Oxidation states of Co and Fe in Ba1−xSrxCo1−yFeyO3−δ (x, y = 0.2–0.8) and oxygen desorption in the temperature range 300–1273 K

TitleOxidation states of Co and Fe in Ba1−xSrxCo1−yFeyO3−δ (x, y = 0.2–0.8) and oxygen desorption in the temperature range 300–1273 K
Publication TypeJournal Article
Year of Publication2009
AuthorsHarvey, AS, F. Litterst, J, Yang, Z, Rupp, JLM, Infortuna, A, Gauckler, LJ
JournalPhysical Chemistry Chemical Physics
Volume11
Issue17
Pagination3090 - 3098
Date Published2009///
Abstract

Four compositions of Ba1-xSrxCo1-yFeyO3-delta were studied for phase, oxygen uptake-release, and transition metal (TM) oxidation states after solid state processing and with in situ heating from 300 to 1273 K in air. X-Ray diffraction showed that all compositions except one had the cubic perovskite structure at all temperatures; that with x, y = 0.2 was a mixture as prepared, becoming predominantly cubic at high temperature. Thermogravimetry showed a reversible oxygen absorption-desorption of approximately +/- 1% from 700 to 1273 K. X-Ray absorption and Mossbauer spectroscopy showed a majority TM3+ valence, with at most 40% TM4+. Up to a temperature of 1073 K, the TM4+ was reduced to TM3+. Further heating of the composition with x, y = 0.2 to 1233 K resulted in the reduction of Co3+ to Co2+. Results from room temperature measurements confirm the thermally activated carrier hopping mechanism with charge fluctuations, while the high temperature delocalized carrier conductivity occurs with a small amount of TM reduction and without phase change for the initially cubic samples.

URLhttp://pubs.rsc.org/en/Content/ArticleLanding/2009/CP/b819414a#!divAbstract