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Published online by Cambridge University Press: 28 February 2011
Molecular dynamics simulations were carried out in an attempt to reproduce and explain the differing composition dependencies of the ionic conductivities of Na(I)-Ba(II)- and Na(I)-Sr(II)- ß' '-alumina. Impedance spectroscopy measurements of Na1.67-2xBaxMg0.67Al10.33O17, where x = 0.0 - 0.835, showed a distinct minimum in the conductivity when x = 0.67, or 80% exchange of Ba(II) for Na(I). Evidence for mobile cation ordering at that composition was seen in the simulation results and the general change in conductivity with Ba(II) content was reproduced rather well. The results of a similar experimental study of Na(I)-Sr(II)-ß' '-alumina did not show a minimum in the conductivity, but our simulations incorrectly predicted the Sr(II) system to behave in the same fashion as the Ba(II) system. Possible reasons for this discrepancy are suggested, including problems with transferring potentials between oxides and the influence of absorbed water on the experimental results.