Papers by Keyword: Skutterudite

Abstract: The organic/inorganic hybrid sol was prepared by hydrolysis polymerization of methyl-triethoxysilane (MTES) with acidic silica sol. Zirconium silicate, zircon sand and refractory fiber were respectively added to the hybrid sol to increase the stability of the coating in high temperature service. P-type skutterudite(SKD) protective coating obtained by multi-layer coating and certain pretreatment. Protective effect was studied by observing the diffusion of antimony from the SKD into the coating. The results show that the coating has the advantages of simple process and high strength and high stability after aging. The sublimation of antimony is suppressed and it is expected to be applied to the protection of SKD in vacuum.

Abstract: We have succeeded in synthesizing new arsenic-based filled skutterudite compounds CaFe₄As₁₂ and BaOs₄As₁₂ under high pressure. These compounds have lattice constants of 8.3288 and 8.5809 Å, respectively. The magnetic properties of CaFe₄As₁₂ and BaOs₄As₁₂ have been studied by means of electrical resistivity, magnetic susceptibility and magnetization measurements. The electrical resistivity and magnetic measurements indicate that CaFe₄As₁₂ is a nearly ferromagnetic metal with spin fluctuations of Fe 3d electrons and BaOs₄As₁₂ is a new superconductor with a transition temperature around 3 K.

Abstract: Skutterudites are an important class of thermoelectric p- and n-type materials and they have already achieved fair efficiencies for the conversion of heat to electricity. Nevertheless researchers try to further enhance the figure of merit, ZT, by various ways. In this work we study microstructure and mechanical properties of two thermoelectric materials: an industrial n-type (Mm,Sm)_yCo₄Sb₁₂ skutterudite and an industrial p-type DD_yFe₃CoSb₁₂ skutterudite, both mixed with 1 wt.% of Ta_0.8Zr_0.2B. Thin lamellae were prepared from the compacted materials using a focused ion beam. Analytical transmission electron microscopy was used on lamellae to study details of microstructure. A fine dispersion of precipitates was found both at nanograin boundaries and in their interiors. Quasistatic and dynamic nanoindentation tests were carried out on planar polished sections in the range of applied loads from 0.01 to 10 mN. The results were complemented with quantitative modulus mapping of local mechanical properties with 10-nm resolution.

Abstract: A DFT study of H⁺ effect on CoO(0 1 0) surface was carried out. What could be seen from the inter atomic distance and the density of states (DOS) was: Co-O bonds were broken strongly and H-O bonds formed strongly when one H⁺ was adsorbed on the O atom, and Co-O bonds were not broken and H-O bond not formed strongly when two H⁺ were adsorbed on the O atom, so the Skutterudite acid leaching process cannot be described as two H⁺ were adsorbed on the O atom and formed the H₂O molecules to enter the solution. But that can be described as one H⁺ was adsorbed on the O atom and formed the OH^- to enter the solution, the OH^- was combined with the H⁺ in the solution to form the H₂O molecule.

Abstract: We have developed a manufacturing system by combination of high-pressure synthesis method using a multi-anvil press, and spark plasma sintering (SPS) method. By means of the system, we have succeeded in synthesizing new filled skutterudite-type thermoelectric materials Mm_xCo₄Sb₁₂ (Mm=mischmetal). The thermoelectric properties of partially filled skutterudite compounds Mm_xCo₄Sb₁₂ synthesized under high pressure have been investigated. The Seebeck coefficient of Mm_xCo₄Sb₁₂ shows negative value, which means n-type conductivity. The highest dimensionless figure of merit ZT value is 0.25 for Mm_0.6Co₄Sb₁₂ at 700 K.

Abstract: Thin films of Yb filled CoSb₃ were prepared on fused silica substrates using pulsed laser deposition method. The stoichiometric Yb_0.19Co₄Sb₁₂ target was prepared by hot pressing method. The deposition conditions were changed with the goal to reach layers of smooth morphology. The target-to substrate distance was kept equal to 4 cm. The ambient argon pressure moved from 0.5 Pa to 13 Pa, laser repetition rate from 3 Hz to 10 Hz, and substrate temperature from 250 °C to 400 °C. We tested laser fluencies from 0.8 J·cm^-2 to 5 J·cm^-2. Films roughness was determined by mechanical profilometer and by atomic force microscopy. The lowest roughness of about 5 nm – 10 nm was reached for low laser fluencies but mechanical quality of films was poor and growth rate low (about 0.1 A/pulse). From WDX analysis follows that there is an excess of Yb and Sb compared to Yb_0.19Co₄Sb₁₂ target.

Abstract: In order to increase the electrical conductivity greatly but maintain a large Seebeck coefficient and a low thermal conductivity simultaneously, the binary-phased LaCeFe₃CoSb₁₂-Sb nanocomposites composed of LaCeFe₃CoSb₁₂ skutterudite nanospheres and semimetal Sb microsized ribbons were fabricated via a hydro/solvo thermal route. The results suggest that the Sb powders result in a disordered structure during a hot-press process at its melting-point temperature and the disordered structure has been partly preserved into the room-temperature materials successfully. The Sb microsized ribbons enhance the electrical conductivity of the binary-phased materials largely, meanwhile the disordered structure increases the Seebeck coefficient obviously even though the thermal conductivity is also increased slightly. Consequently, the figure of merit of the binary-phased materials is improved significantly and the maximum value of 1.54 at 773 K has been realized for the LaCeFe₃CoSb₁₅ material.

Abstract: In_0.25Co_4-xNi_xSb₁₂ skutterudites were synthesized by encapsulated induction melting and consolidated by hot pressing, and their thermoelectric properties were examined at temperatures from 323 to 823 K. A single δ-phase was obtained successfully by subsequent heat treatment at 823 K for 24 h. In_0.25Co_4-xNi_xSb₁₂ was an n-type semiconductor at all temperatures examined, indicating that Ni atoms acted as electron donors by substituting for Co atoms. The thermal conductivity was reduced considerably by In filling and Ni doping due to an increase in phonon scattering and impurity scattering. The thermoelectric properties were improved due to the low thermal conductivity as a result of In filling and the optimum carrier concentration caused by Ni doping.

Abstract: Co_4-xFe_xSb_12-ySn_y skutterudites were synthesized by mechanical alloying and hot pressing, and thermoelectric properties were examined. The carrier concentration increased by doping and thereby the electrical conductivity increased compared with intrinsic CoSb₃. Every specimen had a positive Seebeck coefficient. Fe doping caused a decrease in the Seebeck coefficient but it could be enhanced by Fe/Sn double doping possibly due to charge compensation. The thermal conductivity was desirably very low and this originated from ionized impurity-phonon scattering. Thermoelectric properties were improved remarkably by Fe/Sn doping, and a maximum figure of merit, ZT = 0.5 was obtained at 723 K in the Co₃FeSb_11.2Sn_0.8 specimen.

Abstract: It is the important way to improve thermoelectric properties of skutterudite materials by doping with rare earth elements. The mechanisms of improving properties of bulk RE_xCo₄Sb₁₂ materials prepared by mechanical alloy and spark plasma sintering (MA-SPS) at 650°C were investigated by analyzing the composition, microstructure and atomic occupying locations. According the results it can be considered that the mechanism to improve the thermoelectric properties of rare earth elements is that rare earth element Ce in the samples mainly plays the doping role in reducing the resistivity of the sample and improving the conductivity, so that it makes the figure of merit ZT of samples increase significantly.