Ferrielectric six-layer () and several electric-field-induced subphases in AS657 studied by complementary methods, electric-field-induced birefringence and microbeam resonant X-ray scattering

Abstract

ABSTRACTA 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.