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Apparent tilt angle of SmC* as a function of the electric field, and the corresponding molecular arrangement under the electric field.
Source publication
The study of chiral symmetry breaking in liquid crystals and the consequent emergence of ferroelectric and antiferroelectric phases is described. Furthermore, we show that the frustration between two phases induces a variety of structural phases called subphases and that resonant X-ray scattering is a powerful tool for the structural analysis of th...
Context in source publication
Context 1
... the proper electric field is applied, electric-field induced phase transition to ferroelectric states occurs. Apparent tilt angle and corresponding polarization shows a double hysteresis behavior with respect to the applied field, which is characteristic for antiferroelectric property, as shown in Figure 6a. In the bulk state, a helical structure was also formed like SmC* due to the chirality, in such a molecular arrangement with helix, obliquely incident transmitted spectra are clearly different from that in the ferroelectric SmC* phase. ...
Citations
... Moreover, Huang et al. [7] did not accept the emergence of subphases with unit cells larger than 6 smectic layers; all these subphases between well-characterised phases were considered simply as coexistence regions. In recent publications [8][9][10], however, the definite existence of 1/4, 2/5, and 3/7 with 8-, 10-, and 7-layer unit cells, respectively, was vindicated by using complementary methods of electric-field-induced birefringence (EFIB) and microbeam resonant x-ray scattering (µRXS). This further complicates the subphase emerging sequences actually observed; even when focusing only on prototypal 1/3 and 1/2, the subphase emerging sequences show a variety of the global evolution as pointed out by Sandhya et al. [11] in the binary mixture system of MHPOCBC and MH-POOCBC: The complexity must mainly result from the fact that the orthogonal paraelectric SmA phase plays an important role [12]. ...
... Therefore, the obtained g-T phase diagram does not contain 2/5, which inevitably has the 10-layer unit cell as the (0, π, 0, π, π) structure cannot be realized in the 5-layer unit cell. Now the emergence of 2/5 is vindicated experimentally by using complementary methods, EFIB and µRXS [8][9][10]; we have to consider at least all the possible 95 Ising patterns up to 10 smectic layers and determine the nonflat subphase structures with the lowest free energy for particular parameter values. Such calculations were made actually to obtain the g-T phase diagrams that are illustrated in Fig. 12 of Ref. [24] and Fig. 11 of Ref. [25]; one of them is reproduced in Fig. 1 as this is a basis of the present calculations. ...
... Recently, Feng et al. and Chandani et al. [8][9][10] studied selenium-containing compounds, AS657 and AS620, by drawing the electric field versus temperature phase diagram with EFIB contours and found three additional subphases, an antiferroelectric one between SmC * A and 1/3, and apparently antiferroelectric and ferrielectric ones between 1/3 and 1/2; the simplest probable q T 's for these additional subphases are 1/4, 2/5, and 3/7. They further studied the µRXS profiles and concluded that their approximate Ising structures are 8-layer (FAAAFAAA), 10-layer (FAFAAFAFAA), and 7-layer (FAAFAFA), respectively. ...
Prompted by the existence of biaxial subphases 1/4, 2/5, and 3/7 [Phys. Rev. E 96, 012701 (2017)], we reconsidered the three-phase frustration and the resulting degeneracy lifting by combining the phase diagram of SmCA*, SmC*, and SmA with the discrete flexoelectric effect. We systematically calculated the phase diagrams and tried to understand the overall picture of the phenomena by means of a simple and intuitively clear way in terms of minimal number of parameters. The treatment naturally explains the highly distorted helical structures of the biaxial subphases as well as the microscopic helical short-pitch of SmCα* which increases or decreases accordingly with rising temperature. The regular subphase emerging sequence is SmCA*(SmCα*)–1/4–1/3–2/5–3/7–1/2–SmC*(SmCα*), where the subphases other than 1/3 and 1/2 may or may not emerge. At the same time, we can see a variety of irregular sequences; in particular, any one of the biaxial subphases may singly emerge between SmCA*(SmCα*) and (SmC*)SmCα*. Moreover, the experimentally confirmed extraordinary subphase emerging sequence SmC*–1/2–SmCα* appears for particular parameter values. Contrastingly to these affirmative aspects, some calculated results are contradictory to the previously reported experimental results: the change from SmCA* and SmC* to SmCα* is always continuous, the 6-layer 2/3 subphase is not stabilized, and the subphase emerging sequence SmCA*–1/3–SmC* does not appear. The causes of inconsistency and how to resolve them were discussed in comparisons with experimental findings.
