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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.

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Polycrystalline CoFe2O4 was produced by a ceramic method. The heat-treated powder was pressed, varying the hydrostatic pressure between 87 and 278 MPa, and was heat-treated again at 1350 °C for 24 h. All magnetic parameters showed a clear dependence on this hydrostatic pressure. The saturation magnetization showed a minimum, and the coercivity, the anisotropy, and the magnetostriction showed a maximum at compaction pressures around 150 MPa. This pressure dependence of the magnetic parameters can be explained by a cation redistribution due to the hydrostatic pressure and heat treatment. Additionally, all samples were field-annealed in an external field of 10 T (at 300 °C for 3 h). The field-annealing process causes an induced uniaxial anisotropy, which results in a reduction of the coercivity (in the easy axis) as well as a dramatic increase in the magnitude of the magnetostriction along the hard axis. Maximum magnetostriction value of -400×10-6 was obtained. Additionally, dλ/dH is increased within a factor of three with magnetic heat treatment.

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To elucidate the discrepancies in low-temperature data reported on the quantum critical heavy fermion compound Ce 3 Pd 20 Si 6 and reveal the compound's intrinsic properties, single crystals of varying stoichiometry were grown by various techniques-from the melt and from high-temperature solutions using fluxes of various compositions. The resulting stoichiometry of the crystals as well as their physical properties show sizable dependence on the different growth techniques. The Ce content ⌬Ce varies by more than 3 at. % among all grown single crystals. We have revealed a systematic dependence of the residual resistance ratio, the lattice parameter, the ͑lower͒ phase-transition temperature T L , and the maximum in the temperature dependent electrical resistivity T max with ⌬Ce. This clarifies the sizable variation in the values of T L reported in the literature. We discuss the physical origin of the observed composition-property relationship in terms of a Kondo lattice picture. We predict that a modest pressure can suppress T L to zero and thus induce a quantum critical point.

Thermal expansion was determined for two series of ternary compounds, Ba 8 M x Ge 46−x and Ba 8 M x Si 46−x , with M = Cu, Zn, Pd, Ag, Cd, Pt, and Au and for several quaternary compounds for which we investigated the influence of substitution by Zn/Ni in Ba 8 Zn x Ge 46−x as well as the dependence of thermal expansion on the Si/Ge ratio in Ba 8 Cu 5 Si x Ge 41−x. In the temperature range from 4.2 to 300 K the thermal expansion of all ternary compounds was measured with a capacitance dilatometer, whereas from 300 to 700 K for several selected samples a dynamic mechanical analyzer was employed. The low temperature data compare well with the lattice parameters of single crystals, gained from measurements at three different temperatures ͑100, 200, and 300 K͒. For a quantitative description of thermal expansion the semiclassical model of Mukherjee et al. ͓Phys. Rev. Lett. 76, 1876 ͑1996͔͒ was used, which also provided reliable accurate values of the Debye and Einstein temperatures. Results in this respect show good agreement with the corresponding data derived from temperature dependent x-ray diffraction and specific heat measurements. Furthermore the present paper is a comprehensive collection and discussion of all thermal expansion data of intermetallic type-I-clathrate materials so far available in the literature including our results of thermal expansion measurements of the Ge-and Si-based type-I-clathrates listed above.

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