scholarly journals Insight into the structure of decagonite – the extraterrestrial decagonal quasicrystal

IUCrJ ◽  
2021 ◽  
Vol 8 (1) ◽  
pp. 87-101
Author(s):  
Ireneusz Buganski ◽  
Luca Bindi
Keyword(s):  
Solar System ◽  
Structural Model ◽  
Layer Structure ◽  
Penrose Tiling ◽  
Decagonal Quasicrystal ◽  
X Ray ◽  
Decagonal Quasicrystals ◽  
High Degree ◽  
Insight Into

A set of X-ray data collected on a fragment of decagonite, Al71Ni24Fe5, the only known natural decagonal quasicrystal found in a meteorite formed at the beginning of the Solar System, allowed us to determine the first structural model for a natural quasicrystal. It is a two-layer structure with decagonal columnar clusters arranged according to the pentagonal Penrose tiling. The structural model showed peculiarities and slight differences with respect to those obtained for other synthetic decagonal quasicrystals. Interestingly, decagonite is found to exhibit low linear phason strain and a high degree of perfection despite the fact it was formed under conditions very far from those used in the laboratory.

Disorder in decagonal quasicrystals

2003 ◽  
Vol 218 (2) ◽  
Author(s):  
F. Frey ◽  
E. Weidner
Keyword(s):  
High Temperature ◽  
Neutron Diffraction ◽  
High Temperatures ◽  
Experimental Work ◽  
Diffuse Scattering ◽  
Diffuse Intensity ◽  
X Ray ◽  
Decagonal Quasicrystals ◽  
Ordered Alloys ◽  
Insight Into

AbstractComplementary neutron and x-ray diffuse scattering may provide insight into structural super-ordering and disordering of decagonal quasicrystals (d-phases), and, in consequence, into the formation and stability of aperiodically ordered alloys. Neutron diffraction makes a contrasting almost isoelectronic atomic species possible, as well as a separation of elastic and inelastic diffuse intensity contributions. Experimental work at high temperatures is comparatively unproblematic. The method suffers, however, from the difficulty in obtaining sufficiently sized mono-grain samples and a lack of dedicated neutron diffraction instruments. Recent results, with a main focus on high-temperature (<1000°C) investigations of disordered decagonal Al—Ni—Co phases are reported and some tentative models are discussed.

Structural Studies Of Decagonal Quasicrystals And Approximants Using The High-Angle Annular Dark-Field Method

1998 ◽  
Vol 553 ◽  
Author(s):  
Koh Saitoh ◽  
Kenji Tsuda ◽  
Michiyoshi Tanaka ◽  
An Pang Tsai
Keyword(s):  
Structural Model ◽  
Basic Structure ◽  
Field Method ◽  
Dark Field ◽  
Edge Length ◽  
High Angle ◽  
Decagonal Quasicrystal ◽  
Atom Cluster ◽  
Decagonal Quasicrystals ◽  
Annular Dark Field

AbstractHigh-angle annular dark-field (HAADF) images of an A172Ni20Co8 decagonal quasicrystal and monoclinic Al13Fe4 and τ2-inflated Al13C04 approximants have been presented. We found that a 2 nm atom cluster of Al72Ni20Co8, which have been believed to be tenfold so far, has no tenfold symmetry. A new structural model of Al72Ni20Co8 has been constructed on the basis of the HAADF images and the structure of monoclinic Al13Fe4 approximant. We have found that the monoclinic Al13Fe4 and τ-inflated Al13Co4 approximants are composed of the same basic structure of a pentagonal atom cluster with an edge length of 0.47 nm. We have also found that a fivefold atom-cluster with a 2 nm diameter exists in τ-Al13Co4, which was observed in decagonal quasicrystals of Al-Ni-Fe, Al-Ni-Co, Al-Cu-Co and Al-Co by highresolution electron microscopy. A structural model of τ-inflated Al13Co4 is constructed on the basis of the convergent-beam electron diffraction symmetry, HAADF images and the structure of monoclinic Al13Fe4.

