Influence of the thickness of [N(CH3)4]2Zn0.75Mn0.25Cl4 crystal on the phase-transition temperature

The change in the phase-transition temperature of N(CH₃)₄]₂Zn_0.75Mn_0.25Cl₄ crystal as a function of its size (3500 μm-1 μm) has been investigated. It is established that a decrease in crystal sizes along the spontaneous-polarization axis is accompanied by several effects: a shift of the initial phase-incommensurate phase transition point to higher temperatures, an increase in the temperature range of existence of incommensurate phase, an increase in the temperature range of existence of metastable states of incommensurate structure, the occurrence of new long-period commensurate phases, and an increase in phase-transition temperature hysteresis at T _c and T ₃. The possibility that a size effect exists in the phase diagram of this crystal is discussed.