Superonducting yttrium-barium-copper oxide samples have been highly enriched with ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ (up to 91–96 at. %) by methods that ensure homogeneous distribution of the oxygen isotope throughout all lattice oxygen sites. The preparative routes used include the pyrolysis of nitrates, gas-phase exchange (which does not ensure homogeneous exchange of all sites), oxidation of amorphous ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$ alloy, and hydrolysis oxidation of Y-${\mathrm{BaF}}_2$-Cu thin films. The $T_c$’s of ${}_{}{}^{18}{}_{}{}^{}\mathrm{enriched}$ samples vary with some methods of preparation. Some ${}_{}{}^{17}{}_{}{}^{}\mathrm{enriched}$ samples were also prepared for comparison. The composition and structure of materials derived from the various preparative routes were characteized, and their magnetic and electrical properties were measured.

• Received 7 November 1988

DOI:https://doi.org/10.1103/PhysRevB.39.4285