Superconductivity in Ti, Sb, Yb, Bi, Pb and Y multiply substituted TI1212 system / Wan Faizah Wan Abdullah

The effects of the elemental substitution on the 1212 phase formation and
superconducting properties of (Tl,Bi)(Sr,Ti)2Ca0.9Y0.1Cu2O7 and
(Tl,Pb)(Sr,M)2CaCu2O7 (M = Yb, Sb) series have been investigated. The samples
were prepared using high purity oxides by solid state and precursor method. Crystal
structures of the samples were analyzed using X-ray powder diffraction method
while microstructures were investigated by scanning electron microscope (SEM).
Measurements of electrical resistance were carried out using standard four-pointprobe
method. Powder X-ray diffraction patterns for
Tl0.9Bi0.1Sr2-yTiyCa0.9Y0.1Cu2O7 (y = 0 – 0.5) with Bi, Ti and Y triple substitution
revealed that all the samples consist mostly of major 1212 and minor 1201 crystalline
phases. Temperature dependent resistance measurements on
Tl1-xBixSr1.9Ti0.1Ca0.9Y0.1Cu2O7 (x = 0 – 0.6) showed optimum superconductivity for
x = 0.3 with Tc onset of 93.3 K and Tc zero of 68.2 K Temperature dependent electrical
resistance measurements on Tl1-mPbmSr1.8Yb0.2CaCu2O7 (m = 0.1– 0.5) showed
metallic normal state behaviors and increase in Tc zero from 61.1 K at m = 0.1 to a
maximum value of 101.1 K at m = 0.5. Substitutions of Yb at Sr-site of
Tl0.5Pb0.5Sr2-nYbnCaCu2O7 with n = 0 – 0.6 increased value of in Tc zero from 62.2 K at
n = 0 to a maximum value of 101.1 K at n = 0.2. Substitution of Pb at Tl-site and Sb
at Sr-site in Tl1-qPbqSr1.8Sb0.2CaCu2O7 (q = 0.1 – 0.6) promote 1212 phase formation
and increased in Tc zero from 26.1 K at q = 0.1 to 80.2 K at q = 0.5. From this study, it
is found that apart from the Tl and Ca sites, Sr-site substitution is also effective in
optimizing critical temperature, Tc and critical current density, Jc of Tl1212 samples.
The results were discussed in terms of the concept of average copper valence and
ionic radius of elements.
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