Nanoscale mapping of heterogeneity of the polarization reversal in lead-free relaxor-ferroelectric ceramic composites.

D. Gobeljic,B. Okatan,S. Jesse,S. V. Kalinin,V. V. Shvartsman,C. Groh,A. Belianinov,J. Rödel,D. C. Lupascu

doi:10.1039/c5nr05032d

Abstract

Relaxor/ferroelectric ceramic/ceramic composites have shown to be promising in generating large electromechanical strain at moderate electric fields. Nonetheless, the mechanisms of polarization and strain coupling between grains of different nature in the composites remain unclear. To rationalize the coupling mechanisms we performed advanced piezoresponse force microscopy (PFM) studies of 0.92BNT-0.06BT-0.02KNN/0.93BNT-0.07BT (ergodic/non-ergodic relaxor) composites. PFM is able to distinguish grains of different phases by characteristic domain patterns. Polarization switching has been probed locally, on a sub-grain scale. k-Means clustering analysis applied to arrays of local hysteresis loops reveals variations of polarization switching characteristics between the ergodic and non-ergodic relaxor grains. We report a different set of switching parameters for grains in the composites as opposed to the pure phase samples. Our results confirm ceramic/ceramic composites to be a viable approach to tailor the piezoelectric properties and optimize the macroscopic electromechanical characteristics.

Highlights

A strong piezoelectric effect and efficient electromechanical energy conversion are the key features of ferroelectric materials used in a large number of technological applications such as piezoelectric actuators, transducers, fuel injectors, micropositioning systems etc.[1,2] The underlying reason for their wide applicability is polarization switching under an external electric field
Polarization switching has been probed locally, on a sub-grain scale. k-Means clustering analysis applied to arrays of local hysteresis loops reveals variations of polarization switching characteristics between the ergodic and non-ergodic relaxor grains
The macroscopic measurements reported that the high unipolar strain in these materials can be achieved at relatively low electric fields and that the maximum strain level strongly depends on the amount of the BNT–7BT constituent.[15]

Summary

Introduction

A strong piezoelectric effect and efficient electromechanical energy conversion are the key features of ferroelectric materials used in a large number of technological applications such as piezoelectric actuators, transducers, fuel injectors, micropositioning systems etc.[1,2] The underlying reason for their wide applicability is polarization switching under an external electric field. In most of these materials, polarization switching is a complex process that includes nucleation of new domains and ferroelastic and ferroelectric domain wall motion.[2,3] it is well know that the domain structure and domain movement affect the physical material properties, as dielectric permittivity, piezoelectric coefficient,[4] hysteresis curve,[5] aging, and fatigue.[6]. Due to global health and nature protection regulation acts,[7]

Results

Discussion

Conclusion