The results above highlight how aliovalent doping of solid electrolytes can produce qualitatively different responses, depending on the relative concentrations of competing native defects in the parent undoped system. Aliovalent doping introduces excess charge that causes a shift in the Fermi energy of the system and a corresponding shift in the defect equilibria for all charged defect species. The qualitatively different doping responses under different synthesis conditions can be understood by considering how the concentrations of the native defect species respond to a given shift in the Fermi energy,