Structural and physical properties of n-type skutterudite Ca0.07Ba0.23Co3.95Ni0.05Sb12

Zhang

Journal of Applied Physics

et al. 2010

Self Cite

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 ͑microand nanostructured͒ with didymium ͑DD͒ and mischmetal ͑Mm͒ 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 K͒, whereas for temperatures 300Ͻ T Ͻ 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 ͑1996͔͒ 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 dependent x-ray measurements.

Section: Resultssupporting

confidence: 80%

Section: Introductionmentioning

confidence: 99%

Thermal expansion of skutterudites

Zhang

Journal of Applied Physics

et al. 2010

Self Cite

“…The improved performance of some multiply filled skutterudites 8,[36][37][38][39][40][41][42][43][44][45][46] may be explained in part from nanodomains with avoided crossings at different qvectors. However, in many cases the concentrations of some filler atom are low and in that case defect scattering should also play an important role.…”

Section: Discussionmentioning

confidence: 99%

Modeling correlated motion in filled skutterudites

Keiber

Bridges

2015

Phys. Rev. B

Recent extended X-ray absorption fine structure (EXAFS) studies suggest that in skutterudites, the nearly square rings (such as As4 in CeFe4As12) are quite rigid and may vibrate with low energy modes in one direction, similar to "rattler" atom vibrations. That work suggests that the motions of the square rings and the rattler atoms are coupled. In addition, for LnCu3Ru4O12, the second neighbor pairs about Ln have stiffer effective springs than the nearest neighbor pairs. To investigate these systems, a one dimensional, four mass, linear chain spring model is developed to describe the recent experimental results, and provide insight about the low energy vibrations in such systems. Our model solves the resulting coupled network of overlapping weak and strong springs and determines the eigenfrequencies and eigenvectors. The dispersion curves show an acoustic mode, two different low energy optical rattling modes involving both the rattler and square, and a non interacting optical mode. Each rattler mode can couple to the acoustic mode, which generates avoided crossings characterized by flattening of the modes; this has important consequences for thermal transport. From these results we calculate atomic correlation functions and the Debye-Waller-like function used in EXAFS, σ 2 , as a function of temperature. These calculations show that for the rattler-neighbor pairs, σ 2 is a sum over several modes; it is not the result of a single mode. The inverse slope of σ 2 (T) at high T provides a measure of the effective spring constants, and the results show that for small direct spring constants the effective spring constant can be significantly larger than the direct spring constants. The locations of the avoided crossings (between rattler modes and the acoustic mode) in q-space can be tuned by the choice of both the rattler and the square atoms. Consequently, it may be possible to further reduce the thermal conductivity using a mixture of nanoparticles, each with avoided crossings at different positions in q-space.

“…[1][2][3] Filled skutterudites have the composition RM 4 X 12 , where R is an alkali-earth or rare-earth element, M is a transition metal such as Fe, Co, Rh, or Ir, and X is composed of a pnicogen element such P, As, or Sb. [4][5][6][7] In contrast to the n-type Co 4 Sb 12 with 72 valence electrons, p-type Fe 4 Sb 12 is unstable because it has only 68 valence electrons, and thus a deficiency of 4 electrons. 8 However, it can be stabilized to R 4+ [Fe 4 Sb 12 ] 4À by filling at the voids in the skutterudite structure with R 4+ ions.…”

Section: Introductionmentioning

confidence: 99%

Thermal Stability of La0.9Fe3CoSb12 Skutterudite

Shin

Kim

Park

et al. 2014

Journal of Elec Materi

The thermal stability of the La 0.9 Fe 3 CoSb 12 skutterudite was examined by varying the aging conditions of temperature, time, and atmosphere (air and vacuum). Thermogravimetry, differential scanning calorimetry and x-ray diffraction analyses revealed that the La 0.9 Fe 3 CoSb 12 was significantly oxidized at temperatures above 673 K in air. The Sb-based oxides were preferably formed when aged at high temperatures in air. The thickness of the oxide layers was found to increase with increasing aging temperature and time, while the activation energy for the oxidation of the Fe-Sb-based skutterudite was lower than that of the Co-Sb-based skutterudites. However, when the analysis was performed in a vacuum, the La 0.9 Fe 3 CoSb 12 skutterudite was stable, and no oxide layers were observed after aging at 823 K for 100 h. These results suggest that a protective coating for the skutterudite materials or the encapsulated packaging of the skutterudite modules is required for hightemperature applications.