Crystal structures and proton transport properties of Sr2(Ti1-xMx)O4-δ (M = Fe, Al)

Abstract This study focuses on the effects of acceptor dopants in proton-conductive Sr2TiO4-based layered perovskites. We synthesized Sr2Ti0.9Fe0.1O4-δ (STF10) and Sr2Ti0.95Al0.05O4-δ (STA05) and evaluated the influence of ion substitution on their crystal structures, electrical conductivities, and proton transport properties. Our obtained results suggest that a redox reaction is the more favorable mechanism for the introduction of proton defects to Fe-doped samples compared with water vapor absorption, while the reverse is true for Al-doped samples. STF10 was found to exhibit a larger electrical conductivity at low temperatures than STA05. In addition, STF10 presented a proton transport number of 0.5 at 600 °C, while the corresponding value for STA05 was 0.5–0.6 at 450–600 °C. The higher proton transport number of STA05 at 450–550 °C compared to that of STF10 indicates that the Al-dopant suppressed the electronic conductivity owing to its constant valency. We therefore considered that characterization of the changes in material properties related to ion substitution can serve as a guide for material selection when developing proton-conducting solid oxide fuel cell technologies.