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The influence of next nearest neighbours on cation radii in spinels: the example of the Co3O4-CoCr2O4 solid solution

Published online by Cambridge University Press:  05 July 2018

H. St. C. O’Neill
H. St. C. O’Neill*
Affiliation:
Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia
*
* E-mail: [email protected]
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Abstract

Lattice parameters and crystal structures of the synthetic spinels Co3O4, CoCr2O4, and solid solutions in the binary join Co3O4-CoCr2O4, have been determined by powder X-ray diffraction structural refinements. In all these spinels the cation distribution is completely normal at room temperature, and the tetrahedrally coordinated cation site is occupied only by Co2+. The ionic radius of Co2+(tet) increases from 0.556(3) in Co3O4 to 0.599(4) in CoCr2O4. In the spinel structure, the interatomic distance between the tetrahedral cations and oxygen are geometrically independent of those between the octahedral cations and oxygen; thus the variation in effective ionic radii is ascribed to next-nearest neighbour effects, induced by covalent tendencies in the low-spin Co3+-O bond. The results demonstrate that the assumption of constant ionic radii even within an isomorphic group such as the oxide spinels needs to be made with caution.

Keywords

spinelXRD dataionic radii.
Type
Research Article
Information
Mineralogical Magazine , Volume 67 , Issue 3 , June 2003 , pp. 547 - 554
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2003

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