Bulk Synthesis of Completely and Partially Sn filled CoSb3 Using the Multilayer Repeat Method
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Bulk Synthesis of Completely and Partially Sn filled CoSb3 Using the Multilayer Repeat Method Heike Sellinschegg and David C. Johnson1 University of Oregon, Dept. of Chemistry and Materials Science Institute, Eugene, OR 97403 1
Michael Kaeser, Terry M. Tritt Clemson University, Department of Physics, Clemson, SC 29634 George S. Nolas R & D Division, Marlow Industries, Dallas, TX 75238 E. Nelson U.S. Army Research Laboratory, Adelphi, ML 20783 ABSTRACT Filled skutterudite compounds possess very low thermal conductivities due to the scattering of a wide range of phonon modes caused by a loosely bound cation incorporated in a cavity of the structure. The inclusion of such a filler cation causes several synthetic difficulties since the desired compounds are thermodynamically unstable with respect to disproportionation. Modulated elemental reactants were used in this study to circumvent these difficulties. SnxCo4Sb12 samples with x=0.5 and nearly 1.0 were synthesized using this method. To prevent nucleation of unwanted binary compounds, the repeat unit made up of elemental layers was less than 20 angstroms 500mg of each sample were produced, allowing for the samples to be hot pressed into a pellet. Structural analysis as well as measurements of the physical properties are presented. INTRODUCTION In the development of new materials with higher figures of merit much research has been focused on compounds with a large, complex unit cell and a misfit between a particular lattice site and a so-called filler - cation. The idea behind this concept, originally proposed by Slack [1], is to maintain good electrical conductivity by making the elements with states at the Fermi level part of a rigid covalent network while suppressing the lattice thermal conductivity by the random thermal vibrations of the filler cation which effectively scatters lattice phonons. One class of compounds satisfying Slack’s criteria that has sparked significant interest is the skutterudite compounds. The skutterudites are materials with a complex crystal structure with 32 atoms per cubic unit cell and have shown potential to exhibit extremely promising thermoelectric properties. Many different skutterudite compounds with different filler cations have been synthesized, however, synthetic problems have so far prevented the preparation of some of the targeted materials.
Z10.2.1 Downloaded from https://www.cambridge.org/core. Columbia University Libraries, on 21 Jan 2020 at 20:14:18, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-626-Z10.2
The synthesis of many of these materials is extremely challenging. The weak interactions between the filler cation and the lattice site causes many of the ternary skutterudite compounds to be thermodynamically unstable with respect to decomposition into binary compounds. The filling fraction of cations in the host lattice is usually quite limited, as for example in the case of Ce insertion into a Co4Sb12 host lattice where the maximum filling
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