Statistical electric field and switching time distributions in PZT 1Nb2Sr ceramics: Crystal- and microstructure effects

Abstract

Dispersive polarization response of ferroelectric PZT ceramics is analyzed assuming the inhomogeneous field mechanism of polarization switching. In terms of this model, the local polarization switching proceeds according to the Kolmogorov-Avrami-Ishibashi scenario with the switching time determined by the local electric field. As a result, the total polarization reversal is dominated by the statistical distribution of the local field magnitudes. Microscopic parameters of this model (the high-field switching time and the activation field) as well as the statistical field and consequent switching time distributions due to disorder at a mesoscopic scale can be directly determined from a set of experiments measuring the time dependence of the total polarization switching, when applying electric fields of different magnitudes. PZT 1Nb2Sr ceramics with Zr/Ti ratios 51.5/48.5, 52.25/47.75, and 60/40 with four different grain sizes each were analyzed following this approach. Pronounced differences of field and switching time distributions were found depending on the Zr/Ti ratios. Varying grain size also affects polarization reversal parameters, but in another way. The field distributions remain almost constant with grain size whereas switching times and activation field tend to decrease with increasing grain size. The quantitative changes of the latter parameters with grain size are very different depending on composition. The origin of the effects on the field and switching time distributions are related to differences in structural and microstructural characteristics of the materials and are discussed with respect to the hysteresis loops observed under bipolar electrical cycling. V C 2014 AIP Publishing LLC. [http://dx

Fatigue effect on polarization switching dynamics in polycrystalline bulk ferroelectrics

“…8,20 The IFM-analysis is based on the hypothesis that the local polarization switching occurs according to a step-like process on the logarithmic time scale (in general similar to the KAI-model) with a switching time () E  dependent on the local electric field E utilizing the experimental finding of the strong field dependence of switching dynamics. 21 This approach has proven to work in systems with sufficient randomness in grain orientation, which include all ferroelectric ceramics 17,[22][23][24][25] and at least some canonical relaxors 18 and organic ferroelectrics. 26,27 It allows the direct extraction of statistical distributions of the local electric field and, consequently, of the local switching times.…”

“…These characteristics can be related to phase symmetry and microstructure of a particular material. 22 In special cases, it even is possible to obtain microscopic characteristics of the switching process, such as energy and size of a critical domain nucleus in the polarization reversal process. [23][24][25] Ferroelectric materials are prone to fatigue, a gradual degradation of material properties, when exposed to mechanical or electrical cycling load.…”

“…(2) should be substituted by ) ( Q which makes a difference to the unfatigued material. 17,18,22 The maximum total polarization then reaches a magnitude:…”

“…It was experimentally established that, in fatigued PZT bulk ceramics 17 as well as in various ferroelectric ceramics in the virgin state, 18,[22][23][24][25] logarithmic derivatives of the total polarization with respect to the applied electric field exhibit scaling properties and can be represented as a function of the combined variable of field and time: …”

“…Also the () E  dependence can be extracted from the ) ( max t E function in the same way. 18,[22][23][24][25] Detailed explanations of the measured polarization data handling are given in algorithmic form in Ref. [22].…”