scholarly journals 3D microstructure and critical current properties of ultra-fine-grain Ba(Fe,Co)2As2 bulk superconductors

2021 ◽  
Author(s):  
Yusuke Shimada ◽  
Shinnosuke Tokuta ◽  
Akinori Yamanaka ◽  
Akiyasu Yamamoto ◽  
Toyohiko. J Konno
Keyword(s):  
Grain Boundaries ◽  
Critical Current ◽  
Weak Link ◽  
Three Dimensional ◽  
High Energy ◽  
Dimensional Structure ◽  
Polycrystalline Materials ◽  
Fine Grain ◽  
Pore Length ◽  
Two Parameters

Abstract In iron-based superconductors, randomly oriented grain boundaries have a strong influence on the transport properties via intrinsic weak-link and flux pinning mechanisms. Herein we report the critical current density (Jc) and the three-dimensional microstructure of polycrystalline bulk Co-doped Ba122 superconductors, with highly dense grain boundaries (grain size smaller than 50 nm), produced by high-energy milling. Three-dimensional electron microscopy revealed that the anomalous growth of secondary particles (aggregation) and the inter-aggregation structures were significantly different in the samples with finer grains, which may have extrinsically limited Jc. These important microstructural features were quantified as two parameters—local thickness and total pore length—by reconstructing the three-dimensional structure of the superconducting phase using the adaptive thresholding method. The results obtained in this study suggest that understanding and controlling the microstructural formation process by sintering are instrumental for improving the Jc properties of 122 polycrystalline materials consisting of ultrafine grains.

scholarly journals Crystal structure and thermal behaviour of pyridinium styphnate

2015 ◽  
Vol 71 (2) ◽  
pp. 117-120 ◽  
Author(s):  
Selvarasu Muthulakshmi ◽  
Doraisamyraja Kalaivani
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonds ◽  
Nitro Group ◽  
Benzene Ring ◽  
Three Dimensional ◽  
High Energy ◽  
High Energy Density ◽  
Dimensional Structure ◽  
Molecular Salt ◽  
Ring Motif

In the crystal structure of the title molecular salt, C5H6N+·C6H2N3O8−(systematic name: pyridinium 3-hydroxy-2,4,6-trinitrophenolate), the pyridinium cation and the 3-hydroxy-2,4,6-trinitrophenolate anion are linked through bifurcated N—H...(O,O) hydrogen bonds, forming anR12(6) ring motif. The nitro groupparawith respect to phenolate ion forms an intramolecular hydrogen bond with the adjacent phenolic –OH group, which results in anS(6) ring motif. The nitro group flanked by the phenolate ion and the phenolic –OH group deviates noticeably from the benzene ring, subtending a dihedral angle of 89.2 (4)°. The other two nitro groups deviate only slightly from the plane of the benzene ring, making dihedral angles of 2.8 (4) and 3.4 (3)°. In the crystal, the 3-hydroxy-2,4,6-trinitrophenolate anions are linked through O—H...O hydrogen bonds, forming chains along [100]. These anionic chains, to which the cations are attached, are linkedviaC—H...O hydrogen bonds, forming a three-dimensional structure. Impact friction sensitivity tests and TGA/DTA studies on the title molecular salt imply that it is an insensitive high-energy-density material.

Structure and Properties of Polycrystalline Materials From Simulation: An Interfacial Perspective

1999 ◽  
Vol 586 ◽  
Author(s):  
S. R. Phillpot ◽  
P. Keblinski ◽  
D. Wolf ◽  
F. Cleri
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Diffusion ◽  
Simulation Method ◽  
High Energy ◽  
Grain Boundary Diffusion ◽  
Dynamics Simulation ◽  
Polycrystalline Materials ◽  
Diffusion Creep ◽  
Fcc Metals

ABSTRACTWe have recently developed a novel molecular-dynamics simulation method to grow polycrystals from a melt containing randomly oriented crystalline seeds. The resulting microstructures contain only randomly oriented (i.e., high-energy) grain boundaries. We find that these grain boundaries, which are highly constrained by their close proximity to grain junctions, are highly disordered in fcc metals and amorphous in silicon. From simulations of infinitely extended high-energy grain boundaries in bicrystals, we find that such highly disordered and amorphous grain boundaries are actually the thermodynamic ground state; by contrast, low-energy grain boundaries are crystalline. High-energy grain boundaries in diamond, however, are structurally ordered at the expense of a significant amount of graphite-like bonding. We show that these complex grain boundary structures have important effects on properties including grain boundary diffusion (fcc metals and silicon), grain boundary diffusion creep (silicon) and grain boundary electrical activity and strength (diamond). The implications for engineering materials with prescribed properties are discussed.

