Attrition-enhanced nanocomposite synthesis of indium-filled, iron-substituted skutterudite antimonides for improved perf
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Attrition-enhanced nanocomposite synthesis of indium-filled, iron-substituted skutterudite antimonides for improved performance thermoelectrics James Eilertsena, b, c, Matthias Trottmannb, Sascha Populohb, Romain Berthelota, Charles M. Cookec,d, Michael K. Cinibulkc, Simone Pokrantb, Anke Weidenkaffb, M. A. Subramaniana a Department of Chemistry, Oregon State University, Corvallis, OR 97331, USA b Empa,Solid State Chemistry and Catalysis, Ueberlandstrasse 129, CH-8600 Duebendorf, Switzerland c Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, OH 45433-7817, USA d UES, Inc., Dayton OH 45432, USA ABSTRACT Nanostructuring has been the foremost approach to the manufacture of high-performance thermoelectric materials for nearly a decade. This study explores a novel nanostructuring technique, attrition-enhanced nanocomposite synthesis, in maximum indium-filled, ironsubstituted cobalt antimonide skutterudites. In0.3Fe0.8Co3.2Sb12 was synthesized and subjected to varying degrees of mechanical attrition (via ball milling). These samples exhibited increased indium precipitation coincident with the duration of mechanical attrition. Indium readily diffused through the skutterudite crystal structure and rapidly precipitated forming 20-50 nmsized indium-rich inclusions during sintering. 1. INTRODUCTION The prospect of catastrophic social and economic consequences triggered by global climate change has stimulated unprecedented demand for a host of diverse, clean, and sustainable energy technologies.1 This demand may be satiated in part by high-efficiency thermoelectric materials.2 Consequently, decades of research have focused on enhancing their efficiency. Thermoelectric efficiency is typically reported as a dimensionless figure-of-merit (zT) at a specified temperature (T) (Eq. 1): ܶݖൌ
ఙௌ మ
ܶ
Eq. 1
where ߢ் ൌ ߢ ߢ Eq. 1a The zT is dependent on the electrical conductivity (σ), Seebeck coefficient (S), and lattice (κL) and electronic (κe) thermal conductivities of the material. Enhanced power-factors (VS2) are often observed in moderately to heavily doped semiconductors which can possess both optimum charge carrier concentration and charge carrier mobility while maintaining a relatively high Seebeck coefficient.3,4 The skutterudite crystal structure is comprised of a cage-like framework of transition metal-pnicogen, and pnicgoen-pnicogen bonds. The pnicogens form two large icosahedral voids sites per unit cell, which can be filled with a wide-array of disparate elements. These interstitials are loosely bound and reduce the lattice thermal conductivity substantially while also providing considerable charge carrier density thereby enhancing the electrical conductivity significantly.5-14 The zT of skutterudites, therefore, can be enhanced strongly by icosahedral void-site filling. In addition, nanocomposite thermoelectrics – materials consisting of a polycrystalline matrix with nano-sized inclusions – also exhibit strongly enhanced zT’s.15-20 Attrition-enhanced
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