scholarly journals Contribution to viscosity from the structural relaxation via the atomic scale Green-Kubo stress correlation function

2017 ◽  
Vol 147 (18) ◽  
pp. 184502 ◽  
Author(s):  
V. A. Levashov
Keyword(s):  
Correlation Function ◽  
Structural Relaxation ◽  
Atomic Scale

Pressure-Induced Structural Transformation in Cristobalite Studied by Molecular Dynamic Simulations

1995 ◽  
Vol 398 ◽  
Author(s):  
Lucas Duffrene ◽  
John Kjeffer
Keyword(s):  
Phase Transformation ◽  
Correlation Function ◽  
Molecular Dynamic ◽  
Vibrational Spectra ◽  
Time Correlation ◽  
Time Correlation Function ◽  
Atomic Scale ◽  
Molecular Dynamic Simulations ◽  
Dynamic Simulations ◽  
Transformation Front

ABSTRACTThe phase transformation between the α- and β-cristobalite modifications of SiO2 were studied using molecular dynamic simulations. The transformation was induced isothermally by control of the pressure within the structure, either through an externally applied constant stress or by changing the simulation box volume. The atomic scale mechanisms of the transformation can best be observed by means of a time-correlation function describing the spatial orientation of the planes containing the Si-O-Si bonds. These planes rotate by 90° over the course of the transition. Both, the bulk modulus, calculated for static structures, as well as the vibrational spectra of the Si-O-Si planes, reflect the softening of acoustic modes in the midst of the transition, which is characteristic of displacive phase transformations. Although the aperiodic shift of atomic positions upon passage of the transformation front could be responsible for a momentary softening of the structure, this is not the only reason, since this behavior persists when maintaining the structure at intermediate densities, which corresponds neither to α-, nor to β- cristobalite.

scholarly journals Atomic-scale mechanism of internal structural relaxation screening at polar interfaces

2018 ◽  
Vol 97 (18) ◽  
Author(s):  
Mingqiang Li ◽  
Xiaoxing Cheng ◽  
Ning Li ◽  
Heng-Jui Liu ◽  
Yen-Lin Huang ◽  
...  
Keyword(s):  
Structural Relaxation ◽  
Atomic Scale

The Dynamics of Interacting Systems: Glassy Ionic Conductors and Glass-Forming Materials

1995 ◽  
Vol 411 ◽  
Author(s):  
K. L. Ngai ◽  
A. K. Rizos
Keyword(s):  
Correlation Function ◽  
Structural Relaxation ◽  
Time Range ◽  
Relaxation Techniques ◽  
Ionic Conductors ◽  
Time Dynamics ◽  
Glass Forming ◽  
Interacting Systems ◽  
Glass Forming Materials ◽  
Short Time

ABSTRACTThe dynamics of densely packed interacting systems including glass-forming materials and glassy ionic conductors of various chemical and micro structures have been investigated experimentally by many workers, covering an immense time range from microscopic times shorter than 10−12 s to macroscopic times as long as 104 s. The short time dynamics is fundamental because it can directly reveal the microscopic mechanism of the relaxation. Several experimental investigations of structural relaxation in glass-forming substances have found that the short time dynamics shows exponential relaxation with a correlation function well described by exp(−t/τo) for t<tc where tc is temperature insensitive and has the order of magnitude of a picosecond. The correlation function then crosses over at tc to assumes the stretched exponential form, exp[−(t/τ)β], for t>tc. The relaxation times τ and τo are related by the expression τ = [tc−(1−β)τo]1/β. In this work, we focus on glassy ionic conductors and ionic glass-forming materials and experiments that employ dielectric spectroscopic and conductivity relaxation techniques, the theme of this Symposium. We show that these experimental data exhibit the same feature as described above for structural relaxation and are in accord with the predictions of the coupling model proposed by one of the authors.

Effects of chemical composition on the structural relaxation in ternary Zr-Cu-Al bulk glassy alloys studied by EXAFS and positron annihilation techniques.

2011 ◽  
Vol 1300 ◽  
Author(s):  
A Ishii ◽  
S Mineno ◽  
A Iwase ◽  
Y Yokoyama ◽  
T J. Konno ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Positron Annihilation ◽  
Free Volume ◽  
Structural Relaxation ◽  
Alloy System ◽  
Atomic Scale ◽  
Hypoeutectic Alloy ◽  
Positron Annihilation Lifetime ◽  
Glassy Alloys ◽  
Composition Ratios

ABSTRACTMechanical properties and thermal stability of bulk glassy alloys depend on their chemical composition ratios, although their detailed local structures especially around free volume have not been clarified yet. In order to know the origin of property dependence on alloy composition in Zr-Cu-Al ternary bulk glassy alloys in a view point of atomic scale, positron annihilation lifetime, coincidence Doppler broadening (CDB) and EXAFS (extended X-ray absorption fine structure) measurements have been employed for eutectic Zr50Cu40Al10 and hypoeutectic Zr60Cu30Al10 bulk glassy alloys before and after structural relaxation by annealing below glass transition temperature Tg.The result of CDB experiment, which represents the electron momentum distribution around free volume, shows that significant atomic reordering around free volume does not take place by the annealing in each alloy. Besides, CDB ratio profiles for each alloy suggest that the fraction of Zr atom around free volume does not match the chemical composition of each alloy system. Change in positron lifetime, which is proportional to the size of free volume, during annealing for hypoeutectic alloy almost remains unchanged.

Structure and migration of planar defects in crystals observed in atomic scale

1978 ◽  
Vol 36 (1) ◽  
pp. 284-285 ◽  
Author(s):  
H. Hashimoto ◽  
Y. Sugimoto ◽  
Y. Takai ◽  
H. Endoh
Keyword(s):  
Electron Microscope ◽  
Rotation Angle ◽  
Crystal Surface ◽  
Electron Gun ◽  
Atomic Scale ◽  
Present Observation ◽  
Twist Boundary ◽  
Optical Magnification ◽  
Zinc Crystal ◽  
And Migration

As was demonstrated by the present authors that atomic structure of simple crystal can be photographed by the conventional 100 kV electron microscope adjusted at “aberration free focus (AFF)” condition. In order to operate the microscope at AFF condition effectively, highly stabilized electron beams with small energy spread and small beam divergence are necessary. In the present observation, a 120 kV electron microscope with LaB6 electron gun was used. The most of the images were taken with the direct electron optical magnification of 1.3 million times and then magnified photographically.1. Twist boundary of ZnSFig. 1 is the image of wurtzite single crystal with twist boundary grown on the surface of zinc crystal by the reaction of sulphur vapour of 1540 Torr at 500°C. Crystal surface is parallel to (00.1) plane and electron beam is incident along the axis normal to the crystal surface. In the twist boundary there is a dislocation net work between two perfect crystals with a certain rotation angle.

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