BL-7C/2019G591

Temperature dependent electronic structure of SrTiO3 by means of resonant X-ray
Raman scattering
Mizuki Takahashi1*, Shunsuke Nozawa2, Nobuo Nakajima3, Toshiaki Iwazumi4,and Yasuhisa Tezuka1**
1
Grad. Sch. of Sci. and Tech., Hirosaki Univ., Hirosaki, Aomori 036-8561, Japan2
Photon Factory, Inst. of Mats. Struct. Sci., Tsukuba, Ibaraki 305-0801, japan
3
Grad. Sch. of Sci., Hiroshima Univ., Higashi-Hiroshima, Hiroshima 739-8526, Japan
4
Grad. Sch. of Eng., Osaka Pref. Univ., Sakai, Osaka 599-8531, Japan

2 Experiment
In this study, single crystal of STO(100) was used.
XRS spectra were measured using X-ray emission
spectrometer (Escargot) at BL-7C of Photon Factory. The
scattered photons were dispersed by Ge (400) crystal anddetected using a multi-channel proportional counter(PSPC). The total energy resolution is about 1 eV.
3 Result and Discussion
Figure 1 shows Ti K absorption spectrum and Ti 3dresonant XRS spectra. The emission spectra are plottedagainst the energy loss from the excitation energy (Ramanshift), and two sets of the resonant XRS spectra at RT (red)and 40K (blue) are superimposed. Here, t2g and eg peaks ofTi 3d state, which reflect crystal field splitting under Ohsymmetry, are observed in both LIII and LII spectrum. These
spectra show temperature dependence under Ti 3d resonantcondition, where the eg peak changes its intensity morethan the t2g peak. Since the eg orbit directed to O-ion andresponsible for Ti-O bonding, the result indicates that theTi-O hybridization changes with changing temperature.
Figure 2 shows temperature dependence of the LIII peakintensity excited at 4969.25 eV (#7 in Fig.1), where the eg
peak is dominant in XRS spectrum. It can be seen theintensity is decreasing with dropping temperature. The
result shows increasing Ti 3d state at low temperature, andthen suggests the increasing of Ti-O hybridization.
However, no particular change was observed around thephase transition temperature around 105 K.
It is known that STO has a giant dielectric constant ofε~2×10⁴ in a quantum paraelectric phase under 10 K [3],Photon Energy (eV)
4960
4970
Ti K XAFS

4980

7 10Intensity (arb.unit)

Ti K XRS

4990

5000

SrTiO3(100)1LIIRT eg
40KLIIIeg t2gt2g107470

465

460

1455

Raman Shift (eV)Fig.1: Ti K XAFS and resonant XRS spectra of STO measured
at RT (red) and 30K (blue).
1.0

Intensity

1 Introduction
Perovskite SrTiO3 (STO) is known to maintainparaelectric properties until 0 K, while it undergoes
structural phase transition at zone boundary around 105 K.
On the other hand, another perovskite BaTiO3 undergoes
ferroelectric phase transition at about 400 K and thehybridization between Ti and O has an effect on the phasetransition. In this study, to understand the electronic stateof STO, resonant X-ray Raman scattering (XRS) by
Ti2p3d and Ti2p4p excitations (underline means corehole) [1, 2] and their temperature dependence weremeasured around the Ti K absorption edge.

0.5

SrTiO3
LⅢ peakhν = 4969.25 eV

0.0050 100 150 200 250 300
Temperture (K)Fig.2: Temperature dependence of LⅢ peak intensity at hνex =4969.25 eV (#7 in Fig.1).

while the lowest temperature in this experiment is 24.6 K.
In the future, the electronic structure at low temperature
region should be investigated in detail.
References[1] Y. Tezuka, et al., J. Phys. Soc. Jpn. 83, 014707 (2014).
[2] Y. Tezuka, et al., J. Electron Spectrosc. Relat.
Phenom. 220, 114-117 (2017).
[3] M. I. Marqués, et al., Phys. Rev. B72, 092103 (2005).
**tezuka@hirosaki-u.ac.jp