Synthesis and characterization of nanocrystalline cerium oxide powders by two-stage non-isothermal precipitation

Nanocrystalline CeO2 particles were firstly prepared by two-stage non-isothermal precipitation, i.e. precipitating at 70 degreesC and aging at another temperature. Experimental results showed that the intermediates at the end of precipitation stage were needle-like mixtures of Ce3+- Ce4+ compounds. The subsequent aging temperature played an important role on the shape and size of final products. As the aging temperature suddenly reduced to 0 degreesC, the resultant particles retained their original needle-like structure via the topotactic mechanism, which cannot be obtained by isothermal precipitation. As raising the aging temperature above 50 degreesC, the products were hexagonal and grown up with increasing temperature via the dissolution-recrystallization mechanism. Moreover, all products were cubic-fluorite structured CeO2 with negligible Ce3+ content. As compared to the nanohexagons (aged at 90 degreesC), the nanoneedles (aged at 0 degreesC) exhibited an unordinary red shift in the UV absorption and possessed a smaller bandgap energy. (C) 2004 Elsevier Ltd. All rights reserved.