Materials World Network: Complex Structured "Electron-Poor" Framework Semiconductors With Potential For Thermoelectric Application

Arizona State University, Scottsdale AZ

Investigators

Abstract

Thermoelectric devices cleanly convert heat into electricity through the Seebeck effect and can 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. This international and interdisciplinary research program intends to advance thermoelectric materials research by uncovering new chemical compositions for bulk narrow-gap semiconductors, and by providing new understanding of chemical systems that border/overlap metals and semiconductors. The state-of-the-art thermoelectric material Zn4Sb3 is taken as a starting point and conceptually integrated into a larger class of chemical compounds ? electron poor framework semiconductors (EPFSs) ? which includes elemental boron at one extreme. EPFS materials, made from late transition metal, main group 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. Through a combination of chemical synthesis, structure analysis, computational modeling, and physical property measurements this Materials World Network (i) explores the compositional and structural potential of EPFS materials and (ii) analyzes their chemical bonding properties and the mechanisms behind band gap formation in complex structured intermetallics. The effort is among three institutions, Arizona State University (ASU, USA), Augsburg University (Germany), and Technical University Munich (Germany) and assembles a research group with faculty, staff and students from Chemistry and Physics departments. The merit of the international collaboration is a tight integration of the experimental and theoretical aspects of the research. This is paramount for unveiling the decisive structure-property correlations behind high thermoelectric performance. Participating students perform extensive research stays at the collaborating laboratories and benefit from expertise, techniques and instrumentation that is not available at their home institutions. The aim is to educate especially graduate students on the complexity of today?s materials research and immerse them in interdisciplinary and international research.