Electronic Structure and Properties of CePO$_{4}$

Structural and electronic properties of cerium orthophosphate (CePO$_{4})$, a mixed electronic and protonic conducting electrolyte, are calculated using density functional theory (DFT) and beyond, and compared with experiments. A Hubbard-like parameter U is employed to reduce the self-interaction for localized Ce 4f states. As U is varied from 1-5 eV, the band structure is found to undergo significant changes, with the Kohn-Sham gap varying between 0.8 and 4.3 eV. Interestingly, the lattice parameters are unchanged, indicating structural properties are far less sensitive to U. The valence band energies and the optical band gap of CePO$_{4}$ are measured using photoemission and optical reflectance spectroscopy. The structure was determined using XRD. The choice of U = 4 eV provides the best match between the calculated density of states and the experimental photoemission and optical reflectance spectra. The activation energy of the minimum energy path for proton transfer will be calculated and compared to that of LaPO$_{4}$, another proton conducting electrolyte.