Narrow Results

Pt₄Sn_4.4Sb_7.6 (a = 9.3304(2) Å, space group ) is an unfilled skutterudite member of the solid solution Sn_xPt₄Sn_ySb_12-x. In contrast to Sn_xNi₄Sn_ySb_12-y and Sn_xPt₄Sn_ySb_12-x no Sn could be found in the 2a sites of the Sn/Sb framework. Physical properties have been data for Ni₄Sn₃Sb₉ and Ni₄Sn_3.5Sb_8.5. Resistivity measurements for Pt₄Sn_4.4Sb_7.6 reveal a temperature dependent crossover from metallic to semiconducting behaviour connected with a corresponding change from negative to positive thermopower at 30 K. Vicker's hardness, thermal expansion and elastic moduli compare well with values of other Sb- investigated in the temperature range from 4.2 K to 800 K and have been compared with based skutterudites.

In_xCo₄Sb₁₂ skutterudite compounds have been prepared successfully at different synthesis pressures by high pressure and high temperature (HPHT) method, the processing time has been reduced from a few days to half an hour. In addition, the effect of synthesis pressure on the thermoelectric properties of In_0.4Co₄Sb₁₂ compounds has been investigated in this paper. The structure of In_0.4Co₄Sb₁₂ samples was evaluated by means of X-ray diffraction and scanning electron microscopy (SEM). The Seebeck coefficient, electrical resistivity and thermal conductivity were all measured in the temperature range of room temperature to 673 K. The sample synthesized at 2.0 GPa showed the highest power factor of 29.3 μWcm^-1K^-2 at 373 K. A dimensionless thermoelectric figure of merit (ZT) of 0.51 at 673 K was achieved for n-type In_0.4Co₄Sb₁₂ prepared at 1.3 GPa, which was significantly enhanced in comparison with pure CoSb₃.

A novel chemical alloying method of high-pressure and high-temperature (HPHT) has been used for the synthesis of bulk-skutterudite ${\mathrm{\text{In}}}_{0.5}{\mathrm{\text{Co}}}_4{\mathrm{\text{Sb}}}_{11.5}{\mathrm{\text{Te}}}_{0.5}$. Through HPHT method, the synthesis time has been shortened from a few days to 30min. The samples of ${\mathrm{\text{In}}}_{0.5}{\mathrm{\text{Co}}}_4{\mathrm{\text{Sb}}}_{11.5}{\mathrm{\text{Te}}}_{0.5}$ skutterudites were synthesized at 1.8–3.3GPa. We have studied the phase, the microstructure, and the temperature-dependent thermoelectric properties. The Seebeck coefficient, electrical conductivity and thermal conductivity were measured in the temperature range of 295–673K. As we expected, the thermal conductivity of sample ${\mathrm{\text{In}}}_{0.5}{\mathrm{\text{Co}}}_4{\mathrm{\text{Sb}}}_{11.5}{\mathrm{\text{Te}}}_{0.5}$ decreased with the increase of the synthetic pressure. A maximal ZT of 0.64 was achieved for the ${\mathrm{\text{In}}}_{0.5}{\mathrm{\text{Co}}}_4{\mathrm{\text{Sb}}}_{11.5}{\mathrm{\text{Te}}}_{0.5}$ synthesized at 1.8GPa at 673K. These results revealed that HPHT method may be helpful for optimizing electrical conductivity and thermal conductivity in a comparatively independent way.

The skutterudite CoSb${}_{2.75}$Te${}_{0.20}$Sn${}_{0.05}$ compound was synthesized successfully by high pressure and high temperature (HPHT) method using Co, Sb, Te and Sn powder as raw materials. The effects of pressure on its structure and the thermoelectric properties are investigated systematically from 300 K to 800 K. The electrical resistivity and the absolute value of the Seebeck coefficient for the sample increases with rising synthetic pressure. The thermal conductivity of the sample decreases with synthetic pressure and temperature rising in the range of 300–800 K. In this study, the maximum dimensionless figure of merit (ZT) value of 1.17 has been achieved at 793 K, 3 GPa for this thermoelectric material.

The polycrystalline skutterudite ${\mathrm{\text{Ba}}}_{0.2}{\mathrm{\text{Co}}}_4{\mathrm{\text{Sb}}}_{11.5}{\mathrm{\text{Te}}}_{0.5}$ were successfully synthesized from 1.5 GPa to 3.5 GPa by the high pressure and high temperature (HPHT) method. Negative Seebeck coefficient confirmed the n-type conductivity of all samples. The phase compositions of samples were investigated by X-ray diffraction (XRD) and the microstructures were observed by scanning electron microscopy (SEM). It was found that the grains appeared smaller and the grain boundaries became more abundant when pressures were higher. We measured the electrical properties from room temperature to 723 K. Both the electrical resistivity and absolute value of Seebeck coefficient increase with the increasing synthetic pressure. At 723 K, the maximum power factor of $20.6\mu {\mathrm{\text{Wcm}}}^{-1}{\mathrm{\text{K}}}^{-2}$ was obtained for the sample synthesized under 3 GPa. The maximum ZT value of 0.61 was reached by ${\mathrm{\text{Ba}}}_{0.2}{\mathrm{\text{Co}}}_4{\mathrm{\text{Sb}}}_{11.5}{\mathrm{\text{Te}}}_{0.5}$ synthesized under 3 GPa and measured at 723 K.

