THE EFFECT OF PB DOPING IN HGBA2CA2CU3O8+DELTA SUPERCONDUCTOR

Polycrystalline samples with the starting compositions of (Hg0.8Pb0.2)xBa2Ca2Cu3O8+delta (1.0 less-than-or-equal-to x less-than-or-equal-to 2.5) were prepared under various synthetic conditions. Both powder X-ray-diffraction analysis and energy dispersive X-ray spectroscopy revealed that the Pb ions were successfully doped into the Hg-1223 phase. High-quality Pb-doped Hg-1223 samples for the starting composition with x = 1.5 were obtained when heated at 675-degrees-C only for 1 h. The resistivity (rho) of such a sample was low, being approximately 8 X 10(3) OMEGA cm at 300 K, and the rho versus T curve was linearly extrapolated to zero resistance at 0 K, being similar to the cases of high-quality high-T(c) cuprates. The zero resistance due to superconductivity started at 122.2 K. When the sample was reduced in flowing argon gas, it exhibited a Meissner signal below 132 K and its Meissner volume fraction exceeded 20% at 5 K. According to thermoelectric power measurements, the carrier density in the sample was reversibly dependent on the oxygen partial pressure, and the sample post-annealed in flowing oxygen gas was likely overdoped.