Enhanced Thermoelectric Properties of In-Filled Co4Sb12 with InSb Nanoinclusions

Abstract

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)xIn0.5Co4Sb12 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,.