N.E. Walsöe de Reca

Synchrotron X‐ray diffraction study of the tetragonal–cubic phase boundary of nanocrystalline ZrO2–CeO2 synthesized by a gel‐combustion process

The crystal structures of a number of nanocrystalline ZrO2–CeO2 solid solutions, synthesized by a pH-controlled nitrate-glycine gel-combustion process, were studied. By using a synchrotron X-ray diffractometer, small peaks of the tetragonal phase, which correspond to forbidden reflections in the case of a perfect cubic fluorite structure, were clearly detected. By monitoring the most intense of these reflections, 112, as a function of the CeO2 content, the tetragonal–cubic phase boundary was found to be at 85u2005(5)u2005mol% CeO2. For a CeO2 content up to 68 mol%, a tetragonal phase with c/a > 1 (known as the t′ form) was detected, whereas, between 68 and 85 mol% CeO2, the existence of a tetragonal phase with c/a = 1 and oxygen anions displaced from their ideal positions in the cubic phase (the t′′ form) was verified. Finally, solid solutions with higher CeO2 contents exhibit the cubic fluorite-type phase.

High-temperature X-ray powder diffraction study of the tetragonal-cubic phase transition in nanocrystalline, compositionally homogeneous ZrO2-CeO2 solid solutions

, CO and hydrocarbons from automotiveexhausts , as anodes in fuel cell technologies, and others. Inparticular, the metastable forms of the tetragonal phase havebeen investigated widely since they are the most suitable forapplications Trovarelli, 2002; Di Monte and Kaspar, 2005 .The crystal structure of compositionally homogeneousZrO

Structure of nanoporous zirconia-based powders synthesized by different gel-combustion routes

Zirconia-based ceramics that retain their metastable tetragonal phase at room temperature are widely studied due to their excellent mechanical and electrical properties. When these materials are prepared from precursor nanopowders with high specific surface areas, this phase is retained in dense ceramic bodies. In this work, we present a morphological study of nanocrystalline ZrO2–2.8 mol% Y2O3 powders synthesized by the gel-combustion method, using different organic fuels – alanine, glycine, lysine and citric acid – and calcined at temperatures ranging from 873 to 1173u2005K. The nanopore structures were investigated by small-angle X-ray scattering. The experimental results indicate that nanopores in samples prepared with alanine, glycine and lysine have an essentially single-mode volume distribution for calcination temperatures up to 1073u2005K, while those calcined at 1173u2005K exhibit a more complex and wider volume distribution. The volume-weighted average of the nanopore radii monotonically increases with increasing calcination temperature. The samples prepared with citric acid exhibit a size distribution much wider than the others. The Brunauer–Emmett–Teller technique was used to determine specific surface area and X-ray diffraction, environmental scanning electron microscopy and transmission electron microscopy were also employed for a complete characterization of the samples.