ELASTIC PROPERTIES OF PURIFIED [N(CH3)(4)]2CUCL4 CRYSTALS NEAR THE FERROELASTIC LOCK-IN TRANSITION

The low frequency elastic properties of ferroelastic [N(CH3)(4)]2CuCl4 crystals are investigated by dynamical mechanical analysis in the vic inity of the incommensurate-commensurate phase transition. We show for the first time, that the anomaly of the elastic compliance coefficien t s(55), even of purified crystals, is accompanied by typical nonequil ibrium phenomena such as isothermal relaxations. The s(55)(T) anomaly was not significantly enhanced by the purification treatment. We concl ude, that extended defects induced during crystal growth have a decisi ve influence on the elastic properties of [N(CH3)(4)]2CuCl4.