Coupled mode behavior of the soft mode in single crystals of several perovskite ferroelectrics

Temperature dependent Raman measurements are reported on small single crystals of the ferroelectrics Pb(Ti,Sn)O3 and (Pb,Sr)TiO3. The low frequency E-mode spectra are emphasized since measurements in ceramic samples have been reported to show that the soft ferroelectric E-mode interacts with an impurity induced mode. The single crystal results corroborate the ceramic results and the larger signal to noise enables one to: very clearly the "no crossing"; clearly measure the extra mode when it is on the high energy side of the soft E-mode; directly measure the E-character of the extra mode. We have fit these and the earlier data with parameters in the coupled mode equations and discuss these results. © 1976.