LOW-TEMPERATURE ANOMALIES IN THE CDI2-CD CRYSTALLINE SYSTEM

From the measurements of elastic coefficients, piezooptical constants, and dilatometrical lengthening the existence of an improper ferroelas tic phase transition of first order in the Cdl(2)-Cd single crystallin e system within the temperature range 40 to 60 K is found. Different v alues of the temperature hysteresis are revealed for the piezooptical and elastic constants. From the data obtained an essential role of ele ctron-phonon interaction in the appearance of the mentioned phase tran sitions is concluded. The obtained results clearly show that in the Cd l(2)-Cd single crystalline system at lower temperatures long-range for ces appear between the impurity subsystems, which due to the specific electron-phonon interactions tend to the appearance of the phase trans itions. The behaviour of the elastic constants and the lengthening ind icate the possible ferroelastic nature of these transitions. Simultane ously the existence of the temperature hysteresis reflects the first-o rder nature of the mentioned transitions.