Low thermal conductivity in La-filled cobalt antimonide skutterudites with an inhomogeneous filling factor prepared under high-pressure conditionsElectronic supplementary information (ESI) available: SXRD and XRD Rietveld refinement data and thermoelectric properties of different sample batches. See DOI: 10.1039/c7ta08545a

• Main Authors: Serrano-Sánchez, F, Prado-Gonjal, J, Nemes, N. M, Biskup, N, Varela, M, Dura, O. J, Martínez, J. L, Fernández-Díaz, M. T, Fauth, F, Alonso, J. A
• Format: Journal Article
• Language: English
• Published: 19.12.2017
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/c7ta08545a

La-filled skutterudites La x Co 4 Sb 12 ( x = 0.25 and 0.5) have been synthesized and sintered in one step under high-pressure conditions at 3.5 GPa in a piston-cylinder hydrostatic press. The structural properties of the reaction products were characterized by synchrotron X-ray powder diffraction, clearly showing an uneven filling factor of the skutterudite phases, confirmed by transmission electron microscopy. The non-homogeneous distribution of La filling atoms is adequate to produce a significant decrease in lattice thermal conductivity, mainly due to strain field scattering of high-energy phonons. Furthermore, the lanthanum filler primarily acts as an Einstein-like vibrational mode having a strong impact on the phonon scattering. Extra-low thermal conductivity values of 2.39 W m −1 K −1 and 1.30 W m −1 K −1 are measured for La 0.25 Co 4 Sb 12 and La 0.5 Co 4 Sb 12 nominal compositions at 780 K, respectively. Besides this, lanthanum atoms have contributed to increase the charge carrier concentration in the samples. In the case of La 0.25 Co 4 Sb 12 , there is an enhancement of the power factor and an improvement of the thermoelectric properties. La-filled skutterudites with an inhomogeneous filling factor synthesized by high pressure exhibit a remarkably low lattice thermal conductivity.