Nanoparticles of Ceria and Ceria-Zirconia: Lattice Parameter, Defect Concentration and Phase Stability
报告人：陈小惠 教授
（Dept. of Applied Physics and Applied Mathematics，Henry Krumb
School of Mines，School of Engineering and Applied Science,
Columbia University）
时间： 2007年1月3日（星期三） 10：00 am
地点： 清华大学材料院学术报告厅（逸夫技术科学楼2－321）
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联系人：南策文 教授 62773587
Abstract:
We will start with pure ceria nanoparticles and discuss their structure and lattice parameter changes with particle-size. We will then continue to discuss ceria-zirconia nanoparticles which are widely used as an oxygen storage component of the three-way catalyst in catalytic converters. The stability of the cubic phase (c’) of Ce1-xZrxO2-y is crucial for catalysis. The phase stability as well as crystallite coarsening are studied by x-ray diffraction, transmission electron microscopy, Raman spectroscopy, and X-ray absorption spectroscopy. With decreasing the particle size, the c’-tetragonal phase boundary shifts to higher zirconia concentration. The monoclinic phase of pure zirconia is not observed. A clear relationship between the phase stability of c’ phase with Ce3+ concentration has been found. Higher Ce3+ concentration helps to release the local strain around the Zr4+ ions and stabilize the c’ phase. A new phase stability diagram that accounts for particle size is presented. With annealing performed under reducing environment, the cubic phase is stabilized up to 90% Zr. This proves the role of Ce3+ in stabilizing Ce1-xZrxO2-y.
Introduction to Prof. Siu-Wai Chan
She is a Professor of Materials Science and Engineering, Dept. of Applied Physics and Applied Mathematics, Henry Krumb School of Mines, School of Engineering and Applied Science, Columbia University , USA. She is studying on Nanoparticles, Grain Boundaries, Interfaces, and Defects in Thin Films and Electronic Oxides. At the same time she is interested in high Tc superconductor materials.
In 1980 she graduated from Columbia University in Metallurgy and Materials Science. She obtained Sc.D from Massachusetts Institute of Technology in 1985 in Materials Science and Engineering. She worked as a technical staff in Bellcore from 1986 to1990. Then She was teaching as Associate Professor in Columbia University in the period 1990-2002. She became a full Professor since July 2002.