Abstract
This study has produced a novel double-perovskite (Calcium-Doped Oxygen-deficit Strontium Iron Titanium Molybdenum Oxide (Ca-doped Sr2Fe1.2Ti0.3Mo0.5O6-δ) ceramic interconnect material to address the challenges of poor electrical conductivity and structural instability in dual-atmosphere operations for self-sealing flat-tubular segmented-in-series solid oxide fuel cells (FT-SIS-SOFCs). The Sr2-xCaxFe1.2Ti0.3Mo0.5O6-δ (x = 0, 0.1, 0.2, 0.3) powders were synthesized via a sol-gel method. The phase composition, sintering density, thermal expansion, and electrical conductivities of the Sr2-xCaxFe1.2Ti0.3Mo0.5O6-δ were systematically analyzed. The results demonstrated that Ca doping effectively suppressed the precipitation of metallic Fe under reducing conditions. Although the conductivity in air decreased from 7.61 to 3.04 S cm-1 at 650 °C with increasing Ca content, it significantly increased in a reducing atmosphere (from 3.43 to 13.12 S cm-1). These improvements were caused by lattice contraction strengthening the Ca–O bonds and an increased Mo6+/Mo5+ ratio, which shortens electron transfer pathways. Sr1.8Ca0.2Fe1.2Ti0.3Mo0.5O6-δ exhibited optimal overall performance, demonstrating excellent conductivity in both atmospheres, well-matched thermal expansion with common electrolytes, and robust chemical compatibility with adjacent cell components. Moreover, it showed remarkable long-term stability at 650 °C. This work provides a promising strategy for developing high-performance ceramic interconnects for advanced SOFC configurations.