Enhancement of Tc by Sr substitution for Ba in Hg-2212 superconductor

The Ba substitution by Sr has been studied in two Hg-2212 series: Hg2(Ba1-ySry)2YCu2O8-δ and Hg2(Ba1-ySry)2(Y0.80Ca0.20)Cu2O8-δ. In both series a Tc enhancement of about 40 K is observed when Sr substitutes Ba from y=0 to 1.0. The y=0 compound of the first series is the non-superconducting Hg2Ba2YCu2O8-δ prototype. In the second series, this y=0 compound is already superconducting at 21 K. Indeed the members of this series present a higher charge carrier density in their CuO2 superconducting planes than their homologues of the first series due to the doping introduced by the substitution of 20% of Y by Ca. The compounds of both series were synthesized in high pressure (3.5 GPa)-high temperature (950-1050 deg. C) conditions. In both cases Sr substitution was successful up to the full replacement of Ba (y=1.0). The Hg-2212 phases were characterized by XRD, SEM, EDX and a.c. susceptibility