Atomic ordering in nanosized PtxAu1–x(x= 0, 0.51, 1) by resonant X-ray diffraction and differential atomic pair distribution functions

2012 ◽  
Vol 227 (5) ◽  
pp. 262-267 ◽  
Author(s):  
Valeri Petkov ◽  
Sarvjit Shastri ◽  
Bridgid Wanjala ◽  
Rameshiwori Loukrakpam ◽  
Jin Luo ◽  
...  
Keyword(s):  
Distribution Functions ◽  
X Ray Diffraction ◽  
Atomic Ordering ◽  
X Ray ◽  
Atomic Pair ◽  
Pair Distribution Functions

scholarly journals Natural Nanomaterials: Reappraising the Elusive Structure of the Nano-Sized Mineral Ferrihydrite through X-Ray Absorption Spectroscopy at the Iron K-Edge

2012 ◽  
Vol 730-732 ◽  
pp. 931-935 ◽  
Author(s):  
Maria Ondina Figueiredo ◽  
Teresa P. Silva ◽  
Joao P. Veiga
Keyword(s):  
Distribution Functions ◽  
Mine Wastes ◽  
X Ray Diffraction ◽  
X Ray ◽  
Ferric Oxyhydroxide ◽  
Atomic Pair ◽  
Icosahedral Clusters ◽  
X Ray Absorption ◽  
Pair Distribution Functions ◽  
Tetrahedral Iron

Ferrihydrite is natural ferric oxyhydroxide occurring exclusively nanocrystalline. With ideal formula 5 Fe2 O3 . 9 H2 O, ferrihydrite is quite abundant in sediments, weathering crusts and mine wastes, being characteristic of red pre-soils formed by loose weathered rock plus mineral debris (regoliths) and commonly designated as “2-line” or “6-line” on the basis of the broadened maxima observed in the X-ray diffraction pattern. Synthetic nanocrystalline “6-line” ferrihydrite was recently studied through methods based on atomic-pair distribution functions disclosing the possible occurrence of icosahedral clusters formed by twelve octahedra centred by an inner tetrahedron, all filled by Fe 3+ ions. However, Mössbauer studies were inconclusive about the existence of 4-coordinated iron, thus suggesting that the tetrahedral cation may well be Si4+. In view of such structural uncertainty, a XANES study at the Fe K-edge was undertaken on ferrihydrite from a regolith to ascertain the occurrence of tetrahedral iron. Comparison with data collected from well crystallized iron oxide and hydroxide minerals where Fe 3+/2+ ions occur in octahedral and tetrahedral coordination is described and the results so far obtained are discussed, showing that supplementary study is needed on the elusive structure of ferrihydrite.

scholarly journals Size, Shape, and Internal Atomic Ordering of Nanocrystals by Atomic Pair Distribution Functions: A Comparative Study of γ-Fe2O3Nanosized Spheres and Tetrapods

2009 ◽  
Vol 131 (40) ◽  
pp. 14264-14266 ◽  
Author(s):  
Valeri Petkov ◽  
P. Davide Cozzoli ◽  
Raffaella Buonsanti ◽  
Roberto Cingolani ◽  
Yang Ren
Keyword(s):  
Comparative Study ◽  
Distribution Functions ◽  
Atomic Ordering ◽  
Atomic Pair ◽  
Pair Distribution Functions

scholarly journals Crystal structure solution from experimentally determined atomic pair distribution functions

2010 ◽  
Vol 43 (3) ◽  
pp. 623-629 ◽  
Author(s):  
P. Juhás ◽  
L. Granlund ◽  
S. R. Gujarathi ◽  
P. M. Duxbury ◽  
S. J. L. Billinge
Keyword(s):  
Crystal Structure ◽  
Distribution Functions ◽  
Unit Cell ◽  
Second Step ◽  
X Ray ◽  
Atomic Pair ◽  
Structure Solution ◽  
Pair Distribution Functions ◽  
Atomic Radii ◽  
Periodic Crystal

An extension of the Liga algorithm for structure solution from atomic pair distribution functions (PDFs), to handle periodic crystal structures with multiple elements in the unit cell, is described. The procedure is performed in three separate steps. First, pair distances are extracted from the experimental PDF. In the second step the Liga algorithm is used to find unit-cell sites consistent with these pair distances. Finally, the atom species are assigned over the cell sites by minimizing the overlap of their empirical atomic radii. The procedure has been demonstrated on synchrotron X-ray PDF data from 16 test samples. The structure solution was successful for 14 samples, including cases with enlarged supercells. The algorithm success rate and the reasons for the failed cases are discussed, together with enhancements that should improve its convergence and usability.

