Design of a Scanning Seebeck Coefficient Apparatus: A Tool for Testing Inhomogeneities in Thermoelectric Materials

Abstract

In this paper, we present a simple, 2-D Seebeck coefficient measurement system for scanning thermoelectric samples at several points over its surface. The measuring setup has been tested with a homogeneous constantan (Cu55Ni45 alloy) foil in a temperature range from room temperature to 35 °C. Results show good agreement with the literature reported data with an error less than 7%. In order to test the inhomogeneities detection capability of the system, the sample surface was intentionally modified with a rectangular layer made of nickel-based ink and the system was able to detect this defect. With this setup, temperature measurement is not used directly for the Seebeck coefficient evaluation of the sample, although temperature readings are necessary for calculation of mean Seebeck coefficients of thermocouples used and for determination of mean sample temperature. The system uses a heater and a heat sink to minimize the heat flux through the scanning probe, reducing in this way the measurement error. The developed Seebeck coeffiecient scanning method allows automated measurements in a maximum region of 15 mm $\times 5$ mm with 1-mm steps. The statistical analysis of the Seebeck coefficient through a maximum number of 75 recorded data points can be useful in the detection of inhomogeneities and defective regions along the sample.