The crystallization behavior of CoSb3 and Fe-doped (Co,Fe)Sb-3 thin films prepared by d.c.-magnetron sputtering was studied via ex situ and in situ X-ray diffraction (XRD) measurements. The as-deposited layers are amorphous. Crystallization takes place at temperatures of approximately 160+/-16 degreesC. Decomposition occurs in the temperature ranges of 575-610 degreesC for CoSb3 and of 640-670 degreesC for (Co,Fe)Sb-3. The decomposition products are CoSb and (Co,Fe)Sb, respectively. Both ex situ XRD measurements on annealed layers and in situ measurements on as-deposited samples show a rare dependence of the cubic lattice parameter of the skutterudite type structure on the temperature. Electron probe microanalysis investigations indicate that the composition varies from Co-Sb 1:4 at low temperatures to Co-Sb 1:3 after heating cycles. (C) 2003 Elsevier Science B.V. All rights reserved.