Ca doping effect on superconductivity in (Yb1−xCax)(Ba0.8Sr0.2)2Cu3O6+z

(Yb1−xCax)(Ba0.8Sr0.2)2Cu3O6+z samples with widely ranged values of x and z were successfully synthesized. The as-synthesized samples were annealed in flowing Ar gas in a thermobalance. Totally oxygen-deficient samples whose oxygen contents were 6+z∼6.0 were prepared by annealing the as-synthesized samples at 800°C in flowing Ar gas. For the samples with the oxygen content, 6+z∼6.0, no superconductivity occurred for 0≦x<0.20, but for 0.20≦x≦0.35 Tc increased as x increased.