Paper SS+AS+EN-MoM9
Computational Materials Design^®: Ionic Conduction in Rare-Earth-Metal Oxides from the First Principles-based Studies

Monday, October 19, 2015, 11:00 am, Room 113

Solid oxide fuel cells (SOFC) have been one of the most promising technologies to tap alternative sources of energy. This technology utilizes abundant fuel materials such as H₂, CH₄ and other hydrocarbon materials to lessen our dependence on non-renewable fossil fuels that are nearly depleting. It takes into advantage the efficiency brought about by high kinetics of reaction at the electrolyte sides occurring at high working temperature. With this, ceramic based materials are often used as electrolyte and electrode materials. However, the working temperature of SOFCs is often too high (700˚C to 1000˚C). This limits the application of SOFCs and consequently high cost of producing durable materials for high working temperature. Recently, research related to this technology focuses on materials that work at intermediate temperature (IT-SOFC). This entails finding/designing materials that have high ionic conductivity at IT-SOFC working temperature.

Recent developments in computational simulation techniques, coupled with the rapid progress in computer efficiency, make first principles-based COMPUTATIONAL MATERIALS DESIGN (CMD^®) a relevant field in the world of surface science and condensed matter physics. In this scheme, quantum mechanical calculations are performed to design promising materials and, understand the necessary mechanisms for the realization of an efficient technological device. Here, we employed the CMD^® process and density functional theory-based analysis to study the atomic and electronic properties of several rare-earth-metal oxides (Pr₂NiO₂, La₂GeO₅, LaGaO₃ and CeO₂) which has potential application in IT-SOFC. These materials are known to have different structures according to symmetry, and the mechanism by which O ion conducts, i.e. via oxygen vacancies (O_vac) migration or O interstitial migration. The O ion migration path is dependent on the structure of the material, and the corresponding activation energy barrier for oxygen ion migration (E_ac) is affected by the concentration of O_vac and the presence of dopants, for O ion conduction via vacancies. In most of these systems, dopants with the same ionic radius as the host materials create high probability for O_vac, which then affects ionic conductivity, and the E_ac is found to be least for dopants with ionic radius near to that of the host material. Furthermore, as ionic migration is sensitive to the atomic structure, E_ac is party due to the structural alteration brought about by the presence of impurities such as dopants and creation of heterostructure interfaces. With these understanding, we can comment on the methods by which ionic conductivity can be enhanced in these materials.