A novel calorimetric approach to the redox thermochemistry of non-stoichiometric oxidesenthalpy of oxidation of La1-yCayCrO3-delta

A novel calorimetric approach to the energetics of redox reactions in non-s toichiometric oxides is presented. The method utilizes a step-wise heated a diabatic calorimeter for determination of average enthalpies of oxidation. The measurement uncertainty is dominated by the uncertainty in the determin ation of the mass increment due to the oxidation. An experimental investiga tion of the re-oxidation energetics of reduced La1-yCayCrO3-delta is presen ted. The variation of the average formal oxidation state with temperature a nd oxygen fugacity is calculated from the experimentally determined enthalp y of oxidation and an estimated (lattice and configurational) entropy of ox idation. The calculated curves are in good agreement with experimental dete rminations reported in literature.