Ba-filled Ni-Sb-Sn based skutterudites with anomalously high lattice thermal conductivityIn Memoriam of Dr John F. "Jack" Smith.Electronic supplementary information (ESI) available. See DOI: 10.1039/c6dt01298a

• Main Authors: Paschinger, W, Rogl, G, Grytsiv, A, Michor, H, Heinrich, P. R, Müller, H, Puchegger, S, Klobes, B, Hermann, R. P, Reinecker, M, Eisenmenger-Sitter, Ch, Broz, P, Bauer, E, Giester, G, Zehetbauer, M, Rogl, P. F
• Format: Journal Article
• Published: 05.07.2016
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c6dt01298a

Novel filled skutterudites Ba y Ni 4 Sb 12− x Sn x ( y max = 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 Ni 4 (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 Ni 4 Sb 8.2 Sn 3.8 , Ba 0.42 Ni 4 Sb 8.2 Sn 3.8 and Ba 0.92 Ni 4 Sb 6.7 Sn 5.3 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 Ba 0.73 Ni 4 Sb 8.1 Sn 3.9 and Ba 0.95 Ni 4 Sb 6.1 Sn 5.9 . 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 Ni 4 Sb 8.2 Sn 3.8 to 116 GPa for Ba 0.92 Ni 4 Sb 6.7 Sn 5.3 . The thermal expansion coefficients were 11.8 × 10 −6 K −1 for Ni 4 Sb 8.2 Sn 3.8 and 13.8 × 10 −6 K −1 for Ba 0.92 Ni 4 Sb 6.7 Sn 5.3 . 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. Novel filled skutterudites Ba y Ni 4 Sb 12− x Sn x ( y max = 0.93) have been prepared and thoroughly characterized, which show anomalously high lattice thermal conductivity.