Effect of non-hydrostatic conditions on the elastic behaviour of magnetite: An in-situ single-crystal X-ray diffraction study
Articolo
Data di Pubblicazione:
2007
Citazione:
Effect of non-hydrostatic conditions on the elastic behaviour of magnetite: An in-situ single-crystal X-ray diffraction study / G.D. Gatta, I. Kantor, T. Boffa Ballaran, L. Dubrovinsky, C. McCammon. - In: PHYSICS AND CHEMISTRY OF MINERALS. - ISSN 0342-1791. - 34:9(2007), pp. 627-635.
Abstract:
The high-pressure elastic behaviour and the
pressure-induced structural evolution of synthetic magnetite
were investigated up to 11.11(5) GPa by means of
in situ single-crystal X-ray diffraction with a diamond anvil
cell, using the mix methanol:ethanol:water = 16:3:1 as
pressure-transmitting medium and the ruby-fluorescence
method for pressure-calibration. The evolution of the ruby
R1-fluorescence line with P, with a drastic increase of the
full-width-at-half-maximum (FWHM) of the Lorentzian
profile at P > 9 GPa, shows that the P-medium is not
hydrostatic above 9 GPa. Such a condition is well reflected
by the drastic increase (by 20–22%) of the FWHM of the
diffraction peak profiles of magnetite, by the behaviour of
the Eulerian finite strain versus normalized pressures plot
(fe–Fe plot) and by the slight EoS-misfit. However, the
diffraction data collected during decompression showed a
reversible/complete restoration of the diffraction profiles
and of the elastic behaviour in the fe–Fe plot. The reflection
conditions dictated by the Fd 3m space group confirm that
symmetry of magnetite is maintained within the P-range
investigated. The structural refinements performed at
0.0001, 4.99(3) and 9.21(8) GPa show that the evolution of
the oxygen u-parameter is almost constant within the
P-range investigated. A weighted linear regression through
the data points gives only a slight negative slope and no
discontinuity is observed within the P-range investigated.
A similar continuous behaviour is also observed in the
evolution of the T- and M-polyhedral volumes, bond distances
and angles with P. On the basis of data reported in
this study, it appears that the elastic behaviour and the
structural evolution of magnetite is drastically influenced
by the experimental conditions (i.e., hydrostatic or nonhydrostatic),
and diffraction data of magnetite collected
under non-hydrostatic conditions are unusable for a reliable
description of the elastic behaviour and for the P-induced
structural rearrangements. Comparisons are carried out
between the experimental findings of this study and those
reported in the previous ones, in which an inverse-to-direct
spinel phase transition at P > 8 GPa is suggested.
Tipologia IRIS:
01 - Articolo su periodico
Keywords:
magnetite ; high-pressure ; hard-materials
Elenco autori:
G.D. Gatta, I. Kantor, T. Boffa Ballaran, L. Dubrovinsky, C. McCammon
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