Piezoresponse of ferroelectric films in ferroionic states: time and voltage dynamics

TL;DR

This paper investigates the dynamic electrochemical and ferroelectric responses of thin ferroelectric films in ferro-ionic states, revealing how surface chemistry and frequency influence polarization and electromechanical behavior.

Contribution

It introduces an analytical model combining Ginzburg-Landau-Devonshire theory with Langmuir isotherm to study coupled ferro-ionic states under various conditions.

Findings

Ferro-ionic states are inseparable in thermodynamic equilibrium at low frequencies.

High-frequency dynamics decouple ferroelectric polarization from surface ion charge.

Surface chemistry and frequency significantly affect the polarization and electromechanical response.

Abstract

The interplay between electrochemical surface charges and bulk ferroelectricity in thin films gives rise to a continuum of coupled ferro-ionic states. These states are exquisitely sensitive to chemical and electric conditions at the surfaces, applied voltage, and oxygen pressure. Using the analytical approach combining the Ginzburg-Landau-Devonshire description of the ferroelectricity with Langmuir adsorption isotherm for the ions at the film surface, we have studied the temperature-, time- and field- dependent polarization changes and electromechanical response of the ferro-ionic states. The responses are found to be inseparable in thermodynamic equilibrium and at low frequencies of applied voltage. The states become separable in high frequency dynamic mode due to the several orders of magnitude difference in the relaxation times of ferroelectric polarization and surface ions charge density. These studies provide an insight into dynamic behavior of nanoscale ferroelectrics with open surface exposed to different kinds of electrochemically active gaseous surrounding.