Superconductivity in CoSr2(Y1-xCax)Cu2O7+d

TL;DR

This study explores how aliovalent calcium substitution and high-pressure oxygen annealing induce superconductivity in CoSr2(Y1-xCax)Cu2O7+d, revealing that high-pressure treatment enables superconductivity in otherwise non-superconducting samples.

Contribution

It demonstrates that high-pressure oxygen annealing can induce bulk superconductivity in Co-1212, a Co-based layered copper oxide, which is not achieved by simple substitution alone.

Findings

High-pressure annealing induces superconductivity in Co-1212 samples.

Maximum Tc of ~40 K achieved at x=0.3 after high-pressure treatment.

Oxygen stoichiometry remains nearly constant in as-synthesized samples.

Abstract

The roles of aliovalent Ca(II)-for-Y(III) substitution and high-pressure-oxygen annealing in the process of "superconducterizing" the Co-based layered copper oxide, CoSr2(Y1-xCax)Cu2O7+d (Co-1212), were investigated. The as-air-synthesized samples up to x = 0.4 were found essentially oxygen stoichiometric (-0.03 <= d <= 0.00). These samples, however, were not superconductive, suggesting that the holes created by the divalent-for-trivalent cation substitution are trapped on Co in the charge reservoir. Ultra-high-pressure heat treatment carried out at 5 GPa and 500C for 30 min in the presence of Ag2O2 as an excess oxygen source induced bulk superconductivity in these samples. The highest Tc was obtained for the high-oxygen-pressure treated x = 0.3 sample at ~40 K.