THE INCOMPLETE DEVILS STAIRCASE OF BETAINE CALCIUM-CHLORIDE DIHYDRATE- ACOUSTIC INVESTIGATION AT HIGH-PRESSURES

The influence of the hydrostatic pressure on the temperature dependenc es of the ultrasonic velocities and attenuation coefficients is studie d in the vicinity of the phase transition of BCCD crystals. The result s obtained are considered within the framework of single- and two-soft -mode models. It is shown that acoustic anomalies are well explained o nly by the single-soft-mode model, when only one soft mode P(k), which transforms according to the two-dimensional irreducible representatio n LAMBDA3 of the Pnma space group, is taken into account.