Investigation of physical and electric properties of silver pastes as a binder for thermoelectric materials

The physical and electric properties of several silver pastes, Pb-Sn solder, and indium were systematically investigated as potential binders for attaching electrodes to bismuth-based bulk or nanowire array thermoelectric elements. Scanning electron microscopy observations and x-ray diffraction surface measurements of the silver pastes were performed and the temperature and magnetic field dependence of the resistance were measured to characterize their electrical properties from 300 K down to 15 K and from 0 to 1 T at 15 K, respectively. The silver pastes were not reactive with bismuth and hence were found to be potentially useful as electrically conductive adhesives with bismuth-based materials. The properties of each of the binders were quite different; the typical size of the particles in the silver pastes before solidification were distributed in the range from 3 nm to 20 μm, and the size strongly affected the resistances of the silver pastes, which were distributed over 2 and 3 orders of magnitude at 300 and 15 K, respectively. Therefore, an appropriate selection of binder must be made for a specific purpose, based on the measurement results. For use with bismuth-based thermoelectric materials, the silver nanopaste is a strong candidate binder because it is far superior to other the binders examined in terms of its resistance properties and magnetic field dependence