Yb(NO3)(3).6H(2)O was used as a parent compound for the formation of Yb2O3 at up to 800 degreesC in atmosphere of air. Thermal processes occurring during the decomposition course were monitored by means of differential thermal analysis (DTA), thermogravimetry (TG), and the gaseous decomposition products were identified by mass spectrometry (GC-MS). The intermediates and final solid products were characterized by IR-spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that, Yb(NO3)(3).6H(2)O decomposes completely through I I endothermic mass loss processes. The dehydration occurs through the first six steps at 95, 145, 165, 175 and 200 degreesC, forming crystalline nitrate Yb(NO3)(3), which decomposes to YbO0.5(NO3)(2) at 250 degreesC. The latter, decomposes to non-stoichiometric unstable intermediate YbO0.75(NO3)(1.5) at 335 degreesC, which decompose immediately to a stable and crystalline YbONO3 at 365 degreesC, then to a non-stoichiometric unstable intermediate Yb(O)(1.25)(NO3)(0.5) at 470 degreesC. Finally, Yb2O3 was formed at 510 degreesC. The decomposition course and surface morphology were supported and followed by SEM and textural studies (S-BET). The final product Yb2O3 at 600 degreesC has a large irregular sheet shaped particles containing a large pores, voids and cracks and has S-BET = 45 m(2)/g. The gaseous decomposition products are water vapor, nitric acid and nitrogen oxides (NO, NO2 and N2O5). The activation energy (DeltaE in kJ/mol) was calculated non-isothermally for each thermal processes. (C) 2004 Elsevier B.V. All rights reserved.