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Abstract
The application of Raman spectroscopy for the investigation of phase transitions focused traditionally on the observation of soft modes in displacive systems. The present furthergoing study on displacive and order-disorder systems is based on the observation of systematic changes of the scattering profiles of hard modes during the phase transition. It reveals the temperature evolution of the order parameters, the role of order-parameter fluctuations and phonon density of states effects in model systems like improper ferroelastic Pb3(P1-x As x O4)2, lead diluted ferroelastic (Pb1-x Ba x )3(PO4)2, pure ferroelastic As2O5 and the relaxor ferroelectric Pb(Sc0.5Ta0.5)O3. Allied with supplementary experimental techniques hard-mode Raman spectroscopy (HMRS) is an ideal method for the investigation of order-parameter coupling effects and the characterization of structural phase transitions.
