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Lanthanum Oxyfluoride: Structure, Stability, and Ionic Conductivity
Author(s) -
Jacob Kallarackel T.,
Saji Viswanathan S.,
Waseda Yoshio
Publication year - 2006
Publication title -
international journal of applied ceramic technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.4
H-Index - 57
eISSN - 1744-7402
pISSN - 1546-542X
DOI - 10.1111/j.1744-7402.2006.02086.x
Subject(s) - ionic conductivity , materials science , partial pressure , analytical chemistry (journal) , conductivity , differential scanning calorimetry , oxygen , ionic bonding , phase (matter) , dielectric spectroscopy , ion , inorganic chemistry , electrolyte , chemistry , thermodynamics , electrochemistry , electrode , physics , organic chemistry , chromatography
Structure and phase transition of LaO 1− x F 1+2 x , prepared by solid‐state reaction of La 2 O 3 and LaF 3 , 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 H 2 O.