Synthesis and thermoelectric performance of a p-type Bi 0.4 Sb 1.6 Te 3 material developed via mechanical alloying Sandra Jimenez a , Jose G. Perez a,⇑ , Terry M. Tritt b , Song Zhu b , Jose L. Sosa-Sanchez a , Javier Martinez-Juarez a , Osvaldo López c a Centro de Investigaciones en Dispositivos Semiconductores – Instituto de Ciencias, Benemérita Universidad Autónoma de Puebla, Puebla, Pue., México C.P. 72570, Mexico b Department of Physics and Astronomy, Clemson University, Clemson, SC 29634, USA c Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional (CINVESTAV), México D.F. C.P. 07360, Mexico article info Article history: Received 25 January 2013 Accepted 30 July 2014 Keywords: Mechanical alloying Spark-plasma sintering Figure of merit abstract A p-type Bi 0.4 Sb 1.6 Te 3 thermoelectric compound was fabricated via mechanical alloying of bismuth, anti- mony and tellurium elemental powders as starting materials. The mechanically alloyed compositions were sintered through a spark-plasma sintering (SPS) process. The effect of the milling time was inves- tigated. In order to characterize the powders obtained via mechanical alloying, X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) analysis were used. The morphological evolution was studied by scanning electron microscopy (SEM). Results showed that the p-type Bi 0.4 Sb 1.6 Te 3 compound was formed after 2 h of milling. Further, the variation of milling time showed that the synthesized phase was stable. All the powders exhibit the same morphology albeit with slight differences. Measurements of the electrical resistivity, Seebeck coefficient and thermal conductivity were performed in the temper- ature range 300–520 K for the SPS samples. The resulting thermoelectric figure of merit ZT reaches a maximum of 1.2 at 360 K for the p-type bulk material with a 5 h milling time. This study demonstrates the possibility of preparing thermoelectric materials of high performance and short processing time. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction For many years, thermoelectric materials have attracted much attention in cooling and power generation due to their excellent features such as no moving parts, environmentally benign, high reliability and long operation life [1–3]. Bismuth telluride based compounds are known as a group of the highest performance thermoelectric materials in the temperature range of 200–400 K [4–6]. However, the thermoelectric properties of bulk Bi 2 Te 3 based materials have not been improved for many years, and their typical figure of merit (ZT) with a value of 1 had not changed for many years until recently. Although, this is acceptable for some specialized applications, it is not so, for commercial refrigeration applications at a much larger scale. Mechanical alloying (MA) is a powerful powder processing method in which mixtures of different metals or alloys/compounds are milled together. MA is basically a dry and high energy ball milling process, which has been used to synthesize, oxide- dispersion strengthened alloys [7], amorphous alloys [8], and var- ious intermetallic compounds [9] as well as thermoelectric and magnetic materials. Several efforts have been made to synthesize bismuth telluride-based materials by the MA process [10–11]. Recently, various novel process procedures have been developed to fabricate Bi 2 Te 3 nanoparticles and nanocomposites with higher ZT values, such as: a simple approach employing ball-milling of bulk BiSbTe alloy and subsequent hot pressing has been reported to be effective for producing nanoparticles with average grain size of 20 nm [12,13], and a novel melt spinning technique followed by a quick spark plasma sintering process to obtain p-type Bi 2 Te 3 bulk material with unique microstructure [14–16]. In this work mechanical alloying followed by pulse discharge sintering or spark plasma sintering (MA–SPS), has been used to fabricate bulk Bi 2 Te 3 -based thermoelectric materials. In this pro- cess, MA allows the formation of extremely fine Bi 2 Te 3 (p-type) solid solution crystallites from Bi, Sb, and Te elemental powders through a sequence of collision events inside the ball mill. The mechanically alloyed powders are subsequently compacted into a bulk material by SPS for their thermal and electrical characteriza- tion. In comparison to the conventional hot-pressing process, the http://dx.doi.org/10.1016/j.enconman.2014.07.083 0196-8904/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Address: Centro de Investigaciones en Dispositivos Semiconductores – Instituto de Ciencias, Benemérita Universidad Autónoma de Puebla, Av. 14 sur y Av. San Claudio, Ciudad Universitaria, Col. San Manuel, Puebla, Pue., México C.P. 72570, Mexico. Tel./fax: +52 (222) 2330284. E-mail address: jgperezluna@gmail.com (J.G. Perez). Energy Conversion and Management 87 (2014) 868–873 Contents lists available at ScienceDirect Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman