S.M. Green

SUPERCONDUCTIVITY AND THERMOELECTRIC POWER IN Tl2Ca2Ba2Cu3O10 AND TlCa3BaCu3O9

We report the synthesis and superconducting temperature of the high-Tc compounds Tl2Ca2Ba2Cu3O10 and TlCa3BaCu3O9. The transition to the superconducting state was measured by the magnetic susceptibility changes and by the temperature dependence of the electrical a.c. and d.c. resistivity and by thermoelectric power measurements. For Tl2Ca2Ba2Cu3O10 a superconducting transition with zero resistance at 114.5K have been observed. Higher Tc with zero resistance at 122K have been found in TlCa3BaCu3O9.

Magnetic properties of superconducting EuBa2Cu3O7−x

The magnetic properties of superconducting EuBa2Cu3O7−x with resistiveTc∼96.5 K are measured. The normal state magnetic susceptibility is analyzed within the framework of the Van Vleck-Frank theory, leading to the conclusion that the strong moments of the Eu3+ ions are uncorrelated, and do not affect the superconducting state.

Evidence for anomalous fluctuations in superconducting Bi/sub 1. 75/Pb/sub 0. 25/Ca/sub 2/Sr/sub 2/Cu/sub 3/O/sub 10/

We report very precise measurements of the electrical resistivity of granular Bi1.75Pb0.25-Ca2Sr2Cu3O10 superconducting ceramics from room temperature down to the superconducting percolating temperature. We analyze the temperature behavior of the excess conductivity and of the temperature derivative variation in electrical resistivity in order to extract the superconductivity fluctuation dimensionality regimes. We obtain unusual power law behaviors which do not correspond to predictions based on Aslamazov and Larkin theory (nor to its generalizations) nor to the regimes found in YBa2Cu3O7, e.g., here, dR/dT≃E−11/6 for ln E in [−4,0] with E=|T−Tc|Tc, where Tc is the critical temperature.

FLUCTUATION CONDUCTIVITY EFFECTS ON THERMOELECTRIC POWER OF GRANULAR Bi1.75Pb0.25Ca2Sr2Cu3O10 SUPERCONDUCTOR

We report precise measurements of the thermoelectric power (TEP) of granular superconducting Bi1.75Pb0.25Ca2Sr2Cu3O10. The TEP is strictly linear at high temperature. Superconductivity fluctuations set in at about 140 K. From the temperature derivative of the excess TEP (with respect to a straight line at “high temperature”), the critical behavior is obtained in the mean field regime, and is found identical to that of the temperature derivative of the excess electrical resistivity.

Magnetic properties of GdBa2Cu3O7−x in the normal and superconducting states

The magnetic properties of superconducting GdBa2Cu3O7−x withTc∼95 K are measured. In the normal state, its susceptibility closely follows the Curie law with an effective moment of 7.77μB.Hc1 is determined to be 650 Oe. No superconducting fluctuation can be delineated. Flux pinning indicated behavior of type II superconductors. A 25–405 diamagnetic state indicating bulk superconductivity in GdBa2Cu3O7−x.