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The Spinel Structure

Their great abundance points to a very stable crystal structure. Spinels are predominantly ionic. The particular sites occupied by cations are, however, influenced by several other factors, including covalent bonding effects (e.g., Zn in tetrahedral sites) and crystal field stabilisation energies of transition-metal cations. [Pg.3]

Many different cation combinations may form a spinel structure it is almost enough to combine any three cations with a total charge of eight to balance the charge of the anions. The limits of the cation radii are approximately 0.4-0.9 A (based on the oxide ion radius, Ro, of 1.4 A). The following combinations are known  [Pg.3]

The most important spinels from the magnetic point of view are the oxides 2,3. Some of the sulphides also have interesting magnetic properties [Pg.3]

The spinel structure was first determined by Bragg (1915) and Nishikawa (1915). The ideal structure is formed by a cubic close-packed (fee) array of O atoms, in which one-eighth of the tetrahedral and one-half of the octahedral interstitial sites are occupied by cations. The tetrahedrally coordinated sites and the octahedrally coordinated sites are referred to as the A and B sites, respectively. [Pg.4]

The ideal situation is almost never realised, and the u value for the vast majority of the known spinels ranges between 0.375 and 0.385. u increases because the anions in tetrahedral sites are forced to move in the [111] direction to give space to the A cations, which are almost always larger than the ideal space allowed by the close-packed oxygen, but without changing the overall 43m symmetry. Octahedra become smaller and assume 3m symmetry. In Table 2.1, interatomic distances are given as a function of the unit cell parameter a and the u parameter. [Pg.4]

Li2MCl4 compounds undergo a phase transition to a disordered cation-deficient rocksalt-structured form (space group Fm3m), in which the two cation species are randomly distributed over all the oct sites, which then have an average occupancy of 4 [132, 133]. [Pg.32]


Titanium IV) oxide, T1O2. See titanium dioxide. Dissolves in concentrated alkali hydroxides to give titanates. Mixed metal oxides, many of commercial importance, are formed by TiOj. CaTiOj is perovskite. BaTiOa, per-ovskite related structure, is piezoelectric and is used in transducers in ultrasonic apparatus and gramophone pickups and also as a polishing compound. Other mixed oxides have the il-menite structure (e.g. FeTiOj) and the spinel structure (e.g. MgjTiO ). [Pg.400]

Zirconates and hafnates can be prepared by firing appropriate mixtures of oxides, carbonates or nitrates. None of them are known to contain discrete [M04]" or [MOs] ions. Compounds M ZrOs usually have the perovskite structure whereas M2Zr04 frequently adopt the spinel structure. [Pg.964]

Although Fc304 is an inverse spinel it will be recalled that Mn304 (pp. 1048-9) is normal. This contrast can be explained on the basis of crystal field stabilization. Manganese(II) and Fe" are both d ions and, when high-spin, have zero CFSE whether octahedral or tetrahedral. On the other hand, Mn" is a d and Fe" a d ion, both of which have greater CFSEs in the octahedral rather than the tetrahedral case. The preference of Mn" for the octahedral sites therefore favours the spinel structure, whereas the preference of Fe" for these octahedral sites favours the inverse structure. [Pg.1080]

By contrast, lithium extraction from the tetrahedral sites in Li[Mn2]04, i.e., for 0cubic symmetry of the spinel structure [105, 114, 120]. It is difficult to extract all the lithium electrochemi-cally from Li[Mn2]04, at least at practical voltages, without causing decomposi-... [Pg.310]

It is possible that all three phenomena contribute to the capacity loss of 4V Lix[Mn2]04 electrodes. Nonetheless, all three can be at least partly circumvented by slightly modifying the composition of the spinel electrode. For example, cell performance can be improved by increasing the amount of lithium in the spinel structure [107, 123, 130] and, in particular, by substituting a small amount of manganese on the B sites with lithium [107], which drives the composition a small way down the stoichiometric spinel tie-line, towards... [Pg.311]

Although Li[Ti2]04 and Li4Ti,Ol2 have low theoretical capacities (161 and 175 mAhg-1, respectively), they have excellent structural properties for an insertion electrode. The spinel structures are excep-... [Pg.316]

Structure types have been established. Similar to Al, the M2X3 crystals (M = Ga, In, Tl X = S, Se, Te) are mostly based on M-defect tetrahedral structures, namely W (Ga2S3, In2Se3) and ZB (Ga2Se3, Ga2Te3, In2Te3). At atmospheric pressure, 283 can be present in three modifications. The low-temperature a-form is a cubic close-packed structure of S atoms, where 70% of the In atoms are randomly distributed on octahedral sites and the rest remain on tetrahedral sites. The P-form is related to the spinel structure, and the y-modification is hexagonal. [Pg.49]

