Topological signatures and stability of hexagonal close packing and Barlow stackings

Soft Matter ◽  
2021 ◽  
Author(s):  
Georg Osang ◽  
Herbert Edelsbrunner ◽  
Mohammad Saadatfar
Keyword(s):  
Close Packing ◽  
Hexagonal Close Packing ◽  
X Ray ◽  
3D Rendering

3D rendering of the experimental packing obtained via X-ray CT. A cut-out section shows the bulk crystallisation and partially crystallised regions.

Synthese und Struktur von Nb0,89Fe0,93Te2 und Ta0,77Fe0,90Te2 / Synthesis and Structure of Nb0.89Fe0.93Te2 and Ta0.77Fe0.90Te2

1992 ◽  
Vol 47 (9) ◽  
pp. 1203-1212 ◽  
Author(s):  
Jörg Neuhausen ◽  
Karl-Ludwig Stork ◽  
Elisabeth Potthoff ◽  
Wolfgang Tremel
Keyword(s):  
Single Crystal ◽  
Crystal Structures ◽  
Chemical Transport ◽  
Structure Type ◽  
Close Packing ◽  
Hexagonal Close Packing ◽  
X Ray ◽  
The Relationship

Nb0.89Fe0.93Te2 and Ta0.77Fe0.90Te2 were prepared by chemical transport reactions. The crystal structures of both compounds were determined using X-ray single crystal methods. The structures of the layer compounds Nb0.89Fe0.93Te2 (Pmna, Z = 2, a = 7.951(1) Å, b = 7.241(1) A, c = 6.233(1) Å) and Ta0.77Fe0.90Te2 (Pmna, Z = 2, a = 7.890(2) Å, b = 7.252(2) Å, c = 6.192(1) Å) are based on a hexagonal close packing of Te atoms. Approximately one-half of the octahedral holes in this packing are occupied by Nb (Ta) atoms, about one-quarter of the tetrahedral holes are occupied by Fe atoms. The relationship to the NiAs structure type is discussed.

High-pressure transformations of NbO2F

2000 ◽  
Vol 56 (2) ◽  
pp. 189-196 ◽  
Author(s):  
Stefan Carlson ◽  
Ann-Kristin Larsson ◽  
Franziska E. Rohrer
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
High Pressures ◽  
Ambient Pressure ◽  
Close Packing ◽  
Hexagonal Close Packing ◽  
Rietveld Refinements ◽  
X Ray ◽  
Anion Coordination ◽  
Diamond Anvil

The ReO3-type structure NbO2F, niobium dioxyfluoride, has been studied at high pressures using diamond anvil cells and synchrotron X-ray radiation. High-pressure powder diffraction measurements have been performed up to 40.1 GPa. A phase transition from the cubic (Pm3¯m) ambient pressure structure to a rhombohedral (R3¯c) structure at 0.47 GPa has been observed. Rietveld refinements at 1.38, 1.96, 3.20, 6.23, 9.00 and 10.5 GPa showed that the transition involves an a − a − a − tilting of the cation–anion coordination octahedra and a change of the anion–anion arrangement to approach hexagonal close packing. Compression and distortion of the Nb(O/F)6 octahedra is also revealed by the Rietveld refinements. At 17–18 GPa, the diffraction pattern disappears and the structure becomes X-ray amorphous.

Alkalimetall-Arsenide A3As7 Und Aas (A = K, Rb, Cs). Synthesen, Kristallstrukturen, Schwingungsspektren / Alkaline Metal Arsenides A3As7 and AAs (A = K, Rb, Cs). Preparation, Crystal Structure, Vibrational Spectroscopy

2002 ◽  
Vol 57 (9) ◽  
pp. 963-975 ◽  
Author(s):  
Franziska Emmerling ◽  
Caroline Röhr
Keyword(s):  
Crystal Structure ◽  
Raman Spectroscopy ◽  
Vibrational Spectroscopy ◽  
Structure Type ◽  
Close Packing ◽  
Hexagonal Close Packing ◽  
Alkaline Metal ◽  
Zintl Phases ◽  
X Ray ◽  
Hexagonal Close Packed

The title compounds were synthesized from the elements and characterized via single crystal x-ray studies and Raman spectroscopy. In the Zintl phases A3As7 (A = K, Rb, Cs) the As atoms form nortricyclene-analogous anions As37 with As-As distances ranging from 230 to 254 pm. The three compounds crystallizewithdifferent newstructure types containing different packings of theAs7 anions:K3As7 (orthorhombic, Pbca; a=1291.9(8), b = 2544.1(9), c=1537.7(16) pm) shows a double hexagonal close packing (ABAC stacking of planes of hexagonal close packed anions), Rb3 As7 (monoclinic, P21/c, a = 757.3(5), b = 1310.2(8), c = 2692.7(18) pm , β= 91.972(12)°) hows a hexagonal close packing (AB) and the Cs compound (orthorhombic, Pbca, a = 1022.8(5), b = 1317.6(7), c = 2195.2(11) pm) a cubic close packing (ABC) (also present in theHT-forms of the three compounds) respectively. The alkaline metalmonoarsenides AAs (A = K, Rb) crystallize with the NaP structure type (A = K/Rb: orthorhombic, P212121; a = 661.7(5) / 658.1(8), b = 688.8(6) / 691.6(8), c = 1197.3(10) / 1204.7(10) pm, Z = 8) with approximate fourfold screw axes 41 of As$ chains, whereas the crystal structure of CsAs (hexagonal, P¯62m, a = 1219.7(3), c = 1046.3(2) pm, Z = 18) contains three crystallographically independent three membered rings As33 with As-As distances of 243.0 to 247.5 pm

scholarly journals A closer look into close packing: pentacoordinated silicon in a high-pressure polymorph of danburite

IUCrJ ◽  
2017 ◽  
Vol 4 (5) ◽  
pp. 671-677 ◽  
Author(s):  
Anna Pakhomova ◽  
Elena Bykova ◽  
Maxim Bykov ◽  
Konstantin Glazyrin ◽  
Biliana Gasharova ◽  
...  
Keyword(s):  
High Pressure ◽  
Inorganic Compounds ◽  
Close Packing ◽  
Hexagonal Close Packing ◽  
Pressure Treatment ◽  
Ambient Conditions ◽  
X Ray Diffraction ◽  
High Pressure Treatment ◽  
X Ray ◽  
Unusual Formation

Due to their high technological and geological relevance, silicates are one of the most studied classes of inorganic compounds. Under ambient conditions, the silicon in silicates is almost exclusively coordinated by four oxygen atoms, while high-pressure treatment normally results in an increase in the coordination from four- to sixfold. Reported here is a high-pressure single-crystal X-ray diffraction study of danburite, CaB2Si2O8, the first compound showing a step-wise transition of Si coordination from tetrahedral to octahedral through a trigonal bipyramid. Along the compression, the Si2O7groups of danburite first transform into chains of vertice-sharing SiO5trigonal bipyramids (danburite-II) and later into chains of edge-sharing SiO6octahedra (danburite-III). It is suggested that the unusual formation of an SiO5configuration is a consequence of filling up the pentacoordinated voids in the distorted hexagonal close packing of danburite-II.

(MeSn)4Se6, Geometrie und Schwingungsformen eines Adamantan-Gerüstes aus Zinn-Selen-Bindungen / (MeSn)4Se6, Geometry and Vibrational Modes of an Adamantane Framework Formed by Tin-Selenium Bonds

1981 ◽  
Vol 36 (11) ◽  
pp. 1361-1367 ◽  
Author(s):  
Axel Blecher ◽  
Martin Dräger ◽  
Bernd Mathiasch
Keyword(s):  
Aqueous Solution ◽  
Potential Energy ◽  
Vibrational Spectra ◽  
Normal Modes ◽  
Close Packing ◽  
Force Constants ◽  
Hexagonal Close Packing ◽  
Vibrational Modes ◽  
X Ray ◽  
Atomic Coordinates

Abstract The title compound has been synthesized by reaction of MeSnBr3 and NaHSe in aqueous solution. The X-ray structure determination showed adamantane-like molecules (Sn-Se 253(1), Sn-C 215(1) pm) arranged in a quasi hexagonal-close packing. The atomic coordinates were used for an analysis of the vibrational spectra, yielding information on the distribution of the potential energy for the normal modes in terms of internal co-ordinates and a set of force constants. The valence force constants f(Sn-Se) 154(6), f(Sn-C) 216(2) N/m) are compared with those in related monocyclic molecules.

