Triple Hysteresis Loop of a Ferroelectric Liquid Crystal

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Abstract
A triple hysteresis loop, which was quite different from that of ferrielectricity, was first observed in a ferroelectric liquid crystal with positive dielectric anisotropy. In the ferriclectric case, the direction of the field-induced polarization is the same as that of the original one. On the contrary, it was an inverse direction to that in the present case. When the temperature was near the phase transition point from smectic A to srnectic C* and/or when the applied electric field was sufficiently large, the triple hysteresis loop was easily observed. The temperature dependence of the threshold field for the triple hysteresis loop was analogous to that for electrohydrodynamic instability (EHDI) in smectic C. A similar additional loop to that of the triple hysteresis loop was also observed in the D-E hysteresis loop of MBBA in a very high field. On the basis of these experimental facts, the triple loop is explained by EHDI.