Normal pressure synthesis of Mg-doped Cu0.5Tl0.5Ba2Ca2Mg2Cu5O14−δ superconductor

The Cu0.5Tl0.5Ba2Ca2Mg2Cu5O14−δ (Cu0.5Tl0.5Mgy-1245) superconductor is synthesized by a simple solid-state reaction at normal pressure. This material has a Cu0.5Tl0.5Ba2O4−δ charge reservoir layer and five CuO2 planes. The as-prepared material has shown the zero resistivity critical temperature at 94 K, which is increased to 132.6 K by post-annealing in air atmosphere. The lengths of a and c axes calculated by fitting the diffraction lines to tetragonal structure are 3.916 Å and 21.254 Å, respectively. The most likely explanation of decreased c-axis length is improved inter-plane coupling arising possibly from the substitution of Ca by higher electronegativity Mg. The improved inter-plane coupling is also evidenced by the softening of apical oxygen phonon modes observed by FTIR absorption measurements.