Thermal and chemical expansion of mixed conducting La 0.5Sr 0.5Fe 1− xCo xO 3− δ materials

Abstract

Oxygen deficiency, thermal and chemical expansion of La 0.5Sr 0.5Fe 1− x Co x O 3− δ ( x = 0, 0.5, 1) have been measured by thermogravimetry, dilatometry and high temperature X-ray diffraction. The rhombohedral perovskite materials transformed to a cubic structure at 350 ± 50 °C. The thermal expansion of the materials up to the onset of thermal reduction was 14–18 × 10 − 6 K − 1 . Above 500 °C in air (400 °C in N 2), chemical expansion contributed to the thermal expansion and the linear thermal expansion coefficients were significantly higher, 16–35 × 10 − 6 K − 1 . The chemical expansion, ε c, showed a maximum of 0.0045 for x = 0.5 and 0.0041 for x = 1 at 800–900 °C. The normalized chemical expansion, ε c/Δ δ, was 0.036 for x = 0.5 and 0.035 for x = 1 at 800 °C. The chemical expansion can be correlated with an increasing ionic radius of the transition metals with decreasing valence state.