Electronegative S-filled skutterudite compounds have attracted considerable attention due to scattering of low-frequency phonons (35–50cm${}^{-1}$), but there are few reports on S-filled double-substituted skutterudite. In this work, a series of S-filled Te-Sn double-substituted skutterudite compounds were synthesized using high pressure and high temperature (HPHT) method. The phase composition, microstructure, and thermoelectric properties of S_xCo₄Sb${}_{11}$Te${}_{0.7}$Sn${}_{0.3}$ ($x=0$, 0.05, 0.10, 0.20) samples were systematically determined. The results show that the introduction of S increases the substitution limit of Te in the Sb site. Under the combined effect of the sample synthesis pressure and S filling, the nucleation density of the sample grains increases and the grain size decreases. At the same time, there are numerous special microstructures in the samples synthesized in a high-pressure environment. Thermoelectric performance studies show that a small amount of S filling optimizes the Seebeck coefficient of the sample and increases the power factor (PF). With an increase of the amount of S introduced, the thermal conductivity of the samples decreases significantly. Therefore, the maximum zT value of an S${}_{0.05}$Co₄Sb${}_{11}$Te${}_{0.7}$Sn${}_{0.3}$ sample synthesized at 2.5GPa pressure is 0.17 at room temperature. The maximum zT value of the sample is 1.26 at 773K.

In this paper, a series of S${}_{0.05}$Co₄Sb${}_{11.6}$Te${}_{0.4}$ samples were prepared by high pressure and high temperature (HPHT) method under different pressures. The synthesis time was shortened from several days to 0.5 h. Te doping and S filling simultaneously optimized the thermal and electrical transport properties of the CoSb₃ materials. We found a porous architecture containing rich grain boundaries, different grain sizes, nano- to micrometer-sized pores, and a large number of dislocations, which can scatter a wide spectrum of phonons. Seebeck coefficient $\alpha$, electrical resistivity $\rho$, and thermal conductivity $\kappa$ were measured between 295 K and 773 K. The minimum thermal conductivity of S${}_{0.05}$Co₄Sb${}_{11.6}$Te${}_{0.4}$ synthesized at 3.0 GPa was 1.23 Wm${}^{-1}$ K${}^{-1}$, and its maximum zT value reached 1.07 at 773 K, especially the lattice thermal conductivity was as low as 0.49 Wm${}^{-1}$ K${}^{-1}$.

We prepared In_xPb_xCo₄Sb${}_{12}$ by high-pressure and high-temperature (HPHT) method. Samples were characterized by X-ray diffraction (XRD), electron microprobe analysis and thermoelectric properties measurements. The Seebeck coefficient, electrical resistivity and thermal conductivity of In_xPb_xCo₄Sb${}_{12}$ samples were all performed in the temperature range of 323–723K. With the increasing synthetic pressure, the Seebeck coefficient of In${}_{0.5}$Pb${}_{0.1}$Co₄Sb${}_{12}$ samples, which synthesized between 1.5 GPa–2.3 GPa, showed an obvious increase while the thermal conductivity exhibited a substantial reduction.

Interfacial diffusions and/or chemical reactions are one of the key issues for the reliability of CoSb₃-based skutterudite thermoelectric (TE) joint, especially for the $p$-type joint, which limits the applications of TE devices. We investigate the interfacial evolution for $p$-type Ce_yFe_xCo${}_{4-x}$Sb${}_{12}$/Nb joints ($y=0.5$–1, $x=2$, 3, 4) and combine the previous study on $n$-type Yb${}_{0.3}$Co₄Sb${}_{12}$/Nb joint to demonstrate the effect of TE materials on the interfacial microstructure and interfacial resistivity. The reaction–diffusion kinetic analysis shows that the TE materials has little effect on chemical reactions but strongly influence the Sb diffusions. The low energy barrier of Sb diffusion leads to the absent phase decomposition of skutterudites in Ce_yFe_xCo${}_{4-x}$Sb${}_{12}$/Nb joints. The interfacial resistivity of Ce_yFe_xCo${}_{4-x}$Sb${}_{12}$/Nb joints is related with Fe content and the interfacial reaction layer (IRL) growth. In addition, since the interfacial reaction layer growth rate and interfacial resistivity of Ce_yFe_xCo${}_{4-x}$Sb${}_{12}$/Nb joints are both low, Nb is an adequate barrier layer candidate material.