Zn-doped Cu0.5Tl0.5Ba2Ca3Cu4−yZnyO12−δ (y=0,1,2,3,4), Cu0.5Tl0.5BaSrCa3Cu4−yZnyO12−δ (y=0,1,2,3,4) superconductors.

Abstract The role of the thickness of the charge reservoir layer on the Fermi level and its influence on charge transfer to the conducting CuO2/ZnO2 planes is examined by substituting Sr at the Ba sites in Zn-doped Cu0.5T l0.5Ba2Ca3Cu4−yZnyO12−δ(y = 0, 1, 2, 3, 4) and Cu0.5T l0.5(BaSr)Ca3Cu4−yZnyO12−δ(y = 0, 1, 2, 3, 4) samples. Sr atoms, with atomic/covalent radii of 2.15/1.92˚A, are smaller than Baatoms (2.17/1.98˚A), leading to a more reduced spread of their bonding wavefunctions. The smaller size of Sr is anticipated to reduce the thickness of the charge reservoir layer, potentially affecting the charge transfer mechanism to the conducting planes, where the superconductivity mechanism takes place. The role of spin-carrying 3d9 Cu atoms and their small spin in the high-Tc superconductivity mechanism is further examined by doping Zn at the CuO2 planar sites in Cu0.5T l0.5Ba2Ca3Cu4−yZnyO12−δ(y = 0, 1, 2, 3, 4) and Cu0.5T l0.5(BaSr)Ca3Cu4−yZnyO12−δ(y = 0, 1, 2, 3, 4) samples. These samples are analyzed through X-ray diffraction, resistivity measurements, excess conductivity analysis, and FTIR absorption measurements. They exhibit an orthorhombic crystal structure, with cell parameters decreasing due to Sr and Zn doping in the final compound. The critical temperature for zero resistivity initially increases with Zn doping at the Cu sites for y = 1 and 2, but decreases with higher Zn doping (y = 3, 4). Excess conductivity analysis of resistivity data shows that these samples exhibit no significant changes in intrinsic superconductivity parameters such as ξ c, vF , Bc(0), Bc1(0), Bc2(0), Jc(0), and κ = πξ. These parameters remain relatively unchanged in both Cu0.5T l0.5Ba2Ca3Cu4−yZnyO12−δ(y = 0, 1, 2, 3, 4) and Cu0.5T l0.5(BaSr)Ca3Cu4−yZnyO12−δ(y = 0, 1, 2, 3, 4) samples with Sr and Zn doping. These intrinsic superconductivity parameters are dependent on carrier density and the position of the higher Fermi level of the charge reservoir layer, indicating that a reduction in the thickness of the charge reservoir has a minimal effect on the charge transfer mechanism and, consequently, on superconductivity. Conversely, T lBa2Ca3Zn4O12−δ and T lBaSrCa3Zn4O12−δ samples become semiconducting, with their conductivity following a variable range hopping (VRH) mechanism and exhibiting an energy gap of approximately 6.03 meV and 0.7 meV. This underscores the crucial role of spin-carrying Cu3d9 atoms in the high-Tc superconductivity mechanism, where the interaction of spin and charge density waves plays a significant role in achieving higher Tc in oxide superconductors. Furthermore, the phonon modes associated with apical oxygen atoms and CuO2/ZnO2 planar oxygen atoms in both v samples are softened with increased Zn incorporation, indicating intrinsic Zn doping in the final compounds. The softening of apical oxygen modes, such as Tl-OA-Cu(2) and Cu(1)-OA-Cu(2), along with planar oxygen modes CuO2/ZnO2, further confirms intrinsic Zn doping in these final compounds.