Electrical transport and superconductivity in the Al 2O 3-Bi 2Sr 1.8Ca 1.2Cu 2O y and MgO-Bi 2Sr 1.8Ca 1.2Cu 2O y composites

Abstract

We have measured the resistivities ϱ of Al 2O 3-Bi 2Sr 1.8Ca 1.2Cu 2O y and MgO-Bi 2Sr 1.8Ca 1.2Cu 2O y composites with the nominal Bi 2Sr 1.8Ca 1.2Cu 2O y volume fraction, ϱ 2212, ranging from 0.15 to 1.00. For the Al 2O 3-Bi 2Sr 1.8Ca 1.2Cu 2O y composites, we find for the samples with ϱ 2212≥0.6 that the superconducting transition temperature, T c, is not disturbed by the addition of Al 2O 3. For ϱ 2212<0.3, no zero-resistivity state is observed. For the MgO-Bi 2Sr 1.8Ca 1.2Cu 2O y composites, T c is barely disturbed for the samples with ρ 2212≥0.7. No superconducting state is observed for the samples with ρ 2212<0.35. The variation of ϱ(300 K) with ρ 2212 indicates a three-dimensional percolating Bi-Sr-Ca-Cu-O matrix occurring at ρ 2212≈0.19 and ≈0.15 in Al 2O 3-Bi 2Sr 1.8Ca 1.2 Cu 2O y and MgO-Bi 2Sr 1.8Ca 1.2Cu 2O y , respectively. Both resistivity and magnetization measurements suggest that the reactions of Bi 2Sr 1.8Ca 1.2Cu 2O y with MgO are weaker than with Al 2O 3.