The Synthesis of Metastable Skutterudites and Crystalline Superlattices
We have used controlled crystallization of elementally modulated reactants to prepare a series of kinetically stable, crystalline skutterudites) and crystalline superlattices containing promising thermoelectric materials. For the bulk synthesis of skutterudites, low angle diffraction data demonstrates that the elemental layers interdiffuse at temperatures below 150°C. Nucleation of the skutterudite structure occurs with at large exotherm on annealing at temperatures below 200°C for all systems studied. All of the metastable ternary compounds and the new binary compounds were found to decompose exothermically on higher temperature annealing. The decomposition temperature ranged from 250°C for the binary compound NiSb3 to approximately 550°C for the rare earth containing iron compounds. The occupation of the ternary cation was found to depend on the composition of the initial reactant and was varied from 0 to 1. Full occupancy typically required an excess of the filling cation. Structural analysis of crystalline superlattices containing skutterudites and other promising thermoelectric materials will be presented. Results of electrical and thermal conductivity measurements of representative samples will be discussed.