ICT2014 Abstracts

Harman method has been widely used to characterize the thermoelectric properties in a rapid and simple fashion. However, its validity has been often questioned due to the over-simplified assumptions that this method relies on. For achieving high accuracy from Harman method, Joule heating within the sample, and the heat losses via lead wires, convection, and radiation should be negligible [1]. Here, we study the parasitic thermal effects in Harman method for bulk materials under practical conditions, and seek to determine an intrinsic thermoelectric figure of merit, ZT . We expand the original Harman relation including the parasitic thermal effects, and show the link between the parasitic terms with the sample geometry. To acquire an intrinsic ZT, we systematically vary the sample geometry, measure ZTs, and use the expanded Harman relation. A huge error (~28%) was seen from ZTs obtained by the original Harman method. Furthermore, the measured ZTs with varied sample geometries and lead wire types are used to quantitatively understand and separately evaluate the parasitic terms. This work should help to establish a standard for characterizing thermoelectric bulk materials.

[1] T.C.Harman, Special techniques for measurement of thermoelectric properties, J. of Appl. Phys., 29, 1373 (1958).