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Tetrahedrite compounds Cu(12-x)Mn(x)Sb4S13 (0 ≤x≤ 1.8) were prepared by solid state synthesis. A detailed crystal structure analysis of Cu10.6Mn1.4Sb4S13 was performed by single crystal X-ray diffraction (XRD) at 100, 200 and 300 K confirming the noncentrosymmetric structure (space group I4[combining macron]3m) of a tetrahedrite. The large atomic displacement parameter of the Cu2 atoms was described by splitting the 12e site into a partially and randomly occupied 24g site (Cu22) in addition to the regular 12e site (Cu21), suggesting a mix of dynamic and static off-plane Cu2 atom disorder. Rietveld powder XRD pattern and electron probe microanalysis revealed that all the Mn substituted samples showed a single tetrahedrite phase. The electrical resistivity increased with increasing Mn due to substitution of Mn(2+) at the Cu(1+) site. The positive Seebeck coefficient for all samples indicates that the dominant carriers are holes. Even though the thermal conductivity decreased as a function of increasing Mn, the thermoelectric figure of merit ZT decreased, because the decrease of the power factor is stronger than the decrease of the thermal conductivity. The maximum ZT = 0.76 at 623 K is obtained for Cu12Sb4S13. The coefficient of thermal expansion 13.5 ± 0.1 × 10(-6) K(-1) is obtained in the temperature range from 460 K to 670 K for Cu10.2Mn1.8Sb4S13. The Debye temperature, Θ(D) = 244 K for Cu10.2Mn1.8Sb4S13, was estimated from an evaluation of the elastic properties. The effective paramagnetic moment 7.45 μB/f.u. for Cu10.2Mn1.8Sb4S13 is fairly consistent with a high spin 3d(5) ground state of Mn.

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The frequency equation of Timoshenko beam theory factorises for hinged-hinged end conditions, leading to a first and second spectrum of natural frequencies; the latter is largely inaccurate and can be isolated and disregarded. For the majority of other end conditions, when the frequency equation does not factorise, one may think in terms of pseudosecond spectrum contributions arising when evanescent waves become propagating above the cut-off frequency o co ¼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ffi kAG=rI p , and it is conjectured that these may have a corrupting effect on the frequency predictions. Comparisons with measured and simulated frequencies lead to the conclusion that Timoshenko predictions above the cut-off frequency should be disregarded for those end conditions for which the frequency equation does not factorise. r

Metallic foam was fabricated from 316L stainless steel spheres, where the bonding of the spheres was achieved by a sintering process. The mechanical behavior of a low-density material (0.3 g/ cm 3 ) with 2-and 4-mm sphere diameter and a high-density material (0.6 g/cm 3 ) with 4-mm sphere diameter was investigated in compression and tension. The cell wall material of this hollow sphere structure (HSS) had different morphologies: dense and porous sintered walls were investigated. The cell wall morphology affects the YoungÕs modulus (stiffness) and the ductility of the HSS material. Defects, such as the cell wall porosity, lower the ductility of the material. Besides the quasi-static measurements, the HSS material was tested with a resonance frequency method (dynamic measurement), to obtain detailed information on the stiffness at different temperatures up to 700°C. In-situ compression and tension tests were carried out to understand the deformation mechanisms on the scale of the single hollow spheres. The failure mechanisms in the vicinity of the sintering neck of the spheres was investigated. A doubling of the density leads to an increase of the plateau stress and the ultimate tensile stress of the material, whereas the ductility (strain to fracture) depended mainly on the cell wall morphology. Due to the mainly tensile loading of the cell walls in the vicinity of the sinter neck, the ultimate tensile strength doubled for the high-density HSS, in good agreement with theoretical considerations. In compression, the gain in the plateau stress was not as distinctive compared with the theoretical considerations assuming a bending dominated deformation. The influence of structural parameters, such as cell wall morphology, cell wall thickness, and sphere diameter, on the mechanical behavior is discussed.