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1267-DD08-02

Thermoelectric Properties of Electrodeposited BiSbTe Nanowires Raja S. Mannam, and Despina Davis* Institute for Micromanufacturing (IfM), Louisiana Tech University, Ruston, Louisiana 71270, USA. * [email protected], Ph: 318 257 5142, Fax: 318 257 5104. ABSTRACT Bismuth antimony telluride (BiSbTe) nanowires were electrodeposited at constant potentials into polycarbonate templates from a tartaric-nitric acid baths having different electrolyte compositions. Composition analysis of the nanowires showed that Sb deposits at higher potentials compared to BiTe. Maximum seebeck coefficients of -337.7 µV/K and 227.2 µV/K were obtained for n-type and p-type nanowires samples Bi4.6Te5.4 and Bi4.3Sb5 respectively. Nonmonotonic resistance behavior was observed for all the nanowires. INTRODUCTION Figure of merit of thermoelectric materials is defined as ZT = S 2σT k where, S is the Seebeck coefficient, σ is electrical conductivity, T is the absolute temperature, k is thermal conductivity [1]. The ZT of the current bulk materials is limited to 1; however, a value higher than 3 is required to compete with conventional energy techniques. Increasing the thermoelectric power factor (S2σ) and decreasing the thermal conductivity are the two main approaches to improve ZT. Bismuth Telluride alloy thermoelectric materials are the most efficient for room temperature operation. In superlattice Bi2Te3/Sb2Te3 thin films, a high ZT of 2.4 was obtained mainly by the decreased lattice thermal conductivity [2]. Taking into account the improved density of states resulting in higher power factors and decreased phonon thermal conductivity due to surface scattering, Dresselhaus’s group [3, 4] predicted even higher ZT for one dimensional nanostructures. Semimetallic bulk Bi can be converted in to semiconducting either by controlling the dimensionality of nanowires or by alloying with Sb [5]. Also, properly oriented BiSb nanowires were reported to be good n- type thermoelectric materials [6, 7]. Electrodeposition offers a unique way of preparing nanostructure materials. Stacy’s group [8] was the first to report electrodeposition of BiSbTe nanowires in porous alumina templates using a tartaric-nitric acid based electrolyte, and proposed different mechanisms for the reduction of BiSbTe alloys following the overall reaction: 3HTeO2 + 2(1-x) Bi3+ + 2xSbO+ + (9+4x) H+ + 18 e-
(Bi1-xSbx)2Te3 + (6+2x) H2O. Frari et al. [9,10] studied the optimum conditions for electrodeposition of Bi0.5Sb1.5Te3 alloys from a tartaric-perchloric acid baths and measured a thin film power factor of 600 µWK2 -1 m . Xiao et al. [11] electrodeposited (Bi0.3Sb0.7)2Te3 and Bi1.8Sb0.1Te3.1 nanowires in

polycarbonate template and described their semiconducting nature from the temperature dependent I-V plots. The goal of current research is to analyze the effect of Sb and Te doping on the thermoelectric properties of BiSbTe nanowires. EXPERIMENT BiSbTe nanowires were electrodeposited into polycarbonate membranes using a Solatron 1287 function generator at constant potent