SYNTHESIS AND CHARACTERIZATION OF OVERDOPED HG-1234 AND HG-1245 PHASES - THE UNIVERSAL BEHAVIOR OF T-C VARIATION IN THE HGBA2CAN-1CUNO2N+2+DELTA SERIES

HgBa2Ca3Cu4O10+delta and HgBa2Ca4Cu5O12+delta were prepared by high pr essure/high temperature technique. The phase composition in the Hg-Ba- Ca-Cu-O system was shown to be very sensitive io synthesis conditions. A variation of the oxygen content in the starting oxide mixture by ch anging the BaO/BaO2, ratio allowed the acquisition of Hg-1234 and Hg-1 245 in the overdoped state. The heat treatments (nitrogen and oxygen f lows, oxygen pressure 100 bar and 2000 bar) resulted in a change of T( c)s from initial overdoped (116 and 100 K for Hg-1234 and Hg-1245, res pectively) to underdoped (95 and 85 K) and, finally, to optimally-dope d states (125 and 111 K). The dependencies of T-c vs. alpha-parameter (and, consequently, oxygen content) for these phases exhibit a cupola- shaped behavior, as it was previously found for the lower (n less than or equal to 3) members of the HgBa2Can-1CunO2n+2+delta series. (C) 19 98 Elsevier Science B.V.