Electron paramagnetic resonance investigation of polar nanoregions mobility in the relaxor PbMg1/3Nb2/3O3 and solid solutions PbMg1/3Nb2/3O3 – PbTiO3

Abstract

Electron paramagnetic resonance (EPR) of Mn2+ and Fe3+ ions has been used as a probe of local static and dynamic lattice distortions in the relaxor ferroelectric PbMg1/3Nb2/3O3 (PMN) and solid solutions (1-x)PbMg1/3Nb2/3O3 – xPbTiO3 (x = 0.075–0.33) at temperatures from 290 to 800 K. We have found that the spectrum of the both ions in PMN contains two components: One component corresponds to the resonances from the lattice regions where the perovskite cubic structure is distorted statically while the second component corresponds to the regions where ionic displacements undergo significant dynamic fluctuations. The EPR spectrum from these lattice regions shows the motional narrowing behavior at 350–500 K. We assign these regions with reorientable polar nanoregions responsible for the dielectric relaxation in PMN. From the motional narrowing of the spectral lines, we have determined parameters of the Vogel--Fulcher law describing the rate of ionic hopping between symmetrically equivalent off-center positions. These parameters (Ea = 840–880 K, τ0 ∼ 10−13 s, Tg = 220 K) are in a satisfactory agreement with those reported for the dielectric relaxation. The fraction of polar nanoregions in PMN determined from the EPR intensity is about 20% to 30%. An addition of PbTiO3 to PMN decreases total volume of the polar nanoregions and also suppresses their reorientational dynamics. The EPR spectra do not change in the temperature range from 500 to 800 K, including the temperatures far above the Burns temperature 620 K.