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Enhanced Thermoelectric Properties of Topological Crystalline Insulator Pbsnte Nanowires Grown by a Vapor Transport Approach

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Enhanced Thermoelectric Properties of Topological Crystalline Insulator Pbsnte Nanowires Grown by a Vapor Transport Approach Nano Research 1 DOINano 10.1007/s12274Res -015-0961-1 Enhanced thermoelectric properties of topological crystalline insulator PbSnTe nanowires grown by a vapor transport approach Enzhi Xu1, Zhen Li1, Jaime Avilés Acosta1, Nan Li2, Brian Swartzentruber3, ShiJian Zheng2, Nikolai Sinitsyn4, H. Htoon2, Jian Wang5 and Shixiong Zhang1 (*) Nano Res., Just Accepted Manuscript • DOI: 10.1007/s12274-015-0961-1 http://www.thenanoresearch.com on December. 1, 2015 © Tsinghua University Press 2015 Just Accepted This is a “Just Accepted” manuscript, which has been examined by the peer-review process and has been accepted for publication. A “Just Accepted” manuscript is published online shortly after its acceptance, which is prior to technical editing and formatting and author proofing. 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Nano Res. 64 Enhanced thermoelectric properties of topological crystalline insulator PbSnTe nanowires grown by a vapor transport approach Enzhi Xu1, Zhen Li1, Jaime Avilés Acosta1, Nan Li2, Brian Swartzentruber3, ShiJian Zheng2 , Nikolai Sinitsyn4, H. Htoon2, Jian Wang5 and Shixiong Zhang1* 1Department of Physics, Indiana University, Bloomington, Indiana 47405, USA. 2Center for Integrated Nanotechnologies, Materials, Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA Single-crystalline PbSnTe nanowires were synthesized via a vapor 3Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, New Mexico transport approach, and thermoelectric devices were fabricated to 87185, USA measure electrical conductivity, thermopower and thermal conductivity 4Theoretical Division, Los Alamos National on the same individual nanowires. The PbSnTe nanowires show Laboratory, Los Alamos, New Mexico 87545, USA enhanced thermoelectric figure of merit ZTs than bulk single crystals 5MST-8, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA (Orihashi et al. J. Phys. Chem. Solids 2000, 61, 919-923), owing to both the improved thermopower and the suppressed thermal conductivity. www.theNanoResearch.com∣www.Springer.com/journal/12274 | Nano Research Nano Research DOI (automatically inserted by the publisher) Research Article Enhanced thermoelectric properties of topological crystalline insulator PbSnTe nanowires grown by a vapor transport approach Enzhi Xu1, Zhen Li1, Jaime Avilés Acosta1, Nan Li2, Brian Swartzentruber3, ShiJian Zheng2 , Nikolai 4 2 5 1 Sinitsyn , H. Htoon , Jian Wang and Shixiong Zhang (*) 1 Department of Physics, Indiana University, Bloomington, Indiana 47405, USA. 2 Center for Integrated Nanotechnologies, Materials, Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA 3 Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, New Mexico 87185, USA 4. Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA 5. MST-8, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA Received: day month year ABSTRACT Revised: day month year Bulk lead telluride (PbTe) and its alloy compounds are well-known Accepted: day month year thermoelectric materials for electric power generation. Among all these alloys, (automatically inserted by PbSnTe has recently been demonstrated to host unique topological surface the publisher) states that may have improved thermoelectric properties. Here we report on a vapor transport growth and thermoelectric study of high quality single-crystalline PbTe and PbSnTe nanowires. The nanowires were grown along <001> direction with dominant {100} facets and their chemical compositions are strongly dependent on the substrate position in the growth © Tsinghua University Press reactor. We measured the thermopower, electrical and thermal conductivities of and Springer-Verlag Berlin the same individual nanowires to determine their thermoelectric figure of merit Heidelberg 2014 ZTs. In comparison with bulk samples, the PbSnTe nanowires show both improved thermopower and suppressed thermal conductivity, leading to enhanced ZTs of ~0.018 and ~0.035 at room temperature. The enhanced thermopower may arise from the unique topological surface states and the KEYWORDS suppression of thermal conductivity is possibly due to the increased phonon-surface scattering. Compared with