ORDERING OF CHAIN OXYGEN IN SINGLE-DOMAIN CRYSTALS OF YBCO

We have performed polarized in-situ reflection measurements on YBa2Cu3 Ox single domain crystals (x=6.5) in a temperature range between room temperature and 150 degrees C. The energy range was varied from 150 me V to 6 eV. Using the in-plane anisotropy of the optical properties, we were able to separate the contribution of Cu-O layers and Cu-O chains to the electronic transport properties. Heating up the samples we obs erved a strong decrease of the chain length, the charge carrier concen tration and the Cu+ concentration. These results are in agreement with investigations previously performed on quenched YBa2Cu3Ox (x=6.5) sam ples during room temperature annealing.