The spinel structure (one unit cell). The Mg2+ ions are located in the centers of the tetrahedra (stereo image)... [Pg.210]

Nearly no eddy current losses occur in electrically insulating magnetic materials. This is one of the reasons for the importance of oxidic materials, especially of spinels and garnets. Another reason is the large variability of the magnetic properties that can be achieved with spinels and garnets of different compositions. The tolerance of the spinel structure to substitution at the metal atom sites and the interplay between normal and inverse spinels allow the adaptation of the properties to given requirements. [Pg.238]

The long-known K2Hg(CN)4 and related compounds are still the object of structural studies. Thus, a neutron-diffraction study confirmed the spinel structure of K2Hg(CN)4 at room temperature (298 K) with exactly tetrahedral anions, Hg(CN)42 (r(Hg—C) 215.2, r(C—N) 114.9 pm).112... [Pg.1260]

Spinels have a crystal structure in which there is a face-centered cubic arrangement of O2 ions. There are two types of structures in which cations have octahedral or tetrahedral arrangements of anions surrounding them. In the spinel structure, it is found that the +3 ions are located in octahedral holes and the tetrahedral holes are occupied by the +2 ions. A different structure is possible for these ions. That structure has half of the +3 metal ions located in the tetrahedral holes while the other half of these ions and the +2 ions are located in the octahedral holes. In order to indicate the population of the two types of lattice sites, the formula for the compound is grouped with the tetrahedral hole population indicated first (the position normally occupied by the +2 ion, A) followed by the groups populating the octahedral holes. Thus, the formula AB204 becomes B(AB)04 in order to correctly... [Pg.228]

Fayalite (melting point 1205°C) and forsterite (melting point 1890°C) form continuous solid solutions (the melting diagram of their binary mixtures correspond to the type exemplified in Fig. 2.28). Phase equilibria as a function of pressure, show, however, transition into the spinel structure. (cF56-MgAl204, spinel structural type). [Pg.747]

The beta-alumina structures show a strong resemblance to the spinel structure. They are layered structures in which densely packed blocks with spinel-like structure alternate with open conduction planes containing the mobile Na ions. The and /S" structures differ in the detailed stacking arrangement of the spinel blocks and conduction planes. Fig. 2.9. [Pg.26]

Although X-Ray powder diffraction does confirm the spinel structure of these compounds, it is impossible to evaluate with this technique the Li content neither to confirm the Li existence in the structure. [Pg.179]

In order to estimate the presence of the atomic density of light Li atoms into the spinel structure it is necessary of first of all to estimate the effect of the cut off the Fourier- series on the view of the required (110) projections. It is necessary to do this because the projection of the potential on some plane can be influenced due to the limited amount of the reflections which forms the projection. In fig. 6 the theoretical projection has been calculated for enlarged set Fhki (up to sin G/k 1.6 A ) below. All atoms can be distinguished and are shown by the arrows. The heights of Li-atoms are small but are seen on the projection. [Pg.180]

The spectra of the doped materials (Cr, Ni, Zn +, Li+, Co +, AP+) are similar to those seen for the nominally stoichiometric materials, and sets of resonances between 500 and 700 ppm are seen on cation doping in addition to that of the normal spinel environment (at ca. 500 ppm). Again, these resonances are assigned to lithium ions near manganese-(IV) cations. The lower intensity of the additional resonances seen on Cr + substitution, in comparison to Zn + or Ni + substitution, is consistent with the oxidation of fewer manganese ions near the depart ions. For the Li- and Zn-doped spinels, resonances at ca. 2300 ppm were also observed, which are assigned to lithium ions in the octahedral sites of the spinel structure. In the case of Zn doping, it is clear that the preference of Zn + for the tetrahedral site of the spinel structure forces the lithium onto the octahedral site. [Pg.264]


See other pages where The Spinel Structure is mentioned: [Pg.98]    [Pg.223]    [Pg.247]    [Pg.250]    [Pg.282]    [Pg.183]    [Pg.1049]    [Pg.1118]    [Pg.25]    [Pg.26]    [Pg.308]    [Pg.308]    [Pg.310]    [Pg.800]    [Pg.34]    [Pg.225]    [Pg.226]    [Pg.210]    [Pg.1260]    [Pg.223]    [Pg.15]    [Pg.42]    [Pg.150]    [Pg.405]    [Pg.258]    [Pg.747]    [Pg.219]    [Pg.43]    [Pg.45]    [Pg.46]    [Pg.108]    [Pg.256]    [Pg.258]    [Pg.260]    [Pg.263]   


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Framework Structures The Family of Spinel Compounds

Spinels

Studies of Superconducting Oxides with the Spinel Structure

The normal and inverse spinel structures

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