Synthesis and characterization of single crystals of the superconductors Hg0.8Bi0.2Ba2Can−1CunO2n+2+δ (n=2,3)

Abstract

Single crystals of the 1212 (n=2) and 1223 (n=3) mercury based cuprates have been grown using Bi2O3 as a flux during the growth. The bismuth cations act as stabilizers of the structures which do not require the use of a dry box or high pressure. Electron microscopy and coupled energy dispersive spectroscopy analyses evidence the regularity of the 1212 and 1223 structures with a mercury layer of composition close to Hg0.8Bi0.2. Moreover the structural refinements based on x-ray-diffraction data of these crystals, show at the level of the [(Hg,Bi)Oδ] layer a splitting of the oxygen site around the position (1/21/20). These as-grown superconducting crystals exhibit critical temperatures of 121 and 130 K for 1212 and 1223, respectively. The irreversibility lines (IL) and fishtail lines (FL) of these crystals are compared to those of (Hg,Bi)-1201 crystals and grain aligned Hg-1223 ceramics. These data show that the Hg0.8Bi0.2-1223 IL and FL lie above that of Hg0.8Bi0.2-1212. This suggests that the anisotropy of 1223 is smaller than that of 1212. The similarity of the FL’s location of isostructural Tl-1223 and Hg0.8Bi0.2-1223 illustrates the role of the structure on the superconducting properties. © 1996 The American Physical Society.

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