Nano Atom Clusters and Their Long-Range Quasiperiodic Arrangements in Al-Ni-Ru Decagonal Quasicrystal

2005 ◽  
Vol 475-479 ◽  
pp. 3351-3354
Author(s):  
Wei Sun ◽  
Ze Zhang ◽  
Kenji Hirage
Keyword(s):  
Electron Microscopy ◽  
Long Range ◽  
Structural Features ◽  
Penrose Tiling ◽  
Linear Phase ◽  
Decagonal Quasicrystal ◽  
Wide Region ◽  
Atom Clusters ◽  
Decagonal Quasicrystals ◽  
Quasiperiodic Structure

The structural features of nano-sized atom clusters and their long-rang arrangement in the Al-Ni-Ru decagonal quasicrystal with 1.6 nm periodicity have been studied and compared with those in the Al-Pd-Mn decagonal quasicrystal on the basis of electron microscopy. From the perpendicular-space analysis of the tiling obtained in a wide region, we conclude that long-range arrangement of atom clusters in the Al-Ni-Ru decagonal quasicrystal with 1.6 nm periodicity can form a Penrose-tiling-like quasiperiodic structure which is almost free of linear phase strain. In contrast, the tiling structure of the Al-Pd-Mn decagonal quasicrystal contains heavy phason strain. Our results clearly show that atom clusters formed in the Al-Ni-Ru decagonal quasicrystals and their linkage manner are completely different from those in the Al-Pd-Mn decagonal quasicrystal.

The quasiperiodic average structure of highly disordered decagonal Zn–Mg–Dy and its temperature dependence

2014 ◽  
Vol 70 (2) ◽  
pp. 315-330 ◽  
Author(s):  
Taylan Ors ◽  
Hiroyuki Takakura ◽  
Eiji Abe ◽  
Walter Steurer
Keyword(s):  
Single Crystal ◽  
Decomposition Temperature ◽  
Dark Field ◽  
Penrose Tiling ◽  
X Ray Diffraction ◽  
Decagonal Quasicrystal ◽  
X Ray ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field

A single-crystal X-ray diffraction structure analysis of decagonal Zn–Mg–Dy, a Frank–Kasper-type quasicrystal, was performed using the higher-dimensional approach. For this first Frank–Kasper (F–K) decagonal quasicrystal studied so far, significant differences to the decagonal Al–TM-based (TM: transition metal) phases were found. A new type of twofold occupation domain is located on certain edge centers of the five-dimensional unit cell. The structure can be described in terms of a two-cluster model based on a decagonal cluster (∼ 23 Å diameter) arranged on the vertices of a pentagon-Penrose tiling (PPT) and a star-like cluster covering the remaining space. This model is used for the five-dimensional refinements, which converged to anRvalue of 0.126. The arrangement of clusters is significantly disordered as indicated by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). In order to check the structure and stability at higher temperatures,in-situhigh-temperature (HT) single-crystal X-ray diffraction experiments were conducted at 598 and 648 K (i.e.slightly below the decomposition temperature). The structure does not change significantly, however, the best quasiperiodic order is found at 598 K. The implication of these results on the stabilization mechanism of quasicrystals is discussed.

scholarly journals Investigation of the catalytic triad of arylamine N-acetyltransferases: essential residues required for acetyl transfer to arylamines

2005 ◽  
Vol 390 (1) ◽  
pp. 115-123 ◽  
Author(s):  
James Sandy ◽  
Adeel Mushtaq ◽  
Simon J. Holton ◽  
Pamela Schartau ◽  
Martin E. M. Noble ◽  
...  
Keyword(s):  
Mycobacterium Smegmatis ◽  
Structural Model ◽  
Sequence Data ◽  
Structural Features ◽  
Catalytic Triad ◽  
Site Directed Mutagenesis ◽  
X Ray ◽  
X Ray Crystallography ◽  
Acetyl Transfer ◽  
Insight Into

