EFFECT OF TL DOPING ON THE PHASE-STABILITY OF HG2BA2(Y,CA)(1)CU2O8-DELTA SUPERCONDUCTORS PREPARED BY A HIGH-PRESSURE TECHNIQUE

(Hg, T1) based cuprates with the nominal compositions of (Hg(1-x)T1(x) )(2)Ba2Y1-yCayCu2O8-delta (0 less than or equal to x less than or equa l to 1.0 and 0 less than or equal to y less than or equal to 1.0) were prepared under a high pressure and high temperature. The solubility o f Ca ions into the Hg-2212 phase for various T1 contents was examined by X-ray powder diffraction and energy-dispersive X-ray spectroscopy. The substitution of Ca2+ for the Y3+ Site for the samples with x = 0.3 and 0.5 is realized over a full range of 0 less than or equal to y le ss than or equal to 1.0, while the solubility range is limited for the samples with x less than or equal to 0.15 and x greater than or equal to 0.75. The samples with x = 0.3 exhibited a maximum T-c of 84 K, wh ich was about 30 K higher than the maximum T-c for the samples with x = 0. The significant extension of Ca solubility for the T1 doped sampl es is probably explained by the compensation of excess negative charge s in the (Hg(1-x)T1(x))(2)O-2-delta charge reservoir. The fact that th e Y free Hg-2212 phase is obtained by T1 doping suggests the possibili ty of synthesizing a Hg-22(n - 1)n (n = 3, 4,...) homologous series.