Layer dependence of the superconducting transition temperature of HgBa₂Ca_n-1Cu_nO_2n+2+δ

High-pressure methods have been used to synthesize multiphase compositions in the Hg12{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 Tc = 134 K for n = 3 and then decreases abruptly for n>4, reaching Tc<90 K for n{slanted equal to or greater-than}7. © 1994.