Investigations of high temperature phase transitions in (NH3C2H5)(2)CuCl4 crystals

On the basis of dilatometric, optical, and dielectric investigations of (NH 3C2H5)(2)CuCl4 crystals the existence of phase transitions at T-1 = 364 and T-2 = 356 K was confirmed. Anomalous behaviour of the thermal expansion co efficient and optical birefringence around T-3 = 330 K was related to earli er unknown phase transition. Besides, it was shown that these crystals are characterised by considerable protonic conductivity, the nature of which is fairly well explained in the framework of Grotthus mechanism of proton tra nsport.