Evidence for cooling-rate-dependent icosahedral short-range order in a Cu–Zr–Al metallic glass

2014 ◽  
Vol 47 (6) ◽  
pp. 1906-1911 ◽  
Author(s):  
Helmut Hermann ◽  
Uta Kühn ◽  
Horst Wendrock ◽  
Valentin Kokotin ◽  
Björn Schwarz
Keyword(s):  
Metallic Glass ◽  
Cooling Rate ◽  
Short Range ◽  
X Ray Diffraction ◽  
X Ray ◽  
Rate Dependent ◽  
Icosahedral Clusters ◽  
Thermal Displacements ◽  
The Difference ◽  
Diffraction Patterns

Samples of Cu47.5Zr47.5Al5metallic glass were prepared at different cooling rate,R. The dependence of the X-ray diffraction patterns onRwas analysed by comparing them with corresponding patterns of computer-simulated models generated at different cooling rates as well. The observed changes in the experimental diffraction patterns are reproduced by the simulations, showing an increasing fraction of icosahedral clusters with decreasing cooling rate. The difference of the fractions of icosahedrally coordinated atoms in mould-cast and rapidly quenched Cu47.5Zr47.5Al5averages to 3 (1)%. Different frozen-in thermal displacements and different density are ruled out as a possible origin for the experimental observations.

Evaluation of Freezing Methods by Low Temperature X-Ray Diffraction

1977 ◽  
Vol 35 ◽  
pp. 330-333
Author(s):  
T. Gulik-Krzywicki ◽  
M.J. Costello
Keyword(s):  
Biological Materials ◽  
Molecular Organization ◽  
X Ray Diffraction ◽  
Glass Capillary ◽  
X Ray ◽  
Rate Dependent ◽  
Before And After ◽  
Freeze Etching ◽  
Diffraction Patterns ◽  
Set Up

Freeze-etching electron microscopy is currently one of the best methods for studying molecular organization of biological materials. Its application, however, is still limited by our imprecise knowledge about the perturbations of the original organization which may occur during quenching and fracturing of the samples and during the replication of fractured surfaces. Although it is well known that the preservation of the molecular organization of biological materials is critically dependent on the rate of freezing of the samples, little information is presently available concerning the nature and the extent of freezing-rate dependent perturbations of the original organizations. In order to obtain this information, we have developed a method based on the comparison of x-ray diffraction patterns of samples before and after freezing, prior to fracturing and replication.Our experimental set-up is shown in Fig. 1. The sample to be quenched is placed on its holder which is then mounted on a small metal holder (O) fixed on a glass capillary (p), whose position is controlled by a micromanipulator.

Short-Range Order in KPO3 Glass Studied by Neutron and X-Ray Diffraction

1996 ◽  
Vol 51 (3) ◽  
pp. 179-186 ◽  
Author(s):  
Uwe Hoppe ◽  
Günter Walter ◽  
Dörte Stachel ◽  
Alex C. Hannon
Keyword(s):  
Field Strength ◽  
Electric Field ◽  
Short Range ◽  
Short Range Order ◽  
Range Order ◽  
X Ray Diffraction ◽  
X Ray ◽  
Bond Lengths ◽  
Spherical Cavities ◽  
The Difference

The short-range order of KPO3 glass has been studied by diffraction methods in order to make evident the different behaviour of the P-O bonds within the PO4 tetrahedron. The oxygen sites are devided into bridging and terminal (non-bridging) oxygen sites, corresponding to two P-O bond lengths, the difference of which amounts to 14.5 pm. Previous conclusions about the changes of the P-O bond lengths under the influence of modifier cations of different electric field strength are corroborated. The K-O environments reveal two apparently different distances rKO with equal contributions to the total K-O coordination number of about 6.7. To explain this phenomenon, the K+ cations are suggested to be located in non-spherical cavities

The stability and screw sense of the α -helix in poly- β -benzyl-L-aspartate

1960 ◽  
Vol 259 (1296) ◽  
pp. 110-128 ◽  
Keyword(s):  
Optical Rotatory Dispersion ◽  
Molecular Models ◽  
X Ray Diffraction ◽  
X Ray ◽  
Left Handed ◽  
The Difference ◽  
Diffraction Patterns ◽  
The Stability ◽  
Α Helix ◽  
The Right

A number of polymers and copolymers containing β -benzyl-L-aspartate has been prepared and their optical rotatory dispersion in a variety of solvents has been measured. The results of these measurements together with studies of infra-red spectra, X-ray diffraction patterns, deuteration rates and molecular models lead to the following conclusions. (i) The α -helical form of poly- β -benzyl-L-aspartate is considerably less stable relative to the solvated randomly coiled form than that of poly- γ -benzyl-L-glutamate. (ii) The left-handed α -helix of poly- β -benzyl-L-aspartate is more stable than the right-handed one. (iii) The difference in stability between the two senses of α -helix is much less in the case of poly- β -benzyl-L-aspartate than in that of poly- γ -benzyl-L-glutamate or poly-L-alanine.

