Increased Solubility of Mg at Ca Site in Cu0.5Tl0.5Ba2Ca2Cu3O10−δ Superconductor

The Cu0.5Tl0.5Ba2Ca2−yMgyCu3O10−δ (y=0, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8, 1.0, 1.5, 2.0) superconductor has been synthesized at the atmospheric pressure by the solid-state reaction method. The zero resistivity critical temperature is found to increase to 98 K with Mg concentration of y=0.6, but saturates to 97 K with further enhancement of Mg to y=0.8, 1.0, and 1.5. The Mg doped material grows in tetragonal structure and follows P4/mmm symmetry with a & c-axes lengths of 3.894 Å & 15.091 Å for y=1.5. The axes lengths were decreased with the increase of Mg content in the unit cell, which shows that anisotropy of the material decreases. The critical current density and the quantity of diamagnetism in the samples with Mg contents are higher than in the samples without Mg. In order to realize the effects of decreased axes lengths on the phonon modes of Cu0.5Tl0.5Ba2Ca2−yMgyCu3O10−δ, we have carried out FTIR absorption measurements.