Investigations of the effect of Fe and Ni addition on the PbTe interfacial reactions

Abstract

PbTe based thermoelectric generators are widely employed by the United States Army in space crafts to supply on-board power, and in pacemakers batteries, it's one among the widely used thermoelectric semiconductor material with good chemical stability, good mechanical strength, high melting point, low vapour pressure, and intermediate operating temperature (900 K). But still, the PbTe module suffers from low efficiency, and comparatively research on thermoelectric modules is at a primary stage because of the gap between the material and device technologies. Thermoelectric devices are composed of different layers, such as electrodes, insulators, thermoelectric elements, and bonding interfaces. These layers have different physical features, and to construct thermo mechanically reliable devices. The interfacial reaction between the electrode and the thermoelectric leg has to be considered. Ni and Fe are commonly used as a diffusion barrier and electrode for PbTe because the mismatch of coefficient of thermal expansion is very low comparing with the other materials.in the case of metallization of PbTe with Ni, it was observed that both Ni-Te intermetallic and voids can form near the bonding interface which can lead to high electrical and thermal contact resistance. It is also difficult to get a metallurgical high strength joint with Fe. Fe can only bond at a high temperature which can affect the property of thermoelectric leg PbTe. We have added the atomic present of Fe to Ni to investigate the Effect of Fe addition (Ni-at1%, 2at%, 5at %) in the PbTe/Ni interfacial reaction, and we observed promising results. The experiment is undertaken at different temperatures and time intervals to study the kinetics and based on our results we conclude that Ni-5at%Fe /PbTe 700oC/15min is the best one, if we increase beyond 5at%Fe it would take a longer time to join. The detailed results will be described in chapter 4 of this thesis