No abstract

In this report, we describe the structure of a robust and highly conductive 3D graphene oxide hydrogel. The reduced graphene oxide hydrogel or rGH is fabricated by a crosslinking reaction with ethylene diamine followed by a hydrazine reduction. The material showed a high electrical conductivity of 1351 S m À1 and a specific surface area of 745 m 2 g À1 with 10.3 MPa break strength. When used as electrodes for a supercapacitor, it showed a high specific capacitance of 232 F g À1 .

We analyze the infrared reflectivity of Lal.85Sr0.~sCuO4 single crystals with E parallel to the c-axis. The plasma edge at around 6 meV (50 cm-I), which occurs only for T < T¢, is due to Cooper-pair tunneling. This low value of the plasma edge is shown to be consistent with the c-axis plasma frequency obtained from LDA band structure calculations (> 0.1 eV) if we take into account that the single-particle charge transport along the c-axis is strongly incoherent in the normal state, and remains so in the superconducting state. From a comparison of the optical conductivity with model calculations based on sand d-wave weak-coupling theory in the dirty limit, we find no evidence for a reduction of the c-axis quasi-particle scattering rate below T~. The c-axis scattering rate, the normal-state c-axis plasma frequency, and Tc obey hT > hvp >> 3.5kBTc, which is exactly opposite to the clean limit.

Bi-2212 superconducting single crystals were grown by the travelling solvent floating zone method at different oxygen ambient pressures. Electron probe micro-analysis showed a systematic increase of the Sr/Ca ratio in the as-grown crystals with increasing oxygen ambient pressure and a maximal superconducting transition temperature of Tc~onset= 95 K, and ziT= 1.5 K was obtained for crystals grown at an oxygen ambient pressure of 200 kPa. Thermogravimetric and post-annealing experiments in air at 500 and 800°Chave shown that the oxygen content and the Tconset values in the crystal do not depend only on the annealing temperature, but also on its chemical composition. The in-field current density J~measured at 5 K on crystals grown at 200 kPa oxygen ambient pressure was considerably smaller than that of crystals grown in air.