LAYER DEPENDENCE OF THE SUPERCONDUCTING TRANSITION-TEMPERATURE OF HGBA2CAN-1CUNO2N+2+DELTA

High-pressure methods have been used to synthesize multiphase composit ions in the Hg-12{n-1}n homologous series. The phase assemblages were examined by optical, electron diffraction and X-ray diffraction techni ques, and their stoichiometries verified by electron microprobe. Trans port and magnetic susceptibility measurements were combined with the r esults of the phase analysis to establish superconducting transition t emperatures 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.