Aluminum diffusion and Al-vacancy association in periclase

Orman, James A. Van; Li, Chen; Crispin, K. L.

doi:10.1016/j.pepi.2008.03.008

Cited by 30 publications

(38 citation statements)

References 25 publications

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“…Our calculated binding energy at 4 GPa is in good agreement with previous theoretical studies at 0 GPa which found binding energies of 0.88eV (Colbourne and Mackrodt 1982), 1.01eV (Carroll et al 1988), 0.86 eV . Clearly, they are all much higher than the experimental value of 0.5 eV (Van Orman et al 2009)-which is surprising considering the general good agreement of DFT (and even pair-potentials) with defect and diffusion parameters in minerals.…”

Section: Al-v Mg Dimersmentioning

confidence: 72%

“…Following previous workers (Lidiard 1955;Perkins and Rapp 1973;Van Orman et al 2009), the aluminium diffusion as a function of the aluminium concentration, C Al , depends on the dimer diffusivity, D 2 , and the derivative of the dimer-concentration, p 2 , with respect to the aluminium concentration:…”

Section: Aluminium Diffusion In Periclasementioning

confidence: 79%

“…Although the results of the different studies are broadly similar, there are some important differences. Firstly, the experiments on aluminium diffusion at ambient pressure (Van Orman et al 2009) found a lower binding enthalpy of 0.5 eV for the binding between an aluminium and a magnesium vacancy (we will call this structure dimer) than predicted from theory (Gourdin and Kingery 1979) (0.88 eV). Secondly, the experimental migration enthalpy of 2.1 eV is again lower than the one predicted by theory of 2.5 eV .…”

Section: Introductionmentioning

confidence: 91%

“…Using a 4 9 4 9 4-supercell, we find that binding energies in the dilute limit and those calculated within the supercell are very similar (see Table 3). We therefore use the dilute limit binding energies to calculate the relative number of dimers, trimers and free vacancies as a function of aluminium concentration, temperature and pressure (we assume that the entropy contribution to the Gibbs free energy of binding is small (Van Orman et al 2009). To this end, we solve the two mass-action laws for dimers (T 2 = AlV Mg ) and trimers (T 3 = AlV Mg Al) where G 2 and G 23 are the Gibbs free energies of binding between an aluminium and a magnesium vacancy, and between a dimer and an aluminium, respectively:…”

Section: Al-v Mg -Al Trimersmentioning

confidence: 99%

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Diffusion of aluminium in MgO from first principles

Ammann¹,

Brodholt²,

Dobson³

2012

Phys Chem Minerals

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We have calculated the diffusivity of aluminium in periclase, MgO, under pressures relevant to deep planetary interiors from first principles. We reconcile differences between experimental migration enthalpies and those obtained with previous theoretical studies by finding a lower energy saddle point for the aluminium atom migration. Previous studies did not recognise a bifurcation at the saddle point. We also explain differences between experimental and theoretical binding enthalpies of an aluminium with a magnesium vacancy. We find that binding enthalpies continuously increase with decreasing aluminium concentrations, such that the difference between experimental and theoretical binding energies can be attributed to differing concentrations. We also find that binding energies increase with pressure as the permittivity decreases. Aluminium therefore not only causes extrinsic vacancy formation but also binds some of them, effectively removing them for magnesium diffusion. We discuss the implications for how other 3? ions affect diffusion in oxides and silicates.

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Section: Al-v Mg Dimersmentioning

confidence: 72%

Section: Aluminium Diffusion In Periclasementioning

confidence: 79%

Section: Introductionmentioning

confidence: 91%

Section: Al-v Mg -Al Trimersmentioning

confidence: 99%

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Diffusion of aluminium in MgO from first principles

Ammann¹,

Brodholt²,

Dobson³

2012

Phys Chem Minerals

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“…Demouchy et al (2007) and Mackwell et al (2005) discussed the role of ferric iron in combination with vacancy occurrence (at hydrous-ambient-pressure conditions), whereas Bolfan-Casanova et al (2006) observed that at high pressure, Fe anti-correlates with hydroxyl formation. In particular, Fe-periclase and perovskite can host heterovalent cations through coupled substitutions as well as the creation of point defects (Van Orman et al, 2009) over a wide P-T range. Fe 3+ dwelling in (Mg, Fe)O (i.e.…”

Section: Introductionmentioning

confidence: 99%

Lower mantle hydrogen partitioning between periclase and perovskite: A quantum chemical modelling

Merli

Bonadiman

Diella

et al. 2016

Geochimica et Cosmochimica Acta

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Effects of the Electronic Spin Transitions of Iron in Lower Mantle Minerals: Implications for Deep Mantle Geophysics and Geochemistry

Lin

Speziale

Mao

et al. 2013

Reviews of Geophysics

222

194

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[1] We have critically reviewed and discussed currently available information regarding the spin and valence states of iron in lower mantle minerals and the associated effects of the spin transitions on physical, chemical, and transport properties of the deep Earth. A high-spin to low-spin crossover of Fe 2+ in ferropericlase has been observed to occur at pressure-temperature conditions corresponding to the middle part of the lower mantle. In contrast, recent studies consistently show that Fe 2+ predominantly exhibits extremely high quadrupole splitting values in the pseudo-dodecahedral site (A site) of perovskite and post-perovskite, indicative of a strong lattice distortion. Fe 3+ in the A site of these structures likely remains in the high-spin state, while a high-spin to low-spin transition of Fe 3+ in the octahedral site of perovskite occurs at pressures of 15-50 GPa. In post-perovskite, the octahedral-site Fe 3+ remains in the low-spin state at the pressure conditions of the lowermost mantle. These changes in the spin and valence states of iron as a function of pressure and temperature have been reported to affect physical, chemical, rheological, and transport properties of the lower mantle minerals. The spin crossover of Fe 2+ in ferropericlase has been documented to affect these properties and is discussed in depth here, whereas the effects of the spin transition of iron in perovskite and post-perovskite are much more complex and remain debated. The consequences of the transitions are evaluated in terms of their implications to deep Earth geophysics, geochemistry, and geodynamics including elasticity, element partitioning, fractionation and diffusion, and rheological and transport properties.Citation: Lin, J.-F., S. Speziale, Z. Mao, and H. Marquardt (2013), Effects of the electronic spin transitions of iron in lower mantle minerals: Implications for deep mantle geophysics and geochemistry, Rev. Geophys., 51, 244-275,

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Aluminum diffusion and Al-vacancy association in periclase

Cited by 30 publications

References 25 publications

Diffusion of aluminium in MgO from first principles

Diffusion of aluminium in MgO from first principles

Lower mantle hydrogen partitioning between periclase and perovskite: A quantum chemical modelling

Effects of the Electronic Spin Transitions of Iron in Lower Mantle Minerals: Implications for Deep Mantle Geophysics and Geochemistry

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