Dear Woods,

Ferroelectricity is the result of long range ordering of dipoles or pseudospins resulting in some cases to such ordering which creates macroscopic polarization that is suitable under appropriate amount of externally applied field. Thus, observance of spontaneous polarization and electric field- polarization hysteresis becomes the general features of normal ferroelectric state. Symmetry consideration become important as centrosymmetric systems cannot create preferential direction for such ordering. Therefore, anosotropy is the consequence of this basic feature. Further, the softening of transverse optic mode in displacive type ferroelectrics also needs the symmetry reduction so that there's tons force for such made becomes zero leading to mode softening as could be understood from basic LAST relation. Ferroelectric domain formation is the result of thermodynamics and is simply to minimise the free energy. However, electronic degree of freedom leading to structural distortion may not have the kind regards anisotropy you are pointing out. In fact relaxor state is observed in which the fluctuations grows and gets correlated leading to ergodic transition to relaxor phase without structural phase transition. There are some other mechanisms in which long range ferroic ordering may occur without lattice distortion.

Always. When you look at electric dipole, electric charges on opposite ends are different. Thus the dipole is not centrosymmetric. This is the simplest argument that ferroelectrics containing electric dipoles are not centrosymmetric.

Best regards,

Bartek

In ferroelectrics, dipoles are not locked rather switch their polarity with field. This switching and associated loop gives rise to two states that becomes the basis for memory applications.