SUPERCONDUCTING AND STRUCTURAL-PROPERTIES OF THE HGBA2(CA1-XYX)CU2O6+DELTA SYSTEM

Sample preparation and superconducting properties of the Hg(1212) HgBa2(Ca1-xYx)Cu2O6+delta system are reported. Superconducting transition temperature T-c decreases steadily with yttrium substitution parameter x, indicated that the 126 K parent compound HgBa2CaCu2O6+delta is in the optimum doped region (delta approximate to 0.2). This variation of T-c is different from the almost isostructural Tl(1212) TlBa2(Ca1-xYx)Cu2O7-delta system, where maximum T?c of 116 K was observed in the optimum composition TlBa?2(Ca?(0.8Y0.2)Cu2O7-delta. A metal-insulator transition was observed around x = 0.5 for the present system. T-c variation for other rare earth substitution system HgBa2(Ca(1-x)R(x))Cu2O6+delta (R = Pr, Gd) will also be discussed. The variation of tetragonal lattice parameters depend very much on the substituted rare earth R(3+) ionic size.