The Synthesis of Metastable Skutierudites Using Superlattice Reactants

Abstract

The synthesis by controlled crystallization of elementally modulated reactants of a series of kinetically stable, crystalline skutterudites (M′_1−x M₄ Sb₁₂ where M′ = vacancy, RE, Hf, Al, Sn, Pb, Bi, In, Ga, Al and Y; M = Fe, Co) is discussed. Low angle diffraction data demonstrates that the elemental layers interdiffuse at temperatures below 150°C. Nucleation of the skutterudite structure occurs exothermically on annealing at temperatures near 200°C regardless of the ternary metal. The metastable ternary compounds and the new binary compound were found to decompose exothermically on higher temperature annealing. The decomposition temperature ranged from 300°C for the binary compound FeSb₃ to 550°C for Eu′_1−x Fe₄ Sb₁₂ to higher temperatures for the filled cobalt end members. The occupation of the lattice site for the ternary cation was found to depend on the composition of the initial reactant. Samples up to a half gram in size have been synthesized and hot-pressed into pellets for measurement of both electrical properties and thermal conductivity. Preliminary evidence is presented for the formation of skutterudite superlattices, again synthesized by the controlled crystallization of elementally modulated reactants.