Abstract. Studies of stable phases containing copper have been made when mixtures of Y2O3, BaCO3 and CuO are reacted. It is found that out of four phases there is only one phase which is superconducting and the volume ratio of superconducting to non-superconducting phase decreases rapidly as we move away from the stoichiometry of the superconducting phase having composition YBa2Cu3O8−y.
