CATIONIC SUBSTITUTIONS IN THE 2201-1201-INTERGROWTH HGTL2BA4CU2O10

The study of the substitution of strontium for barium and of mercury f or thallium in the cuprate HgTl2Ba4Cu2O10 has allowed two solid soluti ons to be synthesized, HGTl(2)Ba(4-x)Sr(x)Cu(2)O(10) with 0 less than or equal to x less than or equal to 1.5 and HG(1+y)Tl(2-y)Ba(4)Cu(2)O( 10+delta) with 0 less than or equal to y less than or equal to 0.4. Th e XRD and HREM studies of these phases confirm that they consist of re gular intergrowths of the 1201 (HgBa2CuO4 type) with the 2001 (Tl2Ba2C uO6 type) structures and show that barium and strontium are statistica lly distributed over the two kinds of [AO](infinity) layers (A = Ba, S r). The investigation of the superconducting properties shows that the as-synthesized phases are overdoped and do not superconduct but can b e optimized by annealing in an hydrogenated argon flow. The substituti on of thallium by mercury does not modify the superconducting properti es; a T-c of 50 K is reached for Hg1.4Tl1.6Ba4Cu2O10-delta, i.e., clos e to that observed for HgTl2Ba4Cu2O10. On the opposite the substitutio n of strontium for barium leads to a rapid decrease of T-c for HgTl2Ba 4-xSrxCu(2)O(10), from 50 K for x = 0 to 30 K for x = 0.8, and superco nductivity vanishes for x > 0.8.