Anomalous electrostriction

Starting with the Landau theory, Trebin and coworkers [122], [124] have calculated the electrostriction coefficients by allowing both the wave vectors and scalar amplitudes of the Fourier components to distort. Good agreement with the data is achieved, except for the case of anomalous electrostriction in BPI. The authors therefore conclude that the explanation for this behavior is beyond the capability of the Landau theory. As described earlier, the same group has also proposed a model of the blue phases incorporating bond-orientational order [45], [46]. However, a calculation of the anomalous electrostriction from this model [123] has had only limited success. 

Application of small electric fields results in electrostriction of the BPI and BPII lattices. Except for the case of anomalous dispersion in BPI, this behavior has been explained theoretically. Larger fields cause hexagonal and tetragonal phases to be stabilized. The hexagonal phase has received theoretical justification the tetragonal phase still awaits theoretical treatment. 

The far-infrared spectra suggested that the internal rotational mode with increasing amplitude has a possibility of soft mode in the transition, which may cause a large change in the CFj dipole or the q ntaneous polarization P of the crystal. In other words, the temperature change in the polarization P may originate from the thermal behavior of the optical phonon. The strain c is related with the acoustic phonon. Therefore, the anomalous thermal behavior of the ultrasonic velocity may be interpreted in such a way that the optical phonon is coupled with the acoustic phonon through the piezoelectric interaction OPi), electrostrictive interaction (yP cX and so on. 

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