Photon Factory Activity Report 2018 #36 (2019)
BL-6C / 2017G705

Local Structure Study of A-site Ordered Perovskite CaCu3Ti4O12
by means of X-ray Fluorescence Holography
Haruki KAMIDE1*, Hojun IM1, Takao WATANABE1, Naohisa HAPPO2, Koji KIMURA3,Kenshi HAYASHI3, Shinya HOSOKAWA4, and Yasuhisa TEZUKA1**
1
Grad. Sch. of Sci. and Tech., Hirosaki Univ., Hirosaki, Aomori 036-8561, Japan
2
Grad. Sch. of Inf., Hiroshima City Univ., Hiroshima 731-3194, Japan
3
Grad. Sch. of Phys. and Tech., Nagoya Inst. Tech., Nagoya 466-8555, Japan4Grad. Sch. of Sci. and Tech., Kumamoto Univ., Kumamoto 860-8555, Japan
1Introduction
A-site ordered perovskite CaCu3Ti4O12 (CCTO) exhibitsa dielectric anomaly in which the dielectric constantabruptly decreases below about 100 K without a structuralphase transition, while exhibiting a huge dielectric
constant of ε ~ 104 in the temperature range of 600 K to
100 K [1]. However, the nature of the dielectric anomaly
has not been clarified yet. We have studied the electronic
structure of CCTO by means of X-ray Raman scattering,and discover the relation between the electronic structureand dielectric anomaly [3, 4]. In this study, we investigatedthe local crystal structure of CCTO using X-ray
fluorescence holography (XFH).
2Experiment
The experiment was performed at BL-6C. Single crystal
CCTO(100) made by floating-zone method was used inthis experiment. XFHs using each Kα fluorescence of Ca,
Cu, and Ti were measured. In addition to room temperature,measurements were carried out at 80 K and 120 K, which
is below and just above the dielectric anomaly temperature,respectively.
Results and Discussion
Figure 1 shows an atomic image of the nearest neighbor
Ti plane from central Cu atom obtained from XFH
measurement using Cu Kα fluorescence at Roomtemperature. The atomic positions in the X-ray diffraction
experiment [4] are indicated by open circles. Although
XFH appears to approximate atomic positions, some
images do not match. It is considered that the local
structure which could not be obtained by XRD wasobserved. The result that Ti-ions are located at several

Fig. 1: Atomic image of the nearest neighbor Ti planefrom central Cu atom by Cu Kα XFH at room temperature.

3point could elucidate the giant dielectric constant ofCCTO.
Figure 2 shows a cross-sectional view of a region (y =1.85 Å) between the dotted lines in Fig. 1. The black line
and the red line are the results at 80 K and 300 K,respectively. Basically, the cross-section shows similar
patterns, but the peak at about 6 Å disappeared at 80 K.
The result show the Ti position is regulated in low
temperature, and then elucidate the decrease of dielectric
constant at about 100 K. Further XFH studies are carriedon around the dielectric-anomaly temperature including Ti
K and Ca K XFH measurements. These results would
elucidate the dielectric anomaly of CCTO.

Fig. 2: Cross-sectional view of a region (y = 1.85 Å)
between two dotted lines in Fig. 1. Red line: roomtemperature, Black line: 80 K.
References[1] A. P. Ramirez, et al., Solid State Commun., 115, 217(2000).
[2] Photon Factory Activity Report 2014 (KEK), #32-B,195; 2015 (KEK), #33-B, 378; 2016 (KEK), #34-B, 286;
2017 #35 (2018), 283[3] Y. Tezuka, et al., J. Elec. Spec. Relat. Phenom. 220, 114(2017).
[4] B. Bochu, et al., J. Solid State Chem.29,291(1979).
* h18ms207@hirosaki-u.ac.jp** tezuka@hirosaki-u.ac.jp