Deformational polarisability polarisation

Besides the orientation polarisation we observe a deformation polarisation, identical to that of an induced dipole moment. In a spatial unit the polarisation caused by deformation (due to a shift of the electrical charges) will be... 

The polarisation itself is, just as the molecular polarisability is, the result of deformation polarisation Pd and the orientation polarisation Ps. Accordingly, the total polarisation is equal to P = Pd + Pa. Because of the resistance to motion of the atom groups in the dielectric, there is a delay between changes in the electric field and changes in the polarisation. The deformation polarisation takes place instantaneously (more precisely in a time of the order of 10-14 s) on the application of an electric field. There are two limiting values of e Erxi at short times or high frequencies and es at long times or low frequencies. This means that we have for the deformation polarisation... 

First consider the application of an external electric field to an assembly of rigid molecular dipoles, i.e. let there be no deformational polarisation. If the permanent moment of each dipole is /i, then the potential energy u of a dipole in the applied field will be ... 

Taking into account the possible anisotropy of the deformational polarisability of molecules requires that... 

Freezing of a dipolar liquid is accompanied by a rapid decrease in its electric permittivity [8-10]. Following solidification, dipole rotation ceases and the electric permittivity is almost equal to n, where n is refractive index, as it arises from deformation polarisation only. Investigation of the dynamics of a confined liquid is possible from the frequency dependences of dielectric properties, which allows both the determination of the phase transition temperature of the adsorbed substance and characteristic relaxation frequencies related to molecular motion in particular phases. 

In section 9.2.2 above it is shown that the refractive index of a medium is related to the high-frequency deformational polarisability of its mole-... 

In considering dielectric relaxation it is, however, necessary to remember that there are two dilferent types of contribution to the polarisation of the dielectric, the deformational polarisation and the orientational polarisation so that P = + P. For the sudden application of a... 

Molecular polarisability is discussed in detail in chapter 9. Orientational polarisation involves the rotation, under the influence of an electric field, of molecules, or parts of molecules, that have permanent electric dipoles. This effect clearly leads to a possible mechanism for orienting molecules and, in particular, for reorienting the domains of liquid crystals or LCPs that have permanent dipoles. It is less obvious that deformational polarisation can lead to orientation. If, however, the polarisability of a molecule is anisotropic, as is usually the case, the polarisability and hence the induced electric dipole will differ for different orientations of the molecule in the field. The interaction energy with the field is therefore reduced if the molecule rotates so that its direction of maximum polarisability coincides with the field direction. Electric-field orientation is largely of importance in device applications. 

Another example of the coupling between microscopic and macroscopic properties is the flexo-electric effect in liquid crystals [33] which was first predicted theoretically by Meyer [34] and later observed in MBBA [35], Here orientational deformations of the director give rise to spontaneous polarisation. In nematic materials, the induced polarisation is given by... 

Electric polarisation (P ef deformation, Por orientation polarisation) Momentum coordinate Spatial coordinate... 

For a system under elongational deformation along direction 1, for a beam of light propagating in direction 3, according to (10.17) one obtains different refractive indices for different polarisation of the beam, so that, for polarisation in directions 1 and 2, one has a difference of refractive indices... 

Definition of molecular mass averages, 17 Deformation flexural, 825 plastic, 830 polarisation, 325 properties, 824 uniaxial, 825 De Gennes... 

The structural effects of Zn-doping in LaMni xZnx03, where 0 < x < 0.08, were revealed by shifts in IR and Raman bands from MnOfi deformations.247 Polarised Raman and IR reflection spectra were reported and analysed for HoMn03 single crystals.248... 

This simple model depends on the properties of a deformable core, and is only likely to be significant for heavier, polarisable metals. In addition, there are the directional influences of the valence orbital overlaps, which have been widely explored, and, in general, favour cis geometry in the d-block. For example, the Extended Huckel calculations of Tatsumi and Hoffmann show the dominant role of 4d-n orbitals in stabilising the cis geometry in MoO + [75]. In this... 

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