Investigating Atomic Scale Structure-property Relationships at Grain Boundaries

1998 ◽  
Vol 4 (S2) ◽  
pp. 790-791
Author(s):  
N. D. Browning ◽  
H. O. Moltaji ◽  
E. M. James ◽  
S. Stemmer ◽  
J. P. Buban ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Grain Boundaries ◽  
Atomic Scale ◽  
Structure Property ◽  
Contrast Imaging ◽  
Structure Property Relationships ◽  
Unique Interpretation ◽  
Conventional Structure ◽  
Compositional Changes ◽  
Z Contrast

Although grain boundaries are known to dominate the bulk properties of many technologically important materials, in most cases there is no fundamental atomic scale understanding of why they should have such an effect. One of the problems in developing this understanding is that conventional structure determination techniques, such as phase contrast imaging in TEM or Z-contrast imaging in STEM, produce only a 2-dimensional projection of the crystal structure. Atomic scale compositional changes must be simulated and a unique interpretation is clouded by boundary reconstructions and strain effects. Furthermore, neither technique provides any information on the local changes in the electronic structure that are critical for both the electrical and mechanical properties of the boundary.EELS provides a means to quantify local changes in both composition and electronic structure. However, without a knowledge of the structure, interpretation of any observed changes at grain boundaries is extremely difficult.

Atomic Scale Analysis of a YSZ Bicrystal Grain Boundary

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.

Determining Atomic Structure-Property Relationships at Grain Boundaries in High-Tc Superconductors

1997 ◽  
Vol 3 (S2) ◽  
pp. 657-658
Author(s):  
N. D. Browning ◽  
J. P. Buban ◽  
C. Prouteau ◽  
G. Duscher ◽  
M. F. Chisholm ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Misorientation Angle ◽  
Atomic Scale ◽  
Structure Property ◽  
High Tc ◽  
Structure Property Relationships ◽  
Device Applications ◽  
Bond Valence Sum ◽  
Z Contrast ◽  
Insight Into

The short coherence length in high-Tc superconductors (5-15Å) makes an atomic scale understanding of the electronic properties at defects and interfaces essential for device applications. This understanding is particularly relevant for grain boundaries in YBa2CU3O7-δ (YBCO), where although extensive studies have shown a clear exponential decrease in critical current with misorientation angle, the absolute value can vary by several orders of magnitude at any given misorientation angle.Figure 1 shows Z-contrast images of an [001] low-angle tilt boundary and a 30° [001] asymmetric tilt grain boundary. An interesting feature of both of these boundaries is that there appear to be sites where two atom columns are too close together. However, the problem of like-ion repulsion can be avoided if the columns are taken to be partially occupied. Insight into the effect of this partial occupancy can be obtained through the use of bond-valence sum analysis. Here, the formal valence of an atom is made up of contributions from all of its nearest neighbors, the magnitude of which are determined by the bond length.

Investigating Ca Segregated to a Grain Boundaries in MgO Using Multiple Scattering Analysis of Electron Energy Loss Spectra

1998 ◽  
Vol 4 (S2) ◽  
pp. 776-777
Author(s):  
J. P. Buban ◽  
J. Zaborac ◽  
H. Moltaji ◽  
G. Duscher ◽  
N. D. Browning
Keyword(s):  
Energy Loss ◽  
Grain Boundaries ◽  
Electron Energy ◽  
Structural Model ◽  
Boundary Structure ◽  
Structure Property ◽  
Contrast Imaging ◽  
Scale Properties ◽  
Z Contrast ◽  
Electron Energy Loss

Although grain boundaries typically account for only a small fraction of a material, they can have far reaching effects on the overall bulk scale properties. These effects are usually simply linked to the boundary having a different atomic arrangement to the bulk. A necessary first step in understanding the structure-property relationships is therefore a detailed determination of the boundary structure.One means of obtaining detailed information on the structure of grain boundaries is through correlated Z-contrast imaging and electron energy loss spectroscopy (EELS). The Z-contrast image generates a map of the grain boundary which can be used to position the probe in defined locations for spectroscopy. In the case of oxides, a structural model of the metal atom positions can be determined directly from the image. Furthermore, using a simple bond-valence sum minimization routine, the oxygen atoms can be placed so that the structure contains atoms that have valences consistent with their expected formal valence state.

scholarly journals The Atomic-Scale Origins of Grain Boundary Superconducting Properties

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.

scholarly journals Atomic Scale Structure and Chemistry of Interfaces by Z-Contrast Imaging and Electron Energy Loss Spectroscopy in the Stem

