Transport Properties of Thermoelectric Nanocomposites
- PDF / 264,612 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 115 Downloads / 280 Views
1166-N05-08
Transport Properties of Thermoelectric Nanocomposites Authors: L.M. Woods, A. Popescu, J. Martin, and G.S. Nolas Affiliation: Department of Physics, University of South Florida, Tampa, FL 33620, U.S.A. ABSTRACT We present a theoretical model for carrier conductivity and Seebeck coefficient of thermoelectric materials composed of nanogranular regions. The model is used to successfully describe experimental data for chalcogenide PbTe nanocomposites. We also present similar calculations for skutterudite CoSb3 nanocomposites. The carrier scattering mechanism is considered explicitly and it is determined that it is a key factor in the thermoelectric transport process. The grain interfaces are described as potential barriers. We investigate theoretically the role of the barrier heights, widths, and distances between the barriers to obtain an optimum regime for the composites thermoelectric characetristics. INTRODUCTION Thermoelectric (TE) energy conversion materials offer the possibility of an all-solid-state technology to convert heat into electrical energy. The performance of devices based on such materials is characterized by the dimensionless figure of merit defined as ZT = S 2σT / κ , where S is the Seebeck coefficient (thermopower), σ - the carrier conductivity, κ - the thermal conductivity, and T – the absolute temperature. Larger values of ZT warrant more efficient devices, thus researchers have devoted much effort in finding ways to increase the figure of merit. However, the Seebeck coefficient, carrier and thermal conductivities are interrelated in the usual bulk materials. It is not possible to influence one of them without influencing the others in some disadvantageous ways. This imposes limitations on how much the figure of merit of bulk materials can be improved. For the past several years ZT of materials currently used in commercial devices has been ~ 1 for all applicable temperature ranges1. Other efforts have focused on the possibility to alter the thermoelectric properties independently by approaching nanoscaled dimensions. These include Bi2Te3/Sb2Te3 supperlattices2, quantum dot supperlattices3, or one dimensional quantum wires4 for which the thermal conductivity is reduced thus leading to an increased figure of merit. In addition, bulk materials with nanostructured inclusions have also been demonstrated to have enhanced thermoelectric properties. For example, studies of PbTe with Pb nanoprecipitates5, nanocrystalline CoSb36, and nanogranular PbTe composites7,8 have reported an increased Seebeck coefficient as compared to the bulk counterpart. These investigations5-8 show that the carrier scattering by interfaces present in the bulk matrix is a key factor in the improved TE properties. In fact, it has been shown8,9 that the interface grain barriers filter the low energy carriers, while the higher energy ones diffuse through the specimen. Since the mean energy per carrier is increased, for certain conditions the Seebeck coeffient is increased while the carrier conductivity is not degraded ap
Data Loading...
