| Autor: |
R. W. Robinson, E. M. Palmer, O. Knop |
| Rok vydání: |
1975 |
| Předmět: |
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| Zdroj: |
Acta Crystallographica Section A: Crystal Physics, Diffraction, Theoretical and General Crystallography. 31:19-31 |
| ISSN: |
0567-7394 |
| Popis: |
The general conditions are investigated under which an assembly of point charges will produce a zero electric-field gradient (ZEFG) at a reference point s0(0,0,0). It is shown that for equal charges it is necessary that they form a configuration of cubic or icosahedral symmetry about s0. Unequal charges must be located at the vertices of a centrosymmetric polyhedron of symmetry m3m, m3 or 53m in such a way that the sum of the charge values in a pair of charges related by the centre of symmetry of the polyhedron be the same for all the pairs. Configurations of this kind are self-dual (SD) with respect to interchange of vertices by inversion in the centre of symmetry of the polyhedron. Self-dual configurations containing two kinds of charges (SD2C) are listed for polyhedra of up to 20 vertices and enumerated for all the centrosymmetric cubic and icosahedral Archimedean polyhedra and their duals. The method of enumeration without construction is described. The conditions under which such discrete ZEFG configurations can be embedded in three-dimensional crystal structures to give ZEFG structures are also investigated and a number of examples of such embeddings are given. The potential usefulness of such structures as Mossbauer null matrices is briefly discussed. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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