Ferroics Whose Faintness Index for Ferroelectricity or Ferroelasticity is Unequal to That of the Soft Vibrational Modes

Let y and Y denote a given component of electric polarization vector or mechanical strain tensor and the corresponding component of electric field vector or mechanical stress tensor, respectively. Let n M and n F denote the faintness index for ferroelectricity or ferroelasticity of the soft vibrational modes and of the ferroic phase with respect to the component y . Cases of n M < n F ≤∞ are considered in a general way and also with examples. How y s (s is the initial of “spontaneous”) varies with temperature depends only on n F and not on n M ; the way of dependence on n F is essentially the same as when n F = n M . On the other hand, how the susceptibility (d y /d Y ) s varies with temperature is not necessarily independent of n M ; it can be essentially dissimilar to that when n M = n F .