Damage from Coexistence of Ferroelectric and Antiferroelectric Domains and Clustering of O Vacancies in PZT: An Elastic and Raman Study.

Francesco Cordero,Elena Buixaderas,Carmen Galassi

doi:10.3390/ma12060957

Abstract

It is often suggested that oxygen vacancies (V) are involved in fatigue and pinning of domain walls in ferroelectric (FE) materials, but generally without definite evidence or models. Here the progress of damage induced by the coexistence of FE and antiferroelectric (AFE) domains in the absence of electric cycling is probed by monitoring the Young’s modulus, which may undergo more than fourfold softenings without significant changes in the Raman spectra, but may end with the disaggregation of PZT with ∼5% Ti. At these compositions, the FE and AFE phases coexist at room temperature, as also observed with micro-Raman, and hence the observations are interpreted in terms of the aggregation of V at the interfaces between FE and AFE domains, which are sources of internal electric and stress fields. The V would coalesce into planar defects whose extension grows with time but can be dissolved by annealing above 600 K, which indeed restores the original stiffness. The observed giant softening is interpreted by assimilating the planar aggregations of V to flat inclusions with much reduced elastic moduli, due to the missing Zr/Ti−O bonds. A relationship between the coalescence of a fixed concentration of V into planar defects and softening is then obtained from the existing literature on the effective elastic moduli of materials with inclusions of various shapes.

Highlights

Fatigue and pinning of domain walls in ferroelectric materials subjected to electric cycling are phenomena known for decades and much studied [1,2,3]
On the other hand, aging and degradation may occur in the absence of electrodes and applied electric fields, as demonstrated by softenings of the Young’s modulus down to 1/4 of the original value in PZT with ∼5% Ti [6,7]. At those compositions the FE and AFE domains may coexist at room temperature, and enormous softening may be induced by a few thermal cycles around the AFE/FE
In what follows we will propose a mechanism that may explain the major effects on the elastic properties that occur when FE and AFE domains coexist in quasistatic conditions: (i) softening of the compliance by up to a factor of 4 in the FE/AFE states and up to 2 in the PE phase during aging and thermal cycling; (ii) recovery of the original stiffness with annealing, in high vacuum, between

Summary

Introduction

Fatigue and pinning of domain walls in ferroelectric materials subjected to electric cycling are phenomena known for decades and much studied [1,2,3]. On the other hand, aging and degradation may occur in the absence of electrodes and applied electric fields, as demonstrated by softenings of the Young’s modulus down to 1/4 of the original value in PZT with ∼5% Ti [6,7]. At those compositions the FE and AFE domains may coexist at room temperature, and enormous softening may be induced by a few thermal cycles around the AFE/FE transition or aging at room temperature. It has been shown that these phenomena are peculiar of the long term coexistence of FE and AFE domains, by inducing a total stability through doping with 2% La, which transforms the FE phase into incommensurate AFE [8]

Methods

Results

Discussion

Conclusion