Paola N. Alboni

Thermoelectric properties of La0.9CoFe3Sb12–CoSb3 skutterudite nanocomposites

A hydrothermal nanoparticle-plating technique has been employed in order to grow a layer of CoSb3 nanoparticles on the surface of La0.9CoFe3Sb12 bulk matrix grains. The nanoparticles have a typical size of 30–40 nm while the nano-layer can be up to several hundreds of nanometer thick. The nanoparticle layer, which resides at the grain boundary after hotpressing, provides an extra scattering channel for phonons, in addition to the “rattler” atoms (La), grain boundary scattering, and mass fluctuation mechanisms found within the bulk matrix grain. The electrical resistivity, thermopower, thermal conductivity, and Hall coefficient have been investigated as a function of temperature and the weight percentage (%) of nanoparticles. Largely due to the reduced lattice thermal conductivity, a ZT value of ∼0.5 is attained at 725 K on the sample with 5 wt % of nanoparticles showing a 15% improvement of the ZT from that of the sample without nanoparticles and comparable to the best value reported at this temperature.

High temperature thermoelectric properties of double-filled InxYbyCo4Sb12 skutterudites

Void filling in the CoSb3 skutterudite lattice with different kinds of heavy elements has proved effective in enhancing their thermoelectric performance. In this paper we report the effects of (In,Yb) double filling on the high temperature thermoelectric properties of CoSb3. The InxYbyCo4Sb12 (0≤(x,y)≤0.2) samples have been prepared via a melting-annealing-sintering procedure and characterized by means of x-ray powder diffraction, scanning electron microscopy, Hall coefficient, electrical and thermal conductivities, and Seebeck coefficient measurements. As compared to the In and Yb single-filling approach, the (In,Yb) double-filling approach can effectively reduce the lattice thermal conductivity without degrading the power factor. As a result, several compositions achieve ZT values around unity, while a maximum ZT value of 1.1 is obtained in In0.2Yb0.1Co4Sb12 at 700 K. The difference in the effects of In and Yb filling on the thermoelectric properties is discussed.

Structural and transport properties of Ba8Ga16SixGe30−x clathrates

We report on the structural, chemical, electrical resistivity, Seebeck coefficient, thermal conductivity, and Hall measurements of polycrystalline Si–Ge type-I clathrates with nominal composition of Ba8Ga16SixGe30−x such that a constant Ga-to-group-IV element ratio is maintained while varying the Si-to-Ge ratio. Electrical transport measurements on the n-type specimens show a modest increase in the absolute Seebeck coefficient and a decrease in electrical resistivity with increasing Si content. This may imply a modification in the band structure with Si substitution and reveals a possible approach for optimizing these materials for thermoelectric applications. These data are compared with those of Ba8Ga16Ge30 and Sr8Ga16SixGe30−x.

Thermoelectric properties of p-type half-Heusler alloys Zr1−xTixCoSnySb1−y (0.0<x<0.5; y=0.15 and 0.3)

Half-Heusler alloys Zr1−xTixCoSnySb1−y (0.0<x<0.5; y=0.15 and 0.3) are investigated for their possible use as high temperature thermoelectric materials. In these p-type materials, the Zr site is primarily substituted with Ti to reduce thermal conductivity (κ), while the Sn content is varied to optimize thermoelectric properties. For these compositions, these alloys exhibit moderate resistivity (ρ) in the mΩcm range and high positive thermopower (α), on the order of hundreds of μV∕K. Measured Hall coefficients suggest that holes are dominant charge carriers. Calculated carrier mobilities are rather low in the range of 0.8–1.5cm2∕Vs. Thermal conductivity (κ) values as low as ∼8.5–4.5Wm−1K−1 are also measured. The calculated thermoelectric figure of merit ZT=α2T∕ρκ is as high as 0.2 at T=1000K, implying that these alloys could be potential p-type thermoelectric materials for energy conversion at high temperatures.

Investigation of i-AlCuFe Quasicrystals and their ω and β Approximants as Thermoelectric Materials

In the search for new thermoelectric materials, quasicrystals have been investigated due to their inherently low thermal conductivity. Crystalline phases called approximants which are closely related to the quasicrystals, however, have largely been ignored. These approximants have similar structure, yet the periodicity of a crystal. In this paper, we have investigated an icosahedral i-AlCuFe quasicrystalline phase as well as two of its corresponding approximant phases (ω and β). Electrical and thermal transport properties of these materials are presented. The viability of the i-AlCuFe quasicrystalline system and the ω and β approximant phases as thermoelectric materials is discussed.

Effects of the Addition of Rhenium on the Thermoelectric Properties of the AlPdMn Quasicrystalline System

Partially due to their lack of periodic structure, quasicrystals have inherently low thermal conductivity on the order of 1 - 3 W/m-K. AlPdMn quasicrystals exhibit favorable room temperature values of electrical conductivity, 500–800 (Ω-cm) -1 , and thermopower, 80 μV/K, with respect to thermoelectric applications. In an effort to further increase the thermopower and hopefully minimize the thermal conductivity via phonon scattering, quartenary Al 71 Pd 21 Mn 8-X Re X quasicrystals were grown. X-ray data confirms that the addition of a fourth element does not alter the quasiperiodicity of the sample. Al 71 Pd 21 Mn 8-X Re X quasicrystals of varying Re concentration were synthesized where x had values of 0, 0.08, 0.25, 0.4, 0.8, 2, 5, 6, and 8. Both thermal and electrical transport property measurements have been performed and are reported.

Thermoelectric properties of Sb-doping in the TiNiSn/sub 1-x/Sb/sub x/ half-Heusler system

Half Heusler alloys, MNiSn (M=Zr, Hf, Ti) systems, have recently been studied for their potential as new thermoelectric materials. They have shown both high thermopower (/spl alpha/) values (40-250 /spl mu/V/K) and reasonable values of electrical resistivity, /spl rho/ (0.1-8 m/spl Omega/-cm). However, the thermal conductivity in these systems is high for a potential thermoelectric material, on the order of 4-10 W/m-K. In an effort to reduce the thermal conductivity through alloy scattering, Sb is substituted on the Sn site with compositions TiNiSn/sub 1-x/Sb/sub x/ where x=0 to 0.1. With this substitution, the thermopower is only slightly reduced while the resistivity is reduced by approximately one order of magnitude resulting in marked improvement in the power factor (/spl alpha//sup 2/T//spl rho/). Thermopower, resistivity, and thermal conductivity have been measured on a series of Sb doped TiNiSn samples from 10 K<T<300 K. Heat capacity and Hall measurements on these same samples are measured from 2 K to 350 K and will be discussed. A room temperature power factor in this system has been calculated to be as high as 1.4 W/m-K, making these materials interesting for potential thermoelectric applications.