Dielectric relaxation in the high-pressure hindered plastic crystal phase of ethanol.

By direct fitting of the dielectric relaxation observed in the high pressure (P = 2.0-3.0 GPa) crystal phase of ethanol we have demonstrated that the high-pressure high-temperature crystal phase of ethanol is a plastic crystal with various degrees of orientational disorder (the phase of a hindered plastic crystal). Two distinct relaxational processes are registered in ethanol in it, whose origins can be traced to the Debye and structural (α) relaxations of the liquid phase. These relaxations demonstrate different behavior with decreasing temperature: the characteristic frequency of the low frequency (Debye) relaxation is constantly decreasing (the relaxation "glassifies"), while the high frequency (α) relaxation either vanishes, depending on pressure, indicating transition into another crystal phase or "glassifies" too. This is the first time that such behavior has been observed where two types of disorder are realized in the same system, at low temperatures in one relaxation process.