Title :
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//
Author :
Khan, Nawazish A. ; Nawaz, Shahid
Author_Institution :
Dept. of Phys., Quaid-i-Azam Univ., Islamabad
fDate :
3/1/2006 12:00:00 AM
Abstract :
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
Keywords :
X-ray diffraction; annealing; barium compounds; calcium compounds; copper compounds; doping profiles; electrical resistivity; high-temperature superconductors; inclusions; infrared spectra; magnesium; magnesium compounds; softening; superconducting transition temperature; thallium compounds; 131 K; 400 C; 500 C; 600 C; Cu(2)-OA-Tl; Cu1-xTlxBa2Ca3-yMg yCu4O12-delta:Mg; Mg concentration; Mg doping; X-ray diffraction analyses; apical oxygen mode; carrier over-doping; convex shape; highest hitherto; impurity phase; inclusion; infrared absorption measurements; interplane coupling; optimization; postannealing experiments; predominant single phase; resistivity versus temperature measurements; softening; source enhancement; superconducting properties; unit cell; zero resistivity critical temperature; Composite materials; Conductivity; Doping; Electromagnetic wave absorption; Impurities; Shape measurement; Superconducting materials; Superconductivity; Temperature measurement; X-ray diffraction; Cu; Mg doping; improved interplane couplings; normal pressure synthesis;
Journal_Title :
Applied Superconductivity, IEEE Transactions on
DOI :
10.1109/TASC.2006.869914
