Strontium substitution for barium in mercury superconductors

HgBa sub(2-x)Sr sub(x)CuO sub(4+ delta ) (x identical with 0.06 - 0.45) and Hg sub(1-y)V sub(y)Ba sub(2-x)Sr sub(x)CuO sub(4+ delta ) (x identical with 0.16 - 1.1, y identical with 0.2 - 0.35) series were prepared by the encapsulation method. In the former series the optimum doping level is achieved by annealing under oxygen for x identical with 0.06 and by annealing under nitrogen for x identical with 0.45. This behaviour is explained by different equilibrium oxygen pressures over phases with different Sr content. The decrease of T sub(c) is approx. -8K/x. The latter series is doped by replacing (HgO sub(2)) super(2-) groups by (VO sub(4)) super(3-) tetrahedra and optimum doping is achieved by argon annealing.