CoSb 3 single crystals with low hole concentration ͑down to 10 17 cm Ϫ3 ) at 300 K and 2.6ϫ10 16 cm Ϫ3 at 90 K͒ and the highest observed value of the room-temperature hole mobility ͑the value is up to 6000 cm 2 /V s, i.e., up to about 1.8 times higher than maximum values previously reported͒ were grown. The observed temperature dependence of the Hall coefficient is explained assuming the existence of an acceptor impurity band and an additional deep acceptor level. The values of the activation energies of the shallow and deep acceptors, their concentrations, as well as the concentration of the compensating donors were calculated. It is shown that the scattering due to polar optical phonons and nonpolar optical phonons is most important in the high-temperature region. The value of the valence-band deformation potential is estimated. ͓S0163-1829͑97͒04427-5͔

TiNiSn, ZrNiSn and HfNiSn are members of a large group of intermetallic compounds which crystallize in the cubic MgAgAs-type structure. Polycrystalline samples of these compounds have been prepared and investigated for their thermoelectric properties. With thermopowers of about –200 μV/K and resistivities of a few mΩcm, power factors S2/ρ as high as 38 μW/K2 cm were obtained at 700 K. These remarkably high power factors are, however, accompanied by a thermal conductivity which is too high for applications. In order to reduce the parasitic lattice thermal conductivity, solid solutions Zrl−xHfxNiSn, Zrl−xTixNiSn, and Hfl−xTixNiSn were formed. The figure of merit of Zr0.5Hf0.5NiSn at 700 K (ZT = 0.41) exceeds the end members ZrNiSn (ZT = 0.26) and HfNiSn (ZT = 0.22).

The rare-earth compounds R3Cu3Sb4 (R=La, Ce, Gd, Er) were synthesized in order to evaluate their potential for thermoelectric applications. Melting in closed tantalum tubes was used to get the materials without loss of volatile Sb components. The structure and the thermal expansion coefficients of these compounds were determined by temperature-dependent x-ray diffraction measurements. We also determined the effective magnetic moments of the rare-earth ions and their valence state. The resistivity of the compounds was measured over a large temperature range from 2 to 470 K. Hall-effect measurements were performed in the range from 30 to 470 K. Additionally, the thermopower and the thermal conductivity were determined. On the basis of the measured data, an estimation of the thermoelectric potential of this group of materials will be given.

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Electrical measurements have been carried out on n-type ZrNiSn single crystals. The observed temperature dependence of the Hall coefficient is explained in assuming the existence of an impurity band. The values of the activation energy of the shallow donors, their concentration and the concentration of the compensating acceptors were calculated. It is shown that the scattering due to acoustic phonons and ionized impurities is most important in the high and low temperature region, respectively. The value of the conduction band deformation potential is estimated.