Oxygen nonstoichiometry and valence of copper in the Cu-1222 superconductor

M. Karppinen*, M. Arai, J. M. Lee, T. S. Chan, Y. Morita, J. M. Chen, R. S. Liu, H. Yamauchi

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

3 Citations (Scopus)

Abstract

Essentially single-phase Cu(Ba0.67Eu0.33) 2(Ce0.33Eu0.67)2Cu2O 9±δ samples of the Cu-1222 phase with a fluorite-structured (Ce,Eu)-O2-(Ce,Eu) block between the superconductive CuO2 planes were synthesized in O2 atmosphere to exhibit superconductivity with Tc around 25 K. Wide-range tuning of oxygen content and thereby the overall hole-doping level of the phase was found possible through (i) temperature-controlled oxygen-depletion (TCOD) annealing carried out in a thermobalance in N 2 at various temperatures (for reduction), and (ii) high-pressure oxygenation (HPO) treatments carried out in a cubic-anvil-type high-pressure apparatus in the presence of various amounts of Ag2O2 as an excess oxygen source (for oxidation). For the HPO samples a record-high Tc value of 62 K was achieved. On the other hand, deoxygenation to the oxygen content less than 9±δ≈8.9 was found to kill superconductivity. The degree of hole doping (both in overall and for the CuO2 plane and CuO1±δ charge reservoir separately) in the samples is discussed on the bases of Cu L-edge and O K-edge XANES data.

Original languageEnglish
Pages (from-to)1705-1711
Number of pages7
JournalJournal of Solid State Chemistry
Volume178
Issue number5
DOIs
Publication statusPublished - May 2005
MoE publication typeA1 Journal article-refereed

Keywords

  • Cu valence
  • XANES spectroscopy

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