Thermoelectric materials : synthesis and electrical characterization

Abstract

The objective of the current work has been to synthesize the thermoelectric materials ZnSb with additions of Cr and Mn, respectively, and prepare the samples suitable for measurement of electrical properties and implement locally measurement techniques for the electrical characterization of these kind of samples.

ZnSb doped with 4% and 0.5% percentage Cr and Mn, respectively, were studied in this master thesis. These additions to ZnSb have not been reported before. The materials were synthesized in annealing and reported a low ductility and more cracks. By contrast, the fine grains were found in the sintered materials and showed a high handleability. Samples were prepared as a bar-shape and disk-shape, respectively. The structures were studied by SEM (scanning electron microscope) and XRD (X-ray diffraction). The electrical properties investigation showed that the contact resistance was low, proved the reliability of measurements. By van der Pauw method, the resistivity of disk-shape samples was found around 2-2.5e-2ohmcm in Zn_{1-x}Cr_{x}Sb and 1-2e-2ohmcm in Zn_{1-x}Mn_{x}Sb at RT. The different pieces of materials have also given high values. The carrier type has been determined to be p-type by Hall measurement. The carrier concentration p for all samples are also similar ~10e+17/cm^3(RT), close to intrinsic value. The value of p, carrier concentration, is not proportional to the overall content of Cr and Mn, implying a low doping efficiency. Hall mobilities(RT) have been to determined in the range of 30~70cm^2/Vs. The temperature-dependency of resistivity was measured in the range of 25~350 Celsius by cryogenic measurement and showed a increase with temperature decrease. Thermal conductivity was measured by laser flash, reported at a range of 1.8~2.2W/Km, which is comparable with those done by previous measurements. At the end of this thesis, there are also some interesting phenomena left. The temperature-dependence of resistivity leaves some interesting phenomena which cannot be interpret immediately. However, it could be an attractive topic to be researched in a large temperature range.