Study of Slow Lattice Dynamics in Relaxor Ferroelectric PMN–30%PT by Neutron Spin Echo Technique

Abstract

We have used the neutron spin echo technique to characterize the dynamics of polar nanoregions (PNRs) in the relaxor ferroelectric (1- x )Pb(Mg 1/3 Nb 2/3 )O 3 – x PbTiO 3 (PMN– x PT) with x =30% ( T C ∼400 K). We measured the normalized intermediate scattering function I ( Q , t )/ I ( Q ,0) for a butterfly-shaped diffuse scattering around the (100) Bragg point, which is associated with atomic shifts, i.e., polarizations in PNRs. For T ≥500 K, I ( Q , t )/ I ( Q ,0) shows a peak structure at 0.5 ns, which is ascribed to the coexistence of echo signals from a relaxation mode and those from a low-frequency vibrational mode with ω∼26 µeV. Such a low-frequency vibrational mode for directions indicate a flat free-energy surface between the rhombohedral and tetragonal phases. On cooling below 450 K, the peak structure in I ( Q , t )/ I ( Q ,0) disappears and diffuse scattering intensity increases, which indicates that the condensed or pinned low-frequency mode for directions is the origin of PNRs.