http://www.cnr.it/ontology/cnr/individuo/prodotto/ID292850
Modelling of thermo-chemical properties over the sub-solidus MgO-FeO binary, as a function of iron spin configuration, composition and temperature (Articolo in rivista)
- Type
- Label
- Modelling of thermo-chemical properties over the sub-solidus MgO-FeO binary, as a function of iron spin configuration, composition and temperature (Articolo in rivista) (literal)
- Anno
- 2014-01-01T00:00:00+01:00 (literal)
- Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#doi
- 10.1007/s00269-014-0725-6 (literal)
- Alternative label
Merli M.; Sciascia L.; Pavese A.; Diella V. (2014)
Modelling of thermo-chemical properties over the sub-solidus MgO-FeO binary, as a function of iron spin configuration, composition and temperature
in Physics and chemistry of minerals
(literal)
- Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#autori
- Merli M.; Sciascia L.; Pavese A.; Diella V. (literal)
- Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#url
- http://www.scopus.com/inward/record.url?eid=2-s2.0-84916624989&partnerID=q2rCbXpz (literal)
- Rivista
- Note
- Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#affiliazioni
- Dipartimento di Chimica e Fisica della Terra e Applicazioni alle Georisorse e ai Rischi Naturali, Università degli Studi di Palermo, Via Archirafi 36, Palermo, 90123, Italy; Dipartimento Scienze della Terra \"A. Desio\", Università degli Studi di Milano, Via Botticelli 23, Milan, 20133, Italy; National Reseach Council (CNR), IDPA, Section of Milan, Via Botticelli 23, Milan, 20133, Italy (literal)
- Titolo
- Modelling of thermo-chemical properties over the sub-solidus MgO-FeO binary, as a function of iron spin configuration, composition and temperature (literal)
- Abstract
- Thermo-chemical properties and T-X phase
relations diagram of the (Mg,Fe)O solid solution are modelled
using mixing Helmholtz energy, F(T,x)mixing,
calculated by quantum mechanical and semi-empirical
techniques. The sub-solidus MgO-FeO binary has been
explored as a function of composition, with iron either in
high-spin (HS) or low-spin (LS) configuration. Only the
HS model provides physically sound results at room pressure,
yielding a correct trend of cell edge versus composition,
whereas LS's issues are at variance with observations.
Mixing Helmholtz energy has been parametrized by the
following relationship: F(T,x)mixing = x × y × [U0(T) +
U1(T) × (x - y) + U2(T) × (x - y)2]-T × S(x,y)config,
where y = 1-x and Uj(T) are polynomials in T of the second
order. F(T,x)mixing exhibits a quasi-symmetric behaviour
and allows one to build the T-X phase relations diagram
over the MgO-FeO join. The HS model including vibrational contribution to the Helmholtz energy predicts a
solid solution's critical temperature of some 950 K, remarkably
larger than olivine's and Mg-Fe garnet's. All this
points to a more difficult Mg-Fe mixing in periclase-like
structure than olivine and garnet, which, in turn, provide
more structure degrees of freedom for atomic relaxation.
From F(T,x)mixing, we have then derived H(T,x)excess and
S(T,x)excess. The former, characterized by a quasi-regular
behaviour, has been parametrized through W × x × (1-x),
obtaining WH,Mg-Fe of 17.7(5) kJ/mol. S(T,x)excess, in turn,
increases as a function of temperature, showing absolute figures
confined within 0.1 J/mol/K. Mixing Gibbs energy, calculated
combining the present issues with earlier theoretical
determinations of the magnesio-wüstite's elastic properties,
has shown that the HS configuration is stable and promote
Mg-Fe solid solution up to ?15 GPa. (literal)
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