THE XRD STUDY OF THE EFFECT OF SLIGHT CHANGE IN STRUCTURE ON THE SUPERCONDUCTIVITY OF Y-Ba-Cu-O SYSTEM MATERIAL

1987 ◽  
Vol 01 (07n08) ◽  
pp. 289-293 ◽  
Author(s):  
WANG HUAQIN ◽  
ZHANG SHIYUAN ◽  
JIN TONGZHENG ◽  
HAN SHIYING ◽  
QIU DIRONG ◽  
...  
Keyword(s):  
Single Phase ◽  
Crystal Symmetry ◽  
Epr Spectra ◽  
Processing Conditions ◽  
X Ray Diffraction ◽  
X Ray ◽  
Xrd Study ◽  
The Difference ◽  
Diffraction Patterns ◽  
Flowing Oxygen

In this paper the differences in diffraction intensities from some crystal planes in the X-ray diffraction patterns of high Tc Y-Ba-Cu-O system superconductors prepared by different processing conditions and the difference among various structure cells in references are interpreted using computer fitting. The results suggest that there exists two structure cells in the single phase YBa2Cu3O7−x samples. Both structure cells have the same crystal symmetry and almost the same lattice parameters, a=3.821Å, b=3.892Å and c=11.676Å, but the different distortion degree of Cu2-O plane. According to EPR spectra measured on the same samples, it is considered that the improvement of superconductivity for the samples prepared by two-step annealing in flowing oxygen may be related to concentration of the structure cell with more serious distortion on the Cu2-O plane.

Structure and Dynamic Properties of Molten Lanthanum Tribromide

1999 ◽  
Vol 54 (2) ◽  
pp. 91-94
Author(s):  
Yoshihiro Okamoto ◽  
Toru Ogawa
Keyword(s):  
Molecular Dynamics ◽  
Shear Viscosity ◽  
Short Range ◽  
Md Simulation ◽  
Dynamic Properties ◽  
Structural Features ◽  
X Ray Diffraction ◽  
X Ray ◽  
The Difference ◽  
Short Range Structure

Abstract The structure of molten LaBr3 was investigated by X-ray diffraction and molecular dynamics simu-lations. It was found that the short range structure of molten LaBr3 is very similar to that of molten LaCl 3 , except for some structural features such as interionic distances based on the difference of anion sizes. In the MD simulation, the shear viscosity of molten LaBr3 was estimated from the structurally-optimized MD calculations.

scholarly journals Cooling Rate Dependent Morphology of the γ' Precipitates in Nickel-Base Superalloy Udimet 500

2011 ◽  
Vol 278 ◽  
pp. 108-113 ◽  
Author(s):  
Mohammad Khalili Savadkoohi ◽  
Ahad Samadi ◽  
Rasoul Salehi
Keyword(s):  
Cooling Rate ◽  
Volume Fraction ◽  
Nickel Base Superalloy ◽  
Air Cooling ◽  
X Ray Diffraction ◽  
X Ray ◽  
Rate Dependent ◽  
Compositional Changes ◽  
Nickel Base ◽  
Base Superalloy

The morphology of the γ΄ precipitates during continues cooling of a nickel-base superalloy, Udimet 500, was studied using scanning electron microscopy and X-ray diffraction technique. The samples were full solutioned at 1200oC and then were cooled to ambient temperature under different cooling rates, 15, 1, 0.2, 0.05oC/min and air cooling. The unconstrained γ-γ΄ misfit values for each sample were calculated using the electrolytic extracted γ΄ precipitates. According to the results, by decreasing the cooling rate, not only the size, volume fraction and interparticle spaces of the  precipitates were increased, but also depending on the γ-γ΄ lattice misfits the corresponding  morphology was changed from spherical to cubic, then flower-like and finally dendritic shape. The observations are discussed in view of the compositional changes of γ/γ΄ phases and elastic strain considerations of their interfaces which will be described in detail in the article.

New structure, reconstruction, and behaviour of the coordination polymer framework [CuZn(CN)4]– towards hydrated alkali metal ions

2015 ◽  
Vol 93 (8) ◽  
pp. 913-919 ◽  
Author(s):  
Junpei Yamada ◽  
Shin-ichi Nishikiori
Keyword(s):  
Coordination Polymer ◽  
Crystal Structure Analysis ◽  
Atmospheric Conditions ◽  
X Ray Diffraction ◽  
X Ray ◽  
Square Channel ◽  
Unknown Structure ◽  
The Difference ◽  
Diffraction Patterns ◽  
Polymer Framework

