Chemical and Thermal Stability of Sr_1.9VMoO_6-δ: Implications for High Temperature Energy Conversion Applications

Raman spectroscopy and thermal gravimetric analysis (TGA) were used to evaluate the thermal and atmosphere stability of Sr_1.9VMoO_6-δ (SVMO-19), an A-site deficient double perovskite. Motivated by previous reports describing SVMO-19's unprecedented electrical conductivity under reducing atmospheres, studies described in this work determine SVMO-19's stability under conditions commonly encountered in high temperature solid oxide electrolysis and fuel cell applications. Vibrational Raman data show that SVMO-19 is stable up to 1000 °C under reducing, inert, and CO₂ containing atmospheres. Under air, however, in situ Raman data show that SVMO-19 phase separates at temperatures ≥ 600 °C. The primary degradation products include a scheelite phase (SrMoO₄) as well as a vanadium containing single perovskite, SrVO₃, and a vanadium containing pyrochlore Sr₂V₂O₇. TGA measurements suggest that SVMO decomposition in air begins at even lower temperatures (400 °C). TGA data show that SVMO is stable under N₂ at temperatures as high as 900 °C, consistent with Raman data. SVMO oxidation kinetics are analyzed using both a simple kinetic model consisting of two independent first-order processes and an Avrami model. The data are better described by the pair of first order processes, but an Arrhenius analysis using both models result in an activation energy (E _a) for SVMO degradation between 0.48 and 0.65 eV. Taken together, these findings are considered in the context of properties required by electrode materials used in reversible solid oxide electrochemical cells.