Large electromechanical strain and unconventional domain switching near phase convergence in a Pb-free ferroelectric

Jürgen Rödel,Frederick P Marlton,Laurent Daniel,Valentin Segouin,Abhijit Pramanick,Yang Ren,Lalitha K Venkataraman,Ho Chin Hin,Mads R V Jørgensen,Sanjib Nayak,Sarangi Venkateshwarlu,Dmitry Chernyshov

doi:10.1038/s42005-020-00459-2

Abstract

In many ferroelectrics, large electromechanical strains are observed near regions of composition- or temperature- driven phase coexistence. Phenomenologically, this is attributed to easy re-orientation of the polarization vector and/or phase transition, although their effects are highly convoluted and difficult to distinguish experimentally. Here, we used synchrotron X-ray scattering and digital image correlation to differentiate between the microscopic mechanisms leading to large electrostrains in an exemplary Pb-free piezoceramic Sn-doped barium calcium zirconate titanate. Large electrostrains of ~0.2% measured at room-temperature are attributed to an unconventional effect, wherein polarization switching is aided by a reversible phase transition near the tetragonal-orthorhombic phase boundary. Additionally, electrostrains of ~0.1% or more could be maintained from room temperature to 140 °C due to a succession of different microscopic mechanisms. In situ X-ray diffraction elucidates that while 90° domain reorientation is pertinent below the Curie temperature (TC), isotropic distortion of polar clusters is the dominant mechanism above TC.

Highlights

In many ferroelectrics, large electromechanical strains are observed near regions of composition- or temperature- driven phase coexistence
We examined the effect of Sn2+ substitution on the electrostrain properties of barium calcium zirconate titanate (BCZT) ((Ba0.95Ca0.045Sn0.005) (Ti0.875Zr0.12Sn0.005)O3) ceramics near phase convergence region, which provided large d*33 over a wider range of temperatures from room temperature (RT) to 140 °C as compared to undoped BCZT
Dielectric and phase transition behavior. (Ba0.95Ca0.045Sn0.005) (Ti0.875Zr0.12Sn0.005)O3 ceramics close to the phase convergence region[19] but with broadened phase space of the O phase were selected for the current study

Summary

Introduction

Large electromechanical strains are observed near regions of composition- or temperature- driven phase coexistence. Ren and co-workers suggested that large electromechanical properties in BZT-BCT can be attributed to a vanishing polarization anisotropy near the rhombohedral(R)/tetragonal(T)/cubic(C) triple point, which aids easy polarization rotation and large electromechanical susceptibility[11,18] This view was, challenged by later X-ray diffraction (XRD) and dielectric studies, which instead showed the occurrence of a polymorphic phase transition sequence similar to prototypical BaTiO3 and existence of a fourphase convergence region[13,19]. While presumably easy polarization rotation and low energy barrier for polarization switching near the phase convergence region should aid towards large electromechanical susceptibility, this advantage is largely offset by the lower lattice distortions Following this argument, in principle, introducing local lattice distortions for compositions close to the phase converge region can result in larger electric field-induced strains.

Methods

Results

Conclusion