Ultrasonic Studies of (CH3)2NH2Al(SO4)2 · 6H2O crystals irradiated by γ quanta and electrons

The temperature dependence of the longitudinal-ultrasound velocities in (CH₃)₂NH₂Al(SO₄)₂ · 6H₂O crystals was studied using the echo-pulse technique in the 90–300 K range. The measurements were carried out along mutually perpendicular crystallographic directions X, Y, Z on samples both unirradiated and irradiated to various doses by γ quanta and an electron beam. The ultrasound velocity V in this crystal was shown to be anisotropic, with V_YY>V_XX>V_ZZ. The V_XX=f(T), V_YY=f(T), and V_ZZ=f(T) curves exhibit anomalies in the form of breaks at the ferroelectric phase transition (PT) at T_c1=152 K, as well as in the region of T_c2=218 K. It was established that as the irradiation dose increases, the PT temperature T_c1 decreases and the anomalies in the temperature dependences of the ultrasound velocities are smeared.