Layer Dependence of the Superconducting Transition-Temperature of Hgba2can-1cuno2n+2+Delta

High-pressure methods have been used to synthesize multiphase compositions in the Hg-12{n-1}n homologous series. The phase assemblages were examined by optical, electron diffraction and X-ray diffraction techniques, and their stoichiometries verified by electron microprobe. Transport and magnetic susceptibility measurements were combined with the results of the phase analysis to establish superconducting transition temperatures for both as-prepared and O2- or Ar-annealed materials. It was found that the transition temperature peaks at T(c) = 134 K for n = 3 and then decreases abruptly for n > 4, reaching T(c) < 90 K for n greater-than-or-equal-to 7.