The superconductivity of single phase La1.5-x/2SrxBa1.5-x/2Cu3Oy, 0 =< x =< 0.80 (LSB) compounds with tetragonal triple-perovskite structure was studied. Samples with 0.10 =< x =< 0.80 are superconducting and Tc(zero) is found between 28 and 48 K. With increasing x, both the hole concentration in the Cu2-O layers (the copper oxygen layers in the center perovskite layer) and Tc increase. It is interesting to find that although the hole concentration and oxygen stoichiometry of the LSB series are similar to those of the La1.5-x/2CaxBa1.5-x/2Cu3Oy (LCB) series, the maximum Tc of the LSB series is about 30 K lower than that of the LCB series. The difference in Tc is probably a result of difference in locations of the Ca2+ and Sr2+ ions in the unit cell. The smaller divalent Ca2+ ion prefers the smaller trivalent Y3+ site and acts as a hole dopant for the superconducting Cu2-O layers. On the contrary, the larger divalent Sr2+ ion presumably prefers the larger divalent Ba2+ site, and thus hole doping on the Cu2-O layers is not as prominent as the Ca2+ ion in the Y3+ site.
Physica C: Superconductivity and its Applications 268(1-2), pp.128-132