scholarly journals Beyond sixfold coordinated Si in SiO2glass at ultrahigh pressures

2017 ◽  
Vol 114 (38) ◽  
pp. 10041-10046 ◽  
Author(s):  
Clemens Prescher ◽  
Vitali B. Prakapenka ◽  
Johannes Stefanski ◽  
Sandro Jahn ◽  
Lawrie B. Skinner ◽  
...  
Keyword(s):  
Coordination Number ◽  
Structural Changes ◽  
Packing Fraction ◽  
High Energy ◽  
Silicate Melts ◽  
X Ray Diffraction ◽  
X Ray ◽  
Diamond Anvil ◽  
Coordination Change ◽  
Insight Into

We investigated the structure of SiO2glass up to 172 GPa using high-energy X-ray diffraction. The combination of a multichannel collimator with diamond anvil cells enabled the measurement of structural changes in silica glass with total X-ray diffraction to previously unachievable pressures. We show that SiO2first undergoes a change in Si–O coordination number from fourfold to sixfold between 15 and 50 GPa, in agreement with previous investigations. Above 50 GPa, the estimated coordination number continuously increases from 6 to 6.8 at 172 GPa. Si–O bond length shows first an increase due to the fourfold to sixfold coordination change and then a smaller linear decrease up to 172 GPa. We reconcile the changes in relation to the oxygen-packing fraction, showing that oxygen packing decreases at ultrahigh pressures to accommodate the higher than sixfold Si–O coordination. These results give experimental insight into the structural changes of silicate glasses as analogue materials for silicate melts at ultrahigh pressures.

Structural changes in titanium dioxide nanocrystals during plastic deformation

2005 ◽  
Vol 38 (5) ◽  
pp. 749-756 ◽  
Author(s):  
Ulrich Gesenhues
Keyword(s):  
Structural Changes ◽  
Crystal Size ◽  
Lower Layer ◽  
High Energy ◽  
Primary Crystal ◽  
X Ray Diffraction ◽  
X Ray ◽  
Transmission Electron ◽  
Hall Method ◽  
Means Of Transmission

The polygonization of 200 nm rutile crystals during dry ball-milling at 10gwas monitored in detail by means of transmission electron microscopy (TEM) and X-ray diffraction (XRD). The TEM results showed how to modify the Williamson–Hall method for a successful evaluation of crystal size and microstrain from XRD profiles. Macrostrain development was determined from the minute shift of the most intense reflection. In addition, changes in pycnometrical density were monitored. Accordingly, the primary crystal is disintegrated during milling into a mosaic of 12–35 nm pieces where the grain boundaries induce up to 1.2% microstrain in a lower layer of 6 nm thickness. Macrostrain in the interior of the crystals rises to 0.03%. The pycnometrical density, reflecting the packing density of atoms in the grain boundary, decreases steadily by 1.1%. The results bear relevance to our understanding of plastic flow and the mechanism of phase transitions of metal oxides during high-energy milling.

scholarly journals Structural Evolution in Wet Mechanically Alloyed Co-Fe-(Ta,W)-B Alloys

Metals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 800
Author(s):  
Vladimír Girman ◽  
Maksym Lisnichuk ◽  
Daria Yudina ◽  
Miloš Matvija ◽  
Pavol Sovák ◽  
...  
Keyword(s):  
Structural Changes ◽  
Magnetic Measurements ◽  
Structural Evolution ◽  
High Energy ◽  
Control Agent ◽  
X Ray Diffraction ◽  
Mechanically Alloyed ◽  
X Ray ◽  
Transmission Electron ◽  
X Ray Absorption

In the present study, the effect of wet mechanical alloying (MA) on the glass-forming ability (GFA) of Co43Fe20X5.5B31.5 (X = Ta, W) alloys was studied. The structural evolution during MA was investigated using high-energy X-ray diffraction, X-ray absorption spectroscopy, high-resolution transmission electron microscopy and magnetic measurements. Pair distribution function and extended X-ray absorption fine structure spectroscopy were used to characterize local atomic structure at various stages of MA. Besides structural changes, the magnetic properties of both compositions were investigated employing a vibrating sample magnetometer and thermomagnetic measurements. It was shown that using hexane as a process control agent during wet MA resulted in the formation of fully amorphous Co-Fe-Ta-B powder material at a shorter milling time (100 h) as compared to dry MA. It has also been shown that substituting Ta with W effectively suppresses GFA. After 100 h of MA of Co-Fe-W-B mixture, a nanocomposite material consisting of amorphous and nanocrystalline bcc-W phase was synthesized.

