Jarrod Short

High Temperature Measurement System Design for Thermoelectric Materials In Power Generation Application

Recent interest in thermoelectric materials for power generation applications has initiated the development of a measurement system in our laboratory for characterization of materials in the 80K to 800K temperature range. This system has been specifically designed for measuring thermoelectric power and electrical conductivity as needed for determining the power factor of the measured samples. This is a single sample measurement system based on a continuous flow cryostat. Significant effort has gone into the computer controlled data acquisition and PID controlled temperature stabilization. Investigation of the influence of temperature stability on the measured data will be presented along with important aspects of the system design, development, and testing. Data collected on reference materials and new thermoelectric materials of interest will be presented.

Progress on the Fabrication and Characterization of High Efficiency Thermoelectric Generators

Timothy P. Hogan, Adam D. Downey, Jarrod Short, Jonathan D’Angelo, Eric Quarez, John Androulakis, Pierre F. P. Poudeu, Mercouri G. Kanatzidis, Ed Timm, Kim Sarbo, Harold Schock Department of Electrical and Computer Engineering, Michigan State University, East Lansing, MI 48824, U.S.A. Chemistry Department, Michigan State University, East Lansing, MI 48824, U.S.A. Department of Mechanical Engineering, Michigan State University, East Lansing, MI 48824, U.S.A.

Investigation of Low Resistance Contacts to Pb-Sb-Ag-Te (LAST) Materials for Module Fabrication

Low electrical contact resistance is essential for the fabrication of high efficiency thermoelectric generators. These contacts must be stable to high temperatures and through thermal cycling. Here we present the fabrication procedure and characterization of several contacts to Pb-Sb-Ag-Te (LAST) compounds. Contact materials investigated include tungsten, antimony, tin, nickel, and a bismuth antimony based solder. The contacts were typically deposited by an electron beam evaporation method after careful preparation of the sample surface. The resistances were measured by using the transmission line model (TLM), and ohmic behavior was verified through current vs. voltage measurements. The best contact resistivities of less than 20 µΩ·cm 2 have been measured for annealed antimony to n-type LAST samples. We present these procedures for fabricating low resistance contacts and the use of these contact materials toward the fabrication of high efficiency thermoelectric generator modules.

Characterization of Thermoelectric Power Generation Modules Made from New Materials

Lead-Antimony-Silver-Tellurium (L-A-S-T) materials, synthesized at Michigan State University, show promising thermoelectric properties at high temperatures for use in power generation applications. Recent scaled-up quantities of L-A-S-T show a ZT=1.4 at 700 K approaching the figure of merit for samples made in small quantities [1]. These materials are of great interest for power generation applications with hot side temperatures in the range of 600800 K. Developing these materials into working devices requires minimization of the thermal and electrical parasitic contact resistances, so various fabrication methods are under investigation. To examine each method, a new measurement system has been developed to characterize these devices under various load and temperature gradients. An introduction to the system will be presented, as well as results for devices made of the L-A-S-T materials.

Hall effect measurements on new thermoelectric materials

In the field of thermoelectrics, the figure of merit of new materials is based on the electrical conductivity, thermoelectric power, and thermal conductivity of the sample, however additional insight is gained through knowledge of the carrier concentrations and mobility in the materials. The figure of merit is commonly related to the material properties through the B factor which is directly dependent on the mobility of the carriers as well as the effective mass. To gain additional insight on the new materials of interest for thermoelectric applications, a Hall Effect system has been developed for measuring the temperature dependent carrier concentrations and mobilities. In this paper, the measurement system will be described, and recent results for several new materials will be presented.