Modeling the Role of the Buildup of Magnetic Charges in Low Anisotropy Polycrystalline Materials

2018 ◽  
Vol 54 (11) ◽  
pp. 1-5
Author(s):  
Hatem Elbidweihy ◽  
Anthony S. Arrott ◽  
Virgil Provenzano
Keyword(s):  
Polycrystalline Materials

The Role of Sub-Boundaries in the Brittle Fracture of Polycrystalline Materials

2008 ◽  
pp. 821-822 ◽  
Author(s):  
Gareth Hughes ◽  
Peter Flewitt ◽  
Fabio Sorbello ◽  
Gillian Smith ◽  
Alan Crocker
Keyword(s):  
Brittle Fracture ◽  
Polycrystalline Materials

Twin boundaries in GaAs grown on Ge

1987 ◽  
Vol 45 ◽  
pp. 338-339
Author(s):  
N.-H. Cho
Keyword(s):  
Grain Boundaries ◽  
Growth Surface ◽  
Polycrystalline Materials ◽  
High Electron ◽  
Face Centered Cubic ◽  
Twin Boundaries ◽  
Direct Band ◽  
Dynamical Coupling ◽  
Face Centered

Interest in the structure of grain boundaries in semiconductors has been increasing for many reasons including the important role of boundaries on the electrical behavior of polycrystalline materials. GaAs is of interest because of its particular electrical properties such as its direct band gap and high electron mobility. Specific bicrystals of GaAs were produced on substrates cut from Czochralski-grown germanium bicrystals in a low-pressure organometallic vapor- phase epitaxy system. When the growth surface was parallel to the (110) plane, many microtwins were produced in the GaAs epilayer. The structure of twin boundaries in GaAs can take two forms depending on the relative polarities of the two adjoining grains because GaAs has a sphalerite structure which is a face-centered cubic lattice with a two atom basis. The polarity of the two grains meeting at the grain boundaries can be determined by using the dynamical coupling effects of high-order Laue-zone reflections on the (200) and (200) diffracted beams.

scholarly journals A three-dimensional study of coupled grain boundary motion with junctions

2015 ◽  
Vol 471 (2178) ◽  
pp. 20150127 ◽  
Author(s):  
Anup Basak ◽  
Anurag Gupta
Keyword(s):  
Grain Boundary ◽  
Three Dimensional ◽  
Continuum Theory ◽  
Coupling Factor ◽  
Polycrystalline Materials ◽  
Triple Junctions ◽  
Kinetic Coefficients ◽  
And Migration ◽  
Grain Boundary Motion

A novel continuum theory of incoherent interfaces with triple junctions is applied to study coupled grain boundary (GB) motion in three-dimensional polycrystalline materials. The kinetic relations for grain dynamics, relative sliding and migration of the boundary and junction evolution are developed. In doing so, a vectorial form of the geometrical coupling factor, which relates the tangential motion at the GB to the migration, is also obtained. Diffusion along the GBs and the junctions is allowed so as to prevent nucleation of voids and overlapping of material near the GBs. The coupled dynamics has been studied in detail for two bicrystalline and one tricrystalline arrangements. The first bicrystal consists of two cubic grains separated by a planar GB, whereas the second is composed of a spherical grain embedded inside a larger grain. The tricrystal has an arbitrary-shaped grain embedded inside a much larger bicrystal made of two cubic grains. In all these cases, analytical solutions are obtained wherever possible while emphasizing the role of various kinetic coefficients during the coupled motion.

The Effective Modulus of Random Checkerboard Plates

2015 ◽  
Vol 83 (1) ◽  
Author(s):  
Leon S. Dimas ◽  
Daniele Veneziano ◽  
Markus J. Buehler
Keyword(s):  
Model System ◽  
Specimen Size ◽  
Effective Modulus ◽  
Granitic Rocks ◽  
Polycrystalline Materials ◽  
Effective Moduli ◽  
Bulk Properties ◽  
Analytical Approximations ◽  
Different Characteristics

We investigate the elastic effective modulus Eeff of two-dimensional checkerboard specimens in which square tiles are randomly assigned to one of two component phases. This is a model system for a wide class of multiphase polycrystalline materials such as granitic rocks and many ceramics. We study how the effective stiffness is affected by different characteristics of the specimen (size relative to the tiles, stiff fraction, and modulus contrast between the phases) and obtain analytical approximations to the probability distribution of Eeff as a function of these parameters. In particular, we examine the role of percolation of the soft and stiff phases, a phenomenon that is important in polycrystalline materials and composites with inclusions. In small specimens, we find that the onset of percolation causes significant discontinuities in the effective modulus, whereas in large specimens, the influence of percolation is smaller and gradual. The analysis is an extension of the elastic homogenization methodology of Dimas et al. (2015, “Random Bulk Properties of Heterogeneous Rectangular Blocks With Lognormal Young's Modulus: Effective Moduli,” ASME J. Appl. Mech., 82(1), p. 011003), which was devised for blocks with lognormal spatial variation of the modulus. Results are validated through Monte Carlo simulation. Compared with lognormal specimens with comparable first two moments, checkerboard plates have more variable effective modulus and are on average less compliant if there is prevalence of stiff tiles and more compliant if there is prevalence of soft tiles. These differences are linked to percolation.

