Figure 7.
Free energy diagrams for the formation and diffusion of oxygen vacancies (negative free energies, below the dashed line, indicate spontaneous processes). All energies are relative to the stoichiometric surface and oxygen in the form of water in the gas phase. The correlating charge density of the stoichiometric surface and charge-density differences (the position of the vacancy is marked with a circle) are shown below for ZnO, ZrO2, Cu2O, and LSCF. Charge density is given in units of the elementary charge per Å3 at the height of the vacancy (shown qualitatively with a scale bar that indicates 0; s marks 0 for the stoichiometric surface).