Crystallization of amorphous silica under compression

2019 ◽  
Vol 97 (10) ◽  
pp. 1133-1139
Author(s):  
Nguyen Thu Nhan ◽  
Giap Thi Thuy Trang ◽  
Toshiaki Iitaka ◽  
Nguyen Van Hong
Keyword(s):  
Structural Transformation ◽  
Amorphous Silica ◽  
Pressure Range ◽  
Bond Angle ◽  
3D Visualization ◽  
Structural Phase ◽  
Length Distribution ◽  
Dynamics Simulation ◽  
Structural Phase Transformation ◽  
Bond Length Distribution

The structural phase transformation and crystallization of amorphous silica at 500 K under high pressure are investigated by molecular dynamics simulation. Under compression, there is a structural transformation from tetrahedral- to octahedral-network via SiO5 units. Structural transformation occurs strongly in the 5–15 GPa pressure range and there exist three structural phases corresponding to SiO4, SiO5, and SiO6. Beyond 15 GPa, octahedral-network is dominant. At pressure higher than 20 GPa, octahedral network tends to transform to crystalline phase (stishovite). Mechanism of structural transformation is clarified via coordination-number, bond-angle distributions, bond length distribution, and 3D visualization. The size-distribution of phase regions is also determined in this work.

The structural transition under compression and correlation between structural and dynamical heterogeneity for liquid Al2O3

2019 ◽  
Vol 33 (31) ◽  
pp. 1950380
Author(s):  
P. H. Kien ◽  
P. M. An ◽  
G. T. T. Trang ◽  
P. K. Hung
Keyword(s):  
Structural Transition ◽  
3D Visualization ◽  
Structural Characteristics ◽  
Length Distribution ◽  
Distribution Functions ◽  
Radial Distribution Functions ◽  
Structural Units ◽  
Dynamical Heterogeneity ◽  
Self Diffusion ◽  
Bond Length Distribution

This study reported a simulation of structural transition and correlation between structural and dynamical heterogeneity (DH) for liquid Al2O3. Structural characteristics of liquid Al2O3 were clarified through the pair radial distribution functions, the distribution of [Formula: see text] and [Formula: see text] ([Formula: see text], 4, 5, 6; [Formula: see text], 2, 3) basic structural units, angle and bond length distribution and 3D visualization. Simulation results revealed that network structure of liquid Al2O3 is built mainly by AlO3, AlO4, AlO5 and AlO6 units that are linked to each other through common oxygen atoms. We found the existence of separate AlO4-, AlO5- and AlO6-phases where the mobility of atoms can be determined. The atoms in AlO4-phase are more mobile than the ones in AlO5- and AlO6-phases. The existence of separate phases is evidence of DH in liquid Al2O3. Moreover, the self-diffusion of Al and O atoms was also discussed via characteristics of separate AlO4-, AlO5- and AlO6-phases.

Powder X-ray diffraction and Rietveld analysis of La1−xBaxCoO3 (0

2006 ◽  
Vol 21 (4) ◽  
pp. 304-306 ◽  
Author(s):  
Wanju Luo ◽  
Fangwei Wang
Keyword(s):  
Phase Transformation ◽  
Bond Length ◽  
Structural Properties ◽  
Powder Diffraction ◽  
Bond Angle ◽  
Structural Phase ◽  
Rietveld Analysis ◽  
X Ray Diffraction ◽  
Structural Phase Transformation ◽  
X Ray

Detailed structural properties of La1−xBaxCoO3 (LBCO) have been investigated by means of X-ray powder diffraction and Rietveld analysis. A structural phase transformation from R3c to Pm3m at x=0.30–0.35 has been detected based on a comparison between the refinements of R3c and Pm3m. The Co–O bond length of the CoO6 octahedron expanded rapidly with increasing Ba content when x<0.1, and then it leveled off and kept constant at 0.1⩽x⩾0.35, where the Co–O–Co bond angle reaches 180°. The Co–O bond length expansion resumed with increasing Ba content beyond x=0.35.

