abstract
The electrical conductivity of SSrFe0.67Ta0.33O3 (-) (delta) measured in the oxygen partial pressure range from 10-2 to 0.5 atm at 700-950 degrees 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 Fe2+ 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 SrFe0.67Ta0.33O3 (-) (delta) is significantly higher compared to SrFe0.7Ta0.3O3 (-) (delta) and SrFe0.6Ta0.4O3 (-) (delta) under similar conditions, which may indicate an important role of the interfacial boundary enlarged due to the perovskite phase separation. 0 2013 Elsevier B.V. All rights reserved.
keywords
OXYGEN NONSTOICHIOMETRY; MOSSBAUER-SPECTROSCOPY; MIXED CONDUCTIVITY; PEROVSKITE; TEMPERATURE; TRANSPORT; OXIDATION; FERRITES; VALENCES; OXIDES
subject category
Chemistry; Physics
authors
Patrakeev, MV; Markov, AA; Shalaeva, EV; Tyutyunnik, AP; Tsipis, EV; Waerenborgh, JC; Kharton, VV; Leonidov, IA; Kozhevnikov, VL
our authors
Vladislav Kharton
Invited Principal ResearcherGroups
acknowledgements
This work was partially funded by the Ministry of Education and Science of the Russian Federation (grant no. 8649), Russian Foundation for Basic Research (13-03-00931), and by the FCT, Portugal (projects PTDC/CTM-CER/114561/2009, SFRH/BPD/28629/2006 and SFRH/BPD/88938/2012). The authors are also grateful to the Ural Branch of RAS for support of this study through the regional programs (12-Y-3-1005 and 12-3-2-002 Arctic).