J.L. Mi

Nanostructuring and thermoelectric properties of bulk skutterudite compound CoSb3

Thermoelectric properties of nanostructured skutterudite CoSb3 have been reported. Nanosized CoSb3 powders were synthesized through a solvothermal route. The bulk materials with average grain sizes of 250 and 150nm were prepared by hot pressing and spark plasma sintering from the solvothermally synthesized CoSb3 powders. Both the samples show n-type conduction and the thermal conductivities are reduced compared with that of the sample prepared by the melt-annealing∕hot pressing method. A thermoelectric figure of merit of 0.61 has been obtained for the unfilled CoSb3 skutterudite by spark plasma sintering, which indicates that nanostructuring is an effective way to improve the thermoelectric properties of skutterudite compounds.Thermoelectric properties of nanostructured skutterudite CoSb3 have been reported. Nanosized CoSb3 powders were synthesized through a solvothermal route. The bulk materials with average grain sizes of 250 and 150nm were prepared by hot pressing and spark plasma sintering from the solvothermally synthesized CoSb3 powders. Both the samples show n-type conduction and the thermal conductivities are reduced compared with that of the sample prepared by the melt-annealing∕hot pressing method. A thermoelectric figure of merit of 0.61 has been obtained for the unfilled CoSb3 skutterudite by spark plasma sintering, which indicates that nanostructuring is an effective way to improve the thermoelectric properties of skutterudite compounds.

Improved thermoelectric figure of merit in n-type Cosb3 based nanocomposites

Nanocomposites offer a promising approach to incorporate nanostructured constituents to bulk thermoelectric materials. n-type CoSb3 nanocomposites were prepared by hot pressing the mixture of nanoscale and microsized CoSb3 powders synthesized by solvothermal method and melting, respectively. Microstructure analysis shows that the bulk materials are composed of nano- and micrograins. The nanocomposite structures are effective in reducing thermal conductivity more than electrical conductivity, hence in improving the thermoelectric performance. A dimensionless figure of merit of 0.71 is obtained for the nanocomposite with 40wt% nanopowder inclusions, about 54% increase of that without nanopowder inclusions.

Thermoelectric properties of Yb0.15Co4Sb12 based nanocomposites with CoSb3 nano-inclusion

Bulk skutterudite nanocomposites of Yb filled cobalt antimonide, Yb0.15Co4Sb12, with different contents of CoSb3 nano-inclusion were prepared by spark plasma sintering. The nanocrystals in the bulk composites are less than 100 nm. The Seebeck coefficient is enhanced by potential barrier scattering with the incorporation of a small number of CoSb3 nanoparticles into the bulk materials, but is reduced with a further increase in the content of nanoparticles. Though the nano-inclusion is the unfilled CoSb3, it is effective in reducing thermal conductivity. The figure of merit reaches a maximum of 0.9 for both the nanocomposites with 5% and 10% CoSb3 nano-inclusions, an increase of about 10% compared with the Yb0.15Co4Sb12 matrix. It still exhibits good thermoelectric performance after long-time annealing at 773 K for the nanocomposite due to the improved phase purity and almost unchanged nanostructure.

Thermoelelctric properties of nanostructured skutterudite-related compounds

Nanostructuring is one of the effective approaches to lower the thermal conductivity of materials. Nanostructured skutterudite-related compounds CoSb₃, Fe_0.5Ni_0.5Sb₃, Fe_0.25Ni_0.25Co_0.5Sb₃ and Te-doped CoSb₃ were synthesized by a solvothermal route. The bulk materials were prepared by hot pressing or spark plasma sintering from the solvothermally synthesized nanopowders. The thermal conductivity values of the materials are decreased, which is mainly contributed to the small grain sizes and the high porosity. A thermoelectric figure of merit of 0.61 has been obtained for CoSb₃, which is notably high for the unfilled skutterudites. Filled skutterudites La_0.3Co₄Sb₁₂ and La_0.3FeCo₃Sb₁₂ were also synthesized by solvothermally process followed by annealing under hydrogen atmosphere. The thermoelectric properties are presented and discussed.