Molecular Dynamics Simulation of Size Effect on the Mechanical Properties of Amorphous Silica

2015 ◽  
Vol 30 ◽  
pp. 59-67
Author(s):  
Fang Li Duan ◽  
Cheng Zhang ◽  
Qing Song Liu
Keyword(s):  
Mechanical Properties ◽  
Molecular Dynamics ◽  
Size Effect ◽  
Amorphous Silica ◽  
Bond Angle ◽  
Distribution Functions ◽  
Dynamics Simulation ◽  
Angle Distribution ◽  
Small Model ◽  
Large Model

The frustules of diatoms have excellent elasticity and high strength, but their main composition, amorphous silica, is a kind of typical brittle material. Molecular dynamics simulations of the uniaxial tension were carried out to study the size effect on the mechanical properties of amorphous silica. Stress-strain behavior, the radius of biggest void, radial distribution functions and bond angle distribution were analyzed. Our results show the small model exhibits a better ultimate strength, ductility and toughness than the large model, and the generation and expansion of voids plays an important role in the fracture behavior of the model. For the small model, some of Si-O bonds are stretched, and the average of O-Si-O bond angle decreases from 108o to 95o, which makes the model have a capability to perform larger plastic deformation and lead to a better ductility. However, for the large model, except the change of Si-O-Si bond angle, its structure has no other significant changes. Our results demonstrate that changes of size have significant impact on the mechanical properties and deformation mechanism of intrinsically brittle materials at the nanoscale.

scholarly journals Structure and Correlation Between the Fraction of Structural Units and Bond Angle Distribution in Liquid B2 O3 Under Compression

2018 ◽  
Vol 2 (1) ◽  
Keyword(s):  
Pressure Range ◽  
Bond Angle ◽  
Structural Heterogeneity ◽  
Dynamics Simulation ◽  
Angle Distribution ◽  
Structural Units ◽  
Dynamical Heterogeneity ◽  
Heterogeneous Dynamics ◽  
Bond Angle Distribution ◽  
Spatially Heterogeneous Dynamics

Structure of network-forming liquid B2 O3 is investigated by Molecular dynamics simulation (MDS) at 2000K and in the 0-40 GPa pressure range (corresponding to the 1.71-3.04 g/cm3 density range). Results indicate that network structure of liquid B2 O3 comprises of basic structural units BO3 and BO4 . The topology and size of BO3 and BO4 units at different densities are identical. The O-B-O and B-O-B partial bond angle distributions (BADs) can be determined through the fraction of BO3 and BO4 units. Furthermore, the total BADs are directly related to the partial BADs and the fraction of structural units. It means the fraction of units BOX (X = 3,4) and units OBy (y = 2,3) can be determined from the experimental BADs. The spatial distribution of BO3 and BO4 units is not uniform but forming clusters of BO3 and BO4 . This leads to the polyamorphism in liquid B2 O3 . It also shows that the dynamical heterogeneity in liquid B2 O3 due to the lifetimes of BO3 and BO4 units are very different. The structural heterogeneity is origin of spatially heterogeneous dynamics in liquids B2 O3 .

scholarly journals Study of Structure Transition and Crystallization of Amorphous Silica under Compression

2020 ◽  
Vol 36 (2) ◽  
Author(s):  
Giap Thi Thuy Trang ◽  
Pham Huu Kien
Keyword(s):  
Structural Transformation ◽  
Amorphous Silica ◽  
Md Simulation ◽  
Bond Angle ◽  
Structural Evolution ◽  
Angle Distribution ◽  
Amorphous Sio2 ◽  
Structure Transition ◽  
Bond Angle Distribution ◽  
First Time

In this work, we use molecular dynamic (MD) simulation to study of the structure transition and crystallization of amorphous silica (SiO2) under compression. The structural evolution of amorphous SiO2 is explained through radial distribution function, coordination number distribution, bond angle distribution and visualization. Simulation result shown that there is a structural transformation from tetrahedral to octahedral network through SiO5 units. In the 5-15 GPa pressure range, structural transformation occurs powerfully and there are three structural phases corresponding to SiO4-, SiO5-, and SiO6- ones. At 15 GPa, octahedral-network (SiO6) is dominant. It is the first time we showed that when pressure is higher than 20 GPa, octahedral-network of amorphous SiO2 has a tendency to transform to stishovite crystalline phase.