Microtexture Mapping of Elecrtron Backscattered Diffraction in (Bi,Pb)2Sr2Ca2Cu3O10 Superconductor Tapes

2000 ◽  
Vol 659 ◽  
Author(s):  
Sean Li ◽  
Thiam Teck Tan
Keyword(s):  
Critical Current Density ◽  
Grain Boundaries ◽  
Critical Current ◽  
Current Density ◽  
Crystallographic Orientation ◽  
Weak Link ◽  
Large Angle ◽  
Orientation Distribution ◽  
Weak Links ◽  
Electron Backscattered Diffraction

ABSTRACTGrain boundaries is believed to act as weak-links limiting the critical current density (Jc) of bulk high-Tcsuperconductors. The weak-link problem can be greatly reduced by elimination or minimization of the large-angle grain boundaries. It has been reported that the Jc distribution in the transverse cross-section of (Bi,Pb)2Sr2Ca2Cu3O10+x (Bi2223) superconductor tapes follows a parabolic relationship, with the lowest currents occurring at the center of the tapes. The Jc distribution is proposed to be strongly dependent on the local crystallographic orientation distribution of the Bi2223 oxides. However, the local three dimensional crystallographic orientation distribution of Bi2223 crystals in (Bi,Pb)2Sr2Ca2Cu3O10+×superconductor tapes has not been experimentally determined yet. In this work, Electron Backscattered Diffraction technique was employed to map the crystallographic orientation of the crystals in Bi2223 superconductor tapes. From this, the misorientation of grain boundaries and also their distribution are obtained. Through crystallographic orientation mapping, the relationship of the crystallographic orientation distribution, the boundary misorientation distribution and the fabrication parameters may be understood. This can be used to optimize the fabrication processes thus increasing the critical current density in Bi2223 superconductor tapes.

Three-Dimensional X-Ray Diffraction Microscopy Using High-Energy X-Rays

MRS Bulletin ◽  
2004 ◽  
Vol 29 (3) ◽  
pp. 166-169 ◽  
Author(s):  
Henning F. Poulsen ◽  
Dorte Juul Jensen ◽  
Gavin B.M. Vaughan
Keyword(s):  
Materials Science ◽  
Three Dimensional ◽  
High Energy ◽  
Polycrystalline Materials ◽  
X Rays ◽  
X Ray Diffraction ◽  
X Ray ◽  
Reconstruction Methods ◽  
The Individual ◽  
Individual Grains

AbstractThree-dimensional x-ray diffraction (3DXRD) microscopy is a tool for fast and nondestructive characterization of the individual grains, subgrains, and domains inside bulk materials. The method is based on diffraction with very penetrating hard x-rays (E ≥ 50 keV), enabling 3D studies of millimeter-to-centimeter-thick specimens.The position, volume, orientation, and elastic and plastic strain can be derived for hundreds of grains simultaneously. Furthermore, by applying novel reconstruction methods, 3D maps of the grain boundaries can be generated. The 3DXRD microscope in use at the European Synchrotron Radiation Facility in Grenoble, France, has a spatial resolution of ∼5 μm and can detect grains as small as 150 nm. The technique enables, for the first time, dynamic studies of the individual grains within polycrystalline materials. In this article, some fundamental materials science applications of 3DXRD are reviewed: studies of nucleation and growth kinetics during recrystallization, recovery, and phase transformations, as well as studies of polycrystal deformation.

scholarly journals Efficient Fitting of 3D Tessellations to Curved Polycrystalline Grain Boundaries

