CATALYTIC DYNAMICS AND OXYGEN DIFFUSION IN DOPED PrBaCo2O5.5+δ THIN FILMS.

The Sr and Fe co-doped double perovskites PrBaCo2O5.5+δ (PrBCO) thin films of Pr(Ba0.5Sr0.5)(Co1.5Fe0.5)O5.5+δ (PBSCFO) were epitaxially grown for chemical catalytic studies. The PBSCFO epitaxial films were monitored their resistance behavior R(t) under the switching flow of reducing and oxidizing gases as a function of the gas flow time t. The R(t) vs. t relationships determined at various temperatures show the occurrence of two oxidation processes, Co2.5+ ↔ Co3+ and Co3+ ↔ Co3.5+. The observed R(t) vs. t relationships were fitted to Fick's second law for one-dimensional diffusion of charge carriers to derive the diffusivity D(T) and (T) for the two processes at various temperatures T, and the D(T) vs. T relationships were analyzed in terms of the Arrhenius relationship to find the activation energies Ea for each process. Oscillations in the dR(t)/dt plots, observed under oxidation reactions, were discussed in terms of a layer-by-layer oxygen vacancy exchange diffusion mechanism. Our work suggests that thin films of LnBCO (Ln = lanthanide) with their A and B sites doped as in PBSCFO are excellent candidates for the development of low or intermediate temperature energy conversion devices and gas sensor applications.