Title
Mössbauer study of synthetic <tex>$Mg_{0.22}Fe_{0.78}SiO_{3}$</tex> clinopyroxene
Author
Faculty/Department
Faculty of Sciences. Chemistry
Publication type
article
Publication
Wien ,
Subject
Physics
Chemistry
Biology
Source (journal)
Mineralogy and petrology. - Wien
Volume/pages
73(2001) :4 , p. 235-245
ISSN
0930-0708
ISI
000173021200001
Carrier
E
Target language
English (eng)
Full text (Publishers DOI)
Affiliation
University of Antwerp
Abstract
Transmission Mossbauer spectra of synthetic Ca-free P2(1)/c Mg0.22Fe0.78SiO3 clinopyroxene were collected at temperatures in the range 4.2 to 745 K and in an external magnetic field of 60 kOe at 180 K. The magnetic order-disorder transition temperature was determined by Mossbauer thermoscanning to be 21 +/- 3 K. Above this temperature, all Mossbauer spectra consist of a superposition of two doublets, respectively produced by Fe2+ ions at an almost regular octahedral M I site and at a more distorted octahedral M2 site. The temperature variation of the Fe2+ center shifts were analyzed using the Debye model for the lattice vibrations. The characteristic Mossbauer temperatures were found to be 356 K +/- 35 K for M1 and 333 K +/- 25 K for M2. From the external field (60 kOe) Mossbauer spectrum recorded at 180 K, the principal component V-zz of the electric field gradient (EFG) was determined to be positive for both sites but precise values for the magnitudes of the asymmetry parameters eta of the EFG could not be determined. The temperature variations of the M1 and M2 quadrupole splittings DeltaE(Q)(T) are consistent with the higher distortion of the M2 octahedra. Using the crystal-field model to interpret DeltaE(Q)(T), the energy gaps delta (1) and delta (2) of the first excited electronic states within the D-5 orbital term were estimated to be 410 +/- 50 cm(-1) and 730 +/- 50 cm(-1) for M1 and delta (1) = 1050 +/- 75 cm(-1) for M2.
E-info
https://repository.uantwerpen.be/docman/iruaauth/079ab3/68d6786.pdf
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