  The Ba substitution by Sr has been studied in two Hg-2212 series:
Hg2(Ba(1-y)Sr(y))2YCu2O8-d and Hg2(Ba(1-y)Sr(y))2(Y0.80Ca0.20)Cu2O8-d. In both
series a Tc enhancement of about 40 K is observed when Sr substitutes Ba from y
= 0 to y = 1.0.
  The y = 0 compound of the first series is the non superconducting
Hg2Ba2YCu2O8-d 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 - 1050C) 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.
