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Crystals 2014, 4(3), 390-403; doi:10.3390/cryst4030390

Modeling the Shape of Ions in Pyrite-Type Crystals

IHP, Im Technologiepark 25, 15236 Frankfurt (Oder), Germany
Received: 13 April 2014 / Revised: 22 August 2014 / Accepted: 26 August 2014 / Published: 3 September 2014
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Abstract

The geometrical shape of ions in crystals and the concept of ionic radii are re-considered. The re-investigation is motivated by the fact that a spherical modelling is justified for p valence shell ions on cubic lattice sites only. For the majority of point groups, however, the ionic radius must be assumed to be an anisotropic quantity. An appropriate modelling of p valence ions then has to be performed by ellipsoids. The approach is tested for pyrite-structured dichalcogenides MX2, with chalcogen ions X = O, S, Se and Te. The latter are found to exhibit the shape of ellipsoids being compressed along the <111> symmetry axes, with two radii r|| and r describing their spatial extension. Based on this ansatz, accurate interatomic MX distances can be derived and a consistent geometrical model emerges for pyrite-structured compounds. Remarkably, the volumes of chalcogen ions are found to vary only little in different MX2 compounds, suggesting the ionic volume rather than the ionic radius to behave as a crystal-chemical constant. View Full-Text
Keywords: ionic radius; ionic shape; bonding distance; ionic volume; pyrite-type compounds; di-chalcogenides; di-oxides; di-sulfides; di-selenides; di-tellurides ionic radius; ionic shape; bonding distance; ionic volume; pyrite-type compounds; di-chalcogenides; di-oxides; di-sulfides; di-selenides; di-tellurides
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Birkholz, M. Modeling the Shape of Ions in Pyrite-Type Crystals. Crystals 2014, 4, 390-403.

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