Optimization of the Bi-2201 superconductors with Pb and La co-doping

The hole concentration p was varied with changing the Pb content for the double-doped crystals of Bi2−xPbxSr2−yLayCuO6+δ. Optimal Tc of 40.8 K was obtained for the as-grown crystals with x = 0.3 and y = 0.1. Moreover, the hole concentration was varied by the oxygen annealing process for the crystals with the optimal Tc. The Tc vs. p profile was similar to the one for the as-grown samples, but the optimal Tc was the different value of 34.8 K.