We have measured the electrical resistivity, ρ, thermoelectric power, α, and thermal conductivity, κ, of the skutterudite material IrSb3 in a temperature range from 300 down to 4 K. It is found that the electrical resistivity and thermopower decrease monotonically as the temperature is reduced to 50–60 K. Below approximately 60 K the resistivity rises in a semiconducting manner. It appears the thermopower exhibits a large phonon drag peak at around 20 K and then falls towards zero. The thermal conductivity increases rapidly as the temperature is decreased with a maximum at around 20 K, corresponding to the peak in the thermopower. We will discuss these results and compare them to higher temperature data from G. A. Slack and V. G. Tsoukala [(IrSb3) J. Appl. Phys. 76, 1635 (1994)]. We have also measured some of the so-called ‘‘filled skutterudites,’’ Ir4LaGe3Sb9, Ir4NdGe3Sb9 and Ir4SaGe3Sb9. The thermoelectric properties of these materials are considerably different than those of the unfilled sample. The thermopower is considerably lower and the resistivity is a factor of 2–4 times higher than the unfilled sample at room temperature. The thermal conductivity is markedly reduced by the filling, as much as a factor of 20 reduction for some of the systems.
Resistivity measurements have been performed as a function of temperature (1–300 K) and magnetic field (0–10 T) on antiferromagnetically coupled Fe-Cr-Fe sandwiches. Two types of samples were studied: MBE-grown sandwiches deposited epitaxially on the ZnSe (100) surface, and evaporated polycrystalline sandwiches deposited on glass substrates. The magnetic saturation field Hs determined from the resistivity ρ(H,T) is linear with temperature throughout the full temperature range for all samples. In the polycrystalline sandwiches, where the observed in-plane magnetic anisotropy is small, the linearity of Hs(T) implies that the antiferromagnetic interlayer exchange coupling A12 is also linear with temperature. The magnetoresistance of the sandwiches is constant at low temperature, and decreases linearly with increasing temperature above about 70 K.
Summary. Controlled environment experiments were
conducted to establish some of the requirements for successful mass rearing of
Halotydeus destructor (redlegged earth mite). Numbers of
mites reared on Vicia sativa (common vetch) cv.
Blanchefleur grown alone or on a mixture of vetch with
Trifolium subterraneum (subterranean clover) cv.
Goulburn, were significantly higher than those on subterranean clover or
Arctotheca calendula (capeweed) alone. Populations
reared on vetch grown in a sandy soil were significantly higher than those
reared on vetch grown in a loamy soil, pure sand or pure loam. Covering the
soil surface with a natural pasture mulch increased mite numbers compared with
leaving the soil bare or placing plant pots inside ventilated cages.
Subsequent changes in rearing methodology produced enough mites to enable
summer screening of subterranean clover lines for resistance to
H. destructorfor the first time. Over 20 000 mites can
be produced from vetch at one time for screening tests throughout the year.
When multilayer samples of polycrystalline Ni and amorphous SiC are heated, the sequence of phase formation initiates with a dissolution of Ni into the amorphous phase and is followed first by the formation of NiSi and then Ni2Si. Multilayer samples of a-SiC/Ni with modulation wavelengths of 83.9 nm and with the ratio of the thickness of the SiC layer to the Ni layer equal to 3.8 retain a multilayer structure even after they undergo two phase transitions. When annealing causes reactions to occur, the surface roughness, measured by atomic force microscopy (AFM), increases and was correlated with similar increases in the interface width. AFM measurements may provide a convenient way to observe reactions at buried interfaces.
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