The role of deep acceptor centers in the oxidation of acceptor-doped wide-band-gap perovskites ABO3

The impact of deep acceptor centers on defect thermodynamics and oxidation of wide-band-gap acceptor-doped perovskites without mixed-valence cations is studied. These deep centers are formed by the acceptor-bound small hole polarons whose stabilization energy can be high enough (significantly higher than the hole-acceptor Coulomb interaction energy). It is shown that the oxidation enthalpy Delta H-ox of oxide is determined by the energy CA of acceptor-bound states along with the formation energy E-v of oxygen vacancies. The oxidation reaction is demonstrated to be either endothermic or exothermic, and the regions of EA and Ev values corresponding to the positive or negative Delta H-ox are determined. The contribution of acceptor-bound holes to the defect thermodynamics strongly depends on the acceptor states depth CA: it becomes negligible at CA less than a certain value (at which the acceptor levels are still deep). With increasing CA, the concentration of acceptor-bound small hole polarons can reach the values comparable to the dopant content. The results are illustrated with the acceptor-doped BaZrO3 as an example. It is shown that the experimental data on the bulk hole conductivity of barium zirconate can be described both in the band transport model and in the model of hopping small polarons localized on oxygen ions away from the acceptor centers. Depending on the EA magnitude, the oxidation reaction can be either endothermic or exothermic for both mobility mechanisms.