Photon Factory Activity Report 2017 #35 (2018)

BL-16A/2017G706

Temperature Dependent O K Resonant X-ray Emission Spectra of CaCu3Ti4O12
Yasuhisa TEZUKA1,*, Haruki KAMIDE1, Hojun IM1, Takao WATANABE1,and Nobuo NAKAJIMA2
1
Grad. Sch. of Sci. and Tech., Hirosaki Univ., Hirosaki, Aomori 036-8561, Japan
2
Grad. Sch. of Sci., Hiroshima Univ., Higashi-Hiroshima, Hiroshima 739-8526, Japan

2 ExperimentSingle crystal CCTO(100) made by floating zone
method was used in this study. XRS spectra wereobserved using soft X-ray emission spectrometer atbeamline BL-16A. Vertically polarized light was used andscattering spectra in polarized configuration [5] wereobserved. The energy resolution of XRS measurement
was about 1.0 eV.
3 Results and Discussion
Figure 1 shows O K XAS spectra of CCTO(100)measured by partial photon yield method (O K emission
intensity). Temperature dependence of the XAS wasobserved. Line and circles show the spectra at RT and85K, respectively. No distinct difference was observed inthese spectra. XE spectra were observed under excitationsin this energy range. Vertical bars with numbers denotethe excitation energies in XRS measurements.
Figure 2 shows temperature dependence of O K
resonant XE spectra of CCTO(100). Line and circles
show the spectra at RT and 85K, respectively. Resonantly
enhanced fluorescence peaks were observed at about 523
and 526 eV, while a weak Raman peak was observed atabout 2 eV lower than elastic peak as shown by verticalbars (2, 3). The fluorescence peaks show clear
temperature dependence at O K resonance (3~7), while
the fluorescence peak does not show the dependence athigh excitation energy (11). These peaks are originatedfrom O 2p state that hybridized with both Ti 3d and Cu 3dstates. The temperature dependence results show decreaseof O 2p state at low temperature, suggesting charge

Intensity (arb.unit)

46321

589 10RT85K

711CaCu3Ti4O12(100)O K XAS
PPY525 530 535 540 545 550 555 560
Raman Shift (eV)Fig. 1: Temperature dependence of O K XAS spectra ofCCTO(100). Line: RT, circles: 85K. Vertical bars denote
excitation energies of XE measurements.
CCTO(100)O K XESpol.

1110987

Intensity (arb.unit)

1 Introduction
A-site ordered perovskite CaCu3Ti4O12 (CCTO) has
attached much attention recently, because it shows a giant
dielectric constant (~104) over wide temperature range
from about 100 to 600 K and the dielectric constantdecreases to one-hundredth without structural phasetransition at the temperature under about 100 K [1]. To
clarify the nature of the dielectric anomalies, it isimportant to investigate electronic structure of CCTO.
The CCTO was studied by X-ray Raman scattering(XRS) study, which observes core excitation like 2p3dand 2p4d, where underline denote core hole [2]. The
results of XRS on Cu K edge have been reported [3].
Temperature dependent XRS study showed increasing
both Ti 3d and Cu 3d state at low temperature [4]. In thisstudy, O K resonant X-ray emission (XE) spectra ofCCTO were observed.

65RT85K

520525530
Emission Energy (eV)4321Fig. 2: Temperature Dependence of O K resonant XE
spectra of CCTO(100). Line: RT, circles: 85K. Thin andbold vertical bars denote elastic and Raman scatteringpeaks, respectively. Numbers beside spectra denote
excitation energies in Fig. 1.
transfer to Ti 3d and Cu 3d state. More detailed study ofO K XES would reveal the nature of charge transfer inCCTO.
References[1] A.P. Ramirez, et al., Solid State Commun. 115, 217(2000).
[2] Y. Tezuka, et al., J. Phys. Soc. Jpn. 83, 014707 (2014).
[3] Y. Tezuka, et al., J. Electron Spectrosc. Relat. Phenom.
220, 114 (2017).
[4] Y. Tezuka, et al., PF Activity Report 2014 #32, 195(2015)[5] Y. Harada, et al., J. Synchrotron Rad. 5, 1013 (1998).
* tezuka@hirosaki-u.ac.jp