Change in the lattice parameters of La0.6Sr0.4Co1 − yFeyO3 − δ (y = 0.2, 0.4, 0.6 and 0.8) was observed by in-situ XRD under the various temperature and oxygen partial pressure conditions for thermo-chemical expansivity study. By combination of the lattice parameters and oxygen non-stoichiometry, the linear thermal expansion rates were formulated in each compound. The obtained formulas are expressed as a linear function of temperature and oxygen deficiency with the standard deviations from measured data less than 1.2%. Based on the formulas, apparent thermal expansions were separated into thermally induced part and chemically induced part. Thermal expansion coefficient αth, which is proportional constant for temperature, is increased with increasing Co content in La0.6Sr0.4Co1 − yFeyO3 − δ while chemical expansion coefficient αchem, which is proportional constant for oxygen deficiency, shows very small dependence on the composition. Increase in apparent thermal expansion with increasing Co content in La0.6Sr0.4Co1 − yFeyO3 − δ was caused by the combination of αth and αchem.
► Lattice parameter change of La0.6Sr0.4Co1-yFeyO3-δ was measured by in-situ XRD. ► Lattice parameters as a function of δ and temperature were formulated. ► The thermal expansion rates were formulated as a function of δ and temperature. ► The thermal expansion rates were separated into thermally part and chemically part.