Oxygen Nonstoichiometry And Defect Chemistry Of Perovskite-Type Ca0.25sr0.75fe0.75mo0.25o3-Delta

The oxygen content in mixed-conducting perovskite-type Ca0.25Sr0.75Fe0.75Mo0.25O3-delta was measured as a function of oxygen partial pressure varying in the range 10(-21)-0.5 atm at temperature 750-950 degrees C by coulometric titration technique. The experimental data were satisfactorily simulated with a defect equilibrium model involving reactions of iron oxidation, charge disproportionation on Fe sites, and electron exchange between iron and molybdenum. A comparison of the obtained results with similar data for SrFe0.75Mo0.25O3-delta has shown that calcium substitution provides no observable effect on standard enthalpy and entropy of disproportionation and electron exchange reactions, but decrease standard enthalpy and increase standard entropy of the oxidation reaction, resulting in an almost tenfold decrease in the respective equilibrium constant. A decrease in the concentration of p-type carriers and an increase in the concentration of n-type carriers were revealed in response to calcium substitution for strontium in SrFe0.75Mo0.25O3-delta. (C) 2018 Elsevier B.V. All rights reserved.