Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom InSb nanoparticles dispersion in Yb-flled Co 4 Sb 12 improves the thermoelectric performance Sanyukta Ghosh a , Sahil Tippireddy a , Gyan Shankar b , Anirudha Karati c , Gerda Rogl d , Peter Rogl d , Ernst Bauer e , Sai Rama Krishna Malladi f , B.S. Murty g , Satyam Suwas b , Ramesh Chandra Mallik a, ⁎ a Thermoelectric Materials and Devices Laboratory, Department of Physics, Indian Institute of Science, Bengaluru 560012, India b Department of Materials Engineering, Indian Institute of Science, Bengaluru 560012, India c Department of Chemistry, Indian Institute of Technology, Madras, Chennai 600036, India d Institute of Materials Chemistry, University of Vienna, A-1090 Wien, Austria e Institute of Solid State Physics, TU-Wien, A-1040 Wien, Austria f Department of Materials Science and Metallurgical Engineering, Indian Institute of Technology, Hyderabad, Telangana 502285, India g Department of Metallurgical and Materials Engineering, Indian Institute of Technology, Madras, Chennai 600036, India article info Article history: Received 16 February 2021 Received in revised form 8 May 2021 Accepted 22 May 2021 Available online 25 May 2021 Keywords: Thermoelectrics Nanocomposite EBSD Lattice thermal conductivity Indium antimonide abstract Out of several methods, one of the most explored strategies to decrease the lattice thermal conductivity of Co 4 Sb 12 -based materials are either flling suitable electropositive elements into the voids or the formation of nanocomposites. These two approaches were combined in this work by flling Yb into the void of Co 4 Sb 12 and preparing nanocomposites of Yb 0.2 Co 4 Sb 12 and InSb according to the formula (InSb) x + Yb 0.2 Co 4 Sb 12 (where x = 0.1, 0.2, 0.3, 0.4), via ball-milling and spark plasma sintering. Yb 2 O 3 and CoSb 2 as impurity phases were found at the grain boundaries. EBSD and TEM micrographs showed nanocrystalline InSb phase (20–200 nm) dispersed in the matrix grains. The charge transfer from Yb fller with an oxidation state of +3 to Co 4 Sb 12 yielded a low electrical resistivity (ρ) of the matrix. An increase in ρ and Seebeck coefcient (S) in the composites with x = 0.1 and 0.3 occurred due to the higher amount of oxide impurities in these two samples and the scattering of charge carriers at the interfaces induced by the secondary phases. The other two composites with x = 0.2 and 0.4 exhibited ρ(T) and S(T) similar to the Yb 0.2 Co 4 Sb 12 matrix. The dis- persion of the InSb and Yb 2 O 3 phases at the grain boundaries combined with the anharmonicity introduced by the fllers (Yb) in the voids enhanced the scattering of phonons within a broad wavelength range and reduced the lattice thermal conductivity signifcantly. Hence, a highest zT of ~1.2 at 773 K with a ther- moelectric efciency of 8.89% and 8.28% (423–773 K) were obtained for (InSb) 0.1 + Yb 0.2 Co 4 Sb 12 and (InSb) 0.2 + Yb 0.2 Co 4 Sb 12 nanocomposites, respectively. © 2021 Elsevier B.V. All rights reserved. 1. Introduction Thermoelectricity provides an alternative source for renewable energy by converting heat into electricity. The efciency of a ther- moelectric material is dependent on the dimensionless quantity called the fgure of merit zT = S 2 T/ρκ, where S is the Seebeck coef- fcient, ρ is the electrical resistivity, κ is the thermal conductivity comprising two parts: the electronic contribution (κ e ) and the lattice contribution (κ L ) (κ = κ e + κ L ); and T is the absolute temperature. zT can be increased by enhancing S and decreasing ρ and κ. The limited efciency of the thermoelectric devices stems from the inter-relation of these three parameters, which makes it difcult and challenging to decouple and optimize them independently. Co 4 Sb 12 -based skutterudite materials are highly efcient mid-tem- perature (300–800 K) thermoelectric materials with high charge carrier mobilities [1] and a reasonable bandgap (~ 0.2 eV) [2–5]. The symmetric crystal structure of Co 4 Sb 12 (body-centered cubic (bcc), space group Im3 ¯ ) produces high band degeneracy [6], which is helpful for high thermoelectric efciency. But, the high lattice thermal conductivity (~7.5 W/m-K at room temperature) due to a strong Co-Sb covalent bonding results in a very low zT value (0.05 at 723 K) and a low ther- moelectric efciency [7]. Slack et al. [8] proposed the “phonon-glass- electron-crystal” concept, which suggests flling voids at the 2a Wyckoff position in the Co 4 Sb 12 crystal structure by electropositive elements to https://doi.org/10.1016/j.jallcom.2021.160532 0925-8388/© 2021 Elsevier B.V. All rights reserved. ]] ]] ]]]]]] ⁎ Corresponding author. E-mail address: rcmallik@iisc.ac.in (R.C. Mallik). Journal of Alloys and Compounds 880 (2021) 160532