Pressure Induced Structural Transformations in Nanocluster Assembled Gallium Arsenide

1998 ◽  
Vol 536 ◽  
Author(s):  
S. Kodiyalam ◽  
A. Chatterjee ◽  
I. Ebbsjö ◽  
R. K. Kalia ◽  
H. Kikuchi ◽  
...  
Keyword(s):  
Bond Angle ◽  
Structural Phase ◽  
High Stress ◽  
Distribution Functions ◽  
Structural Phase Transformation ◽  
Spatially Resolved ◽  
Parallel Molecular Dynamics ◽  
Dynamics Simulations ◽  
Pair Distribution Functions ◽  
Single Cluster

AbstractPressure induced structural phase transformation in nanocluster assembled GaAs is studied using parallel molecular dynamics simulations in the isothermal-isobaric ensemble. In this system the spatial stress distribution is found to be inhomogeneous. As a result structural transformation initiates in the high stress regions at the interface between clusters. Structural and dynamical correlations in the nanophase system are characterized by calculating the spatially resolved bond angle and pair distribution functions and phonon density of states and comparing them with those for a single cluster and bulk crystalline and amorphous systems.

On the compression mechanism of FeF3

2006 ◽  
Vol 62 (6) ◽  
pp. 987-992 ◽  
Author(s):  
J.-E. Jørgensen ◽  
R. I Smith
Keyword(s):  
Phase Transitions ◽  
Pressure Range ◽  
Bond Angle ◽  
Structural Phase ◽  
Neutron Powder Diffraction ◽  
Data Sets ◽  
Structural Phase Transitions ◽  
Pressure Derivative ◽  
Compression Mechanism ◽  
Recorded Data

The structure of FeF3, iron trifluoride, has been studied in the pressure range from ambient to 8.28 GPa by time-of-flight neutron powder diffraction. No structural phase transitions were found within the investigated pressure range, and least-squares refinements of the crystal structures were performed in the space group R\overline 3 c for all recorded data sets. It was found that volume reduction is achieved through rotation of the FeF6 octahedra, and the Fe—F—Fe bond angle decreases from 152.5 (2) to 134.8 (3)° within the investigated pressure range. A small octahedral strain was found to develop during compression, which reflects an elongation of the FeF6 octahedra along the c axis. The zero-pressure bulk modulus B_o and its pressure derivative B_o' were determined to be 14 (1) GPa and 12 (1), respectively.

The structural phase-transition pathway under compression and dynamic properties in liquid GeO2

2020 ◽  
Vol 34 (17) ◽  
pp. 2050187
Author(s):  
P. H. Kien
Keyword(s):  
Phase Transition ◽  
Structural Phase Transition ◽  
3D Visualization ◽  
Dynamic Properties ◽  
Structural Phase ◽  
Three Dimensional ◽  
Length Distribution ◽  
High Mobility ◽  
Dynamical Heterogeneity ◽  
Structure Of Liquid

We perform a simulation of the structural phase-transition pathway under compression and dynamic properties in liquid germania (GeO2). The structure of liquid GeO2 is clarified through the pair radial distribution function (PRDF), distribution of GeO[Formula: see text] [Formula: see text] units, bond angle and length distribution, and three-dimensional (3D) visualization. The result shows that the structure of liquid GeO2 is built by GeO4, GeO5 and GeO[Formula: see text]units, which are linked to each other via common oxygen atoms. The GeO[Formula: see text] units lead to form into the separate GeO4-, GeO5- and GeO6-phases. The existence of separate phases is evidence of dynamical heterogeneity (DH) in liquid GeO2. The atoms in GeO5-phase are more mobile compared to other ones. The variation of the self-diffusions of Ge and O atoms under pressure is examined via the characteristics of separate GeO4-, GeO5- and GeO6-phases. We found that under compression, there is diffusion anomaly in liquid GeO2. This is suggested to be related to the very high mobility of Ge and O atoms in the GeO5-phase compared to GeO4- and GeO6-phase.

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