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

2C/2004G013

Soft X-ray emission study of BaTiO3 nanoparticles
Megumi OKI1, Nobuo NAKAJIMA1*, Hiroshi MARUYAMA1,Yasuhisa TEZUKA2, Toshiyuki TODA3
1
Grad. Sch. of Sci., Hiroshima Univ., 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526, Japan
2
Fac. Sci. and Tech., Hirosaki Univ. 3 Bunkyo, Hirosaki, Aomori 036-8561, JapanTODA KOGYO Corp., 1-4, Meiji-Shinkai, Otake, Hiroshima 739-0652, Japan

Results and Discussion
Figure 1 shows the Ti 2p TEY spectra of BTO(50nm).
The assignments of main peaks are labeled in the figure.
A vertical bar indicates excitation energy in the SXE
spectra shown in Fig. 2, in which the spectra are plottedagainst the energy shift from elastic peaks (a dotted line).
A dashed line indicates the Ti Lȕ1 fluorescence peaks. Vertical bars indicate d-d excitations. Statistical accuracy israther low, however, a slight enhance of d-d excitations in
D=85 and 50 were observed, which means that Ti displacement from the body center remains at D=50 eventhough crystal symmetry approaches to cubic. Therefore,
displacement of Ti is a key role for the advent of strong
ferroelectricity in nano-BTO.

t2g eg455t2geg

L3

L2460465470475

Photon Energy (eV)Fig. 1 TEY spectra of BaTiO3(50nm) at Ti 2p-edge. TheL2-eg edge is chosen for the excitation energy of SXEmeasurements shown in Fig. 2BaTiO3

h excite=465.4eV (L2-eg)

120nm

Intensity (a.u.)

Experimental
SXE spectra were obtained at beamline BL-2C. A soft
X-ray monochromator consisting of a Rowland type grazing-incidence monochromator with a 5m spherical grating(1200 lines/mm) [2] was used. X-ray absorption spectra
were obtained by the total electron yield (TEY) method.
Energy resolutions of both TEY and SXE spectra at 450
eV were ~0.1 eV and ~0.4 eV, respectively.
BTO nano particles with averaged diameters (D nm) of
D=30, 50, 85, 120 were prepared. All the experiments
were carried out under room temperature and ultrahigh-9vacuum of the order of 10 Torr.

BaTiO3 50nm
Ti 2p TEY

Intensity (a. u.)

IntroductionBaTiO3 (BTO) is one of the most promising candidates
for the host materials of next-generation high-density
memory devices, because of its well-known strong ferroelectricity. BTO has a perovskite structure with Ti displacement from a body-center in tetragonal symmetry atroom temperature. Recently, nano-sized BTO powders
have been studied intensively. It has been reported that thedielectric constant of nano-BTO has a maximum at a certain diameter, several tens of nm, and rapidly reduces tozero with decreasing the size [1].
0Ti in bulk BTO has nominally 3d configuration, butactually it is strongly mixed with a charge transferred
1 -1
3d L configuration by the covalency hybridization. In thecase of nano-BTO, the crystal symmetry becomes higher(Td•Oh) with decreasing the size, which was confirmed by
X-ray diffraction. Then, what is the origin of enhanced
1 -1
ferroelectricity in nano-BTO? Does 3d L configuration
still remain in nano-BTO? We therefore measured soft Xray emission (SXE) spectra in order to obtain the information of valence-band configuration.

85nm

50nm

30nm

0-5
Raman Shift (eV)Fig. 2 SXE spectra of BTO(D nm) for D=120, 85, 50and 30. The excitation energy is 465.4eV. A dotted anda dashed line indicate the elastic peaks and Ti Lβ1 fluorescence peaks, respectively. Vertical bars indicate thed-d excitation peaks
References[1] M. Yashima et al., J. Appl. Phys., 98 (2005), 014313;
S. Aoyagi et al. J. Therm. Anal. Cal., 81 (2005), 627; S.
Wada et al. Jpn. J. Appl. Phys., 42 (2003), 6188; K. Kinoshita et al., J. Appl. Phys., 47 (1976) 371; G. Arlt et al.,ibid., 58 (1985) 1619; M. H. Frey et al., Ferroelectrics,
206-207 (1998) 1555.
[2] Y. Harada et al., J. Synchrotron Rad. 5 (1998), 1013
*nobuo@hiroshima-u.ac.jp

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