Electrochemical Determination of Gibbs Energy of Formation of LaCrO3 Using a Composition‐Graded Bielectrolyte

Abstract

Presented are new measurements of the standard Gibbs free energy of formation of rhombohedral LaCrO3 from component oxides La2O3 and Cr2O3 in the temperature range from 875 to 1175 K, using a bielectrolyte solid‐state cell incorporating single crystal CaF2 and composition‐graded solid electrolyte (LaF3)y·(CaF2)1−y (y = 0–0.32). The results can be represented analytically as (±2270)/J·mol−1 = −72329 + 4.932 (T/K). The measurements were undertaken to resolve serious discrepancies in the data reported in the literature. A critical analysis of previous electrochemical measurements indicates several deficiencies that have been rectified in this study. The enthalpy of formation obtained in this study is consistent with calorimetric data. The standard enthalpy of formation of orthorhombic LaCrO3 from elements at 298.15 K computed from the results of this study is /kJ·mol−1 = −1536.2 (±7). The standard entropy of orthorhombic LaCrO3 at 298.15 K is estimated as 99.0 (±4.5) J·(mol·K)−1.