Structural stability of WS2 under high pressure

2014 ◽  
Vol 28 (25) ◽  
pp. 1450168 ◽  
Author(s):  
Nirup Bandaru ◽  
Ravhi S. Kumar ◽  
Jason Baker ◽  
Oliver Tschauner ◽  
Thomas Hartmann ◽  
...  
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
High Temperature ◽  
Structural Changes ◽  
High Pressures ◽  
Structural Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Diamond Anvil ◽  
Heating Up

Structural behavior of bulk WS 2 under high pressure was investigated using synchrotron X-ray diffraction and diamond anvil cell up to 52 GPa along with high temperature X-ray diffraction and high pressure Raman spectroscopy analysis. The high pressure results obtained from X-ray diffraction and Raman analysis did not show any pressure induced structural phase transformations up to 52 GPa. The high temperature results show that the WS 2 crystal structure is stable upon heating up to 600°C. Furthermore, the powder X-ray diffraction obtained on shock subjected WS 2 to high pressures up to 10 GPa also did not reveal any structural changes. Our results suggest that even though WS 2 is less compressible than the isostructural MoS 2, its crystal structure is stable under static and dynamic compressions up to the experimental limit.

Synthesis of Nanocrystalline Fe25Al57.5Ni17.5 by Mechanical Alloying

2012 ◽  
Vol 476-478 ◽  
pp. 1318-1321
Author(s):  
Qi Zhi Cao ◽  
Jing Zhang
Keyword(s):  
Thermal Analysis ◽  
Solid Solution ◽  
Differential Thermal Analysis ◽  
Mechanical Alloying ◽  
Ball Mill ◽  
Structural Changes ◽  
Early Stage ◽  
High Energy ◽  
X Ray Diffraction ◽  
X Ray

Nanostructured Fe25Al57.5Ni17.5intermetallics was prepared directly by mechanical alloying (MA) in a high-energy planetary ball-mill. The phase transformations and structural changes occurring in the studied material during mechanical alloying were investigated by X-ray diffraction (XRD). Thermal behavior of the milled powders was examined by differential thermal analysis (DTA). Disordered Al(Fe,Ni) solid solution was formed at the early stage. After 50 h of milling, Al(Fe,Ni) solid solution transformed into Al3Ni2，AlFe3，AlFe0.23Ni0.77 phase. The power annealed at temperature 500 results in forming of intermetallics AlFe3 and FeNi3 after 5h milling. The nanocrystalline intermetallic compound was obtained after 500h milling.

In situ high-energy synchrotron X-ray diffraction studies and first principles modeling of α-MnO2 electrodes in Li–O2 and Li-ion coin cells

2015 ◽  
Vol 3 (14) ◽  
pp. 7389-7398 ◽  
Author(s):  
Zhenzhen Yang ◽  
Lynn Trahey ◽  
Yang Ren ◽  
Maria K. Y. Chan ◽  
Chikai Lin ◽  
...  
Keyword(s):  
First Principles ◽  
Structural Changes ◽  
High Energy ◽  
X Ray Diffraction ◽  
Synchrotron Diffraction ◽  
X Ray ◽  
Li Ion ◽  
Battery Cells

In situ synchrotron diffraction and first principles modeling shows structural changes in α-MnO2 during cycling in Li–O2 battery cells, as lithium and oxygen are incorporated into and removed from tunnels in the structure.