A new framework structure of the coordination polymer [CuZn(CN)4]– has been discovered in the newly synthesized [Na(H2O)n][CuZn(CN)4] (n = 12.7; 1). X-ray crystal structure analysis revealed a 3D framework comprised of tetrahedral Cu(I) and Zn(II) centres with bridging cyanide ligands containing both octagonal and square channel cavities; these channels contain hydrated Na+ ions as guests. In open air, complex 1 is extremely unstable and loses water molecules to form [Na(H2O)n][CuZn(CN)4] (n = 5.2–6.8; 2) within 30 min. Powder X-ray diffraction patterns showed that this change results in the conversion of the framework of complex 1 to the same framework observed in [K(H2O)n][CuZn(CN)4]. The [CuZn(CN)4]– framework of [K(H2O)n][CuZn(CN)4] has a tridymite structure with hexagonal channel cavities occupied by hydrated K+ ions. Like 1, 2 is also unstable under atmospheric conditions, yielding [Na(H2O)n][CuZn(CN)4] (n = 3), which has an unknown structure. While the framework of [K(H2O)n][CuZn(CN)4] is structurally flexible and robust, the framework of 2 is unstable and fragile. This contrast comes from the difference between the nature of the hydrated K+ and Na+ ions present in the frameworks.

EDP2XRD: a computer program for converting electron diffraction patterns into X-ray diffraction patterns

2016 ◽  
Vol 49 (2) ◽  
pp. 636-641 ◽  
Author(s):  
Hongwei Liu ◽  
Matthew Foley ◽  
Qingyun Lin ◽  
Jiangwen Liu
Keyword(s):  
Electron Diffraction ◽  
Region Of Interest ◽  
Volume Ratio ◽  
Small Region ◽  
Homogeneous Distribution ◽  
X Ray Diffraction ◽  
Commercial Software ◽  
X Ray ◽  
The Difference ◽  
Diffraction Patterns

Mny commercial software packages for X-ray diffraction pattern analysis are capable of identifying multiple phases in bulk materials. However, X-ray diffraction patterns cannot record those phases with very small volume ratio or non-homogeneous distribution, which may mean that researchers have to use instead electron diffraction patterns from a very small region of interest. EDP2XRD, a new program for converting electron diffraction patterns into X-ray diffraction patterns, is described here. The program has been developed in order to utilize X-ray analysis software for electron diffraction patterns taken from mixed-phase nanocrystalline materials with a transmission electron microscope. It is specifically designed for material researchers who are engaged in crystallographic microstructure analysis. The difference from other popular commercial software for crystallography is that this program provides new options to convert and plot X-ray diffraction patterns for arbitrary electron diffraction rings and to process raw images to enhance conversion performance. The program contains the necessary crystallographic calculator to list planar d spacings and corresponding X-ray diffraction angles.

X-Ray Diffraction Study of Methanol-Water Mixtures

1994 ◽  
Vol 49 (10) ◽  
pp. 967-972 ◽  
Author(s):  
I. Bakó ◽  
G. Pálinkás ◽  
K. Heinzinger
Keyword(s):  
Structure Functions ◽  
Excess Functions ◽  
X Ray Diffraction ◽  
X Ray ◽  
Thermodynamic Excess Functions ◽  
The Difference ◽  
Diffraction Patterns ◽  
Molecular Dynamics Results ◽  
Experimental Structure ◽  
Good Agreement

Abstract X-ray diffraction patterns o f m ethanol-water mixtures with mole fractions of methanol molecules o f 0.1, 0.25 and 0.9 have been measured. The experimental structure functions of mixtures are compared with those of pure solvents and with recent Molecular Dynamics results. Difference structure functions similar to thermodynamic excess functions are introduced for the analysis of methanol-water interactions. The comparison of the total and the difference structure functions from experiments and simulations shows an overall good agreement.

Microscopic View on Grain Nucleation and Growth Kinetics During Solidification of Aluminum Alloys

2004 ◽  
Vol 840 ◽  
Author(s):  
N. Iqbal ◽  
N. H. van Dijk ◽  
S. E. Offerman ◽  
M. Moret ◽  
L. Katgerman ◽  
...  
Keyword(s):  
Cooling Rate ◽  
Grain Growth ◽  
Nucleation And Growth ◽  
X Rays ◽  
X Ray Diffraction ◽  
X Ray ◽  
Diffusion Limited ◽  
Model Predictions ◽  
The Difference ◽  
First Time

ABSTRACTX-ray diffraction with hard X-rays (E = 70 keV) was used to investigate the grain nucleation and grain growth during solidification of a grain refined Al-0.3Ti-0.02B (wt.%) alloy. The investigations showed for the first time the nucleation profile during solidification and how nucleation rate increases with cooling rate. The results indicate that the nucleation process is complete for solid fraction below 30 %, irrespective of the cooling rate. This is explained in terms of the release of latent heat during solidification. The growth of individual aluminium grains during solidification is experimentally observed and compared to model predictions for the diffusion limited grain growth. The experimental results are only in agreement with the theory in the first stage of the transformation. The difference between the experiment and the theory is discussed qualitatively.

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