D. T. Morelli

Transport properties of ZrNiSn-based intermetallics

Intermetallic compounds of the form MNiSn, where M is titanium, zirconium, or hafnium, are semiconductors with band gaps on the order of 0.2 electron volts. Due to their large conduction band masses, they show promise as thermoelectric materials with high figure of merit. In order to assess this potential, we have studied the thermoelectric properties of pure and doped ZrNiSn and Zr/sub 0.5/Hf/sub 0.5/NiSn mixed crystals. Upon doping with Sb the resistivity can be reduced by a factor of 20-40 with a reduction in the Seebeck coefficient of only a factor of two. The resulting power factors of doped samples at room temperature are comparable to those of state of the art thermoelectric materials. The thermal conductivity of Zr/sub 0.5/Hf/sub 0.5/NiSn is reduced strongly relative to ZrNiSn but must be reduced further to obtain a large figure of merit. The transport properties of these materials are very sensitive to annealing conditions.

Thermal transport properties of SbCl5-graphite and of HOPG in the c-direction

Abstract We report measurements of the c-axis thermal conductivity and thermoelectric power of SbCl 5 -GICs. Thermal conduction is dominated by the lattice, with defects being the dominant scatterers. The thermopower is in good agreement with theoretical predictions for GICs. Finally, results for the very low temperature thermal conductivity of pure graphite in the c-direction are presented and discussed.

Thermoelectric properties of rare earth-ruthenium-germanium compounds

We report our studies of the thermoelectric properties of a class of compounds of composition R3Ru4Ge13 (R=Y, Dy, Ho, and Lu). Magnetization measurements show that the R ion is in the trivalent state in each of these compounds. Each of these compounds displays a semiconductorlike rise in electrical resistivity with decreasing temperature. The magnitude of the resistivity is much larger than typical metals and is similar to that of a heavily doped semiconductor or semimetal. The Seebeck coefficient is positive throughout the temperature range of 2–800K with room temperature values of approximately 40μVK−1. The lattice thermal conductivity is remarkably low and exhibits a very flat temperature dependence. This is consistent with the observed internal disorder associated with the cagelike structure of these compounds. Cobalt substitution for ruthenium enhances the semiconductor character but does not improve the thermoelectric properties.

Influence of neutron irradiation on the thermal conductivity of vapor-deposited diamond

The influence of neutron irradiation on the thermal conductivity κ of diamond films fabricated by hot filament (HF) and microwave plasma assisted (MPA) deposition has been studied. The additional thermal resistivity induced by irradiation is similar to that found in single crystal diamond and is due mainly to the formation of clusters of disordered carbon material. Despite a significant difference in κ prior to irradiation, the thermal conductivity of the HF and MPA films is almost the same after a cumulative dose of 2.7×1017 neutrons cm−2.

ELECTRONIC TRANSPORT IN Mo/Ni SUPERLATTICES

Abstract An experimental relationship between superconductivity, magnetism and localization is explored in short-wavelength (14A ⩽ ⋀ ⩽ 40A) sputtered Mo/Ni superlattices. A crossover to a superconducting state is observed for ⋀

Thermoelectric properties of Co[sub 0.9]Fe[sub 0.1]Sb[sub 3]-based skutterudite nanocomposites with FeSb[sub 2] nanoinclusions

Bulk thermoelectric nanocomposite materials have great potential to exhibit higher figure of merit due to effects arising from the nanostructure. In this paper, we report thermoelectric properties from 80 K to 800 K of Co0.9Fe0.1Sb3 based skutterudite nanocomposites containing FeSb2 nanoinclusions. The nanoscale FeSb2 precipitates are well dispersed in the skutterudite matrix and reduce the lattice thermal conductivity due to additional phonon scattering from the nanoscopic interfaces. Moreover, the nanocomposite samples also exhibit enhanced Seebeck coefficients relative to the regular iron substituted skutterudite samples. As a result, our best nanocomposite sample reached a dimensionless figure of merit of 0.59 at 788 K, a factor of two higher than that of the control sample Co0.9Fe0.1Sb3.

Electrical resistivity of single crystal arsenic at very low temperatures

The authors have carried out high-precision measurements of the electrical resistivity on very high-quality arsenic single crystals along the binary direction below 4K. The results show that rho approximately Tn with n increasing from 3 to 4 below 2K. This strong temperature dependence is a signal of carrier-phonon scattering in this temperature regime. No evidence of a superconducting transition was observed down to as low as 15 mK on the samples.