A Dipole Polarizable Potential for Reduced and Doped CeO$_2$ from First-Principles

A Dipole Polarizable Potential for Reduced and Doped CeO2 from First-Principles. Mario Burbano 1, Dario Marrocchelli2,∗Bilge Yildiz 2, Harry L Tuller 3, Stefan T Norberg 4, Stephen Hull 5, Paul A Madden6, and Graeme W. Watson1† 1 School of Chemistry and CRANN, Trinity College Dublin, Dublin 2, Ireland 2 Department of Nuclear Science and Engineering, Massachusetts Institute of Technology 3 Department of Materials Science and Engineering, Massachusetts Institute of Technology 4 Department of Chemical and Biological Engineering, Chalmers University of Technology 5 The ISIS Facility, Rutherford Appleton Laboratory and 6 Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom In this paper we present the parameterization of a new interionic potential for stoichiometric, reduced and doped CeO2. We use a dipole-polarizable potential (DIPPIM) and optimize its pa- rameters by fitting them to a series of DFT calculations. The resulting potential was tested by calculating a series of fundamental properties for CeO2 and by comparing them to experimental val- ues. The agreement for all the calculated properties (thermal and chemical expansion coefficients, lattice parameters, oxygen migration energies, local crystalline structure and elastic constants) is within 10-15% of the experimental one, an accuracy comparable to that of ab initio calculations. This result suggests the use of this new potential for reliably predicting atomic-scale properties of CeO2 in problems where ab initio calculations are not feasible due to their size-limitations. I. INTRODUCTION Cerium dioxide, CeO2 or ceria, is an important material which has found applications in several tech- nologically relevant areas such as catalysis1 and Solid Oxide Fuel Cells (SOFCs)2,3. In catalysis, it plays an important role thanks to its oxygen storage capability, due to the ready oxidation state change from Ce4+ to Ce3+ upon reduction and the reverse upon oxidation1. These properties are made use of in Three-Way Catalysts (TWC), where the stored oxygen aids in the oxidation of CO to CO2 under reducing conditions while, under fuel-lean conditions, the reduction of NO to N2 is assisted by the uptake of oxygen by ceria. Doping ceria with aliovalent cations, such as Gd, Y or La, leads to high ionic conductivity in the intermediate temperature range (500 – 800◦C), thus raising the prospects of ceria-based electrolytes for application in SOFCs4,5. Over the past 5 years, significant progress has been made in the description of this material by means of ab initio computer simulations6–12, using Density Functional Theory (DFT). In particular, the use of the DFT+U approach, where the U parameter provides an improved description of the strongly correlated cerium 4f states in partially reduced ceria, has led to a much improved understanding of the electronic and structural properties of this material. Unfortunately, DFT calcu- lations are still severely limited by system size and the time-scales that can be studied; this high computational cost usually limits this approach to static calculations only. For this reason, reliable interatomic potentials which allow the study of thousands of atoms on the nanosecond scale are desirable. This is particularly true for the study of the ionic conductivity of ceria. Indeed, the role of grain boundaries in the formation of space charge regions, or the vacancy and/or cation ordering tendencies, which are responsible for the drop in conductivity after a critical vacancy concentration (around 3-4 %), are long-range in nature and necessitate large simulation boxes. In a recent paper, Xu et al.13 compared six differ- ent interatomic potentials for ceria available in the literature14–19 and tested their accuracy by reproducing a series of experimental data (lattice constants, thermal expansion, chemical expansion, dielectric properties, oxygen migration energy and mechanical properties). Two main limitations were found. The first was that none of the reviewed potentials could reproduce all the fundamental properties under study, although some displayed higher accuracy than others. While all the potentials could reproduce the static properties, such as lattice parameters and elastic constants, they all failed at reproducing the thermal expansion coefficient, and, to a lesser degree, the oxygen migration energy, for pure CeO2. Indeed, some potentials gave thermal expansion coefficients which were one order of magnitude smaller than the experimental one and also severely underes- timated the oxygen migration energy. Thermal and chemical expansion properties of ceria are particularly important in the context of SOFCs given that differential expansion of the components has a detrimental effect on the long term durability of the fuel cells20,21. A second problem evinced from the study by Xu et al. was that not all the interatomic potentials have a complete set of parameters available for the study of both doped and reduced C

This content is AI-processed based on open access ArXiv data.