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The Sr and Ba bearing Tl-1212 phase, Tl(Ba,Sr)CaCu 2 O 7 is an interesting superconductor. The Sr only bearing TlSr 2 CaCu 2 O 7 is not easily prepared in the superconducting form. The Ba only bearing TlBa 2 CaCu 2 O 7 on the other hand does not show improvement in the transition temperature with elemental substitution. In this work the influence of multivalent Se (non-metal) and Te (metalloid) substitutions at the Tl-site of Tl 1- x M x (Ba,Sr)CaCu 2 O 7 (M = Se or Te) superconductors for x = 0–0.6 was studied. The samples were prepared via the conventional solid-state reaction method. XRD patterns showed a single Tl-1212 phase for x = 0 and 0.1 Se substituted samples. The critical current density at the peak temperature, T p of the imaginary (χ") part of the AC susceptibility (χ = χ' +χ"), J c-inter (T p) for all samples was between 15 and 21 A cm−2. The highest superconducting transition temperature was shown by the x = 0.3 Se-substituted sample (T c-onset = 104 K, T c-zero = 89 K, T cχ' = 104 K and T p = 80 K). Te suppressed the superconductivity of Tl-1212 phase. The order of highest transition temperatures are as follows: Tl 1- x Te x (Ba,Sr)CaCu 2 O 7

The effects of elemental substitutions at the Tl site of a Tl1−xXx(Ba, Sr)CaCu2O7 superconductor with X = Cr, Bi, Pb, Se, and Te were investigated. This study aimed to determine the elements that enhance and suppress the superconducