Ba-filled Ni-Sb-Sn based skutterudites with anomalously high lattice thermal conductivity.
Novel filled skutterudites BayNi4Sb12-xSnx (ymax = 0.93) have been prepared by arc melting followed by annealing at 250, 350 and 450 °C up to 30 days in vacuum-sealed quartz vials. Extension of the homogeneity region, solidus temperatures and structural investigations were performed for the skutterudite phase in the ternary Ni-Sn-Sb and in the quaternary Ba-Ni-Sb-Sn systems. Phase equilibria in the Ni-Sn-Sb system at 450 °C were established by means of Electron Probe Microanalysis (EPMA) and X-ray Powder Diffraction (XPD). With rather small cages Ni4(Sb,Sn)12, the Ba-Ni-Sn-Sb skutterudite system is perfectly suited to study the influence of filler atoms on the phonon thermal conductivity. Single-phase samples with the composition Ni4Sb8.2Sn3.8, Ba0.42Ni4Sb8.2Sn3.8 and Ba0.92Ni4Sb6.7Sn5.3 were used to measure their physical properties, i.e. temperature dependent electrical resistivity, Seebeck coefficient and thermal conductivity. The resistivity data demonstrate a crossover from metallic to semiconducting behaviour. The corresponding gap width was extracted from the maxima in the Seebeck coefficient data as a function of temperature. Single crystal X-ray structure analyses at 100, 200 and 300 K revealed the thermal expansion coefficients as well as Einstein and Debye temperatures for Ba0.73Ni4Sb8.1Sn3.9 and Ba0.95Ni4Sb6.1Sn5.9. These data were in accordance with the Debye temperatures obtained from the specific heat (4.4 K < T < 140 K) and Mössbauer spectroscopy (10 K < T < 290 K). Rather small atom displacement parameters for the Ba filler atoms indicate a severe reduction in the "rattling behaviour" consistent with the high levels of lattice thermal conductivity. The elastic moduli, collected from Resonant Ultrasonic Spectroscopy ranged from 100 GPa for Ni4Sb8.2Sn3.8 to 116 GPa for Ba0.92Ni4Sb6.7Sn5.3. The thermal expansion coefficients were 11.8 × 10(-6) K(-1) for Ni4Sb8.2Sn3.8 and 13.8 × 10(-6) K(-1) for Ba0.92Ni4Sb6.7Sn5.3. The room temperature Vickers hardness values vary within the range from 2.6 GPa to 4.7 GPa. Severe plastic deformation via high-pressure torsion was used to introduce nanostructuring; however, the physical properties before and after HPT showed no significant effect on the materials thermoelectric behaviour.
Institute of Materials Chemistry & Research, University of Vienna, Währinger Straße 42, A-1090 Vienna, Austria. werner.paschinger@univie.ac.at.
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Paschinger
Institute of Materials Chemistry & Research, University of Vienna, Währinger Straße 42, A-1090 Vienna, Austria. werner.paschinger@univie.ac.at and Christian Doppler Laboratory for Thermoelectricity, Vienna, Austria and Institute for Solid State Physics, TU-Wien, Wiedner Hauptstr. 8, A-1040 Vienna, Austria and Faculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria.
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Rogl
Institute of Materials Chemistry & Research, University of Vienna, Währinger Straße 42, A-1090 Vienna, Austria. werner.paschinger@univie.ac.at and Christian Doppler Laboratory for Thermoelectricity, Vienna, Austria and Institute for Solid State Physics, TU-Wien, Wiedner Hauptstr. 8, A-1040 Vienna, Austria.
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Grytsiv
Institute for Solid State Physics, TU-Wien, Wiedner Hauptstr. 8, A-1040 Vienna, Austria.
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Michor
Institute for Solid State Physics, TU-Wien, Wiedner Hauptstr. 8, A-1040 Vienna, Austria.
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Heinrich
Institute for Solid State Physics, TU-Wien, Wiedner Hauptstr. 8, A-1040 Vienna, Austria.
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Müller
Faculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria.
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Puchegger
Jülich Centre for Neutron Science JCNS and Peter Grünberg Institute PGI, JARA-FIT, Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany.
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Klobes
Jülich Centre for Neutron Science JCNS and Peter Grünberg Institute PGI, JARA-FIT, Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany and Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
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Hermann
Faculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria.
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Reinecker
Institute for Solid State Physics, TU-Wien, Wiedner Hauptstr. 8, A-1040 Vienna, Austria.
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Eisenmenger-Sitter
Faculty of Science, Deparment of Chemistry, Masaryk University, Kotlářská 267/2, 611 37 Brno, Czech Republic.
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Broz
Christian Doppler Laboratory for Thermoelectricity, Vienna, Austria and Institute for Solid State Physics, TU-Wien, Wiedner Hauptstr. 8, A-1040 Vienna, Austria.
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Bauer
Institute of Mineralogy and Crystallography, University of Vienna, Althanstr. 14 (UZA 2), A-1090 Vienna, Austria.
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Giester
Faculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria.
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Zehetbauer
Institute of Materials Chemistry & Research, University of Vienna, Währinger Straße 42, A-1090 Vienna, Austria. werner.paschinger@univie.ac.at and Christian Doppler Laboratory for Thermoelectricity, Vienna, Austria.
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Rogl