Trivalent cations in periclase were attracted to cation vacancies and these defects

tend to associate on adjacent sites to form mobile pairs. A theory was developed to

describe the concentration-dependent diffusion of Al in the presence of Al-vacancy

pairs, and was applied to experiments conducted at 1577 to 2273K and 1atm to

25GPa. In all but one experiment, the Gibbs free energy of binding, inferred from

the diffusion profiles, was between −44 and −60kJ/mol, with an average value of

−50kJ/mol. The absolute value of the entropy of binding was constrained to be less

than 50J/molK, and the volume of binding was constrained to be between −1.8 and

0cm3/mol. The diffusion coefficient of the Al-vacancy pair can be described by:

D2(m2/s) = D2,0exp[−{213(kJ/mol)+ 3.22(cm3/mol)P}/RT]

and log10D2,0(m2/s) = −6.17. Calculations were presented for the diffusion of Al

and Mg as functions of Al concentration, temperature and pressure.

Aluminium Diffusion and Al-Vacancy Association in Periclase. J.A.Van Orman,

C.Li, K.L.Crispin: Physics of the Earth and Planetary Interiors, 2009, 172[1-2], 34-

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