RESUMO
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 â¼0.1 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.
RESUMO
Element distribution in the bark of two 20-year-old clones of Picea sitchensis following wounding was studied using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Bark was sampled at 0, 3, and 43 days after wounding and analysed using a focused Nd:YAG laser (266 nm). Intensities of (13)C, (25)Mg, (27)Al, (31)P, (32)S, (39)K, (48)Ca, (55)Mn, (57)Fe, (63)Cu and (64)Zn were measured by ICP-MS to study elemental distribution across the bark samples during the wound repair process. A clear accumulation of Mg, P and K at the boundary zone between the lesion and healthy tissue was detected in the wounded samples and was more distinctive at 43 than at 3 days after treatment. This zone of accumulation mapped onto the position of formation of the ligno-suberised boundary zone and differentiation of the wound periderm. These accumulations suggest major roles for Mg, P and K in the non-specific response of Sitka spruce both to wounding, possibly as co-factors to enzymes and energy utilisation. The LA-ICP-MS method developed in this work proved useful to study spatial element distribution across bark samples and has great potential for applications in other areas of plant pathology research.
