Engineering of atomic-scale flexoelectricity at grain boundaries

AbstractFlexoelectricity is a type of ubiquitous and prominent electromechanical coupling, pertaining to the electrical polarization response to mechanical strain gradients that is not restricted by the symmetry of materials. However, large elastic deformation is usually difficult to achieve in most solids, and the strain gradient at minuscule is challenging to control. Here, we exploit the exotic structural inhomogeneity of grain boundary to achieve a huge strain gradient (~1.2 nm−1) within 3–4-unit cells, and thus obtain atomic-scale flexoelectric polarization of up to ~38 μC cm−2 at a 24° LaAlO3 grain boundary. Accompanied by the generation of the nanoscale flexoelectricity, the electronic structures of grain boundaries also become different. Hence, the flexoelectric effect at grain boundaries is essential to understand the electrical activities of oxide ceramics. We further demonstrate that for different materials, altering the misorientation angles of grain boundaries enables tunable strain gradients at the atomic scale. The engineering of grain boundaries thus provides a general and feasible pathway to achieve tunable flexoelectricity.

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Conservation Integrals in Nonhomogeneous Materials with Flexoelectricity

Applied Sciences ◽

10.3390/app11020681 ◽

2021 ◽

Vol 11 (2) ◽

pp. 681

Author(s):

Pengfei Yu ◽

Weifeng Leng ◽

Yaohong Suo

Keyword(s):

Electromechanical Coupling ◽

Energy Momentum Tensor ◽

Great Influence ◽

Operator Method ◽

Electric Polarization ◽

Momentum Tensor ◽

Noether Theorem ◽

Strain Gradients ◽

Flexoelectric Effect ◽

Nonhomogeneous Materials

The flexoelectricity, which is a new electromechanical coupling phenomenon between strain gradients and electric polarization, has a great influence on the fracture analysis of flexoelectric solids due to the large gradients near the cracks. On the other hand, although the flexoelectricity has been extensively investigated in recent decades, the study on flexoelectricity in nonhomogeneous materials is still rare, especially the fracture problems. Therefore, in this manuscript, the conservation integrals for nonhomogeneous flexoelectric materials are obtained to solve the fracture problem. Application of operators such as grad, div, and curl to electric Gibbs free energy and internal energy, the energy-momentum tensor, angular momentum tensor, and dilatation flux can also be derived. We examine the correctness of the conservation integrals by comparing with the previous work and discuss the operator method here and Noether theorem in the previous work. Finally, considering the flexoelectric effect, a nonhomogeneous beam problem with crack is solved to show the application of the conservation integrals.

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Image Simulations of Ge Twin Boundaries.

MRS Proceedings ◽

10.1557/proc-295-173 ◽

1992 ◽

Vol 295 ◽

Cited By ~ 1

Author(s):

Stuart Mckernan ◽

C. Barry Carter

Keyword(s):

Grain Boundary ◽

Grain Boundaries ◽

High Angle ◽

Structural Units ◽

Twin Boundaries ◽

Large Unit ◽

Unit Cells ◽

The Individual ◽

Image Simulations

AbstractGeneral high-angle tilt grain boundaries may be described by an arrangement of repeating structural units. Some grain-boundary defects may also be modeled by the incorporation of structural units of related boundary structures into the boundary. The simulation of these structures requires the use of prohibitively large unit cells. The possibility of modeling these boundaries by the superposition of image simulations of the individual structural units isinvestigated.

