The effect of Sn-VO defect clustering on Zr alloy corrosion

Density functional theory simulations were used to study Sn defect clusters in the oxide layer of Zr-alloys. Clustering was shown to play a key role in the accommodation of Sn in ZrO2, with the {Sn-Zr:V-O}(x) bound defect cluster dominant at all oxygen partial pressures below 10(-20) atm, above which Sn-Zr(x) is preferred. {Sn-Zr:V-O} (x) is predicted to increase the tetragonal phase fraction in the oxide layer, due to the elevated oxygen vacancy concentration. As corrosion progresses, the transition to Sn-Zr(x), and resultant destabilisation of the tetragonal phase, is proposed as a possible explanation for the early first transition observed in Sn-containing Zr-Nb alloys.