Photon Factory Activity Report 2005 #23 Part B (2006)
Electronic Structure of Condensed Matter

2C/ 2005G104

Resonant Soft X-ray Raman Scattering of BaTiO3
Yasuhisa TEZUKA*1, Toshiyuki SASAKI2, Yasuo FUJITA1, Megumi OKI2, Nobuo NAKAJIMA2
1
Hirosaki University, 3 Bunkyo-cho, Hirosaki, Aomori, 036-8561, Japan2
Photon Factory, Institute of Materials Structure Science, 1-1 Oho, Tsukuba 305-0801, Japan
Introduction
BaTiO3 is known to be a typical ferroelectric material,
which has no 3d electron, nominally. It is suggested that
the Ti 3d components are strongly mixed with the O 2p
state and the hybridization affects the ferroelectric
properties [1]. Ti oxides have attracted the interest ofresearchers because of their strong hybridization. Many
body effects are observed in these compounds [2, 3].
Experimental
SXE spectra were obtained at beamline BL-2C in
Photon Factory, KEK. A soft X-ray monochromatorconsisting of a Rowland type grazing-incidence
monochromator with a 5-m spherical grating (1200lines/mm) [4] was used. The energy resolution of SXE
spectroscopy (SXES) and XAS measurements was about
0.4 and 0.1 eV at 450 eV, respectively.
Powdered BaTiO3 was measured in this experiment.
BaTiO3 has a perovskite structure that includes TiO6cluster. BaTiO3 undergoes ferroelectric phase transition atabout 400 K. In paraelectric phase (Oh symmetry), the 3dstate is split into a lower t2g and a higher eg state by thecrystal field. Measurements were performed in R.T. At
the temperature, the sample is in ferroelectric phase andhas tetragonal structure (C4v).
Results and Discussions
Figure 1 shows Ti 2p XAS spectrum of BaTiO3. TheXAS spectrum shows four main peaks and two satellites.
In addition, two weak structures are also observed in thepre-edge region. The two lower energy peaks (LIII) in themain structure originate in excitations from Ti 2p3/2 state,while the two higher peaks (LII) originate in excitations
from Ti 2p1/2 state. Each structure is split into two peaksby the crystal field. The satellites are assigned to the CTsatellite.
Figure 2 shows the polarization dependence of resonant
Raman spectra of BaTiO3, which are plotted against theenergy shift from elastic-scattering energy. Numbers
beside the spectra correspond to the numbers in Fig.1.
Vertical bars indicate Ti 3d → 2p fluorescence, which
originate from the Ti 3d state mixed with the O 2p state.
An elastic peak is observed in a polarized configuration
at 0 eV, but not in depolarized configuration. Ramanpeaks that originate from CT excitation are observed atabout 7.0 and 13.3 eV in the polarized configuration.
These results are consistent to those of TiO2 [3]. Inaddition, however, other Raman peaks are observed ataround 1 ~ 3 eV (hatched area) in BaTiO3. In a simple
view, such a low energy peak is thought to originate in d-100

Users' Report

Fig.1 Ti 2p XAS spectrum of BaTiO3. Vertical bars
indicate excitation energies in the SXESmeasurements.

Fig.2 Polarization dependence of Raman spectra ofBaTiO3. The vertical dotted line at 0 eV indicates theelastic peak and the others indicate the Raman peaks.
Vertical bars indicate Ti 3d → 2p fluorescence.
d excitation [5]. However, the origin of these peaks isunknown, since the BaTiO3 has no 3d electron, nominally.
References[1] R.E. Cohen, Nature 358, 136 (1992).
[2] Y. Tezuka et al., J. Phys. Soc. Jpn. 65, 312 (1996).
[3] Y. Harada et al., Phys. Rev. B 61, 12854 (2000).
[4] Y. Harada et al., J. Synchrotron Rad. (1998). 5, 1013.
[5] Y. Tezuka et al., PF Activity Report 2004 #22 Part B,
111 (2005).
* tezuka@si.hirosaki-u.ac.jp