Journal of Power Sources 477 (2020) 228768 0378-7753/© 2020 Elsevier B.V. All rights reserved. Optimizing the thermoelectric performance of FeVSb half-Heusler compound via Hf–Ti double doping A. El-Khouly a, b, * , A. Novitskii a , I. Serhiienko a , A. Kalugina a , A. Sedegov a , D. Karpenkov c , A. Voronin a , V. Khovaylo a, d , A.M. Adam e, ** a National University of Science and Technology MISIS, Moscow, 119049, Russian Federation b Damanhour University, Faculty of Science, Physics Department, 22516, Damanhour, Egypt c Moscow State University, 119991, Moscow, Russia d National Research South Ural State University, Chelyabinsk, 454080, Russian Federation e Sohag University, Faculty of Science, Physics Department, 82524, Sohag, Egypt HIGHLIGHTS • Electrical conductivity was improved due to optimizing the carrier concentration. • A reduction in thermal conductivity was achieved due to point defect scattering. • Signifcant enhancement in thermoelectric fgure of merit (zT) was achieved. • The highest zT value at T = 873 K was achieved for Fe(V 0.8 Hf 0.2 ) 0.8 Ti 0⋅2 Sb sample. • Lower thermal conductivity is attributed to the Hf–Ti dual-doping. A R T I C L E INFO Keywords: Thermoelectric performance Half-heusler alloys Hf–Ti dual-doping Disorder scattering parameters Phonon scattering Lattice thermal conductivity ABSTRACT FeVSb-based half-Heusler (HH) compound has recently been identifed as promising medium-high temperature thermoelectric (TE) materials for power generation applications. In this study, enhanced thermoelectric per- formance of Fe(V 0.8 Hf 0.2 ) 1-x Ti x Sb (x = 0.0, 0.2, 0.4, 0.5, 0.6) HH alloys by Hf–Ti dual-doping was reported studied in a temperature range from 100 to 900 K. A high content of Ti doping not only optimized the carrier concentration but also reduced the lattice thermal conductivity, which all contribute to high zT. As a result, a zT value was increased by ~20% at 873 K for Fe(V 0.8 Hf 0.2 ) 0.8 Ti 0.2 Sb compound. Hf–Ti dual doping signifcantly reduced the lattice thermal conductivity due to enhanced point defect scattering which is mainly attributed to mass fuctuations. Hence, suppressed the material’s total thermal conductivity. A reduction of ~20% was ob- tained for the Fe(V 0.8 Hf 0.2 ) 0.8 Ti 0.2 Sb sample, compared with the single Hf-doped FeVSb sample and of ~80% compared to FeVSb at room temperature. 1. Introduction Thermoelectric (TE) materials have attracted immense interest in recent years due to their promising applications in direct conversion from thermal to electric energy that could lead to considerable saving in energy [1,2]. Half-Heusler (HH) compounds have been investigated for waste heat recovery applications due to their high-temperature stability and potential for high-temperature power generation [3,4]. Moreover, they are usually based on environmentally friendly elements showing stable transport, thermal and mechanical properties, which makes them promising thermoelectric materials for medium to high temperature applications. In recent years, FeVSb based HH compounds, with abundantly available constituent elements, have been found to exhibit excellent thermoelectric performance [5–9]. However, FeVSb alloys have been paid less attention due to its high lattice thermal conductivity and low zT [10–13]. Considering that the performance of a TE material is given by the dimensionless fgure of merit zT = S 2 σT/(κ e + κ l ), where S, σ, T, κ e * Corresponding author. National University of Science and Technology MISIS, Moscow, 119049, Russian Federation. ** Corresponding author. E-mail addresses: a.elhuli@misis.ru (A. El-Khouly), alaa.mohamed@science.sohag.edu.eg (A.M. Adam). Contents lists available at ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour https://doi.org/10.1016/j.jpowsour.2020.228768 Received 31 May 2020; Received in revised form 27 July 2020; Accepted 8 August 2020