Recent high-pressure and high-temperature experiments strongly imply the possibility of non-stoichiometry for Al, Fe
3+ containing MgSiO
3 perovskite and the related Al-phases. Therefore, the non-stoichiometric behavior of perovskites in the MgSiO
3-MgAlO
2.5 system and also in the multi-component system which are similar to natural mantle minerals and rocks was discussed by considering the trivalent cation substitution mechanism: 2
VI Si
4+ ⇔ 2
VI (Al
3+, Fe
3+) + V
O••. Since the behavior of Al coupled with iron in the MgSiO
3 perovskite is much more complicated because of the issue of
fO2 conditions, it is still under discussion. For dealing with the chemical behavior of Fe
3+ in the perovskite, the electron energy-loss spectroscopy (EELS) in transmission electron microscopy (TEM) is becoming a powerful tool by which we can determine the Fe
3+ / ΣFe ratio of coexisting phases separately on a nanometer order of resolution. It is expected that the EELS method combined with TEM techniques will be very useful to characterize synthetic high-pressure mantle minerals.
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