Oxygen nonstoichiometry and defect chemistry of perovskite-structured SrFe1−xMoxO3−δ solid solutions

The oxygen nonstoichiometry ofmixed-conducting perovskite-structured SrFe1−xMoxO3−δ (x=0, 0.07, 0.15 and 0.25) was measured by oxygen coulometric titration in the range of oxygen partial pressure 10−20–0.5 atm and temperature 800–950 °C. Based upon a defect chemical analysis of the non-stoichiometry data it is shown that significant reduction of Mo6+ occurs under reducing conditions. The trend observed in the oxidation enthalpy suggests a weakening of the Fe\\O bond strength along with the degree of substitution of Fe by Mo, which behavior is consistent with the concomitant increase in lattice constant. Atomistic simulations were carried out to support the defect chemical analysis, showing that the Mo cations in SrFe1−xMoxO3−δ retain a full, 6-fold coordination shell, whilst Fe cations can have 0, 1 or 2 oxygen vacancies in the first coordination shell

Redox stability and high-temperature electrical conductivity of magnesium-and aluminium-substituted magnetite

Spinel-type magnetite-based oxides, possessing relatively high electrical conductivity, are considered as promising consumable anode materials for high temperature pyroelectrolysis, a breakthrough low-CO2 steel technology to overcome the environmental impact of classical extractive metallurgy. The present work was focused on the analysis of phase stability, thermal expansion and high-temperature electrical conductivity in (Fe,Mg,Al)(3)O-4 system under oxidizing and mildly reducing conditions. Metastable, nearly single-phase at room temperature (Fe,Mg,Al)(3)O-4 ceramics was obtained by sintering at 1753-1773 K for 10 h in argon atmosphere. Thermal expansion and redox induced dimensional changes were studied on heating, using TG, XRD and dilatometry. The results revealed that magnesium improves the tolerance against oxidative decomposition and minimizes unfavorable dimensional changes in ceramic samples upon thermal cycling. Co-substitution of iron with aluminium and magnesium was proved to be a promising strategy for improvement of refractoriness and phase stability of Fe3O4-based spinels at elevated temperatures, without significant reduction in the electrical conductivity. (C) 2013 Elsevier Ltd. All rights reserved