It is widely recognized that one of the reasons for the lack of understanding of these systems is that several degrees of freedom are intimately interconnected and that the identification of the leading interaction is a challenging task, a typical example being the interplay between orbital ordering (OO) and cooperative Jahn-Teller distortion (cJTd).
The insertion of Mg into the crystal lattice and the relaxation of the position of fluorine atoms have no relevant effects onto the population of the d orbitals of copper, suggesting that (i) the perturbation due to Mg doping is extremely localized, (ii) slight modifications of the Jahn-Teller distortion around Cu have little effect on the orbital ordering, and therefore (iii) the Jahn-Teller distortion and the orbital ordering have different energy scales.
EPR and XAFS show Jahn-Teller distortion around copper in the complex.
The copper complex also shows a Jahn-Teller distortion. XAFS analysis was done on the copper complex and XAFS confirmed the above stated results obtained by other techniques.
Therefore Cu and Zn are mutually replaceable and are surrounded by oxygen molecules in the oxide form, since [Cu.sup.2+], being a [d.sup.9] system, is prone to Jahn-Teller distortion. Hence a EPR study of these ions will provide information about the type of distortion and nature of bonding between metal and ligand.
(3) EPR results suggest that the nano CuZn[O.sub.2] compound Cu(II) ion has undergone Jahn-Teller distortion and is in the tetragonal elongated symmetrical environment which is further supporting the XRD results.
This severe capacity fading is mainly due to the Jahn-Teller distortion on the surface of spinel Li[Mn.sub.2][O.sub.4] , the dissolution of manganese in the electrolyte solution [5, 6], the spinel Li[Mn.sub.2][O.sub.4] with oxygen deficiency , and the decomposition of electrolyte solution on the electrode [8, 9].
Moreover, spinel [Li.sub.1.02][Mn.sub.1.92][Al.sub.0.02][Fe.sub.0.02][Cr.sub.0.02][O.sub.3.92][F.sub.0.08] shows better cycle performance and a slightly higher capacity than the spinel [Li.sub.1.02][Mn.sub.1.92][Al.sub.0.02][Fe.sub.0.02][Cr.sub.0.02][O.sup.4] because the substitution of Mn by Cr, Fe, Al, and Li decreases the unit cell volume and the decrease of [Mn.sup.3+] concentration reduces the Jahn-Teller distortion and also stabilizes the structure integrity of the active.
When these are doped with divalent ion, their resistivity decreases with formation of [Mn.sub.+4], which decreases the Jahn-Teller distortion
, creates double exchange interactions, and hence plays a crucial role in the electrical transport and magnetic properties of these oxides .
The differences in the Ni-N and Cu-N bond lengths could be attributed to Jahn-Teller distortions for the [(e).sup.4][([t.sub.2]).sup.4] and [(e).sup.4][([t.sub.2]).sup.5] electronic configurations in the respective Ni-1MeIm and Cu-1MeIm complexes .
These differences in the energy support the Jahn-Teller distortions observed in Table 1 as a result of unequal occupancy of the [t.sub.2] orbitals in a tetrahedral field.