Photon Factory Activity Report 2017 #35 (2018)

BL-9A, BL-9C, NW10A/2015G679

The local structure of (Ce1-xZrx)O2 solid solutions
1Ikuo Nakai1,*, Ryohei Hisamatsu1, Yingjie Li2 and Makio Kurisu3
Department of Electrical and Electronic Engineering, Tottori University, Tottori, 680-8552, Japan
2
Inner Mongolia Normal University, Hohhot, 010022, China
3
Department of Physics, Ehime University, Matsuyama, 790-8577, Japan

We have investigated the local structure of (Ce1-xZrx)O2 (0≤x≤0.3) solid solutions. The local structure around the Ce atomis different from that of the central Zr atom and also from the average structure obtained from XRD measurements.
1 Introduction
CeO2 has a cubic structure while ZrO2 showspolymorphs such as monoclinic, tetragonal and cubicstructure. The XRD measurements shows that the solidsolution (Ce1-xZrx)O2 with x less than 0.4 maintains thecubic structure where the lattice constant decreases
lineally from 5.4113 Å at x=0 to 5.3110 Å at x=0.4. [1]
We attempt to investigate (Ce1-xZrx)O2 from the viewpointof local structure.
2 Experiment
The solid solutions (Ce1-xZrx)O2 (0≤x≤0.3) wereprepared from CeO2 and ZrO2 powders with the purity of
4N by solid state reaction. A mixture of them were groundin an alumina mortar and then mechanically milled in astainless steel vial of a vibratory ball mill with stainlesssteel balls for 5 hours. The powders were calcined at
1400 °C for 20 hours in air. They were pulverized in themortar and again fired at 1400 °C for 20 hours in air. We
carried out X-ray powder diffraction (XRD) and XAFS
measurements at room temperature to investigate thecrystallographic and local structure.
3 Results and Discussion
X-ray powder diffraction shows that (Ce1-xZrx)O2(0≤x≤0.3) has the cubic fluorite structure (space groupFm-3m). We have obtained the linear decrease of thelattice constant with increasing x by the Rietveld analysisof XRD patterns. This agrees with the previous report. [1]
XANES spectra for Ce L3 and Zr K edges indicate thatboth of Ce and Zr ions in (Ce1-xZrx)O2 (0≤x≤0.3) keep
tetravalent independent of Zr content.
Figure 1 represents the radial structure function aroundthe Zr atom. The first peak around 1.5 Å comes from thenearest neighbor O atoms. The second peak at 3.5 Å for
x=0.1, which we attribute to both of Zr and Ce neighbors,
splits by further x to the two sub-peaks: Zr-Zr and Zr-Cepairs contribute to the sub-peaks at 3.3 and 3.5 Årespectively. This is consistent with the XRD result thatshows a linear decrease of the lattice constant withincreasing x.
The radial structure function of (Ce1-xZrx)O2 at the Ce Kedge is shown in Fig. 2. The peak near 1.7 Å is attributed
to the first O neighbor, which hardly moves at all despite
an increase in the Zr content. The second peak around
3.5Å, which consists of Ce-Zr and Ce-Ce pairs, hardly
shifts and splits in contrast to the Zr surroundings. Thebehavior around the Ce atom is also much different fromchange in the average structure from XRD with the Zrcontent. These results may suggest that the local structurearound Ce ions differs from that of Zr atoms and from theaverage structure derived from XRD.
128400246Fig. 1: Radial structure function of (Ce1-xZrx)O2
for the Zr K edge at 300 K.
128400246Fig. 2: Radial structure function of (Ce1-xZrx)O2
for the Ce K edge at 300 K.
References[1] A. Varez et al., J. Euro. Ceram. Soc. 27, 3677 (2007).
* nakai9265@gmail.com