Crystal Structure of NaCd2

Samson, S.

doi:10.1038/195259a0

Cited by 110 publications

(60 citation statements)

References 7 publications

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“…Typical representatives of GUC intermetallics include clathrate compounds [4], Zintl phases [5], Frank-Kasper phases [6,7], Nowotny chimney-ladder phases [8,9], and quasicrystals and their approximants [10]. The realm of these materials can be expanded by slight variation of the compositions that can lead not only to the expansion of the existing isostructural systems but also to the formation of new crystal structures.…”

Section: Introductionmentioning

confidence: 99%

Synthesis, Crystal Structure, and Magnetic Properties of Giant Unit Cell Intermetallics R117Co52+δSn112+γ (R = Y, La, Pr, Nd, Ho)

2016

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Ternary intermetallics R 117 Co 52+δ Sn 112+γ (R = Y, La, Pr, Nd, and Ho) have been prepared by arc-melting followed by annealing at 800 • C. All the compounds belong to the Tb 117 Fe 52 Ge 112 structure type (space group Fm3m) characterized by a complex giant cubic unit cell with a~30 Å. The single-crystal structure determination of Y-and La-containing compounds reveals a significant structural disorder. A comparison of these and earlier reported crystal structures of R 117 Co 52+δ Sn 112+γ suggests that more extensive disorder occurs for structures that contain larger lanthanide atoms. This observation can be explained by the need to maintain optimal bonding interactions as the size of the unit cell increases. Y 117 Co 56 Sn 115 exhibits weak paramagnetism due to the Co sublattice and does not show magnetic ordering in the 1.8-300 K range. Ho 117 Co 55 Sn 108 shows ferromagnetic ordering at 10.6 K. Both Pr 117 Co 54 Sn 112 and Nd 117 Co 54 Sn 111 exhibit antiferromagnetic ordering at 17 K and 24.7 K, respectively, followed by a spin reorientation transition at lower temperature.

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Section: Introductionmentioning

confidence: 99%

Synthesis, Crystal Structure, and Magnetic Properties of Giant Unit Cell Intermetallics R117Co52+δSn112+γ (R = Y, La, Pr, Nd, Ho)

2016

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“…As this figure shows, there is fair agreement between the crystal coordinates and the mathematically constructed 54-cluster. 10 The aforementioned sites therefore can be thought to correspond to the IT, OT, OH, CO, IC, MC, and OC sites of a 54-cluster the nearest-neighbor distances of which are approximately t times a standard metal bond length. Table 3 shows that seven of the eight structure types have the above-mentioned suite of atoms.…”

Section: Three-dimensional (3d) Projections Of the 16-cellmentioning

confidence: 99%

“…While the types of structures we describe-intermetallic crystal structures with regions consisting entirely of close-packed, slightly distorted tetrahedra-have a rich history of efforts to catalogue and systematize their geometries, [3][4][5][6][7][8][9] we will mention only the observations most directly relevant to this paper. First among these was the realization by Samson and co-workers [10][11][12][13] that large cubic intermetallic structures such as NaCd 2 and Cd 3 Cu 4 contain a pseudo-fivefold symmetry perpendicular to their crystallographic h1 1 0i directions. This same pseudo-fivefold symmetry was later observed by Khare and co-workers [14] for the g-brass structure, and it was pointed out that the axes were inconsistent with those in known quasicrystals and quasicrystal approximants.…”

Section: Introductionmentioning

confidence: 98%

The Mystery of Perpendicular Fivefold Axes and the Fourth Dimension in Intermetallic Structures

Berger¹,

Johnson²,

Nebgen³

et al. 2008

Chemistry A European J

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The structures of eight related known intermetallic structure types are the impetus to this paper: Li21Si5, Mg44Rh7, Zn13(Fe,Ni)2, Mg6Pd, Na6Tl, Zn91Ir11, Li13Na29Ba19, and Al69Ta39. All belong to the F43m space group, have roughly 400 atoms in their cubic unit cells, are built up at least partially from the gamma-brass structure, and exhibit pseudo-tenfold symmetric diffraction patterns. These pseudo-tenfold axes lie in the {110} directions, and thus present a paradox. The {110} set is comprised of three pairs of perpendicular directions. Yet no 3D point group contains a single pair of perpendicular fivefold axes (by Friedel's Law, a fivefold axis leads to a tenfold diffraction pattern). The current work seeks to resolve this paradox. Its resolution is based on the largest of all 4D Platonic solids, the 600-cell. We first review the 600-cell, building an intuition discussing 4D polyhedroids (4D polytopes). We then show that the positions of common atoms in the F43m structures lie close to the positions of vertices in a 3D projection of the 600-cell. For this purpose, we develop a projection method that we call intermediate projection. The introduction of the 600-cell resolves the above paradox. This 4D Platonic solid contains numerous orthogonal fivefold rotations. The six fivefold directions that are best preserved after projection prove to lie along the {110} directions of the F43m structures. Finally, this paper shows that at certain ideal projected cluster sizes related to one another by the golden mean (tau=(1+ radical 5)/2), constructive interference leading to tenfold diffraction patterns is optimized. It is these optimal values that predominate in actual F43m structures. Explicit comparison of experimental cluster sizes and theoretically derived cluster sizes shows a clear correspondence, both for isolated and crystalline pairs of projected 600-cells.