Mechanical Spectroscopy Investigation of Liquid Pb-Bi Alloys

2012 ◽  
Vol 184 ◽  
pp. 434-439 ◽  
Author(s):  
Roberto Montanari ◽  
Alessandra Varone
Keyword(s):  
Distribution Functions ◽  
X Ray Diffraction ◽  
Mechanical Spectroscopy ◽  
X Ray ◽  
Neutron Spallation Source ◽  
Driven System ◽  
Spallation Source ◽  
Accelerator Driven System ◽  
The Mean ◽  
Diffraction Patterns

Liquid Pb–Bi eutectic alloy has been selected as coolant and neutron spallation source for the development of MYRRHA, an accelerator driven system. The alloy has been characterized in liquid state from melting (125 °C) to 650 °C by mechanical spectroscopy. Experiments have been carried out using hollow reeds of austenitic stainless steel filled with the Pb-Bi alloy and sealed at the extremities. From 350 °C to 520 °C modulus shows a remarkable drop accompanied by a broad internal friction maximum. In the same temperature range radial distribution functions, determined from X-ray diffraction patterns, evidenced variations of the mean distance between the 1st nearest neighbour atoms. The anelastic phenomena have been attributed to a structural re-arrangement of liquid metal. For comparison, other alloys of the Pb-Bi system with hypo-eutectic composition have been investigated.

scholarly journals An X-Ray Diffraction Study of Atomic Ordering in Platinum-Rich Copper-Platinum Alloys

1973 ◽  
Vol 14 (4) ◽  
pp. 309-313 ◽  
Author(s):  
Nan-Chung Wu ◽  
Hiroshi Iwasaki ◽  
Shiro Ogawa
Keyword(s):  
Diffraction Study ◽  
X Ray Diffraction ◽  
Atomic Ordering ◽  
X Ray ◽  
Platinum Alloys

Textures Applied to Mechanical Processing Technology Assessment in Ancient Bronze

2005 ◽  
Vol 495-497 ◽  
pp. 719-724
Author(s):  
R.E. Bolmaro ◽  
B. Molinas ◽  
E. Sentimenti ◽  
A.L. Fourty
Keyword(s):  
Orientation Distribution ◽  
Distribution Functions ◽  
Archaeological Sites ◽  
Mechanical Processing ◽  
Post Processing ◽  
X Ray Diffraction ◽  
Mechanical Process ◽  
X Ray ◽  
Pole Figures ◽  
Microscopic Inspection

Some ancient metallic art craft, utensils, silverware and weapons are externally undistinguishable from modern ones. Not only the general aspect and shape but also some uses have not changed through the ages. Moreover, when just some small pieces can be recovered from archaeological sites, the samples can not easily be ascribed to any known use and consequently identified. It is clear that mechanical processing has changed along history but frequently only a "microscopic" inspection can distinguish among different techniques. Some bronze samples have been collected from the Quarto d’Altino (Veneto) archaeological area in Italy (paleovenetian culture) and some model samples have been prepared by a modern artisan. The sample textures have been measured by X-ray Diffraction techniques. (111), (200) and (220) pole figures were used to calculate Orientation Distribution Functions and further recalculate pole figures and inverse pole figures. The results were compared with modern forging technology results. Textures are able to discern between hammering ancient techniques for sheet production and modern industrial rolling procedures. However, as it is demonstrated in the present work, forgery becomes difficult to detect if the goldsmith, properly warned, proceeds to erase the texture history with some hammering post-processing. The results of this contribution can offer to the archaeologists the opportunity to take into consideration the texture techniques in order to discuss the origin (culture) of the pieces and the characteristic mechanical process developed by the ancient artisan. Texture can also help the experts when discussing the originality of a certain piece keeping however in mind the cautions indicated in this publication.

Optical and Structural Properties of α-Si1-xCx Films

1996 ◽  
Vol 423 ◽  
Author(s):  
Zhizhong Chen ◽  
Kai Yang ◽  
Rong Zhang ◽  
Hongtao Shi ◽  
Youdou Zheng
Keyword(s):  
Structural Properties ◽  
Radial Distribution ◽  
Optical Constants ◽  
State Density ◽  
Distribution Functions ◽  
X Ray Diffraction ◽  
Energy Band Gap ◽  
X Ray ◽  
Optical Energy Band Gap ◽  
Atomic Radial Distribution

AbstractIn this paper, we reported experimental results about optical and structural properties of amorphous silicon carbide (α-Si1-xCx). The films of a-Si1-xCx) were grown by CVD on substrate of quartz glass. Optical constants (n-refractive index, a-absorption coefficient, Eg-optical energy band gap) of these films were determined by transmission spectra. The radial distribution functions (RDFs) of α- Sil−xCx) films were drawn out from the data of x-ray diffraction spectra. According to the RDFs, we imagined the statistic scene from which we could obtain the information of atomic radial distribution. The bond lengths and bond numbers of Si-Si, Si-C, and C-C could be also determined by RDFs. From the analysis of Raman spectra, we obtained the information of their vibration state density, and discerned the peaks of bond vibration, which agreed well with the results of α-Si1-xCx) RDF.

The structure of amorphous aluminium phosphate by radial distribution functions derived from X-ray diffraction

1977 ◽  
Vol 12 (5) ◽  
pp. 1039-1049 ◽  
Author(s):  
G. D. Wignall ◽  
R. N. Rothon ◽  
G. W. Longman ◽  
G. R. Woodward
Keyword(s):  
Radial Distribution ◽  
Distribution Functions ◽  
Radial Distribution Functions ◽  
X Ray Diffraction ◽  
Aluminium Phosphate ◽  
X Ray
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