Structure and electronic properties of cerium orthophosphate: Theory and experiment

Using a combination of density functional theory (DFT) calculations and experiments, we determine the structural and electronic properties of cerium orthophosphate (CePO₄), a promising proton-conducting electrolyte for fuel cell applications. To better account for strongly-localized Ce 4f electrons, we use a DFT $+$ U approach, where the exchange-correlation functional is augmented with an adjustable effective Hubbard-like parameter U. We find that the calculated structural properties are in good agreement with x-ray diffraction measurements, largely independent of the value of U used. However, the electronic structure is much more sensitive to U, and values of U $=$ 2.5--3 eV for Ce 4f states provide excellent agreement between the calculated density of states and measured photoemission spectra near the valence-band edge, validating the efficacy of a DFT $+$ U-based approach for this system. With a judicious choice of U determined from photoemission experiments, this work provides a natural starting point for future studies of charge transport and charged defect formation and migration in this important class of compounds.