Single crystals of the 1212 (n=2) and 1223 (n=3) mercury based cuprates have been grown using ${\mathrm{Bi}}_2$${\mathrm{O}}_3$ as a flux during the growth. The bismuth cations act as stabilizers of the structures which do not require the use of a dry box or high pressure. Electron microscopy and coupled energy dispersive spectroscopy analyses evidence the regularity of the 1212 and 1223 structures with a mercury layer of composition close to ${\mathrm{Hg}}_{0.8}$${\mathrm{Bi}}_{0.2}$. Moreover the structural refinements based on x-ray-diffraction data of these crystals, show at the level of the [(Hg,Bi)${\mathrm{O}}_{\mathrm{\delta }}$] 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 ${\mathrm{Hg}}_{0.8}$${\mathrm{Bi}}_{0.2}$-1223 IL and FL lie above that of ${\mathrm{Hg}}_{0.8}$${\mathrm{Bi}}_{0.2}$-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 ${\mathrm{Hg}}_{0.8}$${\mathrm{Bi}}_{0.2}$-1223 illustrates the role of the structure on the superconducting properties. © 1996 The American Physical Society.

• Received 24 June 1996

DOI:https://doi.org/10.1103/PhysRevB.54.16246