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Atomic Scale Analysis of a YSZ Bicrystal Grain Boundary

Microscopy and Microanalysis ◽

10.1017/s1431927600028075 ◽

2001 ◽

Vol 7 (S2) ◽

pp. 400-401

Author(s):

Y. Lei ◽

Y. Ito ◽

N. D. Browning

Keyword(s):

Grain Boundary ◽

Grain Boundaries ◽

Bulk Material ◽

Atomic Scale ◽

Structure Property ◽

Contrast Imaging ◽

Structure Property Relationships ◽

Commercial Applications ◽

Z Contrast ◽

Electron Energy Loss

Yttria-stabilized zirconia (YSZ) has been the subject of many experimental and theoretical studies, due to the commercial applications of zirconia-based ceramics in solid state oxide fuel cells. Since the grain boundaries usually dominate the overall macroscopic performance of the bulk material, it is essential to develop a fundamental understanding of their structure-property relationships. Previous research has been performed on the atomic structure of grain boundaries in YSZ, but no precise atomic scale compositional and chemistry characterization has been carried out. Here we report a detailed analytical study of an [001] symmetric 24° bicrystal tilt grain boundary in YSZ prepared with ∼10 mol % Y2O3 by Shinkosha Co., Ltd by the combination of Z-contrast imaging and electron energy loss spectroscopy (EELS).The experimental analysis of the YSZ sample was carried out on a 200kV Schottky field emission JEOL 201 OF STEM/TEM4.

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Segregation of P and S Impurities to A Σ9 Grain Boundary in Cu

Metals ◽

10.3390/met10101362 ◽

2020 ◽

Vol 10 (10) ◽

pp. 1362

Author(s):

Cláudio M. Lousada ◽

Pavel A. Korzhavyi

Keyword(s):

Grain Boundary ◽

Grain Boundaries ◽

Coordination Number ◽

High Performance ◽

Chemical Properties ◽

Atomic Scale ◽

Atomic Site ◽

Segregation Energy ◽

Physical Chemical ◽

Symmetric Tilt

The segregation of P and S to grain boundaries (GBs) in fcc Cu has implications in diverse physical-chemical properties of the material and this can be of particular high relevance when the material is employed in high performance applications. Here, we studied the segregation of P and S to the symmetric tilt Σ9 (22¯1¯) [110], 38.9° GB of fcc Cu. This GB is characterized by a variety of segregation sites within and near the GB plane, with considerable differences in both atomic site volume and coordination number and geometry. We found that the segregation energies of P and S vary considerably both with distance from the GB plane and sites within the GB plane. The segregation energy is significantly large at the GB plane but drops to almost zero at a distance of only ≈3.5 Å from this. Additionally, for each impurity there are considerable variations in energy (up to 0.6 eV) between segregation sites in the GB plane. These variations have origins both in differences in coordination number and atomic site volume with the effect of coordination number dominating. For sites with the same coordination number, up to a certain atomic site volume, a larger atomic site volume leads to a stronger segregation. After that limit in volume has been reached, a larger volume leads to weaker segregation. The fact that the segregation energy varies with such magnitude within the Σ9 GB plane may have implications in the accumulation of these impurities at these GBs in the material. Because of this, atomic-scale variations of concentration of P and S are expected to occur at the Σ9 GB center and in other GBs with similar features.

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Survey of Grain Boundary Energies in Four Elemental Metals

Materials Science Forum ◽

10.4028/www.scientific.net/msf.715-716.179 ◽

2012 ◽

Vol 715-716 ◽

pp. 179-179

Author(s):

David L. Olmsted ◽

Elizabeth A. Holm ◽

Stephen M. Foiles

Keyword(s):

Grain Boundary ◽

Grain Boundaries ◽

Energy Minimization ◽

Boundary Energy ◽

Atomic Scale ◽

Energy Structure ◽

Grain Boundary Energy ◽

Fcc Metals ◽

Composition And Structure ◽

Boundary Properties

Grain boundary properties depend on both composition and structure. To test the relative contributions of composition and structure to the grain boundary energy, we calculated the energy of 388 grain boundaries in four elemental, fcc metals: Ni, Al, Au and Cu. We constructed atomic-scale bicrystals of each boundary and subjected them to a rigorous energy minimization process to determine the lowest energy structure. Typically, several thousand boundary configurations were examined for each boundary in each element.

