INFLUENCE OF ANNEALING UNDER OXYGEN ON THE CHEMICAL AND SUPERCONDUCTING PROPERTIES OF YBA2CU3OX SINGLE-CRYSTALS

As-grown and annealed under oxygen single crystals of YBa2Cu3Ox have been characterized by micro-Raman spectroscopy and a.c. magnetic susceptibility measurements. As grown single crystals prepared in a CuO-BaO flux exhibit different oxygen contents depending on their thermal treatment as shown by micro-Raman spectroscopy. The onset temperature range (Tc = 70-90 K) as well as the transition width (ΔTc = 5-30 K) have been determined by a.c. susceptibility measurements. An annealing at 773 K of single crystals under dry oxygen atmosphere for three days leads to materials showing both homogeneous oxygen content (6.9 per formula unit) whatever the original oxygen content before annealing and a very sharp superconducting transition at 92.5 K with ΔTc = 0.1 K. A noticeable increase of the critical current density is also recorded. © 1990.