Effects of ac-field amplitude on the dielectric susceptibility of relaxors

The thermally activated flips of the local spontaneous polarization in relaxors were simulated to investigate the effects of the applied-ac-field amplitude on the dielectric susceptibility. It was observed that the susceptibility increases with increasing the amplitude at low temperatures. At high temperatures, the susceptibility experiences a plateau and then drops. The maximum in the temperature dependence of susceptibility shifts to lower temperatures when the amplitude increases. A similarity was found between the effects of the amplitude and frequency on the susceptibility. PACS: 77.22.Ch, 77.80.-e, 77.84.-s, 77.84.Lf Typeset using REVTEX 1 Relaxor ferroelectrics (relaxors) have been studied for nearly 40 years since Pb(Mg1/3Nb2/3)O3 (PMN) was first synthesized by Smolenski et al.. 1 The dielectric response of relaxors is characterized by the diffuse phase transition (DPT) and a strong frequency dispersion. Various models, such as the compositional heterogeneity model, the superparaelectric model, and the glasslike model, et al., were proposed to rationalize the complicated behaviors of relaxors. It is widely accepted nowadays that the presence of polar microregions in nanoscale4–6 is responsible for the relaxor behaviors. The effects of the applied ac field on relaxors7–14 cause great interest since they provide some clue of the relaxation mechanism. Glazounov et al. observed that the dielectric permittivity of PMN increases with increasing amplitude of the applied ac field. A similarity was also found between the effects of the amplitude and frequency on the permittivity. In addition, the ac-drive-enhanced relaxor characteristics and domain breakdown were observed in (PbLa)(ZrTi) (PLZT). There are two possible mechanisms, i. e., domain-wall motion model and superparaelectric model, to explicate the nonlinearity of dielectric permitivity of PMN relaxors. Glazounov et al. suggested that it is related to domain-type process rather than thermally activated flips of the local spontaneous polarization (i.e. superparaelectric model). However, they did not consider the interaction of polar microregions when investigating the superparaelectric model, which is just one of the key points related to response of the external field. In this study, we conduct a Monte Carlo simulation to investigate the influence of measuring field on the dielectric susceptibility of relaxors. We investigate the thermally activated flipping process of the local spontaneous polarization in relaxors. Following the work of Gui et al., the polar microregions are regarded as point dipoles. Then relaxors are modeled to be a system consisting of Ising-like dipoles with randomly distributed interactions: