Control of the hole concentration in the YBa2Cu3O6+z-type superconductors (Yb,Ca)(Ba,Sr)2Cu3O6+z with low and high Ca contents

Abstract

(Yb1−xCax) (Ba0.8Sr0.2)2Cu3O6+z (0≤x≤0.4) solid solutions of the YBa2Cu3O6+z (‘‘1:2:3’’) -type structure were successfully synthesized. The solid-solution samples were characterized with respect to the oxygen content, crystal structure, and superconducting properties. The ‘‘fully oxygenated’’ samples with z∼0.8 were prepared employing postannealing at high oxygen partial pressure atmosphere [P(O2)=400 atm]. The samples had orthorhombic unit cells and showed bulk superconductivity. The superconducting transition temperatures (Tc’s) ranged from 80 to 32 K, depending on the Ca content. Samples with x=0.1 and 0.3, and various oxygen contents (0.36≤z≤0.89 for x=0.1 and 0.10≤z≤0.78 for x=0.3) were prepared by employing quenching and annealing techniques. For (Yb0.7Ca0.3) (Ba0.8Sr0.2)2Cu3O6+z, as the oxygen content z decreased, Tc increased from 40 K first, then peaked at 82 K at z=0.56, and decreased down to 48 K at z=0.10. The relationship between Tc and the hole concentration in the CuO2 sheet, psheet, was obtained. Tc was maximum at psheet=0.18 for both samples with x=0.1 and 0.3.

Source-reported materials — not catalogue approval

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