Crystalline ferroelectric

Liquid crystalline, ferroelectric, and photochromic systems Controlled drug-delivery from polyphosphazenes Use in bone tissue engineering... 

We have shown that although amorphous ferroelectricity as a physical phenomenon is not fully demonstrated, amorphous films of ferroelectric oxides have shown a number of useful properties that may warrant further studies of their structure and properties. It is possible to use them in limited areas in place of crystalline ferroelectrics. 

Leister N, Lehmann W, Weber U, Geschke D, Kremer F, Stein P, Fiiikelmann H (2000) Measurement of the pyroelectric response and of the thermal diffusivity of microtomized sections of single crystalline ferroelectric liquid crystalline elastomers. Liq Cryst 27 289... 

Bums, G., Dacol, RH. Crystalline ferroelectrics with glassy polarization behavior. Phys. Rev. B 28, 2527-2530 (1983)... 

The molecule is a liquid crystalline polymer with chiral smectic C phase forming parts attached as side chains. The field required to switch the direction of polarization of the polymer is very low (0.3 MVm ). There is a lot of interest in liquid crystalline ferroelectric polymers, because of their possible use for fast-switching electro-optical devices. More information about ferroelectric liquid crystals can be found in references [36,37]. 

Fig. 13.2 Hysteresis type dependence of total polarization P on electric field E for a typical crystalline ferroelectric...

Is the SmC phase ferroelectric To answer this question we should look more carefully at the criteria formulated for crystalline ferroelectrics ... 

All crystalline ferroelectrics without exceptions belong to one of the pyroelectric classes and possess spontaneous polarisation (polar class). 

There are two equivalent stable states (bistability) differed by the spontaneous polarisation direction, between which we can switch the direction of P. It seems there is no exception from this criterion among the crystalline ferroelectrics. 

In the low field limit, expanding (9s + 89) we shall find the soft mode susceptibility of the SmC phase using exactly the same procedure as for crystalline ferroelectrics, see Eq. (13.8) ... 

Table A..5-1 The 72 families of ferroelectric materials. The number assigned to each family corresponds to the number used in LB III/36. The numbers in parentheses (A sub>. f+a ) after the family name serve the purpose of conveying some information about the size and importance of the family. The numbers indicate the following A sub the number of pure substances (ferroelectric, antiferroelectric, and related substances) which are treated as members of this family in LB III/36 A f+A the number of ferroelectric and antiferroelectric substances which are treated as members of this family in LB III/36 n, the number of representative substances from this family whose properties are surveyed in Sect. 4.5.4. For some of these families, additional remarks are needed for instance, because the perovskite-type oxide family has many members and consists of several subfamilies because the liquid crystal and polymer families have very specific properties compared with crystalline ferroelectrics and because the traditional names of some families are apt to lead to misconceptions about their members. Such families are marked by letters a-m following the parentheses, and remarks on these families are given under the corresponding letter in the text in Sect. 4.5.3.1...

The symmetry requirements necessary for ferroelectricity in low-molecular mass compounds, which were discussed in Section 1.1.3, are valid for polymer mesophases too. If a tilted chiral smectic phase is stable after a polymerization process it must be ferroelectric. Following this idea, the first polymer liquid crystalline ferroelectric has been synthesized by Shibayev et al. [160]. Its spontaneous polarization did not differ very much from the precursor monomer [161]. After polyvinylidene fiuoride (PVF2)... 

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 ... 

Liquid-Crystalline Ferroelectric Polymers Chiral Smectics C ... 

High Refractive Index, Liquid Crystalline, Ferroelectric, NLO, and Photochromic Side Groups. 

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