The distribution of transition metal cations in spinels
TL;DR: In this paper, the authors applied crystal field theory in conjunction with spectroscopic data to give quantitatively the d-shell splitting and the resulting stabilization of a transition metal ion in a crystal site of given symmetry.
About: This article is published in Journal of Physics and Chemistry of Solids.The article was published on 1957-01-01. It has received 423 citations till now. The article focuses on the topics: Crystal field theory & Tetragonal crystal system.
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TL;DR: In this paper, the effect of composition and surface and catalytic properties of Mg-Al mixed oxides was studied by combining several characterization methods with ethanol conversion reactions, and the nature, density, and strength of surface basic sites depended on the Al content.
1,029 citations
TL;DR: The co-operative Jahn-Teller effect is a phase transition which is driven by the interaction between localized orbital electronic states and the crystal lattice as mentioned in this paper, and the possible origins, symmetries and properties of the electron-lattice interactions and how they lead to possible hamiltonians for the coupled system are discussed.
Abstract: The co-operative Jahn-Teller effect is a phase transition which is driven by the interaction between localized orbital electronic states and the crystal lattice. The possible origins, symmetries and properties of the electron-lattice interactions and how they lead to possible hamiltonians for the coupled system are discussed. The relation of these interactions with quadrupolar interactions and magnetostriction is included. The methods of solution of the hamiltonians lead to an understanding of the electronic states, the phonon spectrum and the mixed normal modes. The wide variety of experimental techniques used on this problem are reviewed in detail and the results are compared with theoretical expressions whenever possible. The application of external stress and magnetic field is of particular significance in the case of the rare earth compounds, because they can product effects which are larger than the low-temperature spontaneous effects.
630 citations
Journal Article•
TL;DR: In this article, a set of cation radii optimized to best fit spinel lattice parameters is presented, where the size of a cation is important in determining its site preference.
Abstract: The size of a cation is important in determining its site preference. In oxide spinels containing 2 (super +) and 3+) ions (2-3 spinels) there is a tendency for the larger ion to prefer the tetrahedral site; the reverse holds for 2-4 spinels. A set of cation radii optimized to best fit spinel lattice parameters is presented.--Modified journal abstract.
575 citations
TL;DR: In this paper, the molar enthalpy of interchange of ions on tetrahedral sites with ions on octahedral sites was calculated from cation distribution data known at a single temperature for each spinel.
526 citations
Abstract: The polarized absorption spectra of Ni2+ and Co2+ in crystals of ZnO, ZnS, and CdS; Ni2+ in crystals of Cs2ZnCl4 and Cs2ZnBr4; and Cu2+ in ZnO have been measured at 4°K, 77°K, and room temperature. The spectra have been interpreted by the use of crystal field theory for the states of the (3d)n configuration acted on by a potential of predominately Td symmetry. Certain details of the spectra are accounted for by smaller contributions from fields of lower symmetry, notably a C3v potential contribution for the transition metal ions in ZnO. Crystal field, electrostatic repulsion, and spin‐orbit parameters have been obtained for all these cases. An empirical correlation between the electrostatic repulsion parameter, B, for the ions in the crystals and the ligand polarizibility has been obtained. Although the configuration mixing between the states of the configurations (3d)n and (3d)n—1 (4p) has been found to give a negligible contribution to the calculated relative energies of the levels, it does partially ex...
498 citations
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TL;DR: In this paper, a detailed x-ray study of a large number of oxides having a spinel structure was carried out, and it was established whether they crystallize in the ''normal'' spinel-type structure, XY2O4, or in the ``inversed'' type of structure, Y(XY)O4.
Abstract: By means of a detailed x‐ray study of a large number of oxides having a spinel structure, it has been established whether they crystallize in the ``normal'' spinel‐type structure, XY2O4, or in the ``inversed'' type of structure, Y(XY)O4, discovered by Barth and Posnjak. Certain rules can be derived which are also applicable to more complicated spinels or to solid solutions of different spinel oxides. Madelung constants have been calculated for different spinel types in order to investigate their stability on the basis of an ionic concept of the chemical bond (Born's lattice theory). The experimental results are only partially explainable on this basis. All exceptions to the electrostatic principles can be understood by assuming that Fe3+, Ga3+, In3+, Zn2+, and Cd2+ favor a configuration having the coordination number 4, because of a considerable covalent contribution to the chemical bond for that configuration.
732 citations
TL;DR: In this article, a new magnetic exchange mechanism was proposed to explain the magnetic properties of spinels, which is consistent with the covalent model of the spinels' magnetic properties.
Abstract: Elastic- and electrostatic-energy considerations are insufficient for an explanation of cation ordering between tetrahedral and octahedral sites in spinels. Tetrahedral, octahedral, and square covalent bonds are also important when cations are to be accommodated in these sites. The square bonds in octahedral sites can cause the tetragonal distortion observed in ${\mathrm{Mn}}_{3}$${\mathrm{O}}_{4}$ $\ensuremath{\gamma}$-${\mathrm{Mn}}_{2}$${\mathrm{O}}_{3}$, Zn${\mathrm{Mn}}_{2}$${\mathrm{O}}_{4}$, Cu${\mathrm{Fe}}_{2}$${\mathrm{O}}_{4}$, Cu${\mathrm{Cr}}_{2}$${\mathrm{O}}_{4}$, Ca${\mathrm{In}}_{2}$${\mathrm{O}}_{4}$, Cd${\mathrm{In}}_{2}$${\mathrm{O}}_{4}$, and metallic indium. A new magnetic exchange mechanism, "semicovalent exchange," which is consistent with the covalent model, is used to explain the magnetic properties of spinels.
534 citations
TL;DR: In this article, the electronic transitions observed in complexes of the transition-metal ions are interpreted in terms of a slightly modified crystal-field theory, and the parameters of chemical interest are derived.
Abstract: The electronic transitions observed in complexes of the transition‐metal ions are interpreted in terms of a slightly modified crystal‐field theory. Parameters of chemical interest are derived.
476 citations
TL;DR: In this paper, the absorption spectra of crystalline hydrates of the first transition group ions have been measured with polarized light at room temperature, and with unpolarized light at a series of lower temperatures.
Abstract: The absorption spectra of crystalline hydrates of the first transition group ions have been measured with polarized light at room temperature, and with unpolarized light at a series of lower temperatures. Some new data on solution spectra have also been obtained. The values of Dq for these compounds are obtained, and are used to explain irregularities in the heats of hydration of the ions. The temperature dependence of the spectra shows that the transitions are vibration‐induced electric‐dipole transitions for the most part. The dichroism has been used to resolve some of the bands and to determine the effect of noncubic components of the crystal field.
353 citations
TL;DR: In this article, a new method is described for obtaining sharp absorption spectra from suspensions of micro-organisms, which does not involve any treatment of the suspension or any change of the optical system of the spectrophotometer.
270 citations