The 90° Brillouin scattering experiment has been performed on a Pb(Zn1/3Nb2/3)O3 single crystal. The frequency shift and linewidth of the c33 pure longitudinal acoustic mode and the c44 pure transverse mode show bending anomalies near Tm=397 K, at which the low-frequency dielectric constant ε has a maximum value. In addition to the acoustic modes, a relaxational mode is found in the form of a central peak. The relaxation time τ of the mode has a temperature dependence similar to that of ε and shows a broad peak anomaly around Tm. The temperature dependence of τ can be analyzed by a modified superparaelectric model.

Light scattering experiment has been performed in a single crystal of 0.89Pb(Zn1∕3Nb2∕3)O3–0.11PbTiO3. The central peak (CP) spectra have been well detected with high resolution over the wide frequency region up to 150GHz. The distribution is discovered in the relaxation time associated with the CP. Moreover, it is found that the maximum relaxation time indicates the dynamical slowing down near the temperature Tm at which the low-frequency dielectric constant has a maximum. This finding strongly suggests that the physical origin of the CP is “polar nanoregions.”

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A light scattering experiment has been performed on two SrTi( 18 O x 16 O 1Ϫx ) 3 single crystal plates with x ϭ0.86 ͑STO18-86͒ and xϭ0.53 ͑STO18-53͒. Each of the c 44 pure transverse acoustic mode and the antiferrodistortive E g mode splits into two modes below T c ; T c ϭ27Ϯ1 K for STO18-86 and T c ϭ20Ϯ2 K for STO18-53. These splits strongly imply that the crystal symmetry becomes lower than tetragonal one below T c , and that the phase transition really occurs at T c . Moreover, the ferroelectric E u soft mode is found above T c , but its softening is not complete. This fact indicates that the phase transition mechanism of SrTi( 18 O x 16 O 1Ϫx ) 3 is of displacive type ͑the instability of the E u mode causes the ferroelectric phase transition͒, but is not the ideal one. The displacive character is found to become stronger with decreasing exchange rate x in the range xϾ0.33.

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