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Effect of Mg doping on the superconducting properties of Cu/sub 1-x/Tl/sub x/Ba/sub 2/Ca/sub 3-y/Mg/sub y/Cu/sub 4/O/sub 12-/spl delta//

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2 Author(s)
N. A. Khan ; Dept. of Phys., Quaid-i-Azam Univ., Islamabad, Pakistan ; S. Nawaz

Superconducting properties of Cu1-xTlxBa2Ca3-yMgy Cu4O12-delta (Cu1-xTlx Mgy-1234) material have been studied in the composition range y=0,1.5,2.25. The zero resistivity critical temperature [Tc (R=0)] was found to increase with the increased concentration of Mg in the unit cell; for y=1.5 [Tc(R=0)]=131 K was achieved which is hitherto highest in Cu1-xTlx-based superconductors. The X-ray diffraction analyses have shown the formation of a predominant single phase of Cu0.5Tl0.5Ba2Ca3-yMgy Cu4O12-delta superconductor with an inclusion of impurity phase. It is observed from the convex shape of the resistivity versus temperature measurements that our as-prepared material was in the region of carrier over-doping, and the number of carriers was optimized by postannealing experiments in air at 400degC, 500degC, and 600degC. The Tc(R=0) was found to increase with postannealing and the best postannealing temperature was found to be 600degC. The mechanism of increased Tc(R=0) is understood by carrying out infrared absorption measurements. It was observed through softening of Cu(2)-OA-Tl apical oxygen mode that improved interplane coupling was a possible source of enhancement of Tc(R=0) to 131 K

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IEEE Transactions on Applied Superconductivity  (Volume:16 ,  Issue: 1 )