Defect Formation and Interface Charge Transfer at Misfit Dislocations in CeO₂/MgO Heterostructure

Among the numerous functionalities of mismatched complex oxide heterostructures and thin films, their application as next-generation electrolytes in solid oxide fuel cells have shown remarkable promise. Lattice-mismatched epitaxial growth of oxide thin films on substrates above critical thickness result in the formation of misfit dislocations, which influence interfacial ion transport in thin film oxide electrolytes. Nevertheless, fundamental understanding of the atomic and electronic structure of misfit dislocations at functional interfaces is lacking. Moreover, little is known about their influence on oxygen vacancy defect formation at the interface. For the experimentally observed epitaxial relationship in CeO₂/MgO heterostructure, we employed first principles density functional theory calculations to elucidate the basic atomic scale structure and electronic structure of misfit dislocations. Thermodynamic stability of the interface structure corroborates recent results, which show that the rotation of CeO₂ thin film eliminates the surface dipole resulting in experimentally observed epitaxy. In the Gd-doped CeO₂ thin film, energetics and electronic structure of oxygen vacancy formation in the neighborhood of misfit dislocations will be reviewed and contrasted against their behavior in the bulk and at surfaces of ceria. We will further examine the disparities in oxygen vacancy formation in the substrate and the thin film. Changes in the electronic density of states and interface charge transfer due to defect formation near misfit dislocations and their impact on ionic transport will be discussed. Since the electronic structure of misfit dislocations at such complex interfaces and their influence on oxygen vacancy formation and associated interface charge transfer has not been studied in the literature, our results offer new opportunities to unravel the untapped potential of oxide thin films and heterostructures.<br/>We acknowledge support from NSF CAREER Award DMR-2042311.