Preparation and Evaluation of Phosphide Skutterudites

This report summarizes a three and a half year program on the synthesis of phosphide skutterudite compounds using direct reaction and flux methods as well as a newly developed technique, the molten salt electrodeposition. A number of successfully prepared materials were measured for their thermoelectric properties as a function of temperature. It was found that some of these phosphide compounds exhibited semiconducting behavior in contrast to their antimonide analogs. This provided an opportunity to investigate skutterudite compounds having electrical properties ranging from semiconductors to semimetals/metals when phosphorus was replaced by antimony. In addition, the effect of anion size and mass on thermal conductivity of these compounds were experimentally verified. By extending our study to a binary cobalt phosphide-arsenide solid solution, we found that the thermoelectric properties were improved. We expected that this result could be applied to other filled ternary compounds, including the state-of-the-art CeFe4Sb12.