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Trinity College Dublin

Intrinsic Defects in CeO2

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Lead PI: 
Prof. Graeme Watson
P. R. L. Keating, D. O. Scanlon, B. J. Morgan, N. Galea and G. W. WatsonCeO2 (ceria) has emerged in recent years as an important material for a wide variety of applications. CeO2 can be found in many catalytic processes, most notably in the catalytic converters of cars, both as a support and an active catalyst. CeO2 is also a promising candidate for the electrolyte material in solid oxide fuel cells, a highly efficient and environmentally friendly form of energy production. There is even evidence of intrinsic ferromagnetism in nano-sized CeO2 suggesting possible applications as a dilute magnetic semiconductor. Despite an abundance of research on the properties of CeO2, a full study of its native defects does not currently exist in the literature. We shall investigate the formation of intrinsic defects within CeO2 using density functional (DFT) theory with on-site Coulomb correction (DFT U). The ability of DFT U to correctly model the electronic structure of certain defects in CeO2, such as localized electrons from the formation of oxygen vacancies, has been well documented in the past, but other defect states involving holes produced by p-type defects have not received the same attention. We shall demonstrate that the calculations of intrinsic defects in CeO2 can be improved by introducing two U parameters, one on Ce4f states and another on O2p states. By employing an ab initio fitting procedure we hope to determine a value of U{O2p} that reproduces the localized nature of the p-type defect states. We carry out chemical potential and temperature dependence analyses to find the formation energies of the intrinsic defects and their relative abundance in CeO2.
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