title: On the True Indium Content of In-Filled Skutterudites.
abstract: The incongruently melting single-filled skutterudite InxCo4Sb12 is known as a promising bulk thermoelectric material. However, the products of current bulk syntheses contain always impurities of InSb, Sb, CoSb, or CoSb2, which prevent an unbiased determination of its thermoelectric properties. We report a new two-step synthesis of high-purity InxCo4Sb12 with nominal compositions x = 0.12, 0.15, 0.18, and 0.20 that separates the kieftite (CoSb3) formation from the topotactic filler insertion. This approach allows conducting the reactions at lower temperatures with shorter reaction times and circumventing the formation of impurity phases. The synthesis can be extended to other filled skutterudites. High-density (>98%) pellets for thermoelectric characterization were prepared by current-assisted short-time sintering. Sample homogeneity was demonstrated by potential and Seebeck microprobe measurements of the complete pellet surfaces. Synchrotron X-ray diffraction showed a purity of 99.9% product with traces (≤0.1%) of InSb in samples of nominal composition In0.18Co4Sb12 and In0.20Co4Sb12. Rietveld refinements revealed a linear correlation between the true In occupancy and the lattice parameter a. This allows the determination of the true In filling in skutterudites and predicting the In content of unknown AxCo4Sb12. The high purity of InxCo4Sb12 allowed studying the transport properties without bias from side phases. A figure of merit close to unity at 420 °C was obtained for a sample of a true composition of In0.160(2)Co4Sb12 (nominal composition In0.18Co4Sb12). The lower degree of In filling has a dramatic effect on the thermoelectric properties as demonstrated by the sample of nominal composition In0.20Co4Sb12. The presence of InSb in amounts of ∼0.1 vol% led to a substantially lower degree of interstitial site filling of 0.144, and the figure of merit zT decreased by 18%, which demonstrates the significance of the true filler atom content in skutterudite materials.
authors.affiliation: †Institut für Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Universität, Duesbergweg 10-14, D-55099 Mainz, Germany.
authors.forename: Eduard
authors.initials: E
authors.lastname: Visnow
authors.affiliation: †Institut für Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Universität, Duesbergweg 10-14, D-55099 Mainz, Germany.|‡Graduate School Materials Science in Mainz, Johannes Gutenberg-Universität, Staudinger Weg 9, 55128 Mainz, Germany.
authors.forename: Christophe P
authors.initials: CP
authors.lastname: Heinrich
authors.affiliation: §Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR), Institut für Werkstoff-Forschung, Linder Höhe, D-51147 Köln, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Schmitz
authors.affiliation: §Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR), Institut für Werkstoff-Forschung, Linder Höhe, D-51147 Köln, Germany.
authors.forename: Johannes
authors.initials: J
authors.lastname: de Boor
authors.affiliation: †Institut für Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Universität, Duesbergweg 10-14, D-55099 Mainz, Germany.
authors.forename: Patrick
authors.initials: P
authors.lastname: Leidich
authors.affiliation: ⊥Jülich Centre for Neutron Science JCNS and Peter Grünberg Institute PGI, JARA-FIT, Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany.
authors.forename: Benedikt
authors.initials: B
authors.lastname: Klobes
authors.affiliation: ⊥Jülich Centre for Neutron Science JCNS and Peter Grünberg Institute PGI, JARA-FIT, Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany.|∥Faculté des Sciences, Université de Liège, B-4000 Liège, Belgium.
authors.forename: Raphael P
authors.initials: RP
authors.lastname: Hermann
authors.affiliation: §Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR), Institut für Werkstoff-Forschung, Linder Höhe, D-51147 Köln, Germany.|#Institute of Inorganic and Analytical Chemistry, Justus Liebig University Giessen, Heinrich-Buff-Ring 58, D-35392 Giessen, Germany.
authors.forename: Wolf Eckhard
authors.initials: WE
authors.lastname: Müller
authors.affiliation: †Institut für Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Universität, Duesbergweg 10-14, D-55099 Mainz, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Tremel