Theoretical study of the defect distribution of trivalent cation impurities in MgO

Carroll, J.; Corish, J.; Henderson, B.; Mackrodt, W. C.

doi:10.1007/bf00547457

Cited by 19 publications

(15 citation statements)

References 29 publications

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“…All corrections give the same value if one extrapolates the corrected values by Lany and Zunger (2009) or Leslie and Gillan (1985) by fitting a linear function (µ1/L). 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 Dimerssupporting

confidence: 93%

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 Dimerssupporting

confidence: 93%

Diffusion of aluminium in MgO from first principles

Ammann¹,

Brodholt²,

Dobson³

2012

Phys Chem Minerals

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“…Synthetic diffusion profiles based on Equation (5) with the appropriate boundary conditions were found to provide a good description of the experimental diffusion profiles at all conditions, from 1577-2273 K and 1 atm to 25 GPa. The average binding energy of the Al-vacancy pair derived from fitting the experimental diffusion profiles, −50 kJ/mol, is in good agreement with the temperaturecorrected theoretical values derived from shell model calculations (Gourdin and Kingery 1979;Carroll et al 1988). The activation energy and activation volume for diffusion of the (V Mg Al Mg )′ pair were found to be similar to those for Mg self-diffusion.…”

Section: Group Iiia and Iiib Trivalent Cationssupporting

confidence: 80%

“…Cation vacancies also may bind to positively charged trivalent cations to form either negatively charged pairs, neutral dimers consisting of two trivalent ions and a vacancy on adjacent cation sites, or larger clusters. In general, the larger defect associates (dimers and clusters) are expected to be significant only at relatively high concentrations and low temperatures (e.g., Carroll et al 1988), but cation-vacancy pairs may be present at significant concentrations over a broad range of conditions. The formation of these pairs impedes the motion of cation vacancies, and thus reduces the diffusivity of unbound cations that diffuse by a vacancy mechanism.…”

Section: General Considerationsmentioning

confidence: 99%

Diffusion in Oxides

Orman

Crispin

2010

Reviews in Mineralogy and Geochemistry

170

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“…Each vacancy creates two lowlying hole states in adjacent O ions that are filled with excess electrons of two Cr 3+ donors. The concept of mutual interactions between the Mg vacancies and the Cr centres has been successfully used to describe the optical and spin spectra measured on MgO Cr bulk samples, providing solid evidence for the anticipated Cr 3+ charge state [27].…”

Section: Discussion: Structural Aspectsmentioning

confidence: 99%

Cathodoluminescence of near-surface centres in Cr-doped MgO(001) thin films probed by scanning tunnelling microscopy

2012

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Crystalline MgO films with a defined level of Cr dopants (MgO Cr ) are prepared by either subsequent or simultaneous deposition of Cr and Mg atoms in an oxygen ambience onto a Mo(001) support. The structural and morphological parameters of the doped films are investigated using lowenergy electron diffraction and scanning tunnelling microscopy (STM). Whereas at low Cr concentration the doped oxide has similar properties to pristine MgO(001), a new Cr/Mg mixed oxide develops at higher Cr load. The nature of the Cr impurities in the MgO matrix is deduced from cathodoluminescence spectroscopy performed by electron injection from the STM tip into the oxide film. In agreement with earlier studies on MgO Cr bulk crystals, the majority of Cr adopts a 3+ charge state and occupies Mg substitutional sites. The dopants give rise to sharp emission lines at about 700 nm, arising from radiative electron transitions between the Cr 3d levels split in the MgO crystal field. From the spectral evolution upon annealing the MgO Cr films, we deduce a strong tendency of the dopants to accumulate in a near-surface region. Our experiments demonstrate that high-quality MgO Cr films with similar optical properties as bulk samples can be prepared on conductive supports, being a first step to make doped oxide materials accessible to surface science studies.

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Theoretical study of the defect distribution of trivalent cation impurities in MgO

Cited by 19 publications

References 29 publications

Diffusion of aluminium in MgO from first principles

Diffusion of aluminium in MgO from first principles

Diffusion in Oxides

Cathodoluminescence of near-surface centres in Cr-doped MgO(001) thin films probed by scanning tunnelling microscopy

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