ANHARMONICITY OF THE POTENTIAL OF THE A(1)(1TO)-MODE VIBRATIONS IN PZT CERAMICS

Raman spectroscopy between 11 and 680 K was used together with room-te mperature x-ray diffraction experiments for structural studies of ferr oelectric Nd-modified PbTiO3 (PNT) and lead-zirconate-titanate (PNZT) ceramics at the morphotropic phase boundary. The amount of Nd varied b etween 0 and 10 % of A-cation sites in PNT ceramics and between 0 and 4 % in PNZT ceramics. Raman results revealed a subpeak structure of te tragonal A(1)(1TO)-mode frequencies both in PNT and PNZT ceramics in a greement with earlier findings in PbTiO3 single crystals. The observed subpeak frequencies of the A(1)(1TO) mode were approximately fit by e nergy levels of an anharmonic double-well potential in asymmetric (fer roelectric) form from the mean-field approach in both PNT and PNZT cer amics. In addition to the four subpeaks, an additional mode was also f ound at about 55 cm(-1) in PNZT ceramics. Nd addition was found to hav e a strong effect on the balance between tetragonal and trigonal phase s in the PZT structure. The tetragonal phase fraction increased and th e size of trigonal domains decreased with increasing Nd addition. Howe ver, Nd addition decreased the intensities of tetragonal A(1)(1TO)-mod e subpeaks. Nd addition had also a strong effect on the relative inten sities between different subpeaks, which is discussed here on the basi s of our mean-field approach for the double-well potential.