PHASE-TRANSITIONS IN [NH(CH3)(3)](2)MECL(4) (ME=CD,ZN,CU) CRYSTALS

Dielectric properties of the new [NH(CH3)(3)]2ZnCl4 and [NH(CH3)(3)]2C dCl4 crystals from the [(CH3)(n)NH4-n](2)MeCl(4) group have been inves tigated in a wide temperature range (4.2-320 K). A series of phase tra nsitions has been discovered at T-3 = 325 K, T-4 = 251 K, T-5 = 193 K, for [NH(CH3)(3)]2CdCl4 and at T-3 = 309 K, T-4 = 282 K, T-5 = 269 K f or [NH(CH3)(3)]2ZnCl4. A ferroelectric phase has been discovered in th e temperature interval T-4-T-5 from the temperature and frequency depe ndence of the dielectric permittivity epsilon(T, nu). According to opt ical investigations the existence of ferroelastic phases in the temper ature interval T-1 = 349 K-T-2 = 391 K and below T-5 for [NH(CH3)(3)]2 CdCl4 and both above T-3 and below T-5 for [NH(CH3)(3)]2ZnCl4 has been ascertained.