley and Sons.
ID Code:95037
Deposited On:09 Nov 2012 06:30
Last Modified:09 Nov 2012 06:30

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