Photon Factory Activity Report 2018 #36 (2019)

BL-NW10A, BL-9c, Bl-10A/2013G542, 2015G505, 2015G506

Temperature Dependence of the Pre-edge Features in the XANES Spectra ofTetragonal and Cubic ATiO3 (A = Sr, Ba and Pb) and PbZrO3
Akira YOSHIASA1,*, Ginga KITAHARA1, Hidetomo HONGU1 and Kei-ichiro MURAI2
1
Graduate School of Sciences and Technology, Kumamoto Univ., Kumamoto 860-8555, Japan
2
Graduate School of Technology, Industrial and Social Sciences,Tokushima University, Tokushima 770-8506, Japan
1 Introduction
Characterization of the pre-edge structure in the Kedge XANES spectra of 3d and 4d transition metals isuseful for understanding materials in the fields of physics,
chemistry and earth sciences. Perovskite-type ATiO3 (A =Sr, Ba and Pb) compounds undergo several structuralphase transitions. PbTiO3 and BaTiO3 perovskites havebeen intensively studied because of their ferroelectric
property under ambient conditions and because they areuseful as functional materials [1,2]. Here, we reportquantitative comparison of the pre-edge peaks of ATiO3(A = Sr, Ba and Pb) and PbZrO3 perovskite-typecompounds in a wide temperature range using AIIP
standardization [3] and the change of the intensity of thepre-edge with temperature[4].
2 Experiment
The XAFS spectra near the Ti and Zr K-edge weremeasured in transmission mode at beamlines BL-9C PFand NW10A AR, KEK. The measurements wereperformed in the temperature range 20–900 K under ahelium atmosphere. To clarify the temperaturedependence, the difference spectra (D spectra) between
the low-temperature spectrum and those at higher
temperatures were determined. The reason for
determining the D spectra is to detect only thetemperature-dependent parts of the spectra. When only
the temperature changes for the same sample, thedifference spectrum shows only the temperaturedependent parts because the other factors cancel out.
Figure 1a and 1b show the Ti K-edge XANES spectra ofSrTiO3 from 300 to 700 K and the D spectra obtained bytaking the difference between the spectrum at the lowest
temperature (300 K) and those at higher temperatures(400–700 K) [4].
3 Results and Discussion
Figure 2 shows the pre-edge peak spectra of BaTiO3and PbTiO3 at various temperatures. For PbTiO3, the A2
peak intensity greatly decreases with increasing
temperature and the peak-top energy shifts to the higher
energy side. The peak-top energy also shifts to the higher
energy side for BaTiO3. The shape of the A2 peak forPbTiO3 is similar that for BaTiO3. The shift values are inthe range 0.2–0.3 eV, which are too large to be an energy
shift of an electron orbital by thermal energy.
Figures 3 show 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 for

PbTiO3. It is also confirmed that some orbitals overlap
near the A2 peak and the A2 peak-top position does not
represent the energy of the electronic transition. The preedge peak positions of the A2 peaks are clearly different
from the peak positions of the D2 peaks. The transitions
to orbitals with different temperature dependencies can beseparated by determining the D spectra. The true
temperature dependence of the transition to each orbital is
obtained from the D spectra.

Fig. 1: a) Ti K-edge XANES spectra of SrTiO3 at 300–700 K. (b)Difference spectra of SrTiO3, which are the difference between thespectrum at 300 K and those at higher temperatures (400–700 K)[4].

Fig. 2: Temperature variation of
the pre-edge peaks in Ti K-edge
XANES spectra of tetragonal
perovskite-type BaTiO3 andPbTiO3 [4].

Fig. 3: Pre-edge peaks in the Ti K-edge XANES and the difference
spectra of PbTiO3 (difference between the spectrum at 500 K andthose at 600–800 K)[4].

References[1] Nakatani et al. Acta Cryst. B72 (2016) 151-159.
[2] Yoshiasa et al. Acta Cryst. B72 (2016) 381-388.
[3]Hiratoko et al. J. Synchrotron Rad. 20 (2013) 641-643[4]Yoshiasa et al. Phys. Status Solidi B (2018) 1800050(8pages) https://doi.org/10.1002/pssb.201800050* yoshiasa@kumamoto-u.ac..jp