Abstract :
The results of oxygen nonstoichiometry are
presented for the perovskite-type undoped cobaltite
LaCoO3-d, doped with strontium La0.7Sr0.3CoO3-d, and
doped with copper LaCo0.7Cu0.3O3-d as a function of
oxygen partial pressure pO2 and temperature. The
modeling of the defect structure of these oxygen
deficient perovskites is carried out. Two different
defect structure models are evolved. Within the
framework of the first model electrons are treated as
quasi-free in LaCoO3-d, partly trapped in La0.7Sr0.3-
CoO3-d and LaCo0.7Cu0.3O3-d, whereas holes are
assumed to be itinerant in all oxides studied. The
intrinsic electronic disordering process is taken into
account as well. According to the second model
electrons and holes are assumed to be localized.
Thermal excited charge disproportionation of cobalt
is considered as well. The corresponding equations for
the law of mass action, electroneutrality condition, and
mass balance give a set of nonlinear equations in the
both cases. The analytical solutions of these sets yield
general expressions which are used for the verification
of the defect models proposed by nonlinear curve
fitting. The latter showed that both models of the
defect structure of all lanthanum cobaltites studied fit
the experimental data about equally good. It is,
therefore, difficult to rule out either of defect structure
models on the basis of equilibrium data on oxygen
nonstoichiometry solely
