Redox state analysis for understanding the high-Tc superconductivity in highly unstable Ba2Ca2Cu3O8-δ phase with Tc ≈ 124 K and its derivative phase with Tc ≈ 78 K

M. Karppinen*, T. Hosomi, H. Yamauchi

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

11 Citations (Scopus)

Abstract

By means of wet-chemical analysis the redox state was established for a highly unstable Ba2Ca2Cu3O8-δ superconductive phase (Tc ≈ 124 K) obtained by high-pressure synthesis under oxidizing conditions and also for its derivative phase with Tc ≈ 78 K formed immediately when exposing the as-synthesized sample to humid air or H2O/N2 gas. The former phase is of the 0(Ba)2(Ca)23 structure having a relatively thin blocking block consisting of only two BaO layers in between two superconductive CuO2-Ca-CuO2-Ca-CuO2 layer blocks. On the other hand, the latter phase possesses a structure of H-m(Ba)2(Ca)23 (m ≈ 5) with an expanded blocking block due to accommodation of water in the structure. Wet-chemical analysis clearly manifested much higher oxidation state for the 0(Ba)2(Ca)23 phase than for its water-containing derivative. This suggests that the driving force for the phase transformation is the strong tendency of the 0(Ba)2(Ca)23 phase to be reduced. The possible origin of the unusually high overall oxidation state of the 0(Ba)2(Ca)23 phase is discussed on the basis of peroxide-type mixed-valent oxygen in its (BaO)2 blocking block.

Original languageEnglish
Pages (from-to)276-282
Number of pages7
JournalPHYSICA C: SUPERCONDUCTIVITY AND ITS APPLICATIONS
Volume382
Issue number2-3
DOIs
Publication statusPublished - 1 Nov 2002
MoE publication typeA1 Journal article-refereed

Keywords

  • BaCaCuO superconductor
  • HBaCaCuO superconductor
  • Redox state analysis

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