Phase separation-promoted ion conduction in SrFe0.67Та0.33O3− ceramics

Abstract

Abstract The electrical conductivity of SrFe 0.67 Ta 0.33 O 3 − δ measured in the oxygen partial pressure range from 10 − 20 to 0.5 atm at 700–950 °C, exhibits an anomalous and reversible increase in moderately reducing atmospheres, substantially contributed by oxygen ion transport. The coulometric titration studies in combination with the electron and X-ray diffraction analyses show that this trend correlates with the separation of oxygen-deficient disordered cubic perovskite and Ta-rich double perovskite domains of nanometer-scale size. Mossbauer spectroscopy demonstrated that the predominant state of iron cations in the vicinity of this transition is trivalent. Further reduction leads to the formation of Fe 2 + states responsible for increasing n-type electronic conductivity, whilst no traces of wustite or oxygen vacancy-ordered brownmillerite phases were detected. The ion conduction in partially reduced SrFe 0.67 Ta 0.33 O 3 − δ is significantly higher compared to SrFe 0.7 Ta 0.3 O 3 − δ and SrFe 0.6 Ta 0.4 O 3 − δ under similar conditions, which may indicate an important role of the interfacial boundary enlarged due to the perovskite phase separation.