Evolution of Subphases in a Prototype Binary Mixture System as Observed by Electric-Field-Induced Birefringence and Helical Pitch

Abstract

We have constructed the E-T phase diagrams by drawing the field-induced birefringence contours in the prototype MHPOCBC and MHPOOCBC binary mixture system. The obtained subphase evolution in the diagrams clearly indicate that there exist some additional biaxial subphases other than the ordinary ones with three-and four-layer superstructures, and that the field-induced deformation of uniaxial SmC Ã a in MHPOCBC occurs quite differently in the high and low temperature regions. We have discussed the origin and structures of the additional subphases and different types of the field-induced deformations in terms of the extended Emelyanenko-Osipov model together with the Devil's staircase character of field-induced unwinding process of the SmC Ã a short-pitch helical structure published by Yamashita et al. in these Proceedings.

Superlattice structures observed in the extraordinary phase sequence and analyzed by the phenomenological Landau model and the partially molecular model

“…Let us begin by summarizing our experimental results of EFIB reported previously [5][6][7][8][9][10][11], for the subphases and their emerging sequences, empirically assigned, agree impressively well with those predicted by Dolganov et al on the basis of the phenomenological Landau model [34][35][36][37]. As is well known, EFIB does not tell exactly the superlattice structures of any subphases, although it can rather easily distinguish the antiferroelectric phases from the ferrielectric as well as the ferroelectric ones.…”

“…3(b) by a factor of 2. Contours show characteristic patterns in these E-T phase diagrams [6][7][8][9]. We can easily identify the four phases, synclinic ferroelectric Sm-C * , four-layer antiferroelectric 1 2 , optically uniaxial Sm-C * α , and nontilted paraelectric Sm-A, which were confirmed to emerge by RXRS [22], as indicated in the lower part of Fig.…”

“…It has been well established that contour lines may form negative closed loops in the prototype antiferroelectric Sm-C * A and four-layer antiferroelectric 1 2 temperature regions [6][7][8][9]; hence several closed contour lines with negative EFIB observed in the temperature region between approximately 60…”

“…In this way, the general tendency of the emerging sequences of subphases as well as their superlattice structures at zero field, which have been identified experimentally [5][6][7][8][9][10][11][12] so far, was reproduced by minimizing the free energy F = F 1 + F 2 + F 3 given in Eqs. (1)-(3).…”

“…In fact, these superlattice structures with the spatial variation of both θ i and ϕ i are very characteristic and should be clearly confirmed experimentally in a subphase such as q T = 1 4 where the tilt angle θ i is rather large. It is also worthwhile trying to reproduce a number of emerging phase sequences experimentally observed [5][6][7][8][9][10][11][12] by properly choosing coefficients in the Landau theory. These problems are left for future study.…”