Partially filled skutterudite antimonides LayCo3.5Fe0.5Sb12 were synthesized through solid-state reaction. Large thermal parameter of filling atom was observed from Rietveld refinement. Raman spectra were studied, and only Fe substitution made little change to Raman spectra, while La filling in the voids in skutterudite structure produced large broadening of the vibrational modes. To corroborate the interaction of filling ions with vibrational modes, thermal transport property was measured. (c) 2005 Elsevier B.V. All rights reserved.