Chemical and Thermal Stability of Sr _1.9 VMoO _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, <i>in situ</i> 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 (<i>E</i> _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.