High Pressure Synthesis of New Filled Skutterudites

Abstract

ABSTRACTFilled skutterudites exhibit properties that comply with the concept of a “phonon-glass electron-crystal”, as proposed by Slack. The optimal filled skutterudite would have filler atoms that exhibit large thermal vibration amplitudes in the voids of the crystal structure. It is desirable that these loosely bound atoms give rise to strong phonon scattering without greatly affecting the essential part of the band structure of the skutterudites. This criterion is difficult to meet. Most attempts have employed charge compensation for filling fractions above 50 %. In this report we present the use of a high-pressure technique for the synthesis of new filled skutterudites. By using our high-pressure synthesis technique CoSb3-based skutterudites filled with group-14 elements (Ge, Sn, and Pb) have been synthesized with up to 100 % filling without charge compensation of the host lattice. The structural analysis reveals that the Sn atoms exhibit very large thermal vibration amplitude, indicative of a large “rattling” motion. The Sn-filled specimens exhibit a low thermal conductivity, lower than that of any previously reported filled skutterudite, while the favorable semiconducting nature of the host lattice is not substantially changed by Sn filling. Tin atoms may therefore be better “rattlers” in the CoSb3 host lattice than lanthanide or actinide atoms.