Oxygen migration in A2B2O7 pyrochlores

Atomic scale computer simulation has been used to predict activation energies for oxygen migration. In total, 54 compounds with the A2B2O7 pyrochlore structure were simulated. In each case, oxygen migration was assumed to proceed via an oxygen vacancy mechanism with oxygen ions hopping between 48f sites. For some compounds the unoccupied 8a interstitial position played an important role in the migration mechanism. The results were analyzed using a contour map of activation energy versus A cation radius along the ordinate and B cation radius along the abscissa. This identified areas of similar cation radii, which exhibit lower activation energy. Results compare favourably with available experimental data.