Valence delocalization Mossbauer spectroscopy

One consequence of thermally activated electron delocalization behaviour is that techniques such as Mossbauer spectroscopy, which might be expected to distinguish between discrete Fe2+ and Fe3+ valences, instead often detect Fe cations in intermediate oxidation states. Such cation species originate when... 

Opacity of mixed-valence minerals. The opacities of many end-member Fe2+-Fe3+ oxide and silicate minerals result from electron hopping between neighbouring cations when they are located in infinite chains or bands of edge-shared octahedra in the crystal structures. Opaque minerals such as magnetite, ilvaite, deerite, cronstedtite, riebeckite and laihunite owe their relatively high electrical conductivities to thermally activated electron delocalization, contributing to intermediate valence states of iron cations which may be detected by Mossbauer spectroscopy. 

Mixed-valency and thermally induced transition between localized and delocalized valence states was observed with Eu Mossbauer spectroscopy of the interme-tallic compound EuNiP [70] (Fig. 2.39). 

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