GROWTH AND CHARACTERIZATION OF (Y,PR)-123 SINGLE-CRYSTALS - INFLUENCEOF AL CONTAMINATION AND POSTANNEALING UNDER OXYGEN-PRESSURE

(Y1-xPrx)Ba2Cu3-2Al2O7-delta (0 less than or equal to x less than or e qual to 1) single crystals of large surface area (up to 9 x 8 mm(2)) a nd thickness between 0.3 and 1.5 mm were grown in Al2O3 crucibles usin g a self-flux method. The crystals were characterized by means of AC s usceptibility, X-ray diffraction, energy dispersive X-ray spectrometry , optical reflectance measurements and Raman spectroscopy. To ensure t hat the crystals are fully oxygenated, post-annealing of the crystals was performed under high oxygen pressure (100-200 bar) in a home-made autoclave. With increasing Pr content a strong reduction of T-c, a sof tening of the Raman B-1g mode, a hardening of the Raman A(1g) mode, a red shift of the plasma edge and a strong decrease of the in-plane opt ical conductivity in the infra-red region were observed. The Raman dat a indicate that the valency of Pr is close to +3. EDX measurements as well as Raman measurements show, that the Al contamination of the crys tals (which results from crucible corrosion) increases with increasing Pr content. The complete disappearance of the free carrier concentrat ion which was determined by optical reflectivity measurements is affec ted by the Al contamination.