Low-pressure ferroelastic phase transition in rutile-type AX2 minerals: cassiterite, pyrolusite and sellaite

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Marco E. Ciriotti
Messaggi: 26364
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
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Low-pressure ferroelastic phase transition in rutile-type AX2 minerals: cassiterite, pyrolusite and sellaite

Messaggio da Marco E. Ciriotti » ven 01 nov, 2019 11:07

Prossima pubblicazione.

Referenza:
▪ Curetti, N., Merli, M., Capella, S., Benna, P., Pavese, A. (2019): Low-pressure ferroelastic phase transition in rutile-type AX2 minerals: cassiterite (SnO2), pyrolusite (MnO2) and sellaite (MgF2). Physics and Chemistry of Minerals, 46, (in press).

Abstract:
The structural behaviour of cassiterite (SnO2), pyrolusite (MnO2) and sellaite (MgF2), i.e. AX2-minerals, has been investigated at room temperature by in situ high-pressure single-crystal diffraction, up to 14 GPa, using a diamond anvil cell. Such minerals undergo a ferroelastic phase transition, from rutile-like structure (SG: P42/mnm) to CaCl2-like structure (SG: Pnnm), at ≈ 10.25, 4.05 and 4.80 GPa, respectively. The structural evolution under pressure has been described by the trends of some structure parameters that are other than zero in the region of the low-symmetry phase’s stability. In particular, three tilting-angles (ω, ω′, ABS) and the metric distortion of the cation-centred octahedron (quantified via the difference between apical-anion and equatorial-anion distances Δ|Xax−Xeq|) are used to express the atoms’ readjustment, i.e. relaxation, taking place in the CaCl2-like structures under pressure. The crystallographic investigation presented is complemented with an analysis of the energy involved in the phase transition using the Landau formalism and adopting the following definition for the order parameter: Q = η11–η22, ηij being the spontaneous strain tensor. The dependence of ω, ω′, ABS and Δ|Xax−Xeq| on Q allows determination of a correlation between geometrical deformation parameter and energy. Lastly, the relaxation mechanisms that exploits ω, ω′, ABS and Δ|Xax−Xeq| may be related to the ionic degree of bonding, the latter modelled via quantum mechanics and Bader theory. Sellaite, the mineral exhibiting the highest degree of ionic bonding among those investigated, tends to accomplish relaxation through pure rotation of the octahedron, rather than a metric distortion (Δ|Xax−Xeq|), which would shorten inter-atomic distances thus increasing repulsion between anions.
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

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Marco E. Ciriotti
Messaggi: 26364
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
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Re: Low-pressure ferroelastic phase transition in rutile-type AX2 minerals: cassiterite, pyrolusite and sellaite

Messaggio da Marco E. Ciriotti » sab 23 nov, 2019 12:38

Pubblicazione effettuata.

Referenza:
▪ Curetti, N., Merli, M., Capella, S., Benna, P., Pavese, A. (2019): Low-pressure ferroelastic phase transition in rutile-type AX2 minerals: cassiterite (SnO2), pyrolusite (MnO2) and sellaite (MgF2). Physics and Chemistry of Minerals, 46, 987–1002.
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

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