Hg sub(0.95)Re sub(0.05)Ba sub(2)Ca sub(2)Cu sub(3)O sub(8+ delta ) superconductor: Sample preparation and transport properties under hydrostatic pressure

Samples of the Hg sub(1-x)Re sub(x)Ba sub(2)Ca sub(2)Cu sub(3)O sub(8+ delta ) superconductor (Hg, Re-1223), with low rhenium (Re) content (x identical with 0.05), have been produced with the help of a novel thermobaric analysis technique which could monitor the total pressure inside the quartz tube during synthesis at high temperature. The sample quality was verified by means of Rietveld analysis of the x-ray diffraction data, and by ac susceptibility measurements. The formation and stability of the Hg, Re-1223 phase has also been investigated by varying the oxygen content of the Re sub(0.05)Ba sub(2)Ca sub(2)Cu sub(3)O sub(8+ delta ) precursor, and the mercury filling factor (ff sub(Hg) identical with 0.00 to 0.014 g cm super(-3)). It was observed that the reduction of oxygen content in the precursor (Re sub(0.05)Ba sub(2)Ca sub(2)Cu sub(3)O sub(8+ delta )) and the increase of the mercury partial pressure inside the quartz tube enhanced the yield of the superconductor phase. Resistance measurements as a function of temperature under hydrostatic pressure (0-1.0 GPa) show an increase in the superconducting transition temperature which can be fitted with a parabolic curve. The reduction of the lattice volume induced by external hydrostatic pressure is similar to the one induced by chemical pressure due to rhenium (Re) doping (0.00 < x < 0.10); however T sub(C) does not depend on the chemical pressure. This behaviour can be understood on the basis of the pressure-induced charge transfer model (PICTM) modified by Almasan et al.