  We have examined the effects of 20 keV electron irradiation on
[-Cu(1)-O(1)-]n chain oxygen arrangements in oxygen deficient but otherwise
twin-free YBa2Cu3O6+x single crystals. Comparison of polarized Raman spectra of
non-irradiated and irradiated areas provides evidence that electron
bombardments instigate the collective hopping of oxygen atoms either from an
interstitial at O(5) site to a vacant O(1) chain site or by reshuffling the
chain segments to extend the average length of chains without changing the
overall oxygen content. This oxygen ordering effect, while counter-intuitive,
is analogous to that found in the photoexcitation induced ordering in which
temporal charge imbalance from electron-hole pair creation by inelastic
scattering of incident electrons causes a local lattice distortion which brings
on the atomic rearrangements.
