Refinement of thermodynamic data for LaMnO3

The standard Gibbs energy of formation of LaMnO3 has been measured in the temperature range from 900 to 1400 K using a solid-state cell incorporating a buffer electrode. The oxygen potential corresponding to the three-phase mixture MnO 1 La2O3 1 LaMnO3 has been measured using pure oxygen gas at 0.1 MPa as the reference electrode, and yttria-stabilized zirconia as the solid electrolyte. The buffer electrode prevented polarization of the three-phase electrode and ensured accurate data. The measured oxygen chemical potential corresponding to the decomposition of LaMnO3-delta to MnO, La2O3 and O-2 gas is in fair agreement ( +/- 6 kJ mol(-1)) with most data available in the literature and can be represented by the equation, Deltamu(O2)/ J mol(-1) ( +/- 520) = 583160 + 170.55 ( T/ K) Combining this with available information on oxygen potential variation with the non-stoichiometric parameter delta, the standard Gibbs free energy of formation of LaMnO3 from MnO, La2O3 and O-2 was evaluated. The correction for non-stoichiometry was similar to1.6( +/- 0.7) kJ mol(-1). The heat capacity of LaMnO3 has been measured by a differential scanning calorimeter from 400 to 1060 K. Information on low-temperature heat capacity available in the literature was joined smoothly with the high-temperature data to evaluate the standard entropy of LaMnO3 at 298.15 K as 116.68 J mol(-1) K-1. The "third- law'' analysis of the Gibbs energy values obtained in this study yields a value of -155.93 ( +/- 0.8) kJ mol(-1) for the standard enthalpy of formation of LaMnO3 from MnO, La2O3 and O-2 at 298.15 K. This value provides a critical test of calorimetric data on enthalpy of formation of LaMnO3. A consistent set of thermodynamic data for LaMnO3 is presented from 298.15 to 1400 K based on the results obtained in this study and other supporting information in the literature.