Anisotropic chemical expansion due to oxygen vacancies in perovskite films

AbstractIn scientifically intriguing and technologically important multifunctional ABO3 perovskite oxides, oxygen vacancies are most common defects. They cause lattice expansion and can alter the key functional properties. Here, it is demonstrated that contrary to weak isotropic expansion in bulk samples, oxygen vacancies produce strong anisotropic strain in epitaxial thin films. This anisotropic chemical strain is explained by preferential orientation of elastic dipoles of the vacancies. Elastic interaction of the dipoles with substrate-imposed misfit strain is suggested to define the dipolar orientation. Such elastic behavior of oxygen vacancies is anticipated to be general for perovskite films and have critical impacts on the film synthesis and response functions.

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Domain evolution of tetragonal Pb(ZrxTi1−x) O3 piezoelectric thin films on SrTiO3 (100) surfaces: combined effects of misfit strain and Zr/Ti ratio

Journal of Materials Chemistry C ◽

10.1039/c4tc00643g ◽

2014 ◽

Vol 2 (29) ◽

pp. 5836-5841 ◽

Cited By ~ 21

Author(s):

Qi Yu ◽

Jing-Feng Li ◽

Fang-Yuan Zhu ◽

Jiangyu Li

Keyword(s):

Thin Films ◽

Misfit Strain ◽

Epitaxial Thin Films ◽

Combined Effects ◽

Piezoelectric Thin Films ◽

Domain Evolution ◽

Ferroelectric Domains ◽

Substrate Constraint

The ferroelectric domains of tetragonal Pb(ZrxTi1−x)O3 epitaxial thin films have been studied comprehensively to reveal their piezoelectric responses under substrate constraint.

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A Numerical Scheme for Generalized Peierls-Nabarro Model of Dislocations Based on the Fast Multipole Method and Iterative Grid Redistribution

Communications in Computational Physics ◽

10.4208/cicp.130114.270315a ◽

2015 ◽

Vol 18 (5) ◽

pp. 1282-1312 ◽

Cited By ~ 4

Author(s):

Aiyu Zhu ◽

Congming Jin ◽

Degang Zhao ◽

Yang Xiang ◽

Jingfang Huang

Keyword(s):

Boundary Conditions ◽

Long Range ◽

Numerical Scheme ◽

Fast Multipole Method ◽

Dislocation Core ◽

Elastic Interaction ◽

Epitaxial Thin Films ◽

Fast Multipole ◽

Multipole Method ◽

Grid Points

AbstractDislocations are line defects in crystalline materials. The Peierls-Nabarro models are hybrid models that incorporate atomic structure of dislocation core into continuum framework. In this paper, we present a numerical method for a generalized Peierls-Nabarro model for curved dislocations, based on the fast multipole method and the iterative grid redistribution. The fast multipole method enables the calculation of the long-range elastic interaction within operations that scale linearly with the total number of grid points. The iterative grid redistribution places more mesh nodes in the regions around the dislocations than in the rest of the domain, thus increases the accuracy and efficiency. This numerical scheme improves the available numerical methods in the literature in which the long-range elastic interactions are calculated directly from summations in the physical domains; and is more flexible to handle problems with general boundary conditions compared with the previous FFT based method which applies only under periodic boundary conditions. Numerical examples using this method on the core structures of dislocations in Al and Cu and in epitaxial thin films are presented.

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Computational Analysis of Coupled Anisotropic Chemical Expansion in Li2-XMnO3-δ

MRS Advances ◽

10.1557/adv.2016.48 ◽

2016 ◽

Vol 1 (15) ◽

pp. 1037-1042 ◽

Cited By ~ 2

Author(s):

Christine James ◽

Yan Wu ◽

Brian Sheldon ◽

Yue Qi

Keyword(s):

Expansion Coefficient ◽

Oxygen Vacancies ◽

Computational Analysis ◽

Coupling Effect ◽

Chemical Expansion ◽

Charge Process ◽

Vacancy Pair ◽

Layered Cathode Materials ◽

O Vacancy ◽

Expansion Coefficients

ABSTRACTDuring the activation and charge process, vacancies are generated in the Li2MnO3 component in lithium-rich layered cathode materials. The chemical expansion coefficient tensor associated with oxygen vacancies, lithium vacancies and a Li-O vacancy pair were calculated for Li2-xMnO3-δ. The chemical expansion coefficient was larger for oxygen vacancies than for lithium vacancies in most directions. Additionally, the chemical expansion coefficient for a Li-O vacancy pair was shown to not be a linear sum of the chemical expansion coefficients of the two vacancy types, suggesting that the oxygen vacancies and lithium vacancies in Li2-XMnO3-δ exhibit a coupling effect.

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Defect-Mediated Mechanics in Non-Stoichiometric Oxide Films

MRS Advances ◽

10.1557/adv.2018.9 ◽

2018 ◽

Vol 3 (10) ◽

pp. 537-545 ◽

Cited By ~ 1

Author(s):

Jessica G. Swallow ◽

Mostafa Youssef ◽

Krystyn J. Van Vliet

Keyword(s):

Thin Films ◽

Elastic Modulus ◽

Oxygen Vacancy ◽

Elastic Properties ◽

Oxygen Vacancies ◽

Experimental Results ◽

Chemical Expansion ◽

Chemomechanical Coupling ◽

Defect Content ◽

Material Volume

ABSTRACTChemomechanical coupling is a hallmark of the functional oxides that are used widely for energy conversion and storage applications including solid oxide fuel cells (SOFCs). These oxides rely on the presence of oxygen vacancies to enable important properties including ionic conductivity and gas exchange reactivity. However, such defects can also facilitate chemical expansion, or coupling between material volume and defect content. Such chemomechanical coupling is particularly relevant with the recent interest in thin film SOFCs which have the potential to decrease operating temperatures and enable portable applications. Thin films present a particular challenge for modelling, as experimental results indicate that film defect chemistry can differ significantly from bulk counterparts under the same experimental conditions. In this study, we explore the influence of point defects, including oxygen vacancies and cation dopants, on the elastic properties of a model material, PrxCe1-xO2-δ (PCO), using density functional theory (DFT + U) simulations. Previously, we showed that PCO films exhibit a decrease in Young’s elastic modulus E due to chemical expansion, but that this decrease can be larger than predicted based on bulk defect models. Here, we apply DFT + U to show that the biaxial elastic modulus of PCO decreases with increased oxygen vacancy content in both bulk and membrane forms. We consider the relative influences of oxygen vacancies and cation dopants on this trend, and highlight local structural changes in the presence of such defects. By relating our computational and experimental results, we evaluate the relative importance of increased oxygen vacancy content and finite thickness on the mechanical properties of oxides that are subject to chemical expansion under operando conditions. This work informs the design of μ-SOFCs, emphasizing the need to characterize thin films separately from bulk counterparts and demonstrating how functional defect content can influence development of stress and strain in devices by changing both material volume and elastic properties.

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