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“…Das erste Modell der NaCd 2 -Struktur nach Samson (1962) unterscheidet sich in zwei wichtigen Punkten von der verfeinerten Struktur nach Andersson (1987 Im Andersson-Modell haben viele Gitterplätze eine Mischbesetzung, ihre Gesamtbesetzung durch Na und Cd ist aber immer 1. Das heißt, die Gitterplätze sind vollständig besetzt, bei einem bestimmten Na/Cd-Verhältnis.…”

Section: Atomkoordinaten Für Nacdunclassified

Sich durchdringende polare und unpolare Untergitter in intermetallischen Phasen: die Struktur von NaCd₂

2007

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In den 1960er Jahren bestimmte Samson die Strukturen einiger der komplexesten intermetallischen Phasen, darunter NaCd2, Mg2Al3 und Cu3Cd4, die jeweils über 1000 Atome pro Elementarzelle aufweisen. Basierend auf den bemerkenswerten Arbeiten von Samson und Andersson verwenden wir quantenmechanische Rechnungen zur Beschreibung dieser Strukturen. Der formale Aufbau der Struktur auf der Grundlage der elektronischen Verhältnisse beginnt mit der relativ einfachen Mg17Al12‐Struktur und setzt sich bis zu Samsons NaCd2‐Struktur fort, wobei die Aufteilung in elektronenreiche und elektronenarme Gitterplätze (bezüglich der durchschnittlichen Elektronenzahl) bei beiden Strukturen das Vorliegen von Fragmenten des MgCu2‐Typs aufdeckt. Die äußeren und inneren Bereiche eines solchen Fragments weisen unterschiedliche Bindungsverhältnisse auf: Der innere Bereich ist eher polar, während die Grenzflächen relativ unpolar sind. Dieser Sachverhalt kann mit der Geometrie der Grenzflächenplätze begründet werden, die zugleich an elektronenreichen wie auch elektronenarmen Gittern beteiligt sind. Die polaren und unpolaren Gitterplätze in NaCd2 sind durch eine Minimalfläche, die D‐Fläche, voneinander getrennt. Die Argumente, die für eine solche Struktur sprechen, beruhen auf elektronischen Überlegungen. Ein entscheidendes Merkmal besteht darin, dass sich polare und unpolare Bindungstypen gegenseitig durchdringen. Diese Methode lässt sich auch auf andere Strukturen anwenden.

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Crystal Structure of NaCd2

Cited by 110 publications

References 7 publications

Synthesis, Crystal Structure, and Magnetic Properties of Giant Unit Cell Intermetallics R117Co52+δSn112+γ (R = Y, La, Pr, Nd, Ho)

Synthesis, Crystal Structure, and Magnetic Properties of Giant Unit Cell Intermetallics R117Co52+δSn112+γ (R = Y, La, Pr, Nd, Ho)

The Mystery of Perpendicular Fivefold Axes and the Fourth Dimension in Intermetallic Structures

Sich durchdringende polare und unpolare Untergitter in intermetallischen Phasen: die Struktur von NaCd₂

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Crystal Structure of NaCd2

Cited by 110 publications

References 7 publications

Synthesis, Crystal Structure, and Magnetic Properties of Giant Unit Cell Intermetallics R117Co52+δSn112+γ (R = Y, La, Pr, Nd, Ho)

Synthesis, Crystal Structure, and Magnetic Properties of Giant Unit Cell Intermetallics R117Co52+δSn112+γ (R = Y, La, Pr, Nd, Ho)

The Mystery of Perpendicular Fivefold Axes and the Fourth Dimension in Intermetallic Structures

Sich durchdringende polare und unpolare Untergitter in intermetallischen Phasen: die Struktur von NaCd2

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Sich durchdringende polare und unpolare Untergitter in intermetallischen Phasen: die Struktur von NaCd₂