A New Type of the Ferroelectric Phase Transition

It, is suggested that a ferroelectric phase transition could be triggered by an instability of the crystal with respect to another phase transition parameter η. The spontaneous polarization P and spontaneous η may occur either successively or simultaneously (at the same temperature), the latter case being always a first order phase transition. The necessary condition for the existence of a triggered ferroelectric phase transition (TFT) is that η 2 P 2 is the lowest order interaction term in the free energy expansion. The symmetry change due to TFT is discussed.