  Large scale first-principles calculations based on density functional theory
(DFT) employing two different methods (atomic orbitals and plane wave basis
sets) were used to study the energetics, geometry, the electronic charge
redistribution and migration for adsorbed atomic and molecular oxygen on
defect-free SrTiO3(001) surfaces (both SrO- and TiO2-terminated), which serves
as a prototype for many ABO3-type perovskites. Both methods predict substantial
binding energies for atomic O adsorption at the bridge position between the
oxygen surface ions and an adjacent metal ion. A strong chemisorption is caused
by formation of a surface molecular peroxide ion. In contrast, the neutral
molecular adsorption energy is much smaller, ~0.25 eV. Dissociative molecular
adsorption is energetically not favourable, even at 0 K. Adsorbed O atoms
migrate along the (001) direction with an activation energy of ~1 eV which is
much larger than that for surface oxygen vacancies (0.14 eV). Therefore, the
surface O vacancies control encounter with the adsorbed O atoms and oxygen
penetration to the surface which is the limiting step for many applications of
ABO3-type perovskites, including resistive oxygen sensors, permeation ceramic
membranes and fuel cell technology.
