Superconductivity at 27 K in modulation-free Bi2-xPbxSr2-yLayCuO6 phases with x≅y+0.2

{Structural and physical properties are reported for compounds made by simultaneous substitution of Bi by Pb and of Sr by La in the 10 K superconducting Bi cuprate Bi2-xPbxSr2-yLayCuOz. The phase diagram in the x-y plane was was established. It contains two phases separated by a region of two-phase coexistence: the O(1) phase of the starting material (x=y=0), which is pseudotetragonal, and the O(2) phase found at higher Pb concentrations, which is orthorhombic. In agreement with TEM observations, which show the disappearance of the modulation in the O(2) phase, a single crystal of Bi1.2Pb0.8Sr1.5La0.5CuO6 showed orthorhombic symmetry and no modulation by X-ray diffraction, with the space group Pnan and cell parameters a=5.328(1) Å