Electron irradiation induced oxygen ordering in YBCO twin-free crystals.

Oxygen ordering in CuO chain plane of YBCO is interesting topic because the distribution of oxygen, or the length of chain-fragments, plays an important role in carrier-doping of the CuO2 plane; longer chain-fragments are more effective in hole doping and result in higher Tc under the same overall oxygen stoichiometry. In this presentation, we report on the low energy electron irradiation effects in twin-free oxygen deficient YBCO single crystals via comparative Raman spectroscopy studies of electron irradiated and non-irradiated areas at room temperature. We observed that low energy electrons heal the existing point defects of CuO chains and enhances oxygen ordering of twin-free but oxygen deficient YBCO. The comparison of the polarized Raman spectra from non-irradiated and irradiated areas provides clear indications of extended average length of the chains without changing the overall oxygen content.