Electro-chemo-mechanical studies of perovskite-structured mixed ionic-electronic conducting SrSn1-xFexO3-x/2+δ Part III: Thermal and chemical expansion
The thermal and chemical expansion of a potential solid oxide fuel cell (SOFC) cathode material SrSn0.65Fe0.35O3–0.35/2+δ (SSF35) were investigated to assess its thermo-chemo-mechanical stability at SOFC operating temperatures and to establish the correlation between defect concentrations (oxygen vacancies and electrons) and chemical expansion with the aid of the defect chemical model reported in part I of this study. Thermochemical expansion was measured as a function of temperature and oxygen partial pressure. The chemical expansion of SSF35 showed a strong correlation with changes in oxygen nonstoichiometry associated with changes in Fe valence state. Coefficients of both chemical (CCE) and thermal (CTE) expansion were calculated and found to be smaller than that of the closely related mixed conducting perovskite oxide SrTi0.65Fe0.35O3–0.35/2+δ (STF35). The thermal expansion coefficient of SSF was found to be close to that of YSZ (most popular solid oxide electrolyte), which makes SSF35 more attractive in terms of overall thermo-chemical stability. The chemical expansion of SSF35 showed decreasing CCE with increasing temperature and decreasing CTE with increasing oxygen deficiency, both opposite to the trends observed for STF35. Distortion in symmetry from the cubic structure seems to be responsible for the smaller coefficients and increasing asymmetry with expansion seems accountable for opposite trends of CCE and CTE compared to the STF counterpart.
KeywordsChemo-mechanics Chemical expansion Perovskite oxide Sofc cathode Oxygen non-stoichiometry Defect chemistry
This research was carried out as a part of the activity of the Skoltech-MIT Center for Electrochemical Energy Storage. Structural characterization of the materials was conducted in the MRSEC Shared Experimental Facilities at MIT, supported by the National Science Foundation under award number DMR-1419807. Thanks go to Dr. Charlie Settens for assistance with XRD.
- 5.C.S. Kim, S.R. Bishop, H.L. Tuller, Electro-chemo-mechanical studies of perovskite-structured mixed ionic-electronic conducting SrSn1-xFexO3-x/2+δ part II: Electrical conductivity and cathode performance. J. Electroceram., 1–8 (2017)Google Scholar
- 14.I. Yasuda, M. Hishinuma, Lattice expansion of acceptor-doped lanthanum chromites under high-temperature reducing atmospheres. Electrochemistry 68, 526 (2000)Google Scholar