Ultrasonic studies of (CH3)(2)NH2Al(SO4)(2) center dot 6H(2)O crystals irradiated by gamma quanta and electrons

The temperature dependence of the longitudinal-ultrasound velocities in (CH 3)(2)NH2Al(SO4)(2) . 6H(2)O crystals was studied using the echo-pulse techn ique in the 90-300 K range. The measurements were carried out along mutuall y perpendicular crystallographic directions X, Y, Z on samples both unirrad iated and irradiated to various doses by gamma quanta and an electron beam. The ultrasound velocity V in this crystal was shown to be anisotropic, wit h V-YY > V-XX > V-ZZ. The V-XX= f (T), V-YY = f (T) , and V-ZZ = f (T) curv es exhibit anomalies in the form of breaks at the ferroelectric phase trans ition (PT) at T-c1 = 152 K, as well as in the region of T-c2 = 218 K. It wa s established that as the irradiation dose increases, the PT temperature T- c1 decreases and the anomalies in the temperature dependences of the ultras ound velocities are smeared. (C) 2001 MAIK "Nauka/ Interperiodica".