Redox transitions in strontium vanadates: Electrical conductivity and dimensional changes

Compromising Between Phase Stability and Electrical Performance: SrVO3–SrTiO3 Solid Solutions as Solid Oxide Fuel Cell Anode Components

“…The conductivity was measured isothermally with a step‐wise increase of the oxygen partial pressure and equilibration at each p (O 2 ) step until a continuous drop of conductivity values was observed. The degradation of the conductivity was attributed to the onset of the oxidative decomposition of the cubic perovskite phase and precipitation of the low‐conducting Sr 3 (VO 4 ) 2 phase ( σ ≈5×10 −5 S cm −1 at 900 °C). The presence of Sr 3 (VO 4 ) 2 was confirmed by XRD analysis of the samples after cooling.…”

“…The results of the thermogravimetric studies demonstrated that, similar to the parent SrVO 3− δ , SrV 1− y Ti y O 3− δ solid solutions with moderate additions of Ti ( y= 0.1–0.3) show variable oxygen content almost down to room temperature after equilibration with a reducing atmosphere at 1000 °C (Figure B). Note that room‐temperature oxygen deficiency in parent SrVO 3− δ after cooling under identical conditions corresponds to δ ≈0.07 . SrV 1− y Ti y O 3− δ ( y= 0.5–0.8) exhibited variable oxygen content at temperatures above approximately 300–450 °C, whereas the Ti‐rich composition, SrV 0.1 Ti 0.9 O 3− δ , is characterized by rather negligible oxygen content variations.…”

“…Perovskite‐type SrVO 3− δ and SrTiO 3 ‐based phases have been identified, among others, as promising ceramic components for anodes of hydrocarbon‐fueled SOFCs . SrVO 3− δ is known to exhibit high metallic‐like electronic conductivity under typical anode operation conditions: approximately 1000 S cm −1 at 800 °C and p (O 2 ) of circa 10 −20 bar . Non‐negligible oxygen deficiency in the perovskite lattice ( δ =0.08–0.10) implies the contribution of oxygen‐ionic transport to electrical transport, which is favorable for electrochemical activity.…”

“…The stability domain of the perovskite SrVO 3− δ phase is restricted to reducing conditions, with upper‐ p (O 2 ) stability limit of the perovskite phase in the order of approximately 10 −15 bar at 900 °C and 10 −17 bar at 800 °C . Exposure to air at elevated temperatures (>500 °C) results in a fast transformation to an insulating strontium pyrovanadate phase, Sr 2 V 2 O 7 . This transformation is accompanied by a large volume expansion and is not fully reversible (due to kinetic and topotactic reasons) at temperatures ≤1000 °C .…”

“…This complicates the fabrication of SOFCs with SrVO 3 ‐based anodes and introduces the risks of anode degradation owing to accidental oxidation. Excessive thermochemical expansion (TEC=22.7 ppm K −1 at 500–950 °C) hampers the thermomechanical compatibility with common solid electrolyte materials based on zirconia, ceria and lanthanum gallate.…”