NSF-Europe: Nano-Structured Ionic Materials: Impact on Properties and Performance

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In this project, we undertake a comprehensive study of the effects of grain boundaries on the ionic and electronic transport properties of nanoscale ionic materials in which space charge effects may dominate transport even within the core of the grains. Thin-film processing methods will be used to generate fluorite (e.g. ceria) and perovskite (e.g. LSM)-based films with controlled microstructures resulting in columnar or equi-axed grain structures with grains sizes ranging from the nano- to the micro-scale. In-diffusion techniques will further allow selected boundaries to be doped with a variety of elements with differing ionic radii and charge. Structural and chemical analysis of the specimens will be carried out by SEM and TEM. HRTEM will be used to obtain detailed information about the structure of grain boundaries. Photolithographic methods will be used to fabricate microelectrodes with ability to focus attention on one or a small number of boundaries and to examine the role of triple phase boundaries in a highly systematic manner by both electrical and electrochemical means. Instrumentation will be developed to enable such studies to be performed in situ as functions of temperature and atmosphere. Models describing the combined roles of grain boundary structure and chemistry and grain size on defect equilibria and transport will be refined and examined in relation to the measurements performed in this study.Ionic and mixed ionic-electronic conductors (MIEC) are of interest for strategic applications related to energy conversion and environmental monitoring including batteries, fuel cells, permeation membranes and sensors. Fuel cells, for example, with high-energy conversion efficiencies and low emissions show promise as a replacement for combustion-based electrical generators of all sizes. Using nanostructured ionic materials within fuel cells could potentially facilitate lower temperature operation and thereby provide faster start-up times, improved stability, reduced cost and less complicated thermal management. Micro-fuel-cells, fabricated from thin films with nanodimensions, further promise extended operation of portable electronic devices such as laptop computers. This study will examine how the properties of materials optimized for fuel cell operation are influenced by extension to the nanoscale and how these differences can be utilized in improving the performance of these and related devices.This NSF project is co-funded by the Office of Multidisciplinary Activities, and the Division of Materials Research (Ceramics) and the International Office (Western Europe) as a Cooperative Activity in Materials Research between the NSF and Europe (NSF 02-135). This project is being carried out in collaboration with the University of Karlsruhe, Karlsruhe, Germany and the Max Planck Institute for Solid State Research, Stuttgart, Germany.