Raman scattering studies of Nd-modified lead titanate ${\mathrm{Pb}}_{1-3y/2}{\mathrm{Nd}}_y{\mathrm{TiO}}_3$ (PNT), $y=0.02,$ 0.10, and $\mathrm{Pb}\left({\mathrm{Zr}}_x{\mathrm{Ti}}_{1-x}\right){\mathrm{O}}_3$ (PZT), $x=0.10,0.20,$ bulk ceramics were made at ambient temperatures between 4.2 and 297 K. Our measurements reveal splitting of the $E\oplus B_1$ symmetry peak at low temperatures in both the PNT and PZT samples. Some splitting of three $E\left(\mathrm{TO}\right)\mathrm{}$ peaks in the PZT samples [except for the $E\left(2\mathrm{}\mathrm{TO}\right)$ peak in the sample with $x=0.10\mathrm{}]$ and of the $E\left(3\mathrm{}\mathrm{TO}\right)$ peak in the PNT samples was also found. We discuss the phase stability of lead titanate based perovskites from the point of view of our experimental results and recent theoretical calculations. Raman results reveal that all $A_1\left(\mathrm{TO}\right)$ symmetry modes in all samples are anharmonic down to the lowest measurement temperature.

• Received 14 July 1998

DOI:https://doi.org/10.1103/PhysRevB.59.12