A. Dauscher

Beneficial effect of Ni substitution on the thermoelectric properties in partially filled CayCo4−xNixSb12 skutterudites

We have investigated the influence of nickel doping in a series of n-type CoSb{sub 3} skutterudite materials partially filled with Ca. The electrical resistivity, thermopower, and thermal conductivity have been measured in the 300-800 K temperature range on Ca{sub y}Co{sub 1-x}Ni{sub x}Sb{sub 12} compounds prepared by a powder metallurgy route. The chemical composition and structure have been analyzed by electron probe microanalyses and x-ray diffraction, respectively. It was found that the presence of nickel substantially decreases the electrical resistivity without any detrimental effect on the thermopower, resulting in an improvement of the power factor. The dimensionless thermoelectric figure ZT increases with increasing temperature and reaches a maximum value of 1 at 800 K.

Promising thermoelectric properties in AgxMo9Se11 compounds (3.4 ≤ x ≤ 3.9)

Polycrystalline Mo9 cluster chalcogenides AgxMo9Se11 (3.4≤x≤3.9) have been prepared by powder metallurgy techniques, sintered by spark plasma sintering and characterized by x-ray diffraction. Their thermoelectric properties (electrical resistivity, thermopower, thermal conductivity) have been determined in the 300–800 K temperature range. The AgxMo9Se11 compounds show p-type conduction characteristics. The outstanding low lattice thermal conductivities give rise to a rather high value of the dimensionless thermoelectric figure of merit ZT of ∼0.65 at 800 K for x=3.8–3.9, making this family of materials particularly promising for thermoelectric power generation applications.

Influence of Ni impurities on the thermoelectric properties of Ca-partially filled skutterudites CaxCo4Sb12

Polycrystalline samples of the skutterudite compounds CaxCo4Sb12 were synthesized and investigated by means of electrical resistivity, thermal conductivity, and thermopower in the 300–800 K temperature range. Additional Hall effect measurements were performed between 2 and 300 K. Both Ni-free and Ni-containing Co powders were used as starting materials to elucidate the impact of Ni impurities at the ppm level on the thermoelectric properties. The presence of minute amounts of Ni atoms in the crystal structure leads to enhanced thermopower values with respect to the Ni-free samples, likely associated with the development of additional electron pockets near the Fermi level. Ni impurities, thus, play a significant role on the transport properties and lead to a spectacular increase in the dimensionless thermoelectric figure of merit ZT of up to 150% at 800 K.

Beneficial influence of Ru on the thermoelectric properties of Mo3Sb7

Zintl phases have recently been identified as potential thermoelectric materials typified by the discovery of a high thermoelectric figure of merit in the Yb14MnSb11 compound above 1000 K. We report on the synthesis and the thermoelectric properties measurements over a wide temperature range (300–1000 K) of other Zintl phases exhibiting a complex crystalline structure, namely, Mo3Sb7 and its related compounds Mo3−xRuxSb7. While the binary compound displays low figure of merit values due to its metallic nature, we show that the partial substitution of Mo by Ru significantly improves its value to reach 0.45 at 1000 K in Mo2.2Ru0.8Sb7.

High thermoelectric power factor in Fe-substituted Mo3Sb7

Thermoelectric properties of the Mo2.57Fe0.43Sb7 compound, a ternary derivative of Mo3Sb7, are reported from 2 up to 1000 K. Even though Fe substitution keeps low electrical resistivity values, high thermopower values are achieved at high temperatures. Electronic band structure calculations show that the high thermopower observed arises from the beneficial influence of iron d-states contribution to the density of states at the Fermi level. A high power factor similar to those of the best state-of-the-art thermoelectric materials emerges which, coupled with magnetic excitations that help to keep very low thermal conductivity values, leads to a dimensionless thermoelectric figure of merit of 0.55 at 1000 K.

Transport and magnetic properties of Mo2.5Ru0.5Sb7−xTex

Transport properties including electrical resistivity, thermopower, and thermal conductivity of polycrystalline Mo2.5Ru0.5Sb7−xTex compounds for 0≤x≤1 have been investigated in the 2–1000 K temperature range. Additional information on the concentrations and the scattering mechanisms of the charge carriers as well as on the magnetic properties has been obtained through Hall effect and magnetic susceptibility measurements performed in the 5–300 K temperature range. The enhancement in the Te content results in a decrease in the carrier concentration which is at the origin of the simultaneous increase in the electrical resistivity and thermopower. A single parabolic band model with acoustic phonon scattering enables to explain the compositional and temperature dependence of the thermopower while such a simple model fails to adequately describe the electronic thermal conductivity. This characteristic together with the unusual dependence of the thermal conductivity upon alloying might be a direct consequence of...

Thermoelectric Properties of BixSbyTezSew Nanocomposite Materials

Nanopowders of n-type (Bi0.95Sb0.05)2(Te0.95Se0.05)3 and p-type (Bi0.2Sb0.8)2Te3 have been synthesized by laser fracture of micron-sized powders in water. These alloys are the best conventional thermoelectric materials for use in room temperature applications. The nanopowders have been characterized by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The nanopowders have been mechanically mixed in different ratios with the micron sized powders. These mixtures have then been cold pressed in order to perform thermoelectric characterization and to see the influence of nano-particle inclusions on the transport properties.

Reducing Thermal Effect on Thermoelectric Thin Films Fabrication Using Mechanical Chopper Coupling with CO2 Laser Ablation

The aim of this experiment was to use mechanical chopper coupling with CO2 laser ablation to reduce thermal effect on thermoelectric thin film fabrication. The average power at 10 W of sealed tube CO2 laser together with the mechanical chopper was used for the thermoelectric (TE) thin film fabrication on silicon substrate in vacuum system. The 1.02 ms of pulse duration with 600 Hz of repetition rate were generated by the optimized speed of chopper at 4500 rpm with 8 channels of circular apertures which were used for the reduction of thermal effect on the bismuth antimony telluride (Bi-Sb-Te) target. The experiment results illustrated the thickness and the thin films fabricated by using 10 seconds of exposure time with the chopper, illustrated the smaller grain size than without the chopper while the thickness increased as the exposure time increased at constant speed of chopper. The output efficiency referred to the ratio of the thickness per target lost in unit time which increased from 19.6 to 181.8 μm/g per hour, due to the increase of the exposure time with the chopper while without the chopper resulted in 55.0 μm/g per hour caused by the higher temperature raise on the thermoelectric target which affected to the as-deposited thin films and the re-evaporation occurred. In this experiment, the chopper speed was measured by the digital tachometer, the target loss was analyzed by the digital analytical balance and the morphology of the 600 tilted surface of thin film was characterized by scanning electron microscope (SEM).

Thermoelectric properties of the new skutterudites (Ce-Yb)/sub y/Fe/sub 4-x/(Co/Ni)/sub x/Sb/sub 12/

Polycrystalline p-type and n-type skutterudites belonging to the family (Ce-Yb)/sub y/Fe/sub 4-x/(Co/Ni)/sub x/Sb/sub 12/ have been synthesized using a standard arc-melting method and subsequent annealing. They have been characterized using X-ray diffraction (XRD) and electron probe microanalysis (EPMA). Yb valence state was estimated using X-ray absorption spectroscopy (XAS) at the Yb L/sub 3/ edge which evidences an evolution of the Yb mixed valence state in the various series. Thermoelectric properties have been investigated between 120K and 800K by mean of thermopower and electrical conductivity measurements.