A Resistance Ratio Analysis for CoSb3-Based Thermoelectric Unicouples

In the search for desirable materials for use in thermoelectric generators, CoSb₃-based skutterudites have stimulated much scientific interest due to their high performance capabilities even at high temperatures. In this work, we tested the electrical power-generation characteristics of CoSb₃-based unicouples. We manufactured power-generation unicouples using n-type In_0.25Co_3.95Ni_0.05Sb₁₂ and p-type In_0.25Co_3.0Fe_1.0Sb₁₂ legs. The dimensions of the thermoelectric legs were 10?mm in diameter and 10?mm in height, with Cu sheets and Cu/Mo alloy as the electrode materials. For our unicouples, we evaluated the resistance ratio m?? (=R _o/R), which represents the ratio of the load resistance to the internal resistance of the unicouple. From this analysis of the resistance ratio m??, we obtained a considerable amount of information about the loss factors that caused the difference between the measured power output and the theoretical value. Through these analyses of two types of loss factors, we sought to improve the open-circuit voltage and internal resistance of a unicouple with CoSb₃/Ti/electrode interfaces. In addition, a long-term durability test of the unicouple at high temperature was performed to test the stability of the thermoelectric materials and of the interface between the electrodes and the thermoelectric legs at the same time.