Transition to an Insulator from a Superconductor due to Substitution of Ca by Rare-earth Elements in Bi₄Sr₄RE₂Cu₄O_16+δ (RE=Nd, Eu, Y)

Abstract

X-ray diffraction analyses and electrical properties were determined for Bi 4 Sr 4 RE 2 Cu 4 O 16+δ , where RE=Nd, Eu and Y. Samples sintered at 920°C showed identical XRD patterns with that of superconducting Bi 4 Sr 4 Ca 2 Cu 4 O 16+δ , however, their electrical properties were insulating. Oxygen content for the Y-substituted sample Bi 4 Sr 4 Y 2 Cu 4 O y was y =16.75 and the Cu average valence was 1.875. The compounds seem to correspond to the ground state of Bi 4 Sr 4 Ca 2 Cu 4 O 16+δ , where no holes are doped in Cu-O levels, equivalent to the reduced semiconductor REBa 2 Cu 3 O 6 in REBa 2 Cu 3 O 7-δ systems.