Photon Factory Activity Report 2004 #22 Part B (2005)
Electronic Structure of Condensed Matter

2C/2003G005

Polarization dependence of soft-x-ray Raman scattering of Ti2O3
Yasuhisa TEZUKA1*, Takahiro MAEDA1, Yoshihisa HARADA2, Tomoyuki TAKEUCHI2,Hitoshi OSAWA3, Shik SHIN2,3, and Nobuo NAKAJIMA4
1
Hirosaki University, 3 Bunkyo-cho, Hirosaki 036-8561, Japan
2
RIKEN Harima Institute, 1-1-1 Koto, Mikazuki-cho, Sayo-gun, Hyogo 679-5148, Japan
3I SSP, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa-shi, Chiba 277-8581, Japan4Hiroshima University, 1-3-1 Kagamiyama, Higashi-hiroshima 739-8526, JapanIntroduction
Ti2O3 is known to be the typical MH type semiconductorsthat have narrow band gap (Egap < 0.1 eV) in the insulator phase,
which has one 3d electron nominally. It is known that the Ti 3dcomponents are strongly mixed in the O 2p state [1]. Early TM
compounds including Ti compounds have attracted the interestof researchers because of their strong hybridization energies.
Many body effects are observed in these compounds [2-4].

Experimental
SXE spectra were obtained at beamline BL-2C in Photon
Factory, KEK. A soft X-ray monochromator consisting of aRowland type grazing-incidence monochromator with a 5-m
spherical grating (1200 lines/mm) [5] 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 Ti2O3 was measured in this experiment. Ti2O3
has a corundum structure with a trigonal Bravais lattice. The
structure includes the TiO6 octahedron. In Oh symmetry, the 3dstate is split into a lower t2g and a higher eg state by a crystal
field. The TiO6 cluster in the corundum structure is distorted.
Therefore, the t2g state is split further into a1g and eg states.

Fig.1 Ti 2p X-ray absorption spectrum of Ti2O3. Vertical bars
indicate excitation energies in the SXES measurements.

Results and Discussions
Figure 1 shows the XAS spectrum of Ti2O3. The XAS
spectrum shows four main peaks and two satellites. The twolower peaks (LIII) in the main structure originate from theexcitation of Ti 2p3/2 electrons, while the two higher peaks (LII)
originate from the excitation of Ti 2p1/2 electrons. Each structureis split into two peaks by the crystal field. The satellites are
assigned to the CT satellite.
Figure 2 shows the polarization dependence of resonant
Raman spectra of Ti2O3, which are plotted against the energy
shift from elastic scattering energy. Numbers beside the spectra
correspond to the numbers in Fig.1. Vertical bars indicate Ti 3d→2p3/2 fluorescence. The lower energy peak corresponds to theTi 3d state just below the Fermi energy, while the higher energy
peak corresponds to the Ti 3d state mixed with the O 2p state.
The spectra observed in a polarized configuration show
the elastic peak at 0 eV, while the spectra in depolarized
configuration do not show the elastic peak. The peak near 0 eV
in the depolarized spectrum 4 is not elastic peak, but afluorescence peak, since it has finite energy shift from 0 eV.
On the other hand, two Raman peaks are observed atabout 1.0 and 3.0 eV, indicated by dotted lines in Fig. 2. Thesepeaks are thought to originate in the d-d excitation. Since the t2g
state is split into a1g and eg states in a trigonal symmetry, several
d-d excitations would be possible.
These results are in contrast to that of TiO2 [4], in which
several CT excitations are observed at 5-13 eV but no d-d
excitation is observed. The 3d electron just below the Fermi
energy considerably affects the resonant SXE spectra.

Fig.2 Polarization dependence of Raman spectra of Ti2O3.
The vertical dotted line at 0 eV indicates the Fermi energyand the others indicate the Raman peaks. Vertical barsindicate Ti 3d → 2p fluorescence.
References[1] K. Okada et al., J. Electron Spectrosc. Relat. Phenom.,
62, 131 (1993).
[2] T. Uozumi, et al., J. Phys. Soc. Jpn., 65, 1150 (1996).
[3] Y. Tezuka et al., J. Phys. Soc. Jpn. 65, 312 (1996).
[4] Y. Harada et al., Phys. Rev. B 61, 12854 (2000).
[5] Y. Harada et al., J. Synchrotron Rad. (1998). 5, 1013.
* tezuka@si.hirosaki-u.ac.jp

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