Effect of cesium substitution on the superconducting properties of Bi-2212 samples prepared via solid-state reaction and laser floating zone technique

Abstract

In this work, the effect of cesium substitution on the structural and superconducting properties of Bi2Sr2Ca1-xCsxCu2O+y (where x = 0.0, 0.025, 0.050, 0.075, 0.10, 0.125, and 0.15) samples prepared by the solid-state reaction route and by directional growth using the laser floating zone (LFZ) technique has been studied. X-ray diffraction has shown that both kinds of samples present the 2212 phase as the major one, with pseudo tetragonal structure, accompanied by minor amounts of (Sr,Ca)CuO2 and Bi2(Sr,Ca)4O6 + d secondary phases. SEM-EDX results indicate that Bi-2212 phase is the major one, with small amounts of secondary phases. Cs substitution diminishes the size and content of secondary phases. Magnetization measurements reflect different behavior for sintered and LFZ grown samples. Although the diamagnetic transition is very wide for the former samples, it is very sharp for the last ones. The critical onset temperatures, TC, are around 80 and 90 K, for sintered and LFZ grown samples, respectively. Moreover, M–H measurements indicate that LFZ grown samples exhibit larger areas than the sintered ones. The intragranular critical current, JC, calculated from the M–H loops and Bean’s formula, is maximum for x = 0.025Cs sintered and x = 0.05Cs LFZ grown samples. The maximum pinning forces, FPmax, determined in these samples are higher than those obtained in undoped ones, reaching 9 × 107 Oe*A/cm2 and 10 × 108 Oe*A/cm2, at 10 K, for sintered and LFZ grown samples, respectively.