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Composition‐Graded Solid Electrolyte for Determination of the Gibbs Energy of Formation of Lanthanum Zirconate
Author(s) -
Jacob K. Thomas,
Dasgupta Niladri,
Waseda Yoshio
Publication year - 1998
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1998.tb02568.x
Subject(s) - gibbs free energy , lanthanum , electrolyte , monoclinic crystal system , enthalpy , pyrochlore , solid solution , cubic zirconia , fluoride , solubility , zirconate , chemistry , inorganic chemistry , materials science , mineralogy , analytical chemistry (journal) , electrode , crystallography , crystal structure , thermodynamics , metallurgy , ceramic , physics , organic chemistry , phase (matter) , titanate , chromatography
A composition‐graded solid electrolyte has been used to determine the standard Gibbs free energy of formation of lanthanum zirconate (La 2 Zr 2 O 7 ) from the component oxides lanthana (La 2 O 3 ) (A‐rare earth) and zirconia (ZrO 2 ) (monoclinic) in the temperature range of 870–1240 K. The cell used for measurement can be represented as Pt, O 2 , CaO + CaF 2 ∥ CaF 2 | (LaF 3 ) x (CaF 2 ) 1‐x ∥LaF 3 + La 2 Zr 2 O 7 + ZrO 2 , O 2 , Pt x=0 x=0.32 A composition‐graded electrolyte has been introduced to compensate the solubility effects of the electrode material (lanthanum fluoride, LaF3) in the solid electrolyte (calcium fluoride, CaF2). The ability of the graded electrolyte to gen‐erate a Nernstian response is demonstrated, using electrodes with known fluorine chemical potentials. For the reaction La 2 O 3 (A‐rare earth) + 2ZrO 2 (monoclinic) → La 2 Zr 2 O 7 (pyrochlore), the Gibbs free energy change (ΔG ° f,ox ) is given by the formula −133800 −10.32 T (±4500) (in units of J/mol). The enthalpy and entropy of formation of La 2 Zr 2 O 7 obtained in this study are in good agreement with calorimetric data. The “third‐law” enthalpy of formation of La 2 Zr 2 O 7 , from the component oxides at 298.15 K, is −133.8 ± 5 kJ/mol.