Experimental evidence of enhancement of thermoelectric properties in tellurium nanoparticle-embedded bismuth antimony te
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Sung Wng Kim WCU Department of Energy Science, Sungkyunkwan University, Jangan-gu, Suwon 440-746, South Korea (Received 30 April 2012; accepted 27 July 2012)
We present experimental evidence of enhancement of thermoelectric properties in tellurium (Te) nanoparticle-embedded bismuth antimony telluride (BiSbTe) alloys. Bi0.5Sb1.5Te3 films with a high density of Te particles of 10–20 nm size were prepared by growth of alternating multilayers of ultrathin Te and Bi0.5Sb1.5Te3. As the amount of Te nanoinclusions increased up to ;15%, the Seebeck coefficient and thermoelectric power factor were increased. Based on the concept of band bending at heterointerfaces as a carrier energy filter, the energy relaxation calculation was made to confirm that the Te nanoinclusions result in a carrier energy filtering effect in p-type bismuth antimony telluride. In addition, thermal conductivities were reduced in the Te-embedded samples, permitting possible further enhancement of the thermoelectric figure of merit. The advantages of Te nanoinclusions in p-type Bi0.5Sb1.5Te3 alloys on thermoelectric performance are experimentally realized by both electron- and phonon scattering.
I. INTRODUCTION
Bismuth antimony telluride (BiSbTe) thermoelectric alloys, which are possibly the only thermoelectric materials suitable for use at near room temperature, have great application potential for cooling, heating, and power generation.1 Thermoelectric solid state cooling can enable next-generation cooling with higher efficiency to replace vapor-compression refrigeration/air-conditioning, and thermoelectric power generation can be utilized for lowgrade waste heat harvesting to improve power efficiency in many industries including the automotive sector. However, applications remain constrained by the need for higher efficiency thermoelectric materials, characterized by a high dimensionless figure of merit (ZT); ZT 5 (S2r/j)T, where S, r, j, and T are Seebeck coefficient, electrical conductivity, thermal conductivity, and absolute temperature, respectively. To increase ZT, a large S, high r, and low j are essential. ZT of commercial BiSbTe bulk alloys has remained at around 1 for the past half-century. Emergence of high-ZT thermoelectric materials is highly demended to widen the thermoelectric application area.
Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] This paper has been selected as an Invited Feature Paper. DOI: 10.1557/jmr.2012.273 J. Mater. Res., Vol. 27, No. 19, Oct 14, 2012
Recent efforts to enhance ZT in BiSbTe bulk alloys have focused on reduction of the lattice thermal conductivity jlatt without severe reduction of associated electrical conductivity r through a phonon glass electron crystal approach by developing homogeneous or heterogeneous nanostructures.2–9 Poudel et al. obtained a maximum ZT of 1.4 at 373 K by reducing jlatt to 0.35–0.4 W/(m K) in nanocrystalline BixSb2 xTe3 bulk alloys with high-density grain boundaries.10 Cao et al. developed bismuth telluride (Bi2Te3)/
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