Article

Thermal expansion of skutterudites

Institute of Physical Chemistry, University of Vienna, Währingerstr. 42, A-1090 Wien, Austria
Journal of Applied Physics (Impact Factor: 2.21). 03/2010; DOI: 10.1063/1.3284088
Source: IEEE Xplore

ABSTRACT The current paper gives an overview of the newly obtained thermal expansion coefficients of skutterudites as well as those so far available in literature. Thermal expansion was determined for CoSb 3 , Pt 4 Sn 4.4 Sb 7.6 , for As- and Ge-based skutterudites as well as for various high-ZT skutterudites (micro- and nanostructured) with didymium (DD) and mischmetal (Mm) as filler atoms in frameworks of ( Fe 1- x Co x )4 Sb 12 and ( Fe 1- x Ni x )4 Sb 12 , and for double and triple-filled skutterudites such as Ca 0.07 Ba 0.23 Co 3.95 Ni 0.05 Sb 12 and Sr 0.025 Ba 0.075 Yb 0.1 Co 4 Sb 12 . For low temperatures, a capacitance dilatometer was used (4–300 K), whereas for temperatures 300≪ T ≪750 K , a dynamic mechanical analyzer was employed. For a set of Ge-, P-, and Sb-based skutterudites, lattice parameters of single crystals, measured at three different temperatures, were used to derive the thermal expansion coefficient. The semiclassical model of Mukherjee [Phys. Rev. Lett. 76, 1876 (1996)] has been successfully used to quantitatively describe the thermal expansion coefficient in terms of Einstein and Debye temperatures, which compare well with the corresponding results from specific heat, electrical resistivity, or temperature depend-
ent x-ray measurements.

0 Bookmarks
 · 
86 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: During waste heat recovery applications, thermoelectric (TE) materials experience thermal gradients and thermal transients, which produce stresses that scale with the TE material's coefficient of thermal expansion (CTE). Thus, the temperature-dependent CTE is an important parameter for the design of mechanically robust TE generators. For three skutterudite thermoelectric compositions, n-type Co{sub 0.95}Pd{sub 0.05}Te{sub 0.05}Sb{sub 3} (with and without 0.1 at. % cerium doping) and p-type Ce{sub 0.9}Fe{sub 3.5}Co{sub 0.5}Sb{sub 12}, the CTE was measured using two methods, i.e. X-ray diffraction on powder and bulk specimens and dilatometry on bulk specimens. Each bulk specimen was hot pressed using powders milled from cast ingots. Between 300 K and 600 K, the mean CTE values were 9.8-10.3 x 10{sup -6} K{sup -1} for the non-cerium-doped n-type, 11.6 x 10{sup -6} K{sup -1} for the 0.1 at. % cerium-doped n-type and from 12.7 to 13.3 x 10{sup -6} K{sup -1} for the p-type. In the literature, similar CTE values are reported for other Sb-based skutterudites. For temperatures >600 K, an unrecovered dilatational strain (perhaps due to bloating) was observed, which may impact applications. Also, the submicron particle sizes generated by wet milling were pyrophoric; thus, during both processing and characterization, exposure of the powders to oxygen should be limited.
    Philosophical Magazine 04/2012; 92(10-10.1080/14786435.2011.644815):1261. · 1.60 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper presents a self-calibrating mathematical model and simulation results of the direct piezoelectric effect of a new tilt-sensor that measures inclination angles around two orthogonal axes. Using a fundamental description of the mechanical stress generated in suspended beams under static loading, we propose a model of the sensor's direct piezoelectric effect that is only a trigonometric function of its genetic behavior in two orthogonal planes. The significance of the proposed approach lies in the independence of the model from the structural dimensions of the piezo-system and the electro-mechanical properties of the piezoelectric layer. The effect of these structural properties and other external stimuli on the proposed model is implicitly contained, and inherently carried by the genetic data which is curve-fitted using a polynomial approximation. The feasibility of the proposed method and the accuracy of the model are verified by cross-comparison with simulation results. These simulations are performed on a CAD model of the piezoelectric tilt sensor for a case-study operation range of 0 - 90° . An overall considerable accuracy level was noted between the simulated and modeled data over the full operation range, with an average relative peak error of 1.9%.
    IEEE Sensors Journal 05/2012; 12(5):1033-1042. · 1.48 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: During the post-annealing and cooling process of CoSb3 thin films deposited on thermally oxidized Si(100) substrates, cracks occur at the surface of the films, which can be caused by the difference in thermal expansion coefficient of the substrate and the film. To investigate the crack formation, 40-nm-thick CoSb3 films were deposited at room temperature under ultra-high vacuum (UHV) conditions onto various substrates, exhibiting different thermal expansion coefficients (2 × 10−6 to 12 × 10−6 K−1). All samples were post-annealed in UHV at 500 °C for 1 h. The composition of the films was verified by Rutherford backscattering spectrometry. The phase formation and elastic stress of the films were analyzed by X-ray diffraction, confirming the formation of the desired skutterudite phase, while the individual grains were studied by electron backscatter diffraction. In addition, the surface morphology and the roughness of the films were investigated by atomic force microscopy. For substrates with a thermal expansion coefficient between 9 × 10−6 and 11 × 10−6 K−1, crack formation can be prevented and a minimum in roughness was found, resulting also in a minimal value of the electrical resistivity.
    physica status solidi (a) 01/2013; 210(1):140-146. · 1.21 Impact Factor

Full-text (2 Sources)

View
15 Downloads
Available from
May 30, 2014