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Atomic Scale Characterisation of Electrodeposited Nanocrystalline Ni-P Alloys

MRS Proceedings ◽

10.1557/proc-581-517 ◽

1999 ◽

Vol 581 ◽

Cited By ~ 3

Author(s):

Matthias Abraham ◽

Mattias Thuvandert ◽

Helen M. Lane ◽

Alfred Cerezo ◽

George D.W. Smith

Keyword(s):

Heat Treatment ◽

Grain Boundary ◽

Grain Boundaries ◽

Three Dimensional ◽

Boundary Segregation ◽

Atom Probe ◽

Atomic Scale ◽

Grain Boundary Segregation ◽

P Concentration

ABSTRACTNanocrystalline Ni-P alloys produced by electrodeposition have been characterised by three-dimensional atom probe (3DAP) analysis. In the as-deposited materials, there are indications of some variation in P concentration between grains and segregation to grain boundaries. After heat treatment however, strong grain boundary segregation and the formation of Ni3P precipitates have been observed.

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Distributed flexoelectric modal signals on circular cylindrical shells

Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science ◽

10.1177/0954406217697999 ◽

2017 ◽

Vol 232 (6) ◽

pp. 952-961 ◽

Cited By ~ 3

Author(s):

Hua Li ◽

Kaiming Hu ◽

HS Tzou

Keyword(s):

Strain Gradient ◽

Cylindrical Shells ◽

Mechanical Strain ◽

Electric Polarization ◽

Design Parameters ◽

Flexoelectric Effect ◽

Bending Strain ◽

Longitudinal Bending ◽

Circular Cylindrical Shells ◽

Sensing Characteristics

Flexoelectricity exhibits both direct effect and converse effect. For direct flexoelectric effect, mechanical strain gradients induce a homogeneous electric polarization in dielectrics. Thus, the induced electric field between the electrodes can be measured. Compared with the piezoelectric sensors, the main advantage of the flexoelectric sensors is that they are not sensitive to the in-plane strains. This paper presents segmented flexoelectric sensors laminated on circular cylindrical shells, and investigates the electromechanical strain-gradient/signal-generation characteristics and distributed modal flexoelectric signals on the cylindrical shells. The dynamic equations of the proposed flexoelectric sensor are derived based on the direct flexoelectric effect and thin shell assumptions. The model of modal signal is derived to investigate the sensing characteristics. In case studies, the effects of design parameters, i.e. size and thickness of the sensors and geometry of the shells, are evaluated and compared. Numerical results indicate that the contribution of longitudinal bending strain gradient is dominant in the total signals of most evaluated modes, except that in modes 1 and 2, where the contribution of the circumferential bending strain gradient is slightly higher. The amplitudes of the modal signals decrease with the shell radius, but increase with the sensor thickness.

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Constrained Grain Boundary Diffusion In Thin Copper Films

MRS Proceedings ◽

10.1557/proc-821-p1.2 ◽

2004 ◽

Vol 821 ◽

Cited By ~ 4

Author(s):

Markus J. Buehler ◽

Alexander Hartmaier ◽

Huajian Gao

Keyword(s):

