Abstract
A mixture of two selenium-containing compounds, 80 wt. % AS657 and 20 wt. % AS620, are studied with two complementary methods, electric-field-induced birefringence (EFIB) and microbeam resonant x-ray scattering (). The mixture shows the typical phase sequence of Sm-–––Sm-–Sm-–Sm-, where and are two prototypal ferrielectric and antiferroelectric subphases with three- and four-layer unit cells, respectively. Here we designate the subphase as its number defined by the ratio of , where and are the numbers of synclinic ferroelectric and anticlinic antiferroelectric orderings in the unit cell, respectively. The electric field vs temperature phase diagram with EFIB contours indicates the emergence of three additional subphases, an antiferroelectric one between Sm- and and antiferroelectric and apparently ferrielectric ones between and . The simplest probable 's for these additional subphases are , and , respectively, in the order of increasing temperature. The profiles indicate that antiferroelectric and approximately have the eight-layer () and ten-layer () Ising unit cells, respectively. The remaining subphase may be ferrielectric with a seven-layer unit cell, although the evidence is partial. These experimental results are compared with the phenomenological Landau model [P. V. Dolganov and E. I. Kats, Liq. Cryst. Rev. 1, 127 (2014)] and the quasimolecular model [A. V. Emelyanenko and M. A. Osipov, Phys. Rev. E 68, 051703 (2003)].
7 More- Received 20 February 2017
- Revised 30 March 2017
DOI:https://doi.org/10.1103/PhysRevE.96.012701
©2017 American Physical Society