Partial substitution of Ba for Sr in the cuprate superconductor Bi ₂ (Sr,La) ₂ CuO _{6+ δ}

Polycrystalline samples of the Bi-based cuprate superconductors Bi ₂ Sr _{2- x - y} Ba _x La _y CuO _{6+ δ} (y(La) = 0, 0.4, 0.6) have been prepared by the conventional solid-state reaction method to increase the superconducting transition temperature, T _c , in the so-called Bi-2201 phase. It has been found that the solubility limit of Ba is x(Ba) = 0, 0.2 and 0.3 for y(La) = 0, 0.4 and 0.6, respectively. Accordingly, the La-substitution for Sr is effective for the Ba-substitution for Sr. Superconductivity has also been observed for the Ba-substituted samples, but the increase in T _c through the Ba-substitution is only a few Kelvins.