Photon Factory Activity Report 2017 #35 (2018)

BL-4A/2016G604

Chiral smectic transition phases appearing near the electric field-induced phasetransition observed by resonant micro-beam X-ray scattering (4)Atsuo Iida1,*, Yoichi Takanishi2, Atsuo Fukuda3, and Jagdish K. Vij3
Photon Factory, Institute of Materials Structure Science, 1-1 Oho Tsukuba, Ibaraki 305-0801, Japan2
Department of Physics, Faculty of Science, Kyoto University, Sakyou-ku Kyoto 606-8502, Japan3
Department of Electronic and Electrical Engineering, Trinity College, The University of Dublin,Dublin 2, Ireland
11 Introduction
Various subphases of chiral smectic-C liquid crystals(LCs), which are characterized by an azimuthalarrangement of molecular orientations among the layers,
were discovered between the lower-temperature SmC*A(antiferro) and higher-temperature SmC* (ferro) phases.

In an electric field, these LCs undergo an electric fieldinduced phase transition to the SmC* phase withincreasing electric field.
For the smectic phase
identification, resonant X-ray scattering (RXS) has playeda crucial role. In our previous RXS measurement [1, 2],12-layer and n-layer (n = 5 to 8) periodicity subphases
were revealed in Br- and Se-containing LCs, respectively,
near the field-induced phase transition. The observed
transitional subphases, however, were different for thetwo LC samples. In this report, we use a Se-containing
mixture LC sample which shows the typical case of thefrustration between the SmC*A and SmC* phases [3].
2 Experiment
A Se-containing LC mixture sample comprises 80%AS657 and 20% AS620 (Kingston Chemicals Ltd,
University of Hull, Hull, U.K.) and is sandwiched
between 80 m thick glass plates coated with indium tinoxide as an electrode. The sample had a typical phasesequence of SmC*A (85.8 °C) SmC* (87.7 °C) AF(89.8 °C) SmC* with heating. The applied electric field
was a square wave form with 100 Hz. RXS experiments
were performed on the beam line 4A using a KB focusingsystem. The incident energy was set at the absorption
edge of Se (12.65 keV) and the beam size was less than 5x 5 m2. A pixel array detector (Pilatus-100K, DECTRIS)
located at 100 cm from the sample (focusing point) wasused for the measurement.
3 Results and Discussion
The transitional subphases were formed during thetransition from the three-layer periodicity phase to theferroelectric phase. In the lower temperature range(86.3 °C, see Fig.1) where the three-layer SmC* phaseappeared under the low electric field (Fig1(a)), nine-layer(Fig.1(b)) and six-layer subphases (Fig.1(c)), and “streak”
pattern appeared in sequence after the transition from theSmC* phase with increasing applied electric field; theferroelectric phase was finally realized (Fig.1(d)). In thehigher temperature range (88.0 °C) where the four-layer

AF phase appeared under a low electric field, the AF
phase changed to a three-layer phase at the medium
electric field. The twelve-, nine-, and six-layer subphases
subsequently appeared in sequence, and finally theferroelectric phase was generated with increasing electricfield.
For the molecular arrangements of the newly-foundnine-layer periodicity phase, the {RRR RRL RRL}
configuration is found to be a potential candidate, where{· · · } represents the molecular configuration in a unit
cell, and “R” and “L” indicate the smectic layer withdirectors tilted to the right and left, respectively.

Fig.1 A series of RXS profiles obtained at applied fields
from ±45.0 V to ±52.0 V at 86.3 °C. Open circles in (b)and filled circles in (c) indicate positions wherereflection peaks owing to nine- and six-layer
configurations, respectively, are expected to appear.
Inset in (a) shows a original two-dimensional
diffraction pattern.
References[1] A.Iida et al., Phys. Rev. E 89 (2014)032503[2] A.Iida et al., Phys. Rev. E 94 (2016)052703[3] A.Iida et al., Phys. Rev. E 97 (2018)062702* Atsuo.iida@kek.jp