The mechanism of oxygen intake by YBaCo4O7+δ – Based solid solutions

Abstract

The oxygen sorption from air by Y_0.8Ca_0.2BaCo₄O_7+δ and Y_0.8Ca_0.2BaCo₃FeO_7+δ (114–type structure) is studied by nonisothermal TG measurements. In both oxides, oxygen intake occurs via a single-step reaction with an activation energy of 190–200 kJ/mol and a frequency factor of about 10¹⁵ s⁻¹. The reaction mechanism is characterized by a 3D random nucleation and growth. The kinetic triplet values – activation energy, frequency factor, and reaction mechanism – remain nearly invariable regardless of the iron content. The data suggest that oxygen sorption occurs predominantly within the kagome layers, which agrees with the preference of iron to occupy the trigonal structural layers. The DFT calculations support kagome layers providing the favorable positions for the captured oxygen to reside in and jump over with the activation energy near 90 kJ/mol and, thus, confirm the oxygen sorption of 114-type oxides governed by the local structural reconstruction and stress effects induced by the growth of the oxygen-rich nuclei.