  Plasticity in zirconium alloys is mainly controlled by the interaction of 1/3
1210 screw dislocations with oxygen atoms in interstitial octahedral sites of
the hexagonal close-packed lattice. This process is studied here using ab
initio calculations based on the density functional theory. The atomic
simulations show that a strong repulsion exists only when the O atoms lie in
the dislocation core and belong to the prismatic dislocation habit plane. This
is a consequence of the destruction of the octahedral sites by the stacking
fault arising from the dislocation dissociation. Because of the repulsion, the
dislocation partially cross-slips to an adjacent prismatic plane, in agreement
with experiments where the lattice friction on screw dislocations in Zr-O
alloys has been attributed to the presence of jogs on the dislocations due to
local cross-slip.