Cu3Sn – understanding the systematic absences

2014 ◽  
Vol 70 (5) ◽  
pp. 879-887 ◽  
Author(s):  
Carola J. Müller ◽  
Sven Lidin
Keyword(s):  
Intermetallic Compound ◽  
Antiphase Boundary ◽  
Structure Type ◽  
Close Packing ◽  
Hexagonal Close Packing ◽  
X Ray Diffraction ◽  
Orthorhombic Space Group ◽  
X Ray ◽  
Long Period ◽  
Diffraction Patterns

The intermetallic compound Cu3Sn has previously been described as a long-period antiphase boundary superstructure of the Cu3Ti structure type. While the compound itself has been reported as a tenfold and an eightfold superstructure, ternary doped alloys show shorter repetitions. Interestingly, the diffraction patterns of these compounds show non-crystallographic absences that cannot be explained using the superstructure models. Since the compound exhibits phase broadening, these models are not satisfactory because the paucity of observed data does not allow for a refinement of the composition. Here, an alternative, superspace model in the orthorhombic space groupXmcm(0β0)000 is proposed, with the centering vectors (0,0,0,0) and (½,0,0,½). The presence of the non-crystallographic absences is explained as a result of a dominating occupational modulation that is accompanied by a weaker displacive modulation. In consistency with the EDXS results, the composition has been refined to Cu3 + xSn from single-crystal X-ray diffraction data. It is further demonstrated that by varying the length and the direction of the modulation wavevector in the superspace model, the ternary Cu3Sn compounds and other colored hexagonal close packing (h.c.p.) structures can be produced.

scholarly journals Atomic structure and phason modes of the Sc–Zn icosahedral quasicrystal

IUCrJ ◽  
2016 ◽  
Vol 3 (4) ◽  
pp. 247-258 ◽  
Author(s):  
Tsunetomo Yamada ◽  
Hiroyuki Takakura ◽  
Holger Euchner ◽  
Cesar Pay Gómez ◽  
Alexei Bosak ◽  
...  
Keyword(s):  
Atomic Structure ◽  
Diffuse Scattering ◽  
Waller Factor ◽  
Close Packing ◽  
Icosahedral Quasicrystal ◽  
X Ray Diffraction ◽  
X Ray ◽  
Large Atom ◽  
Debye Waller Factor ◽  
The Difference

The detailed atomic structure of the binary icosahedral (i) ScZn7.33quasicrystal has been investigated by means of high-resolution synchrotron single-crystal X-ray diffraction and absolute scale measurements of diffuse scattering. The average atomic structure has been solved using the measured Bragg intensity data based on a six-dimensional model that is isostructural to the i-YbCd5.7one. The structure is described with a quasiperiodic packing of large Tsai-type rhombic triacontahedron clusters and double Friauf polyhedra (DFP), both resulting from a close-packing of a large (Sc) and a small (Zn) atom. The difference in chemical composition between i-ScZn7.33and i-YbCd5.7was found to lie in the icosahedron shell and the DFP where in i-ScZn7.33chemical disorder occurs on the large atom sites, which induces a significant distortion to the structure units. The intensity in reciprocal space displays a substantial amount of diffuse scattering with anisotropic distribution, located around the strong Bragg peaks, that can be fully interpreted as resulting from phason fluctuations, with a ratio of the phason elastic constantsK2/K1= −0.53,i.e.close to a threefold instability limit. This induces a relatively large perpendicular (or phason) Debye–Waller factor, which explains the vanishing of `high-Qperp' reflections.

scholarly journals HTR-PROTEUS Pebble Bed Experimental Program Cores 1, 1A, 2, and 3: Hexagonal Close Packing with a 1:2 Moderator-to-Fuel Pebble Ratio

2012 ◽  
Author(s):  
John D. Bess ◽  
Barbara H. Dolphin ◽  
James W. Sterbentz ◽  
Luka Snoj ◽  
Igor Lengar ◽  
...  
Keyword(s):  
Close Packing ◽  
Experimental Program ◽  
Hexagonal Close Packing ◽  
Pebble Bed
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