SYNTHESIS OF METASTABLE POST-TRANSITION-METAL IRON ANTIMONY SKUTTERUDITES USING HE MULTILAYER PRECURSOR METHOD

Modulated elemental reactants were used to form amorphous ternary reac tion intermediates of the desired compositions. The amorphous reaction intermediate for each system crystallizes exothermically below 200 de grees C forming kinetically stable ''filled'' skutterudites of general formula M1-xFe4Sb12 where M = Sn, Al, Ga, In, and Zn. These metastabl e compounds can only be prepared by controlling the reaction intermedi ates, avoiding the formation of more thermodynamically stable binary c ompounds. We propose that the desired compounds nucleate from the amor phous precursor because slow solid-state diffusion rates hinder dispro portionation into the more stable mix of binary compounds and elements . If modulated elemental reactants are prepared with layer thicknesses above a critical value (similar to 40 Angstrom), the thermodynamicall y stable binary compound FeSb2 interfacially nucleates, preventing for mation of the desired metastable ternary compounds. The use of low-ang le X-ray diffraction and calorimetry provide the data necessary to dev elop an understanding of the reaction mechanism.