Nanoscale Imaging of CaCu3Ti4O12 Dielectric Properties: The Role of Surface Defects

2007 ◽  
Vol 131-133 ◽  
pp. 443-448 ◽  
Author(s):  
Vito Raineri ◽  
Patrick Fiorenza ◽  
Raffaella Lo Nigro ◽  
Derek C. Sinclair
Keyword(s):  
Dielectric Properties ◽  
Scanning Probe Microscopy ◽  
Surface Defects ◽  
Polycrystalline Materials ◽  
Surface Imperfections ◽  
Polycrystalline Ceramics ◽  
Local Sample ◽  
Nanoscale Imaging ◽  
Sample Structure

Scanning probe microscopy with conductive tips has been used to image the dielectric properties of ceramics with giant permittivity. In particular, measurements in impedance mode and of local resistivity allowed to image the permittivity map on polycrystalline materials. Such imaging allows to correlate the dielectric properties with the local sample structure and with defects inside the single grains of the polycrystalline ceramics. However, artifacts due to surface imperfections should be distinguished from bulk properties and eliminated.

scholarly journals Deformation compatibility in a single crystalline Ni superalloy

2016 ◽  
Vol 472 (2185) ◽  
pp. 20150690 ◽  
Author(s):  
Jun Jiang ◽  
Tiantian Zhang ◽  
Fionn P. E. Dunne ◽  
T. Ben Britton
Keyword(s):  
Electron Backscatter Diffraction ◽  
Deformation Gradient ◽  
Advanced Characterization ◽  
Image Correlation ◽  
Polycrystalline Materials ◽  
High Angular Resolution ◽  
Resolution Electron ◽  
Backscatter Diffraction ◽  
Deformation Gradients

Deformation in materials is often complex and requires rigorous understanding to predict engineering component lifetime. Experimental understanding of deformation requires utilization of advanced characterization techniques, such as high spatial resolution digital image correlation (HR-DIC) and high angular resolution electron backscatter diffraction (HR-EBSD), combined with clear interpretation of their results to understand how a material has deformed. In this study, we use HR-DIC and HR-EBSD to explore the mechanical behaviour of a single-crystal nickel alloy and to highlight opportunities to understand the complete deformations state in materials. Coupling of HR-DIC and HR-EBSD enables us to precisely focus on the extent which we can access the deformation gradient, F , in its entirety and uncouple contributions from elastic deformation gradients, slip and rigid body rotations. Our results show a clear demonstration of the capabilities of these techniques, found within our experimental toolbox, to underpin fundamental mechanistic studies of deformation in polycrystalline materials and the role of microstructure.

scholarly journals Polymolybdates and Peroxomolybdates: Candidates for Catalysts in Industry

2014 ◽  
Vol 70 (a1) ◽  
pp. C589-C589
Author(s):  
Wieslaw Lasocha ◽  
Anna Szymanska ◽  
Marcin Oszajca ◽  
Graham Appleby ◽  
Katarzyna Pamin ◽  
...  
Keyword(s):  
Polycrystalline Materials ◽  
Full Understanding ◽  
Variable Size ◽  
Cyclic Hydrocarbons ◽  
Oxidation Of Hydrocarbons ◽  
The Family ◽  
The Individual ◽  
Insight Into ◽  
Selection Of

Progress in catalysis depends on a full understanding of the role of the individual components of catalytic materials. Crystallographic studies offer insight into crystal structure, which enables the rational selection of reagents and better planning of the syntheses of novel materials and catalysts. In this paper we have studied the process of the oxidation of hydrocarbons and terpenes with oxygen from the air. Processes of this type are important in so-called "Green Chemistry." Their application can reduce the amount of environmentally harmful pollutants formed through conventional oxidation based on nitric acid. While investigating the catalytic activity of peroxo- and polymolybdates(VI) in the oxidation of cycloalkanes, we found a number of intriguing relationships. To explain them, we designed, synthesized and solved the crystal structures of the family of new peroxomolybdates, tri-, octa- and pentamolybdates of amines. Both single crystal and polycrystalline materials were investigated using laboratory as well as synchrotron radiation. Next, we used these compounds as catalysts in certain interesting for industry processes (e.g. oxidation of cyclic hydrocarbons). We have concluded that: – The activity of peroxocompounds is enhanced by the coordination of N-oxide groups to Mo atoms. – The activity of anionic polymeric trimolybdates decreases when `surface of polymeric fiber' is blocked by cations. – The anionic layers of pentamolybdates are separated by cations of variable size. The distance between layers plays a role similar to that of the size of channels in zeolites. Summary: Peroxomolybdates and polyoxomolybdates show great prospects for new industrial uses (besides cracking and desulfurization).

The role of Electron Microscopy in the study of grain boundaries

1990 ◽  
Vol 48 (4) ◽  
pp. 330-331
Author(s):  
William A. T. Clark
Keyword(s):  
Grain Boundaries ◽  
Optical Microscopy ◽  
Interfacial Structure ◽  
Polycrystalline Materials ◽  
Defect Structures ◽  
General Acceptance ◽  
Transmission Electron ◽  
Ray Methods ◽  
Detailed Picture

Our understanding the nature of interfaces in polycrystalline materials has depended critically on observations obtained in the transmission electron microscope. This is especially true in the case of interfacial structure, where developments in models of atomic and defect structures in interfaces have closely paralleled advances in techniques available for their study. The general acceptance that the crystallography and relative misorientation of the two crystals forming an interface dictate the interfacial structure, and many of its properties, results in large part from direct TEM studies of interfaces.Grain boundaries were originally considered structureless, amorphous, films, because optical microscopy could not provide information at the necessary resolution, and inferences about the nature of boundaries had to be made from measurements of mechanical properties. However, the development of X-ray methods in the 1920's quickly showed that the crystalline structure of the grains was preserved right up to an interface, and that the boundary could be thought of as a “transition lattice” from one crystal to the other, a concept remarkably similar to many of those still current today. Although there was some earlier optical microscopy of decorated low-angle boundaries in Si, it was not until 1956 that the development of the TEM provided the first detailed picture of dislocations and grain boundaries in opaque materials.

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