Polarization ferroelectrics

B01 F. Bauer, U.S. Patent, No. 4,611,260, Method and Device for Polarizing Ferroelectric Materials, September 9, 1986. 

X-ray measurements on LC elastomers have shown [6-8] that the reversible transition between a chiral smectic C phase with and without a helical superstructure can be induced mechanically. The helix untwisted state corresponds in this case to a polar ferroelectric monodomain. The piezoelectricity arising from this deformation of the helical superstructure (which does not require a complete untwisting) has been demonstrated [9] for polymers cross-linked by polymerization of pendant acrylate groups (Figure 15). 

To understand the principle of operation of this mode, let s suppose we have a polarized ferroelectric film, which is also piezoelectric. Once the film has been polarized, its thickness D will vary when a voltage is applied between the top and the bottom surface of the film. Due to an oscillating applied voltage, the thickness of the film will also oscillate at the same frequency. The response to the applied voltage depends on the polarization state of the film. When the applied electric field is parallel to the spontaneous polarization, the thickness of the piezoelectric film increases, while for a small electric field opposite to the polarization, the thickness D decreases. If the top sm face is in contact with the EFM tip and the sample has been polarized, the tip will... 

Figure 18.2 Perovskite crystal structure, (a) The nonpolar paraelectric cubic phase (b) A polar ferroelectric phase due to tetragonal distortion. Data for PbTiOs stem from Ref [10].

Fig. 13.28 Non-polar dipolar structure of a bilayer and a lamellar phase (a) and antifcaroelectric phase (b) formed by polar bilayers. A strraig electric field E applied along the y-axis converts the antiferroelectric phase (b) into polar ferroelectric phase (c)...

Huang, L. and Tiersten, H.F. 1998. Electroelastic equations describing slow hysteresis in polarized ferroelectric ceramic plates. Journal of Applied Physics Vol. 83 No. 11, 6126-6139. 

The plethora of liquid crystal structures and phases is categorized into two main classes thermotropic and lyotropic liquid crystals. While thermotropic liquid crystals are formed by, e.g., rod- or disc-shaped molecules in a certain temperature range, lyotropic liquid crystals are liquid crystalline solutions, built up by, e.g., aggregates of amphiphilic molecules in a certain concentration range. Many liquid crystal phases are found in thermotropic as well as in lyotropic systems. In some cases, however, the lyotropic analog of a thermotropic phase has never been observed. The probably most interesting of these missing link cases is the thermotropic chiral smectic C (SmC ) phase, which has become famous as the only spontaneously polarized, ferroelectric fluid in nature. 

Li J, et al. Surface charge regulation of osteogenic differentiation of mesenchymal stem cell on polarized ferroelectric crystal substrate. Adv Healthc Mater 2015 4(7) 998-1003. 

Keller, P., Shao, R., Walba, D. M., and Brunei, M., The first high polarization ferroelectric main chain liquid crystalline polymers. Liq, Cryst., 18, 915-918 (1995). 

Keller P, Shao RF, Walba DM, Brunet M (1995) The first high polarization ferroelectric... 

Similar effects can be described for other phases. The smectic A phase of chiral compounds may show electroclinic effect (Effect (a)) or can be transferred to the TGBa phase (Effect (c)). The smectic C phase of chiral compounds may have hehcal ordering (Effect (b)), but can have polar ferroelectric properties (Effect (a)) even without helical structures. Further, a TGBc phase or a Sd phase might be induced (Effect (c)). 

In the absence of any constraints, the direction of Ps rotates from one smectic layer to the next, with a period equal to the smectic C pitch, and so the average polarization for a sample would be zero. However, surface treatment or application of a field can cause the helix to untwist, resulting in a permanently polarized sample. The spontaneous polarization arises from a preferred alignment of molecular dipole components which are perpendicular to the molecular long axis, but it behaves differently from the ferroelectric and ferromagnetic polarization characterised for crystals. The liquid crystalline ferroelectric phases identified so far are improper ferroelectrics, since the spontaneous polarization results from a symmetry constraint, whereas in proper ferroelectrics the polarization results from dipole -dipole interactions. The Curie-Weiss law for proper ferroelectrics predicts a second order phase transition at the Curie temperature from the high temperature paraelectric state to a permanently polarized ferroelectric state ... 

M ribbons, chromonics 996 Mach-Zehnder interferometer 132 macrocyeles, hydrocarbon cores 719 f macrocyclic complexes, metallomesogens 926 macroscopic flow, chiral nematics 379 macroscopic polarization, ferroelectrics 541 ff macroscopic properties... 

If some physical property is described by two or three coefficients, the application of the above cited rules is impossible. In this case we have to deal with the combined properties [4. An example of a combined property in a 1-3 type composite is the electromechanical transducer consisting of noopiezoelectric polymer matrix and polarized ferroelectric thin rods. 

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