Effect of vacuum annealing on the structure and superconductivity of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} single crystals.
The effect of annealing on the structure and superconductivity of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} 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 x 10{sup -1} to 5 x 10{sup -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, T{sub c} was found to be affected more strongly by the annealing oxygen partial pressures, p(O{sub 2}), than by the annealing temperature. T{sub c} decreases considerably from 92 to 29 K with decreasing p(O2) from 1 down to 4 x 10{sup -2} bar, however, increases surprisingly to 62 K with further decreasing p(O{sub 2}) to 5 x 10{sup -4} bar. The transitions remain relatively sharp for the samples annealed under p(O{sub 2})=8 x 10{sup 01}-4 x 10{sup 02} 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 both a- and b-axis contract slightly with decreasing p(O{sub 2}). The relation between T{sub c} and the c-axis lattice parameter suggests that the change of T{sub c} 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(O{sub 2}) < 4 x10{sup -2} bar. The one-dimensional incommensurate superstructure along the b-axis was observed by TEM in the crystal annealed at p(O{sub 2})=1 x 10{sup -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 T{sub c}.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- DE-AC02-06CH11357
- OSTI ID:
- 961451
- Report Number(s):
- ANL/ET/JA-47953; TRN: US201012%%1514
- Journal Information:
- Physica C, Vol. 366, Issue 4 ; Feb. 1, 2002
- Country of Publication:
- United States
- Language:
- ENGLISH
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Related Subjects
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ANNEALING
BISMUTH OXIDES
CALCIUM OXIDES
COPPER OXIDES
CRYSTALS
EMISSION SPECTROSCOPY
HIGH-TC SUPERCONDUCTORS
HOLES
LATTICE PARAMETERS
LAYERS
MAGNETIZATION
MONOCRYSTALS
OXYGEN
PARTIAL PRESSURE
POWDERS
QUARTZ
SOLVENTS
STRAINS
STRONTIUM OXIDES
SUPERCONDUCTIVITY
SYMMETRY
TRANSITION TEMPERATURE
TRANSMISSION ELECTRON MICROSCOPY
X-RAY DIFFRACTION
ZONE MELTING