P. Kuzel et al., BRILLOUIN AND ULTRASONIC STUDIES OF PHASE-TRANSITIONS IN CS2CDBR4 .1.EXPERIMENTAL, Physical review. B, Condensed matter, 49(10), 1994, pp. 6553-6562
The phase transitions in Cs2CdBr4 have been studied by means of Brillo
uin scattering and ultrasonic measurements. The sequence Pnma <-> 252
K incommensurate <-> 235 L P2(1)/n11 gives rise to significant anomali
es of both real and imaginary parts of the elastic constants. In the c
ase of C44, a strong asymmetric broadening of the Brillouin lines was
observed in the IC phase and several degrees above the Pnma <-> IC tra
nsition. The differences between Brillouin and ultrasonic results conc
erning C22 and C44 suggest a strong frequency dependence of the proces
s governing the above-mentioned sequence of phase transitions. A low-t
emperature transition at 156 K has been studied; it presents a conside
rable softening of shear stiffness constants. Selection rules for Bril
louin scattering are greatly affected at the transitions to monoclinic
and triclinic phases, allowing to measure the shear stiffness constan
ts with a good accuracy. A detailed discussion of the phenomena linked
to the monoclinicity is provided. In addition, the ultrasonic experim
ents have confirmed the existence of a previously reported phase trans
ition at 208 K.