Phase evolution and electrochemical performance of iron doped lanthanum strontium chromite in oxidizing and reducing atmosphere

Abstract

Effect of oxygen partial pressure (PO2) on the processing and phase evolution in (La0.8Sr0.2)0.95Cr0.7Fe0.3O3 (LSCF) is investigated under high temperature electrochemical device fabrication conditions at 1400 °C and oxygen partial pressure (PO2) varying from 0.21 to 10−10 atm. Formation of Fe enriched phase is identified in the samples exposed to reducing atmosphere and the amount of the phase increases with decrease in PO2. LSCF dissociates and forms FeOx when exposed to Ar-3%H2-3%H2O at 1400 °C. LSCF decomposition and the formation of FeOx is in agreement with the thermodynamic simulation results obtained using ThermoCalc with the La-Sr-Cr-Fe-O thermodynamic database. Electrochemical impedance spectroscopy measurement on the symmetrical cell of configuration LSCF-YSZ/YSZ/LSCF-YSZ shows high polarization resistance in oxidizing atmosphere when compared to reducing atmosphere under operating conditions (T ∼ 950 °C and PO2 ∼ 0.21–10−16 atm). No degradation and microstructural changes are identified in the samples exposed to air for 80 h. Surface of LSCF phase is significantly modified in Ar-3%H2-3%H2O atmosphere after electrochemical testing for 80 h. Higher stability and electrochemical performance of LSCF is obtained in air when compared with Ar-3%H2-3%H2O. Unlike oxidizing atmosphere, post characterization TEM results show thin SrZrO3 layer formation at the LSCF/8YSZ interface in reducing atmosphere.