Thermal and chemical expansion of Sr-doped lanthanum cobalt oxide (La1-xSrxCoO3-δ)

The equilibrium thermal expansivity (beta(T)) and oxygen-vacancy chemical expansivity (beta(C)) of polycrystalline La1-xSrxCoO3-delta (LSC; x = 0.2, 0.4, and 0.7) have been measured at 600 degrees C < T < 900 degrees C and 10(-4) atm < P-O2 < 0.21 atm using controlled-atmosphere dilatometry. These measurements show only a moderate dependence Of beta(T) on temperature, suggesting that increases often observed in the coefficient of thermal expansion when measured at constant P-O2 are primarily thermally induced chemical expansion associated with changes in oxygen stoichiometry. The dependences of beta(T) and beta(C) on the temperature, oxygen-vacancy concentration, and Sr content (x) were characterized and found to follow a consistent nonlinear trend, which may result from the relaxation of lattice strain with increasing defect concentration. A slowly relaxing secondary expansion effect (and/or expansion hysteresis) was also discovered. Possible causes of this behavior, including phase transition/segregation at high vacancy concentration, are discussed.