Mechanical properties of filled antimonide skutterudites

Time-of-flight and resonant ultrasound spectroscopy techniques were employed for elastic moduli measurements on a set of various Fe4Sb12- and Co4Sb12-based skutterudites filled by mischmetal, didymium, or alkaline earths (Ca, Sr, Ba). A weak temperature influence on the longitudinal modulus C11 indicates weak degradation of elastic properties within the thermoelectric working temperature range. Elastic moduli for Co4Sb12-based skutterudites are only slightly higher than for Fe4Sb12-based skutterudites, and the influence of various filler atoms or filling fractions on the elastic moduli is even smaller. Ball milled and hot pressed samples (grain size ∼250 nm) illustrate an obvious improvement of elastic properties in relation to those hot pressed from hand milled powders (grain size ∼50 μm). Debye temperatures calculated from sound velocity measurements are comparable to the values obtained from the parameters fitted to thermal expansion, which indicate that Co4Sb12-based skutterudites having slightly higher values than Fe4Sb12-based skutterudites. Vickers hardness is increased by Co or Ni substitution and demonstrates a linear dependence on density, Youngʹs modulus, and shear modulus.