The NATs (arylamine N-acetyltransferases) are a well documented family of enzymes found in both prokaryotes and eukaryotes. NATs are responsible for the acetylation of a range of arylamine, arylhydrazine and hydrazine compounds. We present here an investigation into the catalytic triad of residues (Cys-His-Asp) and other structural features of NATs using a variety of methods, including site-directed mutagenesis, X-ray crystallography and bioinformatics analysis, in order to investigate whether each of the residues of the catalytic triad is essential for catalytic activity. The catalytic triad of residues, Cys-His-Asp, is a well defined motif present in several families of enzymes. We mutated each of the catalytic residues in turn to investigate the role they play in catalysis. We also mutated a key residue, Gly126, implicated in acetyl-CoA binding, to examine the effects on acetylation activity. In addition, we have solved the structure of a C70Q mutant of Mycobacterium smegmatis NAT to a resolution of 1.45 Å (where 1 Å=0.1 nm). This structure confirms that the mutated protein is correctly folded, and provides a structural model for an acetylated NAT intermediate. Our bioinformatics investigation analysed the extent of sequence conservation between all eukaryotic and prokaryotic NAT enzymes for which sequence data are available. This revealed several new sequences, not yet reported, of NAT paralogues. Together, these studies have provided insight into the fundamental core of NAT enzymes, and the regions where sequence differences account for the functional diversity of this family. We have confirmed that each of the three residues of the triad is essential for acetylation activity.

The Evaluation of SrBi2Ta2O9 Films for Ferroelectric Memories

1996 ◽  
Vol 433 ◽  
Author(s):  
C.D. Gutleben
Keyword(s):  
Photoelectron Spectroscopy ◽  
Layer Structure ◽  
Secondary Phases ◽  
X Ray Diffraction ◽  
X Ray ◽  
Annealing Conditions ◽  
Complete Knowledge ◽  
Scientific Goal ◽  
Ferroelectric Memories ◽  
Insight Into

AbstractFor use in ferroelectric memories, the layer structure ferroelectric SrBi2Ta2O9 (SBT) appears to have some stability-related advantages over the more commonly known PZT class of ferroelectrics. Currently we are evaluating the feasibility of integrating this material into a state of the art CMOS memory process. Our primary scientific goal is to identify the intrinsic limitations of SBT which may restrict the engineering applications of films grown by even perfectly optimized processes. To this end we have utilized a wide variety of microanalysis probes to examine polycrystaline SBT films grown under various conditions by both MOD and Flash MOCVD. We have found that X-ray diffraction methods must be supplemented by high resolution X-ray photoelectron spectroscopy (XPS) in order to fully analyze the secondary phases which are commonly incorporated in SBT films. The more complete knowledge of film microstructure that this provides has enabled us to relate phase structure to growth and annealing conditions. XPS has also given us some insight into the initial stages of the growth chemistry of SBT on various Pt surfaces.

Bismuth on GaSb(110): Structural Determination of the 1×1 and 1×2 Phases by Surface X-Ray Diffraction

1998 ◽  
Vol 05 (05) ◽  
pp. 1043-1052 ◽  
Author(s):  
L. Lottermoser ◽  
T. Van Gemmeren ◽  
O. Bunk ◽  
R. L. Johnson ◽  
E. Landemark ◽  
...  
Keyword(s):  
Structural Model ◽  
Layer Structure ◽  
Zigzag Chain ◽  
X Ray Diffraction ◽  
Surface Geometry ◽  
X Ray ◽  
Reconstructed Surface ◽  
Thermal Stability Of ◽  
Good Agreement

The surface geometry of the 1×1 and 1×2 phases of bismuth on GaSb(110) has been determined using surface X-ray diffraction with synchrotron radiation. The bismuth atoms form zigzag chains along the [Formula: see text] direction of the substrate. For the 1×1 phase four different registries of the bismuth chains with respect to the GaSb(110) substrate are possible. It was found that only the epitaxial continued layer structure was in good agreement with the experimental data. In the 1×2 reconstruction every second zigzag chain in the uppermost substrate layer is missing. The reconstructed surface is terminated with a full monolayer of Bi atoms which also form zigzag chains. The Bi atoms in the chains bond alternately to the first and second layer substrate atoms and the Bi chains are inclined at 34° to the surface. This new structural model explains the higher thermal stability of the 1×2 phase compared to that of the 1×1 phase.

scholarly journals Vibrational exciton nanoimaging of phases and domains in porphyrin nanocrystals

2020 ◽  
Vol 117 (13) ◽  
pp. 7030-7037 ◽  
Author(s):  
Eric A. Muller ◽  
Thomas P. Gray ◽  
Zhou Zhou ◽  
Xinbin Cheng ◽  
Omar Khatib ◽  
...  
Keyword(s):  
Energy Transport ◽  
Near Field ◽  
Many Body ◽  
Invasive Approach ◽  
Correlation Lengths ◽  
X Ray ◽  
X Ray Scattering ◽  
Nanoscale Structure ◽  
High Degree ◽  
Insight Into

