Transition metal oxides that can tolerate a large number of oxygen vacancies, specifically systems such as CeO2and Zr-doped CeO2, are crucial ingredients for generating renewable fuels via two-step, oxide-based solar thermochemical (STC) reactors. However, any predictive modeling, such as using density functional theory (DFT) calculations, needs to accurately describe the energetics of redox reactions involving transition metals, if new candidate materials are to be found. Specifically, theoretical models that can accurately predict the extent of achievable off-stoichiometry, i.e., the extent of oxygen deficiency within the oxide, will be crucial. Hence, this talk will focus on using the sub-lattice formalism in combination with SCAN+Ucalculations to accurately predict off-stoichiometries in CeO2and Zr-doped CeO2. The sub-lattice formalism is a common tool used to thermodynamically assess experimental data and build temperature-composition phase diagrams in a variety of binary, ternary, quaternary, etc. systems. Although the sub-lattice model has been primarily used to “fit” to existing experimental data, the framework is general and can be used alongside DFT-based data. Hence, we build a sub-lattice model entirely based on SCAN+Ucalculations (where Uvalues are obtained from previous work) and observe fair agreement between experimental and predicted oxygen off-stoichiometries in CeO2and Zr-doped CeO2. The talk will also touch upon extending the sub-lattice formalism to predict off-stoichiometries in other ternary, quaternary, quinary, etc. oxides.

Estimating off-stoichiometry using density functional theory-based calculations and the sub-lattice formalism

2019 Spring National Meeting

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