tailieunhanh - Ferroelectrics Physical Effects Part 12

Tham khảo tài liệu 'ferroelectrics physical effects part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 430 Ferroelectrics - Physical Effects a b Fig. 2. a Simplified model of bent-core molecule and two directors n and p b Primary n and secondary p directors in the X Y Z laboratory reference frame. In B2 phase the n director is tilted with respect to the smectic plane normal Z by the angle 0 or -0. The n director is the average direction of the long molecular axis. The secondary director p is the average position for the short molecular in-plane axis. The other short axis is perpendicular to the n p plane. Because of the tilt sign or - of the n director Fig. 2 b and two directions of the p polar director p and - p there are four different structures of B2 phase 1. Synclinic ferroelectric SmCSPF - the tilt angle is positive or negative in all smectic layers and p vectors are parallel 2. Synclinic antiferroelectric SmCSPA 3. Anticlinic ferroelectric SmCAPF and 4. Anticlinic antiferroelectric SmCAPA . The last one shows up for two symmetric compounds 12OSOR and 14OSOR studied in this work. A general symbol of B2 phase can be written as follows SmCSAPFA where index S stands for synclinic A - for anticlinic order of molecules in two neighboring layers F - for ferroelectric and A - antiferroelectric order of polarization vectors. Banana-shaped compounds may form both lamellar and or columnar mesophases Szydlowska 2003 that have become a subject of intensive experimental Reddy Tschierske 2006 and theoretical studies Vaupotic 2006 in the last decades. In the first place research on electro-optic switching in ferro- and anti-ferroelectric phases composed of bent-core molecules has been done because of possible practical applications Walba el al. 2000 Reddy Tschierske 2006 . Since the discovery of ferroelectric order in smectic B phases composed of polar achiral banana-shaped molecules many experimental studies have been done that confirm ferro- or antiferroelectric order inside the layers and positive ferroelectric or negative antiferroelectric correlations between the .