Much of the electronic transport, photophysical, or biological functions of molecular materials emerge from intermolecular interactions and associated nanoscale structure and morphology. However, competing phases, defects, and disorder give rise to confinement and many-body localization of the associated wavefunction, disturbing the performance of the material. Here, we employ vibrational excitons as a sensitive local probe of intermolecular coupling in hyperspectral infrared scattering scanning near-field optical microscopy (IR s-SNOM) with complementary small-angle X-ray scattering to map multiscale structure from molecular coupling to long-range order. In the model organic electronic material octaethyl porphyrin ruthenium(II) carbonyl (RuOEP), we observe the evolution of competing ordered and disordered phases, in nucleation, growth, and ripening of porphyrin nanocrystals. From measurement of vibrational exciton delocalization, we identify coexistence of ordered and disordered phases in RuOEP that extend down to the molecular scale. Even when reaching a high degree of macroscopic crystallinity, identify significant local disorder with correlation lengths of only a few nanometers. This minimally invasive approach of vibrational exciton nanospectroscopy and -imaging is generally applicable to provide the molecular-level insight into photoresponse and energy transport in organic photovoltaics, electronics, or proteins.

scholarly journals Using EXAFS data to improve atomistic structural models of glasses

2018 ◽  
Vol 25 (4) ◽  
pp. 981-988 ◽  
Author(s):  
Daniel T. Bowron
Keyword(s):  
Structural Model ◽  
Structure Refinement ◽  
Structural Models ◽  
Exafs Data ◽  
X Ray ◽  
Reference Potential ◽  
Potential Structure ◽  
Single Data ◽  
Scientific Challenge ◽  
Insight Into

Quantitative characterization of the atomic structure of multi-component glasses is a long-standing scientific challenge. This is because in most cases no single experimental technique is capable of completely resolving all aspects of a disordered system's structure. In this situation, the most practical solution for the materials scientist is to apply multiple experimental probes offering differing degrees of insight into a material's properties. This powerful and widely adopted approach does, however, transfer the characterization challenge to the task of developing a coherent data analysis framework that can appropriately combine the diverse experimental insight into a single, data-consistent, structural model. Here, taking a terbium metaphosphate glass as an example system, it is illustrated how this can be achieved for X-ray diffraction and extended X-ray absorption fine-structure (EXAFS) spectroscopy data, using an empirical potential structure refinement approach. This methodology is based on performing a Monte Carlo simulation of the structure of a disordered material that is guided to a solution consistent with the provided experimental data, by a series of pairwise perturbation potentials operating on a classical reference potential foundation. For multi-component glasses the incorporation of EXAFS data into the resulting bulk structural models is shown to make a critical contribution that is required to properly account for the increase in local structural order that can develop in the melt-quench process of glass formation.

scholarly journals Redetermination of the crystal structure of NbF4

2016 ◽  
Vol 72 (8) ◽  
pp. 1211-1213 ◽  
Author(s):  
Jascha Bandemehr ◽  
Matthias Conrad ◽  
Florian Kraus
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
Powder Diffraction ◽  
Structural Model ◽  
Layer Structure ◽  
Powder Diffraction Data ◽  
X Ray Diffraction ◽  
X Ray ◽  
Anisotropic Displacement Parameters ◽  
Atomic Coordinates

Single crystals of NbF4, niobium(IV) tetrafluoride, were synthesized by disproportionation of Nb2F5at 1273 K in a sealed niobium tube, extracted and studied by single-crystal X-ray diffraction. Previous reports on the crystal structure of NbF4were based on X-ray powder diffraction data and the observed isotypicity to SnF4[Gortsema & Didchenko (1965).Inorg. Chem.4, 182–186; Schäferet al.(1965).J. Less Common Met.9, 95–104]. The data obtained from a single-crystal X-ray diffraction study meant the atomic coordinates could now be refined as well as their anisotropic displacement parameters, leading to a significant improvement of the structural model of NbF4. In the structure, the Nb atom is octahedron-like surrounded by six F atoms of which four are bridging to other NbF6octahedra, leading to a layer structure extending parallel to theabplane.

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