Thermodynamic Predominance Diagrams for Defect Species in Doped High Temperature Proton Conductors

In the limit of low defect concentration Kroger-Vink diagrams showing the depencence of defect concentrations on selected partial pressures were simulated for HTPCs. The prototypical HTPC SrCe(0.95)Yb(0.05)O(3-alpha) a as introduced by Iwahara et al. was studied in detail since constants for the defect equilibria are available for this compound. In a predominance diagram with O(2) and H(2)O pressures as coordinates domains can be mapped in which the different lattice species such as OH(center dot), vacancies on the O-sublattice, electrons and electronic holes dominate. Such a graph provides easy graphical guidance for the experimental conditions under which the HTPCs have the desired properties such as optimum proton - but little electronic conductivity. Deviations from the above zeroth order approximation are also discussed.