Photon Factory Activity Report 2014 #32 (2015) B

BL-4A/2012G635

Chiral smectic transition phases appearing near the electric field-induced phasetransition observed by resonant micro-beam X-ray scattering (2)Atsuo Iida1 and Yoichi Takanishi2
1
Photon Factory, Institute of Material Structure Science, 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan
2
Kyoto University, Kitashirakawaoiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan
1 Introduction
Liquid crystals show rich structures and complex phasetransitions due to the temperature change. Among them,chiral smectic C liquid crystals are characterized by a
one-dimensional layer structure and an average molecularorientation tilted from the layer normal. The generalsequence of the sub-phases in the chiral semctic C phase
is SmC* (synclinic), SmCA* (two-layer periodicity),
SmC* (three-layer periodicity) and SmCAF* (four-layerperiodicity) phases as the temperature is decreased.
Recently new phases other than three or four layer
periodicity were reported [1][2]. Since an electric fieldalso induces sub-phases, it is important to investigate
electric field induced phase transition to study the originof these sub-phases [3]. In our previous resonant X-ray
scattering (RXS) measurement [4], a new electric filed
induced transition phase having a very long periodicity oftwelve-layer was found in a novel Br-contained liquidcrystal. In this paper, a Se-contained liquid crystal,widely used for the RXS measurement, was investigatednear the electric-field induced phase transition.

6 layer periodicity. At higher applied voltages, the peakintensity decreases (fig.1(e)) and then only the streak isobservable (fig.1(f)). After the ferroelectric (SmC*)
transition, RXS disappears. In this sample, in contrast to
the Br-contained liquid crystal [4], no twelve-layer
periodicity phase appeared near the phase boundary
between the SmC* and SmC*. The phase sequences atother temperature are now under investigation.
References[1]Y.Takanishi et al., Phys. Rev. E87(2013)050503(R)[2] S.Wang et al., Phys. Rev. Lett. 104(2010)027801[3] K. L. Sandhya et al., Liq. Cryst. 36, 1101 (2009).
[4] A.Iida et al., Phys. Rev. E. 89 (2014)032503[5]L.S.Matkin et al., Phys. Rev. E64(2001)021705* atsuo.iida@kek.jp

2 Experiment
The Se contained liquid crystal used was AS657 [5]and is sandwiched between 80 m thick glass plates
coated with indium tin oxide as an electrode. The phasesequence of the material is Iso 95.8°C SmA 88.2°C
SmC* 86.3°C SmCA*(qT=1/2) 83.6°C SmCA*(qT=1/3)
82.6°C SmCA*(qT=0). The applied electric field was asquare wave form with 100Hz.
RXS experiments were performed on the beam line 4A
using a KB focusing system. The incident energy was setat the absorption edge of Se (12.65 keV) and the beam
size was less than 5 x 5 m2. A pixel array detector(Pilatus-100K, DECTRIS) located at 80 cm from thesample (focusing point) was used for the measurement.
3 Results and Discussion
Figure.1 sows the intensity distributions along the layer
normal for various applied field at 80.1°C as afunction of the normalized scattering vector
obtained from the 2D diffraction pattern. Below
30V, the RXS diffraction pattern shows the SmCA*
phase (fig.1(a)). At 30V, the SmC* phase appears(fig.1(b)) and it lasts until 80.0 V. No transition phase
was observed at 30V. Above 80.2V, the 1/3 order peakshifts to the low q value and becomes broad while a newpeak appears as shown in fig.(d) which indicates the new

Fig.1 RXS intensity distributions along thelayer normal. A dotted line in fig (f) shows thediffraction pattern from the ferroelectric phase at86V. Missing data q/qo = 0 through 0.18 are due tothe shadow of a direct beam stopper.