Complex structured "electron-poor" framework semiconductors with potential for thermoeletric application

• Antragsteller: Professor Dr. Thomas F. Fässler; Professor Dr. Wolfgang Scherer
• Fachliche Zuordnung: Experimentelle Physik der kondensierten Materie
• Förderung: Förderung von 2010 bis 2015
• Projektkennung: Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 172434187

Thermoelectric devices cleanly convert heat into electricity and play an important role in satisfying the future global demand for efficient energy management. However, there exists a significant barrier to improving thermoelectric devices and that is the thermoelectric materials themselves. The most promising candidate materials are (heavily doped) narrow-gap semiconductors with low thermal conductivity. While crystal chemical mechanisms have been identified for reducing the thermal conductivity, a rationale selection of compositions and structures leading to bulk narrow-gap semiconductors is not well established. We present an international and interdisciplinary research program aimed at advancing thermoelectric materials research to uncover promising materials and provide new scientific understanding of materials that border/overlap metals and semiconductors. Taking the state-of-the-art thermoelectric Zn4Sb3 as a starting point, we conceptually integrate this material into a larger class of chemical compounds – electron poor framework semiconductors (EPFSs) – which includes elemental boron at one extreme. EPFS materials, made from metal and semimetal atoms, form a common, weakly polar framework containing multi-center bonded structural entities. The localized multi-center bonding feature is thought to be the key to structurally complex semiconductors. Binary and ternary EPFS materials that have so far been identified and characterized show promising thermoelectric properties; especially remarkable is their low thermal conductivity. Through a combination of chemical synthesis, structure analysis, computational modeling, and physical property measurements we explore systematically the compositional and structural potential of EPFS materials, and analyze their bonding properties and the mechanisms behind their peculiar, but desirable, low thermal conductivity. The effort will be carried out as collaborative activity among three institutions, Arizona State University (ASU, USA), Augsburg University (Germany), and Technical University Munich (Germany) assembling a research group with faculty, staff and students from Chemistry and Physics departments.Intellectual merit of the proposed activity: The major intellectual merit of the proposed activity will be the prediction, preparation and characterization of new narrow gap semiconductors with desirable thermoelectric properties. Additionally, new and conclusive insights into the intricate structure and bonding mechanisms of chemical systems that border/overlap metals and semiconductors – including boron-based refractory semiconductors – will be achieved. Our research will yield a significantly improved understanding of the microscopic mechanisms fundamental to thermoelectric properties, especially lattice thermal conductivity. This will be used to formulate principles to be used in the rational design of outstanding thermoelectric materials. Through the international collaboration, the experimental and theoretical aspects of the proposed research project will be closely integrated. This is paramount for unveiling the decisive structure-property correlations behind high thermoelectric performance. Unique instrumentation at the German high flux neutron source FRM-II (Munich) will become accessible to the project.Broader impacts resulting from the proposed activity: Energy technology has become one of the most demanding and challenging issues of society. The project described here contributes to energy technology through fundamental research related to optimization of thermoelectric energy conversion. In particular, it exploits the potential of intermetallic compounds to combine structural complexity with a narrow electronic band gap. Intermetallic compounds are a large class of inorganic solids, with a range of distinct physical and chemical properties. This project advances the understanding of bonding and structure-property correlations in complex intermetallics, laying the groundwork for opening up this class of compounds as useful materials also for other areas of energy technology. To accelerate the effort, a workshop assembling international expertise on chemical bonding in intermetallic compounds will be organized. The increasing societal impact of energy technology is further addressed by disseminating aspects of the proposed research to K-12 students (by developing lucid but appropriately targeted class room demonstrations and providing support to teachers) and professional science master’s (PSM) students (by incorporating the topic in the nanoscience seminar course to these emerging technology leaders in` Arizona). The international/interdisciplinary character of the proposed research offers unique opportunities for student training. An international exchange program has been designed to integrating research (through extended research visits to collaborating laboratories and facilities) and education (through accessing the renowned international masters program of the German partners). The aim is to educate graduate students on the complexity of today’s materials research and immerse them in interdisciplinary and international research.

• DFG-Verfahren: Sachbeihilfen
• Internationaler Bezug: USA
• Beteiligte Personen: Professor Dr. Ulrich Häussermann; Professor Dr. Otto F. Sankey