the PbTe nanowires, the PbSnTe has Type keywords lower thermopower but significantly higher electrical conductivity. Our work PbSnTe, highlights nanostructuring in combination with alloying as an important thermoelectrics, approach to enhancing thermoelectric properties. topological crystalline insulator, nanowire 1 Introduction promising approaches to harvesting renewable energy [1, 2]. The energy conversion efficiency is Address correspondence to [email protected] Converting waste heat into electric power quantified by the so-called figure of merit ZT of through the Seebeck effect is one of the most the material that is used in the thermoelectric Nano Res. 2 generator. The ZT is dependent on the material study the thermoelectric properties of PbSnTe properties, i.e. thermopower S, electrical nanowires. As a prototypical PbTe-based alloy, conductivity s, and thermal conductivity κ in a Pb1-xSnxTe can form a complete solid solution relation of ZT=S2 σT/κ. The small bandgap (0≤x≤1) and its bulk bandgap can be tuned semiconductor lead telluride (PbTe) with a continuously from 0.3 eV to -0.18 eV by changing rock-salt crystal structure is one of the most x from 0 to 1. The Pb1-xSnxTe alloy with a Sn widely studied thermoelectric materials [3]. concentration of x>0.37 has a negative bulk While the ZT of pure PbTe bulk samples is less bandgap and has recently been demonstrated to than 1, it can be dramatically increased by possess unique topological surface states that are alloying with other compounds or by doping protected by crystalline mirror symmetry [47-49]. with impurities [4-8]. Indeed, bulk Pb1-xSnxTe Recent theoretical studies have suggested that alloys exhibit a maximum ZT of ~ 1 [9, 10] and topological surface states may have enhanced the doped PbTe1-xSex alloys have a peak ZT as thermoelectric properties than bulk states owing high as ~ 1.8 [7, 8]. The enhanced thermoelectric to their unique electronic band structures [50, 51]. properties are attributed to the fact that alloying Nanowires are anticipated to have more not only reduces thermal conductivity by advantages than bulk samples in the sense that inducing additional phonon scatterings, but also they have significantly higher influences thermal power and electrical surface-area-to-volume ratio which could conductivity favorably by modifying electronic magnify contributions from surface states. band structures [3]. Single-crystalline PbSnTe nanowires were Another effective approach to enhancing ZT grown by a vapor transport approach with Au is to fabricate nanostructured materials [11, 12]. nanoparticles as catalysts. The nanowires were Quantum confinement effect in nanostructures grown along <001> direction of the rock-salt gives rise to an increased thermopower, while crystal structure and their chemical compositions surface/boundary scattering of phonons are strongly dependent on the substrate position suppresses thermal conductivity [13, 14]. As an in the growth reactor. The thermopower, example, PbTe-based nanostructures, such as electrical and thermal conductivities were quantum dot superlattices [15] and dual-phase systematically measured on the same nanocomposites [16], have shown improved ZTs single-nanowire devices to accurately determine than their bulk counterparts. One-dimensional their figure of merit ZTs. In comparison with bulk nanowires (NWs) are another format of samples of nearly the same chemical composition, nanostructures that have enhanced PbSnTe nanowires show both enhanced thermoelectric properties as demonstrated in thermopower and reduced thermal conductivity, many material systems [17-38]. The PbTe NWs leading to a significantly improved ZT. The same have been fabricated by a variety of synthetic growth and thermoelectric studies were carried approaches, including chemical vapor transport out on the undoped PbTe nanowires for [22, 27, 34, 39], template-directed comparison. electrodeposition [40] and hydrothermal process [41, 42]. Thermoelectric studies have indeed 2 Experimental details shown enhanced thermopower and/or reduced The PbTe and PbSnTe NWs were grown by a vapor thermal conductivity of NWs than their bulk transport approach that was widely employed for counterparts [22, 27, 34, 38, 39, 41-46]. the controlled synthesis of single-crystalline In this work, we combined an alloying nanostructures of SnTe [52-57] and its related approach with the nanostructuring strategy to compounds
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