Tetrahedral 8a Sites Research Articles

Insertion/extraction reactions of lithium with LiV 2O 4

Lithium has been inserted into, and extracted from, the spinel Li ∼1.0V 2O 4 both electrochemically and chemically. Electrochemical and structural data show that in the system Li 1+xV 2O 4, for 0 < x ≤ 0.5, Li + ions are inserted into the interstitial octahedral sites of the A tet[B 2] octX 4 spinel structure. At x ≈ 0.5, Li + ions in the tetrahedral A-sites are displaced into the remaining octahedral sites to yield, at x = 1, a rocksalt phase Li 2V 2O 4; the [B 2]X 4 framework is unperturbed by the lithiation process. This framework also remains intact when Li + ions are removed from Li ∼1.0V 2O 4 to a composition Li 0.67V 2O 4. Further extraction of lithium from the structure is accompanied by migration of some vanadium ions from the B-sites to the interstitial octahedral sites of the spinel structure. This process reduces the crystal symmetry from cubic to trigonal symmetry. In Li 0.27V 2O 4 the structure resembles that of Li 0.22VO 2, obtained by delithiation of layered LiVO 2, in which the vanadium cations are distributed in a 2:1 ratio between alternate cubic-close-packed oxygen layers; in the LiV 2O 4 spinel this ratio is 3:1.

Ratio of exchange integrals in connection with angles between partial magnetizations in ferrimagnetic spinels

Synopsis Allowing the spin direction of magnetic ions in one sublattice of (octahedral) B-sites to differ from that in the other sublattice of B-sites (as assumed by Yafet and Kittel for a spinel with only one kind of magnetic ions) a mixed crystal spinel containing two kinds of magnetic ions is considered, taking into account the different physical nature of the ions. Here a situation may be realized where the partial magnetizations are neither parallel nor antiparallel but where in one sublattice (say BinI) two special spin directions occur for the two kinds of magnetic ions and in the other (BinII) another couple of spin directions lying with the former set symmetrical with respect to the single spin direction of ions on the (tetrahedral) A-sites. The A-A interaction is neglected and consequently a subdivision of the A-lattice is not taken into account. Compositions of the mixed crystal are possible where such a non-rectilinear case is just possible, i.e. where the mutual deviations of the spin directions on the B-sites are very small, their angles with the spin direction on A-sites being nearly π. From three of such compositions the ratios of exchange integrals can be determined.