In situelectrochemical high-energy X-ray diffraction using a capillary working electrode cell geometry

2017 ◽  
Vol 24 (4) ◽  
pp. 787-795 ◽  
Author(s):  
Matthias J. Young ◽  
Nicholas M. Bedford ◽  
Naisheng Jiang ◽  
Deqing Lin ◽  
Liming Dai
Keyword(s):  
Structural Changes ◽  
Active Material ◽  
High Energy ◽  
Distribution Functions ◽  
Atomic Scale ◽  
X Ray Diffraction ◽  
Active Materials ◽  
X Ray ◽  
Working Electrode ◽  
Electrochemically Active

The ability to generate new electrochemically active materials for energy generation and storage with improved properties will likely be derived from an understanding of atomic-scale structure/function relationships during electrochemical events. Here, the design and implementation of a new capillary electrochemical cell designed specifically forin situhigh-energy X-ray diffraction measurements is described. By increasing the amount of electrochemically active material in the X-ray path while implementing low-Zcell materials with anisotropic scattering profiles, an order of magnitude enhancement in diffracted X-ray signal over traditional cell geometries for multiple electrochemically active materials is demonstrated. This signal improvement is crucial for high-energy X-ray diffraction measurements and subsequent Fourier transformation into atomic pair distribution functions for atomic-scale structural analysis. As an example, clear structural changes in LiCoO2under reductive and oxidative conditions using the capillary cell are demonstrated, which agree with prior studies. Accurate modeling of the LiCoO2diffraction data using reverse Monte Carlo simulations further verifies accurate background subtraction and strong signal from the electrochemically active material, enabled by the capillary working electrode geometry.

Effects of High Energy Ion Irradiation on Crystallization of Amorphous Germanium Films Deposited on Calcium Fluoride Substrates

1995 ◽  
Vol 396 ◽  
Author(s):  
Setsuo Nakao ◽  
Kazuo Saitoh ◽  
Masami Ikeyama ◽  
Hiroaki Niwa ◽  
Seita Tanemura ◽  
...  
Keyword(s):  
Thin Film ◽  
Calcium Fluoride ◽  
Structural Changes ◽  
Rutherford Backscattering Spectrometry ◽  
Ion Irradiation ◽  
High Energy ◽  
The Other ◽  
Ion Current ◽  
X Ray Diffraction ◽  
X Ray

AbstractAmorphous (a-) Ge films were deposited on air-cleaved CaF2 (111) substrates at different deposition temperatures (Td). The films were irradiated with 0.9 MeV Ge or Si ions at low ion current intensity (1c) l00nA/cm2. Their structural changes were studied by Rutherford backscattering spectrometry (RBS) -channeling technique and thin film x-ray diffraction (XRD) measurement. It was found that the films were epitaxially crystallized by Ge and Si ion irradiation although they included randomly oriented grains. Ge ion irradiation was more effective for the crystallization than Si ion irradiation. However, the amount of the randomly oriented grains was slightly higher when using Ge ions. On the other hand, ion irradiation to the films prepared at high Td also exhibited higher incidence of randomly oriented grains.

The Structure of Gallium Phosphate Glasses by High-energy X-ray Diffraction

2002 ◽  
Vol 57 (8) ◽  
pp. 709-715 ◽  
Author(s):  
U. Hoppe ◽  
D. Ilieva ◽  
J. Neuefeindb
Keyword(s):  
Coordination Number ◽  
Short Range ◽  
High Energy ◽  
Phosphate Glasses ◽  
X Ray Diffraction ◽  
Strong Decrease ◽  
X Ray ◽  
Coordination Numbers ◽  
Tetrahedral Sites ◽  
Gallium Phosphate

X-ray diffraction experiments are used to obtain short-range order information of gallium phosphate glasses of meta- and pyrophosphate compositions. Parameters of the first-neighbor peaks, such as coordination numbers and distances, are obtained. A strong decrease of the Ga-O coordination number from 6.0±0.2 to 4.6±0.2 upon Ga2O3 addition is found, which is accompanied by a shortening of the Ga-O distances. Only GaO6 octahedra exist at the metaphosphate composition. Close to the pyrophosphate composition, the majority of Ga atoms occupies already tetrahedral sites. The Ga-O coordination number behaves equivalent with the ratio MTO = n(OT)/n(Ga), thus, with the number n(OT) of terminal oxygen atoms (OT) in phosphorus-OT bonds which are available for the coordination of each Ga atom. Thus, P-OT-Ga bridges are formed for all OT atoms. The GaOn polyhedra neither share OT atoms nor form Ga-O-Ga bridges. With increasing fraction of GaO4 tetrahedra and decreasing lengths of the phosphate chains the network expands.

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