The mechanisms by which Mg2+ and Al3+ ions were transported through the

MgAl2O4 spinel lattice were investigated using atomic scale computer simulation.

Both vacancy and interstitial cation processes were considered. Stable vacancies

can be generated on either the magnesium or aluminium sub-lattices but the Mg2+

and Al3+ cation interstitials were most stable when located in split form with

another Mg2+ ion about a vacant Mg2+ site. The pathways for diffusion of defects

both via vacancy and interstitial mechanisms were analysed in detail with

calculation of the energy barriers and the associated exponential pre-factors. The

results showed that vacancies can be exchanged between the two sub-lattices resulting in the formation of antisite defects (though these processes have a high

activation energy); that the Mg2+ ions were more mobile than the Al3+ ions and that

the preferred mechanism for Al3+ ion diffusion was via a vacancy mechanism on

the magnesium sub-lattice. Although the calculated values of the pre-factors can

differ in size by an order of magnitude, in this system it was the relative size of the

energy barriers that dominate the diffusion rates.

Cation Diffusion in Magnesium Aluminate Spinel. S.T.Murphy, B.P.Uberuaga,

J.B.Ball, A.R.Cleave, K.E.Sickafus, R.Smith, R.W.Grimes: Solid State Ionics,

2009, 180[1], 1-8