Ti-doped (Cu0.5Tl0.5)Ba2Ca2 (Cu3−xTix)O10−δ (x = 0, 0.25, 0.50, 0.75) superconductors

► Ti-doped (Cu0.5Tl0.5)Ba2Ca2 (Cu3−xTix)O10−δ superconductors. ► Suppression of superconductivity after carriers' optimization in all Ti-doped samples. ► Hardening of the planer oxygen mode is due to the smaller mass of Ti (47.90 amu) as compared to that of Cu (63.54 amu). ► Existence of two different masses in CuO2/TiO2 planes may suppress the population of phonon modes. ► Suppression of superconductivity in Ti-doped samples indicates that the electron-phonon interactions are essential.