Thermally stimulated oxygen desorption in Sr₂FeMoO_6-δ

Polycrystalline Sr₂FeMoO_6-δ specimens have been obtained by solid state synthesis from partially reduced SrFeO_2,52 and SrMoO₄ precursors. It has been shown that during oxygen desorption from the Sr₂FeMoO_6-δ compound in polythermal mode in a 5%H₂/Ar gas flow at different heating rates, the oxygen index 6-δ depends on the heating rate and does not achieve saturation at T = 1420 K. Oxygen diffusion activation energy calculation using the Merzhanov method has shown that at an early stage of oxygen desorption from the Sr₂FeMoO_6-δ compound the oxygen diffusion activation energy is the lowest Е_а = 76.7 kJ/mole at δ = 0.005. With an increase in the concentration of oxygen vacancies, the oxygen diffusion activation energy grows to Е_а = 156.3 kJ/mole at δ = 0.06. It has been found that the dδ/dt = f (Т) and dδ/dt = f (δ) functions have a typical break which allows one to divide oxygen desorption in two process stages. It is hypothesized that an increase in the concentration of oxygen vacancies V_o^•• leads to their mutual interaction followed by ordering in the Fe/Mo-01 crystallographic planes with the formation of various types of associations.