Ferroelectrics polar groups

D. Miyajima, F. Araoka, H. Takezoe, J. Kim, K. Kato, M. Takata, T. Aida, Ferroelectric columnar liquid crystal featuring confined polar groups within core-shell architecture. Science 336, 209-213 (2012)... 

Small polar lateral substituents have been made of considerable use in the development of materials that exhibit smectic C phases for applications as host systems for ferroelectric display devices [31]. Small polar groups do not depress mesophase formation greatly, and in addition they can be po-... 

S. Tasaka, T. Shouko. and N. Inagaki Ferroelectric polarization reversal in polyurca with odd number of CH] groups. Jpn. J. AppL Pkys. 3i L1066 (1992). 

The most important materials among nonlinear dielectrics are ferroelectrics which can exhibit a spontaneous polarization PI in the absence of an external electric field and which can spHt into spontaneously polarized regions known as domains (5). It is evident that in the ferroelectric the domain states differ in orientation of spontaneous electric polarization, which are in equiUbrium thermodynamically, and that the ferroelectric character is estabUshed when one domain state can be transformed to another by a suitably directed external electric field (6). It is the reorientabiUty of the domain state polarizations that distinguishes ferroelectrics as a subgroup of materials from the 10-polar-point symmetry group of pyroelectric crystals (7—9). 

Crystals with one of the ten polar point-group symmetries (Ci, C2, Cs, C2V, C4, C4V, C3, C3v, C(, Cgv) are called polar crystals. They display spontaneous polarization and form a family of ferroelectric materials. The main properties of ferroelectric materials include relatively high dielectric permittivity, ferroelectric-paraelectric phase transition that occurs at a certain temperature called the Curie temperature, piezoelectric effect, pyroelectric effect, nonlinear optic property - the ability to multiply frequencies, ferroelectric hysteresis loop, and electrostrictive, electro-optic and other properties [16, 388],... 

The Tokyo Tech group assigned a C2 structure for the layers in the B2 phase, and ferroelectric packing of such layers to form a locally polar C2v macroscopic structure, as indicated in Figure 8.20. Other early workers in the field also adopted this structural model for the B2 phase. Brand et al. had discussed a C2 smectic chevron structure in their 1992 theoretical study,29 and while they seem to be referring to an all-anticlinic bilayer smectic, their actual graphic is basically identical to that shown in Figure 8.20. Furthermore,... 

Displacive ferroeiectrics where a discrete symmetry group is broken at Tc and the ferroelectric transition can be described as the result of an instability of the anharmonic crystal lattice against soft polar lattice vibration (e.g., BaTiOs). 

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