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要旨:
High quality single crystals of Tl2Ba2CuO6+delta have been obtained by a
CuO self-flux method. The synthesized crystals have an average chemical
composition of Tl1.85(4)Ba1.94(4)Cu1.15(2)O6+delta as determined by
electron probe microanalysis (EPMA), suggesting a possible substitution
of Cu for Tl. Single-crystal X-ray diffraction experiments and structure
refinement show that the crystal exhibits tetragonal symmetry (space
group I4/mmm), with lattice parameters a = 3.8608 (4) angstrom and c =
23.1332 (9) angstrom. Site occupancy refinements indicated completely
occupied Ba and Cu sites within the structure, and a deficiency in the
scattering power of the Tl site. The final structure refinement
corresponds to a composition Tl1.87(2)Ba2Cu1.13(2)O6+delta, which is
consistent with the EPMA results. The quality of the diffraction data
allow Tl and O (which comprise the Tl2O2 layers) to be unambiguously
assigned to split sites of the type xOz, as opposed to xxz sites. There
is no evidence for long-range ordering of the displacements of the atoms
in the T1202 layers of this crystal. The as-grown single crystals have a
superconducting transition temperature, T(c), of 12.4 K. The T(c) of the
as-grown crystals could be enhanced via low temperature annealing in a
reducing atmosphere.
