Distinguished Lecture: Design of Materials Properties by Microstructure and External Fields
Abstract: The mechanical, physical and chemical properties of materials are determined by their microstructure. Modern materials science uses the complex interplay of defects, such as impurities, phases, point and line defects and interfaces, to tailor properties and obtain high-performance metallic alloys and ceramics. In this approach of materials design, properties can only be changed by modifying their microstructure, for example by initiating grain growth during annealing at elevated temperatures. Such a behavior, that fixes the properties irreversibly to the microstructure, is advantageous for many applications of materials, where long-term stability of the properties is required. Two examples for designing materials properties will be presented: nanoglasses and equiatomic multicomponent single-phase oxides. Metallic glasses offer interesting properties due to their disordered atomic structure. Because they are prepared predominantly by rapid quenching, only a certain range of microstructural parameters has yet been explored. Nanoglasses will be discussed as an example of materials that exhibit novel effects by tailoring the microstructure. Nanoglasses consist of two distinct structural components, which differ in their free volume and elemental constitution, and have been shown to exhibit drastic property changes. Equiatomic multicomponent single-phase oxides are oxides with simple crystallographic structures consisting of up to 10 different cations, and they've been prepared by different synthesis routes. Nebulized spray pyrolysis has been shown to be the most flexible and versatile technique. Some examples of different structures for transition and rare earth metal oxides and perovskites will be presented. In contrast, tuning using external fields such as electric offers completely new opportunities for the fully reversible control of materials properties. Such tuning of physical properties will be demonstrated for several nanostructures, i.e. (epitaxial) thin films, nanoporous, nanoparticulate structures and nanowires. Tuning can be either achieved using dielectric/ferroelectric gating, well known from semiconductor physics, or by electrolyte gating using liquid or solid electrolytes. Furthermore, using electrochemical ion intercalation, fully reversible properties with substantially larger effect magnitude can be achieved. Finally, the concepts employed for tuning properties of nanostructures can be employed in applications as well. As an example, field-effect transistors based on inorganic nanoparticles as the channel material and solid electrolyte for the gating will be described.
Bio: Horst Hahn is director of the Institute for Nanotechnology and head of the Programs of Science and Technology of Nanosystems at the Karlsruhe Institute of Technology (KIT). He also is the founding director of the Helmholtz Institute Ulm Electrochemical Energy Storage and head of the KIT Joint Research Laboratory Nanomaterials at the Technical University Darmstadt. Previously, Hahn held positions at the Argonne National Laboratory, University of Illinois at Urbana-Champaign and Rutgers University, and from 1992 to 2004, he was full professor at Technische University Darmstadt.His major research areas are nanostructured materials, tunable properties of nanostructures, materials for energy conversion and storage, nanomagnetism and printed materials. Hahn is an elected member of the German Academy of Sciences Leopoldina and the European Academy of Sciences, and a Fellow of the Materials Research Society. He received the Robert Franklin Mehl Award of The Minerals, Metals and Materials Society and the Heyn Denkmünze of the Deutsche Gesellschaft für Materialkunde. He is a co-author of more than 350 scientific papers and has numerous invitations to international conferences. In addition, he holds 15 patents in the area of nanomaterials and materials for energy storage.