Strontium substitution for barium in mercury superconductors

HgBa2-xSrxCuO4+delta (x = 0.06 - 0.45) and Hg1-yVyBa2-xSrxCuO4+delta (x = 0 .16 - 1.1, y = 0.2 - 0.35) series were prepared by the encapsulation method . In the former series the optimum doping level is achieved by annealing un der oxygen for x = 0.06 and by annealing under nitrogen for x = 0.45. This behaviour is explained by different equilibrium oxygen pressures over phase s with different Sr content. The decrease of T-c is similar to -8 K/x. The latter series is doped by replacing (HgO2)(2-) groups by (VO4)(3-) tetrahed ra and optimum doping is achieved by argon annealing.