Thin Films ◽

Theoretical Analysis ◽

Grain Boundary ◽

Grain Boundaries ◽

Boundary Diffusion ◽

Grain Boundary Diffusion ◽

Atomic Scale ◽

Diffusional Creep ◽

Copper Films ◽

And Diffusion

AbstractIn a recent study of diffusional creep in polycrystalline thin films deposited on substrates, we have discovered a new class of defects called the grain boundary diffusion wedges (Gao et al., Acta Mat. 47, pp. 2865-2878, 1999). These diffusion wedges are formed by stress driven mass transport between the free surface of the film and the grain boundaries during the process of substrate-constrained grain boundary diffusion. The mathematical modeling involves solution of integro-differential equations representing a strong coupling between elasticity and diffusion. The solution can be decomposed into diffusional eigenmodes reminiscent of crack-like opening displacement along the grain boundary which leads to a singular stress field at the root of the grain boundary. We find that the theoretical analysis successfully explains the difference between the mechanical behaviors of passivated and unpassivated copper films during thermal cycling on a silicon substrate. An important implication of our theoretical analysis is that dislocations with Burgers vector parallel to the interface can be nucleated at the root of the grain boundary. This is a new dislocation mechanism in thin films which contrasts to the well known Mathews-Freund-Nix mechanism of threading dislocation propagation. Recent TEM experiments at the Max Planck Institute for Metals Research have shown that, while threading dislocations dominate in passivated metal films, parallel glide dislocations begin to dominate in unpassivated copper films with thickness below 400 nm. This is consistent with our theoretical predictions. We have developed large scale molecular dynamics simulations of grain boundary diffusion wedges to clarify the nucleation mechanisms of parallel glide in thin films. Such atomic scale simulations of thin film diffusion not only show results which are consistent with both continuum theoretical and experimental studies, but also revealed the atomic processes of dislocation nucleation, climb, glide and storage in grain boundaries. The study should have far reaching implications for modeling deformation and diffusion in micro- and nanostructured materials.

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The Atomic-Scale Origins of Grain Boundary Superconducting Properties

Microscopy and Microanalysis ◽

10.1017/s1431927600023564 ◽

1998 ◽

Vol 4 (S2) ◽

pp. 688-689

Author(s):

S. J. Pennycook ◽

J. Buban ◽

C. Prouteau ◽

M. F. Chisholm ◽

P. D. Nellist ◽

...

Keyword(s):

Grain Boundary ◽

Grain Boundaries ◽

Atomic Scale ◽

Contrast Imaging ◽

Qualitative Understanding ◽

Quantitative Understanding ◽

Bond Valence Sum ◽

Z Contrast ◽

Coherence Lengths ◽

Contrast Image

Due to the extemely short coherence lengths of the high-Tc superconductors (around 30 Å in the a-b plane), defects such as grain boundaries are obvious barriers to the flow of supercurrent. Within a few months of the discovery of these materials, it was shown how the critical current dropped four orders of magnitude as the grain boundary misorientaion increased from zero to 45°. Even today, there is no quantitative understanding of this behavior. A qualitative understanding is however possible through atomic resolution Z-contrast imaging on YBa2cu3O7-δ and SrTiO3 bicrystal grain boundaries, combined with bond-valence-sum analysis.The Z-contrast image of a YBa2cu3O7-δ low angle grain boundary in Fig. 1 shows the same kind of reconstructed dislocation cores as seen in SrTiO3, containing reconstructions on both the Cu and Y/Ba sublattices.

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Atomic Scale Characterization of Oxygen Vacancy Segregation at SrTiO3 Grain Boundaries

MRS Proceedings ◽

10.1557/proc-654-aa1.7.1 ◽

2000 ◽

Vol 654 ◽

Cited By ~ 1

Author(s):

R.F. Klie ◽

N. D. Browning

Keyword(s):

Grain Boundary ◽

Grain Boundaries ◽

Oxygen Vacancies ◽

Elevated Temperatures ◽

Theoretical Models ◽

Atomic Scale ◽

Close Proximity ◽

Scale Characterization

AbstractWe have examined the structure, composition and bonding at an un-doped 58° [001] tilt grain-boundary in SrTiO3 in order to investigate the control that the grain boundary exerts over the bulk properties. Room temperature and in-situ heating experiments show that there is a segregation of oxygen vacancies to the grain boundary that is increased at elevated temperatures and is independent of the cation arrangement. These measurements indicate that the widely observed electronic properties of grain boundaries may be due to an excess of mobile oxygen vacancies that cause a highly doped n-type region in the close proximity ( ≍ 1 unit cell) to the boundary. These results are shown to be consistent with both theoretical models and lower resolution chemical analysis.

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