Incommensurate instability and diffuse scattering at Brillouin zone boundary in Zr-rich lead zirconate titanate.

Detailed study of the X-ray diffuse scattering in the paraelectric phase of the PbZr_0.985Ti_0.015O₃ was carried out. We concentrated on the analysis of the scattering peculiarities in the vicinities of M- and R- points of the Brillouin zone. We have observed a critical increase of the diffuse scattering at the position Q ≈ (0.47 + h 0.53 + k l) slightly aside of M point on cooling to the intermediate phase. We attribute observed critical scattering to a mixed mode containing both oxygen octahedral tilts and antiparallel cationic displacements. Tentative conclusion is made describing earlier reported complicated set of the satellite peaks around M-point as the result of the soft-mode driven incommensurate phase transition. [ABSTRACT FROM AUTHOR]