Photon Factory Activity Report 2014 #32 (2015) B

BL-9A/2013G572

Time-Resolved X-ray Absorption Spectroscopy of BaTiO3Under Pulsed Electric FieldAkihiko Sano1,*, Nobuo Nakajima1, Jun-ichi Adachi2, Yasuhiro Niwa2 and Yasuhisa Tezuka3
1
Grad. Sch. of Sci., Hiroshima Univ., Higashi-Hiroshima, Hiroshima 739-8526, Japan2
Photon Factory, Tsukuba, Ibaraki 305-0801, Japan
3
Grad. Sch. of Sci. and Tech., Hirosaki Univ., Hirosaki, Aomori 036-8561, Japan
1 Introduction
The external electric field induces lattice strain inferroelectric BaTiO3 by the inverse piezoelectric effect.
Recently, there are several papers discussing the responseof the BaTiO3 lattice to the electric field based on X-ray
diffraction (XRD) data [1, 2]. A pulsed field seems toinduce nonlinear elastic strains in contrast to a static field.
The dynamic response of the lattice strain is an essential
property of dielectric materials, and it is important tounderstand the response from an electronic point of view.
In this report, the results of the time-resolved X-ray
absorption experiments of a dielectric material are briefly
shown. We discuss the dynamical behavior of theferroelectric moment to explore hidden dielectric
properties. This work leads to the development of newdielectrics with high dielectric constant.
2 Experiment
A BaTiO3 (001) single crystal with the size of
5×5×0.5t mm was clamped by copper electrodes.
Rectangular pulsed high-voltage (HV) was applied along
the thickness direction with a repetition rate of 10 kHz.
The pulse width (tw) was tuned to 5 s or 20 s, andvoltage amplitude was changed up to 1.0 kV (2.0 kV/mm).
Ti K-edge X-ray absorption spectra (XAS) weremeasured on the beamline BL-9A. The linearly polarized
X-ray beam was incident on a (100) side surface of thesample. The polarization vector of the X-ray was parallelto the electric field, and therefore to the direction of
spontaneous polarization of sample. Ti K fluorescence
was detected by a high-speed silicon drift detector(Amptek XR-100SDD). Digitized pulse signals from amultichannel analyzer (Amptek PX4) were gated by
300 ns logic pulses with several delay times (td) from therise of the HV pulse, and were recorded by a counter. In
this method, total counts of the signals are limited by thewidth of the gate signals, so that it is necessary to sum
several spectra in order to increase statistical accuracy. A
sub-microsecond response is detectable by this technique.
3 Results and Discussion
Figure 1 shows comparison of spectra at different delaytimes (td = 0 s, 15 s) under HV pulse with tw = 20 s.
The delay time origin (td = 0 s) was set to the rising edgeof the trigger pulse which was applied to a HV powersupply. Each spectrum was obtained by adding 30 spectra.
The pre-edge features between 4965 and 4975 eV as well
as a shoulder peak at 4980 eV are insensitive to the HV
pulse and remain unchanged. On the other hand, the main

peak at 4985 eV shows a slight energy shift of about
0.2 eV. The main peak is due to the 1s-4p dipole
transition. Since the electronic response to the electricfield is faster than the our present time-window, thisenergy-shift is not simply due to a change of the electronorbital.
One possible explanation is the charging effect whose
time-scale is governed by the capacitance of the BaTiO3
sample. Indeed, slight energy shift was observed withtw = 5 s. The depletion of the electrons may changes thevalence of Ti ions. This is a first experimental result that
confirm the influence of the HV pulse on the electronicstates. Much larger changes can be expected in thin films,
since the larger effective electric field may induces
additional piezoelectric effect to increase electrondepletion.

Figure 1. Ti K-edge time-resolved X-ray absorption
spectra of a BaTiO3 single crystal under HV pulse. The
red (blue) line represents a spectrum with a delay time oftd = 0 s (td = 15 s). The main peak shows an energy
shift of about 0.2 eV as indicated by arrows.
References[1] R. Tazaki,
D. Fu,
M. Itoh,
M. Daimon and
S. Koshihara, J. Phys.: Condens. Matter. 21, 215903(2009).
[2] C. Moriyoshi, S. Hiramoto, H. Ohkubo, Y. Kuroiwa,
H. Osawa, K. Sugimoto, S. Kimura, M. Takata,
Y. Kitanaka, Y. Noguchi and M. Miyayama, Jpn. J.
Appl. Phys. 50, 09NE05 (2011).
* akihiko-sano@hiroshima-u.ac.jp