Jahn—Teller site distortions

The 1-V step in the voltage profile of LF[Mn2]04 limits the capacity of this spinel to one LF per two Mn atoms at either 3.0 V or 4.0 V versus Lithium. The flat 3.0 V plateau reflects a cubic to tetragonal transition of the [Mn2]04 framework due to a cooperative Jahn-Teller site distortion where more than half of the 16 sites are occupied by Mn(III) ions. Octahedral-site, high-spin Mn(III) ions have a localized spin 5 = 2 with one electron occupying an orbitally twofold-degenerate pair of... 

In the present study, we focus on the effects of substituting one of the protons by a deuteron. While giving only one isomer of the unionized molecule, this produces two inequivalent isomers of the Jahn-Teller distorted ion one isomer where the deuteron occupies one of the two sites on the C2 symmetry axes (Hj or H4) and one where it occupies one of the four equivalent remaining sites (H2, H3, H5 or H6). The effects on the ESR spectrum will below be illuminated both theoretically and experimentally. 

An EXAFS study of 3-NiO(OH) indicates that the Ni sites experience Jahn-Teller distortion, with four Ni—O bonds at 1.87 A and two at 2.03 A in the //-phase containing Nim and Ni this is absent.179... 

One study (DeLeo et al., 1988 Fowler et al., 1989) has found that neutral H at the B site in Si has a tendency to preferentially bind to one of the two Si neighbors, leading to an asymmetric configuration, with Si—H distances of 1.48 A and 1.77 A respectively. This tendency was interpreted in terms of a pseudo-Jahn-Teller distortion. However, the potential barrier that leads to the asymmetric position is so low (< 0.2 eV) that it can readily be surmounted by zero-point motion of the proton. Experimental observation of such an asymmetry is therefore unlikely, except maybe through an isotope shift measurement in an infrared experiment (DeLeo et al., 1988). None of the other theoretical approaches has produced this type of asymmetry. 

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