Magnetization of a superconducting epitaxial (Y_0.8Ca _0.2)Ba₂Cu₃O_x film with O₂ anneal

A c-axis epitaxial film of composition (Y0.8Ca 0.2)Ba2Cu3O6+x is found to be superconducting over a wide range of oxygen stoichiometry, from x≊0 to x≊1.0. The oxygen stoichiometry was varied systematically by annealing films over four decades of oxygen partial pressure, ranging from 0.0067%-100% O 2. Both the superconducting transition temperature and the remanent magnetization increase with increasing x and are approximately linear with log oxygen partial pressure over three decades. These increases are attributed mainly to the change in the number of holes in the Cu-O planes caused by oxidation.