Photon Factory Activity Report 2005 #23 Part B (2006)
Crystallography

4B2/2005G157,2005G158,2004G256,2004G058

Electron density distribution in Ce0.8Zr0.2O2 solid solution through synchrotron
powder diffraction data
Takahiro Wakita, Masatomo Yashima*, Takayuki Tsuji, Qi Xu, Toshikazu Ueda, Yoichi Kawaike andRoushown Ali1
Department of Materials Science and Engineering, Interdisciplinary Graduate School of Science andEngineering, Tokyo Institute of Technology, Nagatsuta-cho 4259, Midori-ku, Yokohama, 226-8502;
1
Advanced Materials Loboratory, National Institute for Materials Science, Namiki 1-1, Tsukuba,
305-0044, Japan
Introduction
Three-way catalyst has been known to oxidize CO andHC, and to reduce NOx at the same time. CeO2-ZrO2solid solutions are used as the subcatalysts for
purification of automotive exhaust gases. The
development of CeO2-ZrO2 catalysts requires a better
understanding of the diffusion mechanism of oxideions.The crystal structure of the CeO2-ZrO2 solidsolutions has been investigated by Yashima et al. [15].They reported the existence of three metastable
tetragonal forms of t, t’ and t’’. The three tetragonalforms belong to the P42/nmc space group. However, thecrystal structure and electron density distribution of theCe0.8Zr0.2O2 at high temperatures have not yet been
investigated in situ. The purpose of this study is toinvestigate the crystal structure and electron-density
distribution in the Ce0.8Zr0.2O2 at 1823 K using thesynchrotron powder diffraction data
Experiment
Synchrotron powder diffraction experiment wasconducted using the multiple-detector system installed at
the beamline BL-4B2 of the Photon Factory, KEK, Japan.
A furnace with MoSi2 heaters [6] was placed on thesample table, and used for synchrotron powder diffraction
measurements 1823 K. Monochromatized 1.200063(2) ÅX-ray was used for the diffraction experiment. The
diffraction data were analyzed by Rietveld method, with acomputer program RIETAN-2000. The electron-density
distribution was studied by a maximum-entropy method(MEM) using the structure factors obtained in theRietveld analysis. The calculation was performed by acomputer program PRIMA with 64×64×64 pixels.
Results and discussion
Structure refinements of the Ce0.8Zr0.2O2 weresuccessfully performed assuming the space group Fm 3 m(Fig.1). Unit-cell parameters were refined to bea=5.4506(3) Å. The weighted reliability factor Rwp was16.34 %. The MEM density map indicates anisotropic
thermal motions around the ideal 8c position. The
direction of bluges of oxide ions is opposite side of the Ceand Zr cations and the oxide ions shift to the position ofthe cavity, 1/2.1/2,1/2 (Fig. 2).

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Users' ReportFigure 1. Rietveld fitting pattern for synchrotron
powder diffraction data of the Ce0.8Zr0.2O2 solidsolution measured at 1823 K.

Figure 2. Equicontour electron density surfaces at 1.0e/Å3 of the Ce0.8Zr0.2O2 solid solution measured at 1823 K.
References[1] M. Yashima et al., J. Am. Ceram. Soc. 76 (1993) 1745.
[2] M. Yashima et al., J. Am. Ceram. Soc. 76 (1993) 2865.
[3] M. Yashima et al., J. Am. Ceram. Soc. 77 (1994) 1067.
[4] M. Yashima et al., J. Am. Ceram. Soc. 77 (1994) 1869.
[5] M. Yashima et al., Appl. Phys. Lett. 72 (1998) 182.
[6] M. Yashima et al., J. Am. Ceram. Soc. 89 (2006) 1395.
*yashima@materia.titech.ac.jp