Time-dependent superconducting behavior of oxygen-deficient YBa2Cu3Ox: Possible annealing of oxygen vacancies at 300 K.

Oxygen stoichiometries in single crystals of YBa{sub 2}Cu{sub 3}O{sub {ital x}} are controlled by quenching from an O{sub 2}-N{sub 2} atmosphere at 520 {degree}C to liquid nitrogen. After quenching, the superconducting behavior and lattice parameters are found to be time dependent. {Tc} increases as much as 15 K in a period of several days. Apparently, annealing, with increasing oxygen vacancy order, occurs at room temperature.