THE JOINT INFLUENCE OF CATION AND OXYGEN NONSTOICHIOMETRY ON SUPERCONDUCTING PROPERTIES IN 123 CUPRATE

Abstract

As shown earlier, there is a “slow” constituent (γ) into oxygen nonstoichiometry in superconducting 123-cuprates doped with rear-earth elements. The aim of this paper is to study possible effect of changing “slow” oxygen content on electrophysical properties of HTSC cuprates. Magnetization of Sm-doped samples YBa1.90Sm0.10Cu3Ox was measured in a vibrating sample magnetometer in scanning magnetic field and temperature. Two series of samples YBa1.90Sm0.10Cu3O6+δ+γ were prepared for measurements from the same batch of material: with maxim (γmax = 0.10) and minimum (γmin = 0.00) values of “slow” oxygen content and corresponding to formulas YBa1.90Sm0.10Cu3O7.07 and YBa1.90Sm0.10Cu3O6.97 respectfully. Both types of samples were obtained from the same batch of sintered material. Samples (I) were brought to equilibrium at 720°C (lower than Tb1) to maximize the “slow” oxygen content: γmax = 0.10. Then they were cooled to 400°C and kept at this temperature for 1 h to maximize “quick” oxygen content. The final total oxygen content in the samples of this series was established at x (I) = 7.07 (YBa1.90Sm0.10Cu3O7.07). Samples (II) were brought to equilibrium at 900°C (above Tb2) to minimize the “slow” oxygen content: γmin = 0.00 and then they were rapidly (in less then 10 min) cooled to and kept at 400°C for 1 h. The final total oxygen content in the samples of this series was equal to x (II) = 6.97 (YBa1.90Sm0.10Cu3O6.97). The study of magnetic hysteresis in these samples shows that additional oxidation with respect to “slow” component produces HTSC with higher both the critical temperature Tc and intragrain critical current density Jcg in ceramic specimens. The maximum value of Jcg ≈ 3·106 A/cm2 in untextured ceramic specimens was observed.