Oxygen Non-Stoichiometry and Electrical Conductivity of La0.2Sr0.8Fe0.8B0.2O3 − δ, B = Fe, Ti, Ta

Ørjan Fossmark Lohne, Tan Nhut Phung, Tor Grande, Henny J. M. Bouwmeester, Peter Vang Hendriksen, Martin Søgaard, Kjell Wiik

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

The oxygen non-stoichiometry was determined by coulometric titration for the perovskite oxides La0.2Sr0.8FeO3 − δ and La0.2Sr0.8Fe0.8B0.2O3 − δ (B = Ti4+ and Ta5+) in the temperature range 600 °C ⩽ T ⩽ 900 °C and the oxygen partial pressure range: 1⋅10-15po2≤0.209 atm. The non-stoichiometry (δ) is observed to decrease with B-site substitution of Fe. The data can be well fitted with simple defect chemistry models. At low oxygen non-stoichiometry all compositions show a deviation from a localized electrons defect model. The standard and partial molar thermodynamic quantities were obtained and a gradual transition from localized to itinerant electrons with decreasing non-stoichiometry is proposed from the δ-dependency of the configurational entropy. The absolute value of the enthalpy of oxidation decreases upon B-site substitution of Fe proposing a decreased thermodynamic stability for the substituted materials. The electrical conductivity was measured at T = 900 °C in the oxygen partial pressure range: 1⋅10-17po2≤0.209 atm. The electrical conductivity and charge carrier mobility decrease upon 20% substitution of Fe roughly by a factor of 2, but do not show a significant dependence on the nature of the B-site dopant.

Original languageEnglish
JournalJournal of the Electrochemical Society
Volume161
Issue number3
Pages (from-to)F176-F184
ISSN0013-4651
DOIs
Publication statusPublished - 2014

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