In previous work by Prof. Tuller and Prof. Chiang, it was shown the properties of nanocrystalline ionic solids can differ dramatically from those of their microcrystalline counterparts. For example, the electronic conductivity of nanocrystalline CeO2 is several orders of magnitude higher than microcrystalline ceria. This effect can be understood with respect to the space charge model: positive grain boundary cores lead to negative space charge regions that are accumulated with electrons and depleted with oxygen vacancies. These space charge regions dominate the transport properties of nanocrystalline ceria.
Our current work is focused in two parts. We are studying the effect of grain boundary chemistry on the space charge potential, which affects he distribution of ionic and electronic defects in the solid. In addition, we are studying the effects of grain boundary diffusion on the stability of SOFC devices, due to the large electrode/electrolyte interfacial region and high device operation temperatures.