Chemical potentials at experimental conditions: The chemical potentials were chosen to best resemble typical experimental synthesis conditions: sintering at 1200 • C in air, the latter environment has been shown to result in the optimum ionic conductivities in LLZO. The chemical potential of oxygen in this environment can be calculated (µ O =∼ -1.90 eV) using thermochemical tables within the formalism outlined by Reuter and Scheffler: 70