High-resolution Brillouin scattering studies of phase transitions in Ca2MgSi2O7 and Ca2ZnSi2O7 silicates

Temperature-dependent Micro-Brillouin scattering studies of Ca2MgSi2O7 and Ca2ZnSi2O7 single crystals were performed. Step-like decrease of Brillouin shifts and strong broadening of Brillouin bands corresponding to the c33 elastic constant were observed at 351 K for Ca2MgSi2O7 and 407 K for Ca2ZnSi2O7. This behavior was attributed to coupling of strain to the square of the order parameter due to structural transitions into incommensurate phases. Analysis of the observed acoustic anomalies showed critical slowing down behavior of the relaxation time characterizing interaction between the order parameter and acoustic phonon.