Effect of vacuum annealing on the structure and superconductivity of Bi2Sr2CaCu2O8+δ single crystals

B. Liang, C. T. Lin, A. Maljuk, Y. Yan

Research output: Contribution to journalArticlepeer-review

23 Scopus citations

Abstract

The effect of annealing on the structure and superconductivity of Bi2Sr2CaCu2O8+δ has been investigated on high-quality and large single crystals grown by the traveling solvent floating zone technique. Vacuum annealing was carried out on crystals sealed in quartz ampoules under different oxygen pressure ranging from 8 × 10-1 to 5 × 10-4 bar. The as-grown and post-annealed crystals were explored by induction-coupled plasma atomic emission spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM) and magnetization measurements. It was demonstrated that the oxygen homogeneity of the as-grown crystals has a direct influence on the post-annealed samples. The superconducting transition temperature, Tc was found to be affected more strongly by the annealing oxygen partial pressures, p(O2), than by the annealing temperature. Tc decreases considerably from 92 to 29 K with decreasing p(O2) from 1 down to 4 × 10-2 bar, however, increases surprisingly to 62 K with further decreasing p(O2) to 5 × 10-4 bar. The transitions remain relatively sharp for the samples annealed under p(O2) = 8 × 10-1-4 × 10-2 bar, with no evidence of significant structural change by powder XRD measurement. XRD studies indicate that the crystals have orthorhombic symmetry. The refinement result for XRD data shows that the c-axis expands, while botha-and b-axis contract slightly with decreasing p(O2). The relation between Tc and the c-axis lattice parameter suggests that the change of Tc is correlated with a redistribution of holes between the Bi-O layers and the Cu-O planes. Impurity phases were found to segregate from samples annealed under p(O2) < 4 × 10-2 bar. The one-dimensional incommensurate superstructure along the b-axis was observed by TEM in the crystal annealed at p(O2) = 1 × 10-3 bar. The lattice strain caused by the high-vacuum annealing possibly affect the Cu-O-Cu angle and lead to an anomalous change in Tc.

Original languageEnglish
Pages (from-to)254-262
Number of pages9
JournalPhysica C: Superconductivity and its Applications
Volume366
Issue number4
DOIs
StatePublished - Feb 1 2002
Externally publishedYes

Keywords

  • Bi-2212
  • Single crystal
  • Structure
  • Superconductivity

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