2021 ◽  
Vol 8 ◽  
Author(s):  
Lukas Petrich ◽  
Orkun Furat ◽  
Mingyan Wang ◽  
Carl E. Krill III ◽  
Volker Schmidt
Keyword(s):  
Grain Boundaries ◽  
Three Dimensional ◽  
Simulated Data ◽  
Image Data ◽  
Optimization Methods ◽  
Polycrystalline Materials ◽  
X Ray Diffraction ◽  
Gradient Based ◽  
Microstructure Morphology ◽  
Definition Of

The curvature of grain boundaries in polycrystalline materials is an important characteristic, since it plays a key role in phenomena like grain growth. However, most traditional tessellation models that are used for modeling the microstructure morphology of these materials, e.g., Voronoi or Laguerre tessellations, have flat faces and thus fail to incorporate the curvature of the latter. For this reason, we consider generalizations of Laguerre tessellations—variations of so-called generalized balanced power diagrams (GBPDs)—that exhibit non-convex cells. With as many as ten parameters for each cell, it is computationally demanding to fit GBPDs to three-dimensional image data containing hundreds of grains. We therefore propose a modification of the traditional definition of GBDPs that allows gradient-based optimization methods to be employed. The resulting reduction in runtime makes it feasible to find approximations to real experimental datasets. We demonstrate this on a three-dimensional x-ray diffraction (3DXRD) mapping of an AlCu alloy, but we also evaluate the modeling errors for simulated data. Furthermore, we investigate the effect of noisy image data and whether the smoothing of image data prior to the fitting step is advantageous.

Grain boundaries in high-Tc superconductors

1988 ◽  
Vol 46 ◽  
pp. 1008-1009
Author(s):  
M.F. Chisholm
Keyword(s):  
Critical Current Density ◽  
Grain Boundaries ◽  
Critical Current ◽  
Current Density ◽  
Weak Link ◽  
Critical Currents ◽  
Pinning Force ◽  
Conduction Path ◽  
Direct Measurements

One crucial property for most superconductor applications is the materials critical current density. Measurements on single crystals of YBa2Cu3O7, show critical currents to be in excess of 105 A/cm2 at 77K. However, polycrystalline samples show values of 103 A/cm2 or less at 77K. The critical current, unlike other superconductivity properties, is not a property of a specific composition but of a specific sample. Defects, introduced during the material processing, exert a pinning force which makes it possible for Type-II superconductors to carry current without losses. At the same time these defects represent an interruption in the structural and chemical order which has been shown to be necessary for superconductivity in the YBa2Cu3Ox phase, and so they may also act as a weak link in the conduction path. The most direct measurements of the role of individual grain boundaries on the critical current density are those of Chaudhari et al. who examined patterned YBa2Cu3O7 films grown on SrTiO3 substrates.

The brittle fracture of polycrystalline zinc

2007 ◽  
Vol 463 (2085) ◽  
pp. 2129-2151 ◽  
Author(s):  
G.M Hughes ◽  
G.E Smith ◽  
P.E.J Flewitt ◽  
A.G Crocker
Keyword(s):  
Brittle Fracture ◽  
Grain Boundaries ◽  
Fracture Process ◽  
Focused Ion Beam ◽  
Ion Beam ◽  
Three Dimensional ◽  
Geometrical Model ◽  
Polycrystalline Materials ◽  
Fracture Mechanisms ◽  
Polycrystalline Zinc

In polycrystalline materials, grain boundaries provide an important contribution to the resistance to the propagation of both brittle and ductile cracks. Initially, in this paper, a three-dimensional geometrical model of the brittle fracture of polycrystalline zinc is developed, assuming a single (0001) cleavage plane in each grain. The model predicts that about one-half of the fracture process of the material will be associated with accommodation effects at grain boundaries. In contrast, experimental work over a range of temperatures shows that at low temperatures very little grain boundary failure occurs. There are two reasons for this discrepancy. Firstly, cleavage occurs on (0001) and also on the three variants of the {10-10} planes and secondly, deformation twinning plays a major role in the fracture process. The characteristics of these phenomena have been investigated in detail using focused ion beam microscopy, including subsurface examinations and metallographic techniques. The models were then extended to incorporate these additional mechanisms. Comparisons between the predictions and the experimental observations are discussed and enable information to be deduced about the relative energies of the different fracture mechanisms.

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