THE SUPERCONDUCTING HGBA2CAN-1CUNO2N+2+DELTA HOMOLOGOUS SERIES

Syntheses, heat-treatments, structures and the superconducting propert ies of the first four members of the homologous series HgBa2Can-1CunO2 n+2+delta are presented and discussed. Syntheses under high pressure s eem to yield samples which contain less than 5% impurities. The struct ural characterization has been carried out by X-ray diffraction, elect ron microscopy and neutron diffraction. Heat-treatments in oxidizing a tmospheres usually increase T(c). The member with n = 2 does not follo w this rule because the as-prepared sample (T(c) = 104 K) seems to be overdoped. Heat-treatment in N2 at 250-degrees-C for 10 h induces an i ncrease in T(c) to 123 K. Additional heat treatment under N2 (400-degr ees-C, 18 h) decreases T(c) to 110 K. In Hg-1212 superconductivity exi sts in underdoped and overdoped regions.