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Density-functional-theory (DFT) calculations within the generalised gradient approximation (GGA) were used to examine the behaviour of point defects in the cubic BO perovskite-type oxide, ReO. Energies of reduction and of hydration were calculated, and the results are compared with literature data for ABO perovskite oxides. The activation energies of migration were determined for O, H, Li, Na, K and HO. An occupied A site in ReO is found to be beneficial to oxide-ion migration by a vacancy mechanism as well as to proton migration by a Grotthuss mechanism. Na, K and HO exhibit activation energies of migration higher than 2 eV, whereas Li is characterised by a very low migration barrier of 0.1 eV. Reasons for this behaviour are discussed. Our results suggest that H, O, and especially Li, are highly mobile ions in ReO.

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