OPTICAL INVESTIGATION OF ROOM-TEMPERATURE CHAIN ORDERING IN YBA2CU3O7-DELTA

We have investigated the near-infrared (0.5-1.5 eV) optical response o f quenched YBa2Cu3O7-delta samples with intermediate oxygen content as a function of the time tau the samples spent at room temperature. In a previous experiment, we determined the dielectric function in the sp ectral region between 3.8 and 4.3 eV under similar conditions using sp ectroscopic ellipsometry. We find an increase of the concentration of Cu(I)1+ ions with tau, indicating an oxygen-reordering process in the course of which Cu-O dumbells [linearly coordinated O(IV)-Cu(I)-O(IV) complexes] are generated. The reflectance measurements in the infrared regime between 0.5 and 1.5 eV indicate that simultaneously additional carriers are generated in the CuO2 Planes. Both findings are in accor dance with previous explanations of the rise of T(c) with tau.