1993 ◽  
Vol 319 ◽  
Author(s):  
M.M. Mcgibbon ◽  
N.D. Browning ◽  
M.F. Chisholm ◽  
S.J. Pennycook ◽  
V. Ravikumar ◽  
...  
Keyword(s):  
Energy Loss ◽  
Electron Energy ◽  
Electron Energy Loss Spectroscopy ◽  
Structural Information ◽  
Atomic Scale ◽  
Boundary Structure ◽  
Structure Property ◽  
Contrast Imaging ◽  
Z Contrast ◽  
Electron Energy Loss

AbstractThe macroscopic properties of many materials are controlled by the structure and chemistry at grain boundaries. A basic understanding of the structure-property relationship requires a technique which probes both composition and chemical bonding on an atomic scale. The high-resolution Z-contrast imaging technique in the scanning transmission electron microscope (STEM) forms an incoherent image in which changes in atomic structure and composition can be interpreted intuitively. This direct image allows the electron probe to be positioned over individual atomic columns for parallel detection electron energy loss spectroscopy (EELS) at a spatial resolution approaching 0.22nm. In this paper we have combined the structural information available in the Z-contrast images with the bonding information obtained from the fine structure within the EELS edges to determine the grain boundary structure in a SrTiO3 bicrystal.

Atomic resolution determination of the structure and chemistry of ceramic grain boundaries

1995 ◽  
Vol 53 ◽  
pp. 320-321
Author(s):  
N. D. Browning ◽  
M. M. McGibbon ◽  
M. F. Chisholm ◽  
S. J. Pennycook
Keyword(s):  
Grain Boundaries ◽  
Scanning Transmission Electron Microscope ◽  
Atomic Scale ◽  
Secondary Phases ◽  
Contrast Imaging ◽  
Scanning Transmission ◽  
Recent Developments ◽  
Contrast Technique ◽  
Z Contrast

Characterization of grain boundaries in ceramics is complicated by the multicomponent nature of the materials, the presence of secondary phases, and the tendency for the grain boundary plane to “wander” on the length scale of a few nanometers. However, recent developments in the scanning transmission electron microscope (STEM) have now made it possible to correlate directly the structure, composition and bonding at grain boundaries on the atomic scale. This direct experimental characterization of grain boundaries is achieved through the combination of Z-contrast imaging (structure) and electron energy loss spectroscopy (EELS) (composition and bonding). For crystalline materials in zone-axis orientations, where the atomic spacing is larger than the probe size, the Z-contrast technique provides a direct image of the metal (high Z) columns. This image, being formed from only the high-angle scattering, can be used to position the electron probe with atomic precision for simultaneous EELS. Under certain collection conditions, the spectrum can have the same atomic spatial resolution as the image, thus permitting the spectra to be correlated with a known atomic location.

scholarly journals Investigation of the Local Superconducting Properties at Grain Boundaries in High-Tc Superconductors

1998 ◽  
Vol 4 (S2) ◽  
pp. 690-691
Author(s):  
C. Prouteau ◽  
G. Duscher ◽  
N. D. Browning ◽  
S. J. Pennycook ◽  
D. Verebelyi ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Atomic Scale ◽  
Structure Property ◽  
High Tc Superconductors ◽  
High Tc ◽  
Ohmic Behavior ◽  
Structure Property Relationships ◽  
Linear Differential ◽  
Edge Features ◽  
Current Dissipation

Developing an atomic scale study of the structure-property relationships of grain boundaries in high-Tc superconductors is essential to understand their current dissipation mechanism and for incorporating these materials into viable devices. Thin YBa2Cu3O7-δ films have been deposited by pulsed laser deposition (PLD) on SrTiO3 symmetric bicrystals. Transport measurements in a magnetic field have been conducted across the grain boundaries through a wide bridge. The data obtained are consistent with microstructural observation in a VG Microscopes HB603 U and a VG HB501 UX dedicated STEM. Of particular interest in the study of high-Tc materials is the use of EELS, which can highlight the presence of non-superconducting regions through interpretation of the onset positions and finestructure (ELNES) of characteristic core-edge features.The V(I) curves recorded across a 24° boundary for several magnetic fields (fig. 1 - left) show an onset critical current density followed by a linear differential ohmic behavior which gives a negative intercept.

Z-Contrast Imaging of Grain-Boundary Core Structures in Semiconductors

MRS Bulletin ◽  
1997 ◽  
Vol 22 (8) ◽  
pp. 53-57 ◽  
Author(s):  
M.F. Chisholm ◽  
S.J. Pennycook
Keyword(s):  
High Resolution ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Phase Contrast ◽  
Atomic Scale ◽  
Resolving Power ◽  
Boundary Structure ◽  
Contrast Imaging ◽  
Contrast Technique ◽  
Z Contrast

Interest in semiconductor grain boundaries relates to the development of polycrystalline materials for photovoltaics and integrated-circuit interconnects. Although these structures are responsible for deleterious electrical effects, there are few experimental techniques available to study them at the required atomic scale. Therefore models of the physical processes occurring at grain boundaries have necessarily taken a macroscopic approach. Fortunately recent developments have resulted in tools that provide unprecedented glimpses into these interfaces and that will allow us to address anew the connection between grain-boundary structure and properties.Z-Contrast ImagingWhen exploring the unknown, we rely heavily on our eyes (incoherent imaging) to provide a direct image of a new object. In order to explore the unforeseen atomic configurations present at extended defects in materials, it again would be desirable if one could obtain a directly interpretable image of the unfamiliar structures present in the defect cores. Z-contrast electron microscopy provides such a view with both atomic resolution and compositional sensitivity.This high-resolution imaging technique differs from conventional high-resolution phase-contrast imaging. The phase-contrast technique produces a coherent image, an interference pattern formed by recombining the waves diffracted by the specimen. In the Z-contrast technique, the image is incoherent; it is essentially a map of the scattering power of the specimen. Additionally as was first determined by Lord Rayleigh, the incoherent mode of image formation has double the resolving power of the coherent mode.

Atomic-resolution eels for composition and 3-D coordination determination at interfaces and defects

1996 ◽  
Vol 54 ◽  
pp. 530-531
Author(s):  
N. D. Browning ◽  
D. J. Wallis ◽  
S. Sivananthan ◽  
P. D. Nellist ◽  
S. J. Pennycook
Keyword(s):  
Scanning Transmission Electron Microscope ◽  
Atomic Scale ◽  
Atomic Resolution ◽  
Structure Property ◽  
Contrast Imaging ◽  
Angle Scattering ◽  
Structural Differences ◽  
Scanning Transmission ◽  
Composition Structure ◽  
Z Contrast

Materials properties associated with interfaces and defects are dominated by atomic scale fluctuations in composition, structure and bonding. Although electron energy loss spectroscopy (EELS) provides a powerful tool to probe these features, low signal, lens aberrations, image coherence and specimen drift preclude the use of spectrum imaging and energy filtered imaging for these high-resolution problems. However, by utilizing Z-contrast imaging in conjunction with EELS in the scanning transmission electron microscope (STEM), these limitations are largely overcome and EELS appears capable of providing fudamental 3-D characterization of defect and interface structures with atomic resolution and sensitivity.The main premise in utilizing these combined techniques is that the properties of defects and interfaces must be associated with structural differences relative to the bulk. If those structural differences can be located, then it is only necessary to perform spectroscopy in their vicinity to understand the structure property relationship. For crystalline materials in zone-axis orientations, the Z-contrast image provides this atomic resolution structural map. As this direct image is generated with only the high-angle scattering, it can be used to position the electron probe with atomic precision and does not interfere with the low-angle scattering for spectroscopy.

Determining Atomic Structure-Property Relationships at Grain Boundaries

1996 ◽  
Vol 54 ◽  
pp. 334-335
Author(s):  
N. D. Browning ◽  
D. J. Wallis ◽  
P. D. Nellist ◽  
S. J. Pennycook
Keyword(s):  
Energy Loss ◽  
Grain Boundaries ◽  
Multiple Scattering ◽  
Scale Effects ◽  
Dominant Role ◽  
Boundary Plane ◽  
Atomic Scale ◽  
Atomic Resolution ◽  
Contrast Imaging ◽  
Z Contrast

Atomic scale effects at grain boundaries are known to play a dominant role in controlling the bulk properties of many materials. However, a detailed understanding of this role is complicated by the tendency for boundaries to behave in a “non-ideal” manner, i.e. the boundary plane can change on the scale of a few nanometers, altering the number of vacancies and impurities and the presence of second phases. The crucial first step to engineering boundary properties is therefore the ability to observe these changes experimentally with both atomic resolution and sensitivity. Such a capability is provided by the combination of Z-contrast imaging and electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM).The Z-contrast technique generates an incoherent, atomic resolution structural image of a grain boundary which can be used to position the electron probe with atomic precision for spectroscopy. As the spectrum has nearly the same resolution as the image for core-losses >100eV, this arrangement has the unique advantage of allowing compositional fluctuations to be correlated directly with structural features in the boundary plane. Furthermore, multiple-scattering (MS) analysis can be utilized to extract 3- dimensional structural information from the spectrum. MS techniques consider the fine-structure of the spectrum to arise from interference effects occurring when a photoelectron created during the energy loss process is reflected from neighboring atoms. The real-space clusters used in this methodology allow the flexibility to determine whether the contributions to the spectrum arise from single or multiple scattering paths and from which atomic neighbors they originate. This allows the different structural relaxations that occur at boundaries, i.e. vacancies or structural disorder, to be distinguished from the spectrum.

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