Thermoelectric Module For Low Temperature Applications
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THERMOELECTRIC MODULE FOR LOW TEMPERATURE APPLICATIONS Sangeeta Lal†, Sim Loo†, Duck-Young Chung‡, Theodora Kyratsi‡, Mercouri G. Kanatzidis‡, Charles Cauchy*, Timothy P. Hogan† †
Department of Electrical and Computer Engineering, Michigan State University, East Lansing, MI ‡ Chemistry Department, Michigan State University, East Lansing, MI * Tellurex Corporation, Traverse City, MI
ABSTRACT The possibility of a prototype thermoelectric cooling device for operation near liquid nitrogen temperatures has been explored. In these devices, the figure of merit involves a combination of the properties of the two branches of the module. Here, we investigate the fabrication of a module with a new low temperature material, CsBi4Te6 (p-type), and the best known low temperature n-type materials Bi85Sb15. Transport measurements for each of these materials show high performance at low temperatures. Known values for the figure of merit Zmax of CsBi4Te6 is 3.5 x 10-3 K-1 at 225K and for Bi85Sb15 is 6.5 x 10-3 K-1 at 77K. At 100K these values drop to 2.0x10-3 K-1 for CsBi4Te6 and 6.0x10-3 K-1 for Bi85Sb15. Theoretical simulations based on these data show a cooling of ∆T = 12K at 100K, which is almost three times the efficiency of a Bi2Te3 module at that temperature. We present transport measurements of elements used in the fabrication of a low temperature thermoelectric module and properties of the resulting module. INTRODUCTION Thermoelectric coolers with high efficiencies near cryogenic temperatures could open new possibilities for applications of high temperature superconducting devices, improved performance from optical detectors, and other traditional electronic materials such as GaAs, particularly in devices utilizing quantum confinement. A well-known low temperature thermoelectric material is Bi85Sb15, which can be made as an n-type material; however, a high quality p-type Bi85Sb15 has remained elusive. A recently discovered [1], low temperature p-type thermoelectric material is CsBi4Te6. The focus of this work was to investigate the combination of these materials in the fabrication of a low temperature thermoelectric module for cooling applications near 100K. Utilizing optimal properties for these materials, simulations of heat flow and temperature gradients for various current levels through a device is shown in Figure 1 and 2. These simulations are based on the well known formula:
1 QC = S m ITc − K m ∆T − I 2 Rm 2 that relates the heat flow, QC, through the module to the Peltier cooling (SmITc) which includes the thermopower of the module, Sm, the current, I, through the module with a cold side temperature, Tc. The thermal conductance of the module is Km and a temperature gradient, ∆T, is G6.2.1
established across the module. One half of the I2R heating losses go to the cold side of the module, where Rm is the resistance of the module. Temperature dependent thermoelectric properties of samples used in this study are shown in Figures 3 through 6. The Bi85Sb15 sample shows the characteristic high electrical conductivity
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