After fitting Mossbauer spectra for Fe(II)-silicate heated at air to 700degC, I observed uncommon, very high quadrupole splitting parameters for Fe3+, I suspect in very disordered environment (?). When for minerals (silicates) so very high QS : ~2.16 mm/s for Fe3+ can be observed (IS = 0.5 mm/s) ?? What structural constraints could this influence?
Sorry I am not expertise in it but you can contact some PhD candidate who is doing research analysis on this domain.
What silicate are you studying?
It may be that the article to follow collaborates in your investigation:
EFFECTS OF THE ELECTRONIC SPIN TRANSITIONS OF IRON IN LOWER MANTLE MINERALS: IMPLICATIONS FOR DEEP MANTLE GEOPHYSICS AND GEOCHEMISTRY Jung-Fu Lin,1 Sergio Speziale,2 Zhu Mao,1 and Hauke Marquardt2
Dear Carlos,
Thank you for the article. Indeed, I found there information about so high QS for Fe3+ for silicate perovskite and a high-spin to low-spin transition, I haven’t considered low-spin Fe in minerals…but it treats about high-pressure conditions and spin transition results are pressure-induced. I study minnesotaite - close to ferrous talc, but with modulated structure, it was just heated in air, these weird Moss parameters I obtained after heating at 700degC. I am not sure if my results are comparable with the pressure-induced.
Dear Malgorzata,
Coey also report an investigation in samples of minnesotaite -
"Mossbauer spectra of five samples of minnesotaite and one of ferroan talc have been recorded at 296 K and 4.2 K. A single ferrous doublet with isomer shift δ = 1.13 mm/s relative to αFe and quadrupole splitting Δ = 2.74 mm/s is observed in all minnesotaite samples at room temperature. The ferroan talc has a smaller quadrupole splitting, Δ = 2.55 mm/s". .. Mossbauer spectra of minnesotaite and ferroan talc. January 1991, Michael CoeyMichael Coey
Mossbauer effect measurements at low temperatures and X-ray diffraction tests on their samples can also help.
Carlos
Thank you Carlos for your help. I know this work and most of works related to Mossbauer of minnesotaite (there are only few) and also heated minnesotaite (Eg. Mackenzie et al 1986), but my question is not about Fe2+ in natural minnesotaite (that Coey et al described), but about Fe3+ with high QS in heated minnesotaite that transformed to oxidized ferric form. I measured Moss spectra at 300 and 80K, still there are two fraction of Fe3+ with IS=0.5 and QS=2.16 and second with smaller QS. I also performed XRD for heated sample - there is only ferric minnesotaite with slightly changed cell parameters. It is very interesting and intriguing.
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