Short-ranged clusters with tetragonal symmetry in La-modified PbTiO3 relaxor ferroelectrics

Microscopic features associated with the displacive cubic-to-tetragonal phase transition in La-modified PbTiO3 (PLT) were studied using Raman spectroscopy. For this purpose, we separately prepared two distinct types of PLT specimens having cation-site vacancies either at the A-site (PLT-A) or at the B-site (PLT-B). As the La-content increased to 30 at.%, the Raman-forbidden bands appeared in the cubic-phase for both types of PLTs. However, the PLT-A(30) exhibited a continuous narrowing of the bands with decreasing temperature through the cubic-to-tetragonal transition point while the PLT-B(30) relaxor did not show any appreciable variation in the line broadening. These observations were interpreted in terms of the formation of short-ranged clusters with tetragonal symmetry in a globally cubic matrix and of the reduced dipolar interaction between the polar clusters in the PLT-B, as compared with the PLT-A.