The uniform dispersion of nanoparticles in bulk materials is one of the promising ways of enhancing thermoelectric properties through increased phonon scattering at the interfaces. The influence of InSb nanoparticles on the thermoelectric properties of bulk In0.5Co4Sb12 was investigated in the temperature range of 373–723 K. InSb was mixed with In0.5Co4Sb12 via a high-energy ball-milling method, and the composite powder was compacted by a spark plasma sintering technique. The X-ray diffraction was carried out on the sintered pellets of the matrix, which showed the formation of skutterudite structure with impurity phase of CoSb2. Single-phase skutterudite structure was observed for (InSb) x In0.5Co4Sb12 with lower InSb content (x ≤ 0.3). An InSb secondary phase was detected for the sample with x > 0.3. Scanning electron micrographs showed the existence of CoSb2, InSb, and In2O3 secondary phases in the matrix; partially oxidized InSb phase and In2O3 phase in the composite samples which were verified using electron probe micro analyzer. The presence of the In2O3 phase in the samples indicates oxidation of In during the synthesis of the parent compound. The electron back scattered diffraction showed bimodal grain size distribution of matrix phase. Submicrometer-sized InSb precipitates and uniform distribution of InSb nanoparticles inside the matrix grains were observed. The X-ray photoelectron spectroscopy showed covalent bonding between Co and Sb and +1 oxidation state of In inside the voids. Raman spectra revealed the distortion of Sb4 ring due to In-filling. At room temperature, an increase in the Seebeck coefficient (S) was observed in nanocomposites compared to In0.5Co4Sb12 because of the energy-filtering effect of the charge carriers. The addition of InSb nanoparticles in the matrix decreased the electrical conductivity (σ) because of the scattering of charge carriers at the interfaces. The thermal conductivity (κ) of the composite samples decreased significantly because of enhanced phonon scattering at the interfaces. These combined effects resulted in the maximum figure of merit of 1.1 at 723 K for (InSb)0.2In0.5Co4Sb12.

The dispersion of GaSb and InSb nanoinclusions in In-filled Co4Sb12 results in low lattice thermal conductivity and high thermoelectric performance.

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The thermoelectric efficiency of skutterudite materials can be improved by lowering the lattice thermal conductivity via the uniform dispersion of a nanosized second phase in the matrix of filled Co 4 Sb 12 . In this work, nanocomposites of Ba 0.3 Co 4 Sb 12 and InSb were synthesized using ball-milling and spark plasma sintering. The thermoelectric transport properties were studied from 4.2 to 773 K. The InSb nanoparticles of ∼20 nm were found to be dispersed in the Ba 0.3 Co 4 Sb 12 grains with a few larger grains of about 10 μm due to the agglomeration of the InSb nanoparticles. The +2 oxidation state of Ba in Co 4 Sb 12 resulted in a low electrical resistivity, ρ, value of the matrix. The enhancement of the Seebeck coefficient, S, and the electrical resistivity values of Ba 0.3 Co 4 Sb 12 with the addition of InSb can be credited to the energy-filtering effect of electrons with low energy at the interfaces. The power factor of the composites could not be enhanced compared to the matrix because of the very high ρ value. A minimum possible lattice thermal conductivity (0.45 W/m•K at 773 K) was achieved due to the combined effect of rattling of Ba atoms in the voids and enhanced phonon scattering at the interfaces induced by nanosized InSb particles. As a result, the (InSb) 0.15 + Ba 0.3 Co 4 Sb 12 composite exhibited improved thermoelectric properties with the highest zT of 1.4 at 773 K and improved mechanical properties with a higher hardness, higher Young's modulus, and lower brittleness.

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