(
) and several electric-field-induced subphases in AS657 studied by complementary methods, electric-field-induced birefringence and microbeam resonant X-ray scattering
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ABSTRACT
A selenium-containing compound, AS657, is studied with two complementary methods, electric-field-induced birefringence (EFIB) and microbeam resonant X-ray scattering (µRXS). AS657 shows a phase sequence of Sm –
–
– Sm
– Sm
where no Sm
emerges and hence the frustration between Sm
and Sm
plays an important role. In spite of this situation, two additional temperature-induced subphases are observed: (1) antiferroelectric eight-layer
between Sm
and
and (2) antiferroelectric 10-layer
between
and
. A number of field-induced subphases are also shown to emerge. The most notable new finding is the observation of an electric-field-induced ferrielectric subphase of six-layer
(
) between
and Sm
; this subphase is stabilised even at zero field in a mixture of 92.6 wt% AS657 and 7.4 wt% AS620. Another field-induced subphase of six-layer
is also confirmed to emerge in the temperature ranges of SmCA* and
. The nature of the field-induced transitions in the
temperature range is more complex than previously thought; in its high temperature range, wound (not unwound) Sm
with some macroscopic distorted helical director arrangement reappears above
, whereas in the low temperature range, some intriguing sequential field-induced transitions are observed both in the EFIB and µRXS. Last but not the least is the observation of a field-induced subphase found in the low-temperature range of
by EFIB and this is tentatively assigned as
, the detailed structure of which is expected to be clarified by µRXS in the near future.
Graphical Abstract
Acknowledgements
It is a privilege to be invited to write this paper for the Festscrift of Professor J. W. Goodby FRS and we thank the organisers for it. We also thank Mr. Zhengyu Feng and Professor Ken Ishikawa of TIT, Japan for supplying LC cells with copper film electrodes. The authors thank Dr. V. P. Panov for his help with the hardware and software of the birefringence system. This work was partly supported by the Ireland–Japan cooperation SFI funding and 13/US/I2866 Science Foundation Ireland (SFI) grant as part of the USA–Ireland Research and Development Partnership programme jointly administered with the United States National Science Foundation: [Grant Number NSF-DMR-1410649]. The authors would like to thank Professor Atsuo Iida for his preparation of Figures 13 and 17 as well as for having fruitful discussions, Ms Y. Ohtsuka and the staff of the Photon Factory for their assistance during the experiments. This part of the work was carried out under the approval of the Photon Factory Advisory Committee (Proposal Nos. 2012G635 and 2014G638) and partly supported by the Grant-In-Aid for Scientific Research on Priority Area (A): [Grant Number JP23246007] of the Ministry of Education, Culture, Sports, Science and Technology. Ms Neelam Yadav, a visiting doctoral student from the University of Allahabad, India, is thanked for helping us with the figures. μRXS work was partially carried out in the second hutch of Spring-8 BL03XU constructed by the consortium of Advanced Soft material Beamline (FSBL), with proposal No. 2015A7255.
Disclosure statement
No potential conflict of interest was reported by the authors.