Possibility that Nonferroelectric Modes Severally of \barn_M=∞ may Collectively Produce Ferroelectricity

Abstract

Even if two different sets of degenerate soft modes are severally of \barn_M=∞ for ferroelectricity or, in other words, are each neither normally nor faintly ferroelectric, it is possible that some condensation of both sets produces a ferroelectric phase, where it is immaterial whether this condensation of both sets is simultaneous or successive, and (if successive) which set condenses earlier and which later. Examples are presented and discussed. For convenience’ sake, the concept of faintness index which has been introduced for monophone cases (i.e., cases that the soft mode system consists of only one set of degenerate modes) is extended to diphone cases.