THERMAL-DECOMPOSITION OF NOVEL RARE-EARTH SELENITES

TG and DTA have been carried out on new anhydrous rare-earth selenites R2SeaO3+2a (a = 3.5, 4) in order to establish their stability. Decomp osition occurs in three steps attributed to successive losses of SeO2. The first process gives rise to other new group of selenites of compo sition R2Se3O9, which crystallize in two different forms depending on the rare-earth element. The second process leads to isomorphous compou nds R2SeO5. The final product of thermal degradation is R2O3. All prod ucts were characterized by chemical analysis and X-ray powder diffract ion methods.