materials Article Thermoelectric Performance of Mechanically Mixed Bi x Sb 2-x Te 3 —ABS Composites Zacharias Viskadourakis 1, * , Argiri Drymiskianaki 2 , Vassilis M. Papadakis 1 , Ioanna Ioannou 3 , Theodora Kyratsi 3 and George Kenanakis 1, *   Citation: Viskadourakis, Z.; Drymiskianaki, A.; Papadakis, V.M.; Ioannou, I.; Kyratsi, T.; Kenanakis, G. Thermoelectric Performance of Mechanically Mixed Bi x Sb 2-x Te 3 —ABS Composites. Materials 2021, 14, 1706. https://doi.org/10.3390/ma14071706 Academic Editors: Andres Sotelo and Christof Schneider Received: 25 February 2021 Accepted: 26 March 2021 Published: 30 March 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Institute of Electronic Structure and Laser (IESL)—Foundation for Research and Technology—Hellas (FORTH), 100 N. Plastira, Vassilika Vouton, GR-70013 Heraklion, Crete, Greece; billyp@iesl.forth.gr 2 Physics Department, University of Crete, Vassilika Vouton, GR-70013 Heraklion, Crete, Greece; ph4055@edu.physics.uoc.gr 3 Department of Mechanical & Manufacturing Engineering, University of Cyprus, 75 Kallipoleos Ave., P.O. Box 20537, Nicosia 1678, Cyprus; gianna1992@live.com (I.I.); kyratsi@ucy.ac.cy (T.K.) * Correspondence: zach@iesl.forth.gr (Z.V.); gkenanak@iesl.forth.gr (G.K.) Abstract: In the current study, polymer-based composites, consisting of Acrylonitrile Butadiene Styrene (ABS) and Bismuth Antimony Telluride (Bi x Sb 2−x Te 3 ), were produced using mechanical mixing and hot pressing. These composites were investigated regarding their electrical resistivity and Seebeck coefficient, with respect to Bi doping and Bi x Sb 2-x Te 3 loading into the composite. Experimental results showed that their thermoelectric performance is comparable—or even superior, in some cases—to reported thermoelectric polymer composites that have been produced using other complex techniques. Consequently, mechanically mixed polymer-based thermoelectric materials could be an efficient method for low-cost and large-scale production of polymer composites for potential thermoelectric applications. Keywords: thermoelectric materials; Bismuth Antimony Telluride; Seebeck coefficient; polymer- thermoelectric material blends; polymeric nanocomposites 1. Introduction In the last decade, thermoelectric (TE) materials have gained considerable attention in waste heat recovery applications due to their capability to convert heat to electricity utilizing the Seebeck effect. The performance of a TE material can be determined through the thermoelectric figure of merit Z − ZT = S 2 T/κρ—where S is the Seebeck coefficient, κ is thermal conductivity, ρ is electrical resistivity, and T is the absolute temperature. Moreover, thermal conductivity consists of two parts: an electronic one and another one coming from the lattice (phononic), so that κ = κ el + k l , where κ el is the electronic component and κ l is the lattice component. Thus, an efficient thermoelectric material appropriate for commercial applications (ZT > 1) must exhibit high S, along with low κ and ρ. However, all three physical parameters are interrelated such that materials with high Seebeck coefficient values usually also exhibit high resistivity, and materials with low resistivity show a low Seebeck coefficient, leading to reduced ZT values. On the other hand, low resistivity materials usually exhibit a high charge carrier concentration, which results in increased thermal conductivity because high carrier concentration increases the electronic thermal conductivity. Due to this diverging interconnection among S, ρ, and κ, the realization of high ZT materials becomes challenging, since fine optimization between those three quantities is required [1]. Today, state-of-the-art thermoelectrics are mostly inorganic materials, such as tellurides, oxides, skutterudites, half-Heusler alloys, silicon–germanium composites, etc. [2–4]. All these materials exhibit ZT > 1 at a specific temperature regime, and they are all used in Materials 2021, 14, 1706. https://doi.org/10.3390/ma14071706 https://www.mdpi.com/journal/materials