Influence of Sr substitution on structure, hole concentration in CuO2 planes, and irreversibility line in (Hg,Pb) (Ba,Sr)(2)Ca2Cu3O8+delta single crystals

Single crystals of HgBa2Ca2Cu3O8+delta compound with partial substitution o f Sr and Pb have been grown at high gas pressure. Bond valence sum calculat ions show that the substitution of Sr for Ba leads to a more homogeneous di stribution of holes between nonequivalent CuO2 planes. In nonsubstituted cr ystals, the density of holes is significantly higher in the inner CuO2 plan es. The irreversibility field increases on Sr substitution. The thickness o f the charge reservoir decreases with Sr substitution by 0.7 Angstrom.