Investigation of GaBi 1-x Sb x based highly mismatched alloys: Potential thermoelectric materials for renewable energy devices and applications S. AlFaify a, **, 1 , Bakhtiar Ul Haq a, *, 1 , R. Ahmed b, c, *** , Faheem K. Butt d, e , M.M. Alsardia f a Advanced Functional Materials & Optoelectronics Laboratory (AFMOL), Department of Physics, Faculty of Science, King Khalid University, P.O. Box 9004, Abha, Saudi Arabia b Department of Physics, Faculty of Science, Universiti Teknologi Malaysia, UTM, Skudai, 81310, Johor, Malaysia c Centre for High Energy Physics, University of the Punjab, Quid-e-Azam Campus, Lahore, Pakistan d Physik-Department ECS, Technische Universit€ at München, Garching, Germany e Department of Physics, Division of Science and Technology, University of Education, College Road, Township, Lahore, Pakistan f Department of Physics, Sungkyunkwan University, Suwon, 440-746, Republic of Korea article info Article history: Received 4 June 2017 Received in revised form 11 December 2017 Accepted 25 December 2017 Available online 27 December 2017 Keywords: Density functional theory Electronic band structure Seebeck coefficients Power factor Figure of merit abstract The high-performance thermoelectric materials are considered a potential resource for clean and sus- tainable energy. Highly mismatched alloys (HMAs), that are admired for the dramatic modifications in their electronic band structures can essentially play important role in developing high-performance thermoelectric materials. Here, we explore the potential of GaBi 1-x Sb x based HMAs for their thermo- electric applications via density functional theory coupled with the Boltzmann transport theory. To perform a comprehensive analysis, four different Sb alloying compositions such as GaBi, GaBi 0.875 Sb 0.125 , GaBi 0.75 Sb 0.25 , and GaBi 0.625 Sb 0 . 375 , are considered. It is found that the Sb replacement over Bi in GaBi 1- x Sb x has stimulated two major modifications in the electronic band structure: the band-gap enhance- ment, and contraction in the curvature of conduction band minimum. These features have remarkably evolved the thermoelectric properties of GaBi 1-x Sb x as a function of Sb contents. The significant increase in Seebeck coefficient and decrease in the electrical conductivity of GaBi 1-x Sb x alloy as a function of Sb content have resulted in large values of thermoelectric power factor as well as the figure of merit (ZT). Considerable improvement in the ZT values as a function of Sb has been recorded that approaches to ~1.0 for GaBi 0.625 Sb 0.375 at room temperature. The occurrence of optimal thermoelectric coefficient values, at attainable doping levels below the Fermi level reveals the predominantly p-type nature of the GaBi 1-x Sb x . Hence, GaBi 1-x Sb x (GaBi 0.625 Sb 0.375 in particular) exhibits interesting thermoelectric properties at room temperature, and is therefore believed to be good candidate material for room temperature based thermoelectric devices and applications. © 2017 Elsevier B.V. All rights reserved. 1. Introduction The escalating increase in the environmental pollution due to the globalization, the industrial revolution and increased popula- tion demands for the alternative and renewable sources. Therefore researchers have shown a remarkable interest in the quest for finding new and improved methods and resources to bring clean, abundant and renewable sources of energy to the society in har- mony with nature. This worldwide demand can be accomplished for example, by new and highly efficient energy generating devices based on materials that are earth-abundant and non-toxic. Such motives have made thermoelectrics one of the fascinating topics in the field of sustainable energy utilization [1,2]. The feature of direct inter-conversion between heat energy and electrical energy for * Corresponding author. ** Corresponding author. *** Corresponding author. Department of Physics, Faculty of Science, Universiti Teknologi Malaysia, UTM, Skudai, 81310, Johor, Malaysia. E-mail addresses: saalfaify@kku.edu.sa (S. AlFaify), bakhtiar@kku.edu.sa (B. Ul Haq), rashidahmed@utm.my (R. Ahmed). 1 These authors contributed equally. Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom https://doi.org/10.1016/j.jallcom.2017.12.306 0925-8388/© 2017 Elsevier B.V. All rights reserved. Journal of Alloys and Compounds 739 (2018) 380e387