Redox transitions in strontium vanadates: Electrical conductivity and dimensional changes

• Electrical conductivity and thermal expansion of strontium vanadates are measured.
• Conductivity of SrVO3−δ is 106–108 times higher compared to Sr2V2O7 and Sr3V2O8.
• Sr2V2O7 transforms on reduction to SrVO3−δ via (5Sr3V2O8 + SrV6O11) intermediate.
• This process is kinetically stagnated due to good redox stability of Sr3V2O8.
• Large volume changes on Sr2V2O7 ↔ SrVO3 transformation are confirmed by dilatometry.

The reversibility of redox-induced phase transformations and accompanying electrical conductivity and dimensional changes in perovskite-type SrVO3−δ, a parent material for a family of potential solid oxide fuel cell anode materials, were evaluated employing X-ray diffraction, thermal analysis, dilatometry and electrical measurements. At 873–1273 K, the electrical conductivity of SrVO3−δ is metallic-like and 6–8 orders of magnitude higher compared to semiconducting V5+-based strontium pyrovanadate Sr2V2O7 and strontium orthovanadate Sr3V2O8 existing under oxidizing conditions. SrVO3−δ is easily oxidized to a pyrovanadate phase at atmospheric oxygen pressure. Inverse reduction in 10%H2–90%N2 atmosphere occurs in two steps through (5Sr3V2O8 + SrV6O11) intermediate. As Sr3V2O8 is relatively stable even under reducing conditions, the perovskite phase and its high level of electrical conductivity cannot be recovered completely in a reasonable time span at temperatures ⩽1273 K. Dilatometric studies confirmed that SrVO3 ↔ Sr2V2O7 redox transformation is accompanied with significant dimensional changes. Their extent depends on the degree of phase conversion and, apparently, on microstructural features.