A Multiscale Computational Analysis of Defect-assisted Ionic Transport in Plastically Deformed Solid Oxides

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Solid oxide fuel cell (SOFC) directly converts fossil fuel into electricity introducing no pollution but water into the environment. This technology has been developing rapidly but is still limited in practical use due to its high operating temperature. Reducing the SOFC operation temperature towards its widespread applications has triggered an intensive search of super ionic conducting solid oxides. Introducing defects, such as dislocations, into certain oxides has been demonstrated to be promising in achieving a considerably high ionic conductivity at low temperature but this technique is still in a "trial and error" stage due to lack of knowledge on how ions hop under the effects of the defect-induced stress field in plastically deformed solid oxides. To meet this need, this award supports fundamental research on computer simulations of ions hopping in defected solid oxides, across a wide range of length scales. The gained knowledge may be utilized in the development of not only low temperature SOFCs, but also lithium/sodium-ion batteries, perovskite solar cells, corrosion-resistant materials for medical implants, and radiation-resistant materials for nuclear power plants. This project is multidisciplinary in nature. The participating students will be exposed to a broad range of scientific knowledge, methodology, and skills. A mentoring program that links the education of graduate, undergraduate, and high-school students will be fostered. The high operation temperature in SOFC stems from the high ion migration barrier (~1eV) in solid oxides. Distinct from traditional approaches that overcome this barrier by exposing the materials to an elevated temperature, this project presents a plan on promoting ionic transport using severe stress localizations in plastically deformed solid oxides. The local stress's contribution to the ion migration barrier reduction will be quantified through a series of concurrent atomistic-continuum (CAC) simulations. Polycrystalline strontium titanate and multilayered strontium titanate /magnesium oxide containing a high density of grain boundaries (GBs) and phase boundaries (PBs) will be chosen as the model materials. The CAC simulations will bridge the relevant length scales through resolving the GBs and PBs at an atomistic resolution while the dislocations away from them will be dealt in a coarse-grained description. This will enable a prediction of the microscopic-level ionic transport in strained solid oxides without smearing out the atomistic nature of ion hopping near the material defects. Data and insights regarding diffusion under stress, which controls the kinetics of phase transformations, oxidation, creep, and many other engineering processes in solid materials, will be generated.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.