From scheelite to perovskite: Electrical and redox behavior of SrMoO4/SrMoO3 ceramic components for SOFC anodes

Perovskite-type SrMoO₃ was explored as a prospective electronically-conducting ceramic component for solid oxide fuel cell anodes. The study examined the electrical conductivity of SrMoO₃ and its oxidized precursor, scheelite-type SrMoO₄, and the dynamics of redox-driven phase transformation between them. While SrMoO₄ ceramics show very low electrical conductivity (∼10⁻⁵ S/cm at 900°C in air), SrMoO₃ remains oxygen-stoichiometric and exhibits high metallic-like p(O₂)-independent conductivity within the phase stability domain, reaching 1160 S/cm at 900°C and 1620 S/cm at 700°C even for highly porous samples. The scheelite-to-perovskite transformation is comparatively slow even at 900°C, and complete phase conversion requires up to 10 h at 1000°C under reducing conditions. The phase transformation is accompanied by a smooth dimensional shrinkage on reduction and a sharp expansion on reversed re-oxidation. The isothermal reduction of SrMoO₄ ceramics induces an increase in conductivity by ≥ 7 orders of magnitude within 10 h at 900°C, highlighting the potential of SrMoO₃ as a high-conducting component for composite anodes.