| Autor: |
Tabuchi, Mitsuharu, Tatsumi, Kuniaki, Morimoto, Shotaro, Nasu, Saburo, Saito, Tadashi, Ikeda, Yasuhiro |
| Předmět: |
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| Zdroj: |
Journal of Applied Physics; Aug2008, Vol. 104 Issue 4, p043909, 10p, 1 Diagram, 5 Charts, 13 Graphs |
| Abstrakt: |
Origins of various valence states of various Fe ions above the 3+ state for 30% Fe-substituted Li2MnO3 [Li1+x(Fe0.3Mn0.7)1-xO2] with a layered rock-salt structure (R3m) have been investigated using magnetization measurement and 57Fe Mössbauer spectroscopy at less than 300 K. The temperature dependence of magnetization data revealed that small spontaneous magnetization [1.26(9) G cm3/g at 5 K] appeared at less than 81 K and cusps were observed at 24 K under both zero field and field cooling runs. Analyses of 57Fe Mössbauer spectra showed that all samples contained tetravalent (Fe4+) and pentavalent (Fe(5-δ)+) iron ions (20%–40%) along with trivalent ones. High-valence (Fe(5-δ)+) iron might be the result of Fe(3+δ)+/Fe(5-δ)+ charge disproportionation from tetravalent iron, as in SrMn0.5Fe0.5O3. Small paramagnetic iron doublets (2%–5%) with highly negative isomer shift values (-0.5 to -0.6 mm/s) were detected at less than 10 K. They might be pentavalent Fe(5+δ)+ ion. The Fe(5+δ)+ ion can be stabilized under high excess lithium content x (>0.28) according to the chemical formula Li1+x(Fe0.3Mn0.7)1-xO2 close to Li2MO3 composition and by suppressing 3d cation disordering to the Li layer. The unique valence state of Fe ions (>4+ state) might be stabilized in the Mn–Li layer of the Li2MnO3 structure. These results mean that Fe ions at 5+ states are stable ions in oxides not only in a perovskite-related structure but also in a rock-salt-related one. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
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