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As a promising class of thermoelectric materials, skutterudites are featured by the naturally formed oversize cages in its crystal lattice. Cage-filling by guest atoms has thus become an important approach to reducing the lattice thermal conductivity and optimizing the thermoelectric performance. To probe the impact of filler atoms on lattice dynamics, we herein reported specific heatmeasurements in two single-filled skutterudite samples In0.2Co4Sb12 and Yb0.2Co4Sb12, and a double-filled skutterudite sample In0.2Yb0.2Co4Sb12. The low temperature specific heat data was analyzed in the context of combined electronic specific heat (the Sommerfeld term), the Debye mode (long wavelength acoustic phonon modes), and the Einstein modes (localized vibration modes). We found that the specific heat difference between the single and double-filled samples can be well accounted by one extra Einstein mode, as expected from the extra filler atom and confirmed by the results of inelastic neutron scatteringmeasurements. Interestingly, two Einstein modes, in addition to the Sommerfeld term and the Debye term, are needed to satisfactorily account for the specific heat of the single-filled sample. The Einstein mode with lower frequency has the frequency close to the low-lying mode reported in La, Ce, Tl single-filled skutterudites, this mode is largely unaffected when the second type of filler atoms is introduced. The frequency of this mode has been verified by inelastic neutron scatteringmeasurement. The other Einstein mode with higher frequency may be originated from the motion of Sb atoms.

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.

Indium-filled CoSb3 skutterudites have been shown previously to have promising thermoelectric properties but the thermal conductivity still remains somewhat high. In order to further decrease the thermal conductivity, the double-filling approach has been adopted using ytterbium, in conjunction with indium, due to its heavy mass and small size. The In0.1YbyCo4Sb12 (y=0.00, 0.05, 0.10, and 0.20) samples have been prepared by a melting method and subsequently characterized by means of electron microscopy, electrical resistivity, Seebeck coefficient, thermal conductivity, and Hall coefficient measurements. The results show that the ytterbium filling effectively decreases the thermal conductivity without degrading the power factor, resulting in an enhancement of the dimensionless figure of merit ZT. A state-of-the-art ZT value of 0.97 is attained in In0.1Yb0.1Co4Sb12 at 750 K.

Starting from elemental In and Se powders, polycrystalline In4Se3 compound samples were synthesized by mechanical alloying (MA) and subsequent hot pressing (HP). The phase evolution during mechanical alloying and the microstructure of the sintered samples were characterized by X-ray diffraction (XRD), differential thermal analysis (DTA) and field emission scanning electron microscope (FE-SEM) respectively. It was found that In4Se3 compound could be synthesized by mechanical alloying of the elemental powders mixture only for 3h. The density and microstructure of In4Se3 compound could be improved by increasing HP temperature or pressure. A maximum power factor of 533μWm-1K-2 was obtained for the In 4 Se 3 sample hot pressed at 450°C under a pressure of 120MPa.

P-type(Bi0.26Sb0.74)2Te3+3%Te ingots were prepared by cooling at various cooling rates after vacuum melting .In this paper, the chemical composition, structure and thermoelectric properties of the crystals were evaluated by XRD, SEM, EDAX and thermoelectric measurements including Seebeck coefficient, electrical conductivity and thermal conductivity. With increase of cooling rates, Te-rich phase presents in the crystals, the electrical conductivity increases and the Seebeck coefficient decreases. While thermal conductivities of all ingots are all lower than 1.3W/mK. The maximum ZT (T=298K) was 1.12, which was obtained in the p-type(Bi0.26Sb0.74)2Te3+3%Te ingot prepared at a cooling rate of 4K/min.