Ionic Conductivity of Yttria-stabilized Zirconia (YSZ) at Various Levels of Doping in the Absence of a Massless Core/Shell Model
Ka Hung Lee
The Bredesen Center for Interdisciplinary Research and Graduate Education, University of Tennessee, Knoxville
This page shows a visualization of a doped cubic yttira-stabilized zirconia structure at 3 mol% concentration of yttria.
In an energy driven society, there is great interest to find materials that can efficiently convert chemical energy into useful electricity. Solid oxide fuel cells, or SOFCs, while operating at high temperatures, hold great potential in high efficiency conversion and are well suited for internal combustion process of existing technologies that includes fossil fuels and hydrogen fuel. However, high operation temperatures may lead to issues related to both structural and chemical degradation of these materials. Therefore, there is a large push for understanding the underlying phenomenon behind these degrading processes in the development of improved ion-conducting materials.
Due to its exceptional mechanical and electrical properties, yttria-stabilized zirconia (or YSZ) is a commonly used material in high temperature solid state fuel cells and a target for understanding the complex mechanism of ion-transport in oxide materials. Though difficult to study physically through experimentation, insight atomistic understanding of ion-transport through bulk material at high temperature is a valued asset in the community of materials research. It has been known for a long time that different concentrations of dopants in YSZ affects heavily the ionic conductivity property of the material. Atomistic studies of other materials such as calcium-stabilized zirconia and caesium-stabilized zirconia have suggested that the ordering and formation of defect structures within its lattice plays a critical part in the material overall conductivity.1 YSZ itself has been studied extensively using molecular dynamics simulations, or MD simulations, including one from Lau and Dunlap in 2011.2 In their 2011 paper, they have shown that the use of empirically fitted atomic potentials in MD simulations can closely reproduce the experimental ionic conductivity maximum of YSZ.
In order to capture a more correct dielectric constants and lattice vibrational frequencies in such systems, it is necessary to provide a more accurate picture the effects of electronic polarizability of ions that would be present. A model like the massless core/shell model or ReaxFF would be require to describe the transfer of charges among species. For this project, the conductivity of the material as a function of dopant concentration would be compared. However without the implementation of a massless core/shell model it would be difficult to fully gauge the validity of dynamic properties. While the massless core/shell model is not currently implemented in LAMMPS, an approximate version of this model is, the adiabatic core/shell model.3 A direct comparison of the two models in a future study would be of great interest for the modeling of doped YSZ and of their transport properties.
Interactive Structures
Color Legend:
- Blue = Zirconium
- Yellow = Yttrium
- Red = Oxygen
References
1. Li, X.; Hafskjold, B. Molecular Dynamics Simulations of Yttrium-Stabilized Zirconia. J. Phys. Condens. Matter 1995, 7 (7), 1255-1271, doi: 10.1088/0953-8984/7/7/007
2. Lau, K. C.; Dunlap, B. I. Molecular Dynamics Simulation of Yttria-Stabilized Zirconia (YSZ) Crystalline and Amorphous Solids. J. Phys. Condens. Matter 2011, 23 (3), 035401, doi: 10.1088/0953-8984/23/3/035401
3. Mitchell, P. J.; Fincham, D. Shell Model Simulations by Adiabatic Dynamics. J. Phys. Condens. Matter 1993, 5 (8), 1035-1038, doi: 10.1088/0953-8984/5/8/006
Posted: April 2018.
Updated: April 2018.