Photon Factory Activity Report 2017 #35 (2018)

BL-9C, BL-10A/2013G542, 2015G505, 2015G506

Temperature Dependence of the Pre-edge Features in the XANES Spectra ofTetragonal and Cubic BaTiO3 and PbTiO3
Akira YOSHIASA1*, Tsubasa TOBASE1, Ginga KIYAHARA1, Hidetomo HONGU1, Tatsuya
HIRATOKO2, Tomotaka NAKATANI1 and Kei-ichiro MURAI2
1Graduate School of Sciences, Kumamoto Univ. Kumamoto 860-8555, Japan
2
Industrial and Social Sciences, Tokushima University, Tokushima 770-8506, Japan
1 Introduction
Temperature dependence of the intensities of the preedge peaks has been observed for various titanium
compounds. Hashimoto et al.[1] measured the Ti K-edge
XANES spectra of several titanates at varioustemperatures. The pre-edge peak intensities normallyincrease with temperature but the ferroelectric phases
show different temperature dependences. The temperaturedependence is not only because of a phase transition or
local geometrical distortion of the titanium site but also
because of the thermal vibration of the absorbing andscattering atoms. PbTiO3 and BaTiO3 perovskites havebeen intensively studied because of their ferroelectric
property under ambient conditions and because they areuseful as functional materials. We report quantitative
comparison of the pre-edge peaks of BaTiO3 and PbZrO3
perovskite-type compounds in a wide temperature range
using AIIP standardization and the change of the intensityof the pre-edge with temperature. [2].
2 ExperimentSingle crystals of BaTiO3 and PbTiO3 perovskite wereprepared and their structures were confirmed by X-ray
diffraction at beamline BL-10A. The XAFS spectra near
the Ti K-edge were measured in transmission mode atbeamlines BL-9C [2]. The measurements were performedin the temperature range 20–900 K under a helium
atmosphere. To clarify the temperature dependence, thedifference spectra (D spectra) between the lowtemperature spectrum and those at higher temperatures
were determined. The D spectra at different temperatures
were determined for the same sample. The reason for
determining the D spectra is to detect only thetemperature-dependent parts of the spectra. [2].
3 Results and Discussion
Figure 1 shows the pre-edge peak spectra of BaTiO3and PbTiO3 at various temperatures. The arrows in thefigures show the peak-top intensity change and energy
shift with increasing temperature. The A2 peak intensity
greatly decreases with increasing temperature and thepeak-top energy shifts to the higher energy side. The shift
values are in the range 0.2–0.3 eV, which are too large to
be an energy shift of an electron orbital by thermal energy.
Figure 2 shows the pre-edge regions in the Ti K-edge
XANES spectra and the D-spectra between the lowest
temperature spectra and those at higher temperatures forBaTiO3. The temperature dependence of the electrontransitions can be extracted from the D spectra. The preedge peak positions of the A2 peaks are clearly different
from the peak positions of the D2 peaks. The temperaturedependence of the transition to each orbital is different.
The transitions to orbitals with different temperaturedependencies can be separated by determining the Dspectra. The true temperature dependence of the transition
to each orbital is obtained from the D spectra. Thetemperature dependence of A2 peaks can be explained bythe position and decrease of the D2 valley in the Dspectra.

Fig. 1: Temperature variation of the pre-edge peaks in Ti
K-edge XANES spectra of BaTiO3 and PbTiO3.

Fig. 2: Pre-edge peaks in the Ti K-edge XANES andthe difference spectra of PbTiO3 (difference between
the spectrum at 500 K and those at 600–800 K).
References[1] T. Hiratoko, A. Yoshiasa, T. Nakatani, M. Okube, A.
Nakatsuka K. Sugiyama, Journal of Synchrotron
Radiation, 20 (2013) 641-643.
[2] A.Yoshiasa, et al., Phys. Status Solidi B (2018)https://doi.org/10.1002/pssb.201800050.
* yoshiasa@sci.kumamoto-u.ac.jp