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Title: Electrochemomechanics with flexoelectricity and modelling of electrochemical strain microscopy in mixed ionic-electronic conductors

Abstract

Recently, a new scanning probe microscopy approach, referred to as electrochemical strain microscopy (ESM), for probing local ionic flows and electrochemical reactions in solids based on the bias-strain coupling was proposed by Morozovska et al. Then, a series of theoretical papers for analyzing the image formation and spectroscopic mechanism of ESM were published within the framework of Fermi-Dirac statistics, the Vegard law, the direct flexoelectric coupling effect, the electrostriction effect, and so on. However, most of the models in these papers are limited to the partial coupling or particular process, and numerically solved by using decoupling approximation. In this paper, to model the ESM measurement with the coupling electrical-chemical-mechanical process, the chemical Gibbs function variational principle for the thermal electrical chemical mechanical fully coupling problem is proposed. The fully coupling governing equations are derived from the variational principle. When the tip concentrates the electric field within a small volume of the material, the inhomogeneous electric field is induced. So, both direct and inverse flexoelectric effects should be taken into account. Here, the bulk defect electrochemical reactions are also taken into account, which are usually omitted in the existing works. This theory can be used to deal with coupling problems inmore » solids, including conductors, semiconductors, and piezoelectric and non-piezoelectric dielectrics. As an application of this work, a developed initial-boundary value problem is solved numerically in a mixed ion-electronic conductor. Numerical results show that it is meaningful and necessary to consider the bulk defect chemical reaction. Besides, the chemical reaction and the flexoelectric effect have an interactive influence on each other. This work can provide theoretical basis for the ESM as well as investigating the bulk chemical reaction process in solids.« less

Authors:
; ;  [1]
  1. State Key Laboratory for Strength and Vibration of Mechanical Structures, School of Aerospace, Xi'an Jiaotong University, Xi'an 710049 (China)
Publication Date:
OSTI Identifier:
22597705
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 120; Journal Issue: 6; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; BOUNDARY-VALUE PROBLEMS; CHEMICAL REACTIONS; COUPLING; DIELECTRIC MATERIALS; ELECTRIC FIELDS; ELECTROCHEMISTRY; FERMI STATISTICS; IMAGES; MICROSCOPY; PIEZOELECTRICITY; SEMICONDUCTOR MATERIALS; SOLIDS; STRAINS; VARIATIONAL METHODS; VEGARD LAW

Citation Formats

Yu, Pengfei, Hu, Shuling, and Shen, Shengping, E-mail: sshen@mail.xjtu.edu.cn. Electrochemomechanics with flexoelectricity and modelling of electrochemical strain microscopy in mixed ionic-electronic conductors. United States: N. p., 2016. Web. doi:10.1063/1.4960445.
Yu, Pengfei, Hu, Shuling, & Shen, Shengping, E-mail: sshen@mail.xjtu.edu.cn. Electrochemomechanics with flexoelectricity and modelling of electrochemical strain microscopy in mixed ionic-electronic conductors. United States. doi:10.1063/1.4960445.
Yu, Pengfei, Hu, Shuling, and Shen, Shengping, E-mail: sshen@mail.xjtu.edu.cn. 2016. "Electrochemomechanics with flexoelectricity and modelling of electrochemical strain microscopy in mixed ionic-electronic conductors". United States. doi:10.1063/1.4960445.
@article{osti_22597705,
title = {Electrochemomechanics with flexoelectricity and modelling of electrochemical strain microscopy in mixed ionic-electronic conductors},
author = {Yu, Pengfei and Hu, Shuling and Shen, Shengping, E-mail: sshen@mail.xjtu.edu.cn},
abstractNote = {Recently, a new scanning probe microscopy approach, referred to as electrochemical strain microscopy (ESM), for probing local ionic flows and electrochemical reactions in solids based on the bias-strain coupling was proposed by Morozovska et al. Then, a series of theoretical papers for analyzing the image formation and spectroscopic mechanism of ESM were published within the framework of Fermi-Dirac statistics, the Vegard law, the direct flexoelectric coupling effect, the electrostriction effect, and so on. However, most of the models in these papers are limited to the partial coupling or particular process, and numerically solved by using decoupling approximation. In this paper, to model the ESM measurement with the coupling electrical-chemical-mechanical process, the chemical Gibbs function variational principle for the thermal electrical chemical mechanical fully coupling problem is proposed. The fully coupling governing equations are derived from the variational principle. When the tip concentrates the electric field within a small volume of the material, the inhomogeneous electric field is induced. So, both direct and inverse flexoelectric effects should be taken into account. Here, the bulk defect electrochemical reactions are also taken into account, which are usually omitted in the existing works. This theory can be used to deal with coupling problems in solids, including conductors, semiconductors, and piezoelectric and non-piezoelectric dielectrics. As an application of this work, a developed initial-boundary value problem is solved numerically in a mixed ion-electronic conductor. Numerical results show that it is meaningful and necessary to consider the bulk defect chemical reaction. Besides, the chemical reaction and the flexoelectric effect have an interactive influence on each other. This work can provide theoretical basis for the ESM as well as investigating the bulk chemical reaction process in solids.},
doi = {10.1063/1.4960445},
journal = {Journal of Applied Physics},
number = 6,
volume = 120,
place = {United States},
year = 2016,
month = 8
}
  • The frequency dependent Electrochemical Strain Microscopy (ESM) response of mixed ionic-electronic conductors is analyzed within the framework of Fermi-Dirac statistics and the Vegard law, accounting for steric effects from mobile donors. The emergence of dynamic charge waves and nonlinear deformation of the surface in response to bias applied to the tip-surface junction is numerically explored. The 2D maps of the strain and concentration distributions across the mixed ionic-electronic conductor and bias-induced surface displacements are calculated. Furthermore, the obtained numerical results can be applied to quantify the ESM response of Li-based solid electrolytes, materials with resistive switching, and electroactive ferroelectric polymers,more » which are of potential interest for flexible and high-density non-volatile memory devices.« less
  • The frequency dependent Electrochemical Strain Microscopy (ESM) response of mixed ionic-electronic conductors is analyzed within the framework of Fermi-Dirac statistics and the Vegard law, accounting for steric effects from mobile donors. The emergence of dynamic charge waves and nonlinear deformation of the surface in response to bias applied to the tip-surface junction is numerically explored. The 2D maps of the strain and concentration distributions across the mixed ionic-electronic conductor and bias-induced surface displacements are calculated. The obtained numerical results can be applied to quantify the ESM response of Li-based solid electrolytes, materials with resistive switching, and electroactive ferroelectric polymers, whichmore » are of potential interest for flexible and high-density non-volatile memory devices.« less
  • This paper reports on the wetting behavior, reactivity, and long-term electrical conductance of a series of ternary filler metals being considered for brazing lanthanum strontium cobalt ferrite (LSCF) based oxygen separation membranes. Mixed ionic/electronic conducting perovskite oxides such as LSCF and various doped barium cerates are currently being considered for use in high-temperature electrochemical devices such as oxygen and hydrogen concentrators and solid oxide fuel cells. However to take full advantage of the unique properties of these materials, reliable joining techniques need to be developed. Furthermore, if the proposed joining technique were to yield a hermetic ceramic-to-metal junction that wasmore » also electrically conductive, it would additionally benefit the device by allowing current to be drawn from or carried to the electrochemically active mixed conducting oxide component without requiring an separate current collector. A newly developed brazing technique known as air brazing is one such method of joining. In its present form, air brazing uses a silver-copper oxide based filler metal that can be melted directly in air to form a compliant joint that is electrically conductive. Recently, it has been shown that the addition of titania can enhance the wetting behavior of Ag-CuO filler metals on alumina. Here the effect of this wetting agent on the surface wettability, long-term electrical resistance at 750°C, and reactivity with La0.6Sr0.4Co0.2Fe0.8O3- (LSCF-6428 or LSCF) substrates is discussed.« less
  • Mixed ionic-electronic conductors (MIECs) have been widely studied as dense membranes for electrosynthesis (such as partial oxidation of methane and gas separation), as catalytic electrodes for solid-state ionic devices (such as solid oxide fuel cells, batteries, and chemical sensors), and as electrolytes or other components for various devices or systems. General analytical solutions to transport equations are presented for a MIEC subject to various electrical and chemical conditions at the surfaces. The derived general expressions can be used to predict the steady-state distributions of defects and electrical potential within the MIEC as a function of an external stimulus for transport:more » an electric field, a gradient in chemical potential, or a combination of the two. Also, variations in conductivities, transference numbers, current carried by each type of defect, and chemical potential of oxygen within the MIEC can be readily calculated under different conditions. Analyses indicate that the distribution of mobile defects is approximately linear when the amount of uniformly distributed immobile charges is sufficiently small while the electrical potential distributes nearly linearly when the amount of uniformly distributed immobile charges is sufficiently large. In addition, the derived equations can be used to determine the transport properties of an MIEC from observed steady-state behavior of the MIEC under controlled conditions. Further, and in particular, the derived equations can provide valuable guidance in optimizing performances of devices or systems based on MIECs and in improving or redesigning MIECs for various applications.« less
  • Mixed ionic–electronic conductors are widely used in devices for energy conversion and storage. Grain boundaries in these materials have nanoscale spatial dimensions, which can generate substantial resistance to ionic transport due to dopant segregation. Here, we report the concept of targeted phase formation in a Ce 0.8Gd 0.2O 2₋δ–CoFe 2O 4 composite that serves to enhance the grain boundary ionic conductivity. Using transmission electron microscopy and spectroscopy approaches, we probe the grain boundary charge distribution and chemical environments altered by the phase reaction between the two constituents. The formation of an emergent phase successfully avoids segregation of the Gd dopantmore » and depletion of oxygen vacancies at the Ce 0.8Gd 0.2O 2₋δ–Ce 0.8Gd 0.2O 2₋δ grain boundary. This results in superior grain boundary ionic conductivity as demonstrated by the enhanced oxygen permeation flux. Lastly, this work illustrates the control of mesoscale level transport properties in mixed ionic–electronic conductor composites through processing induced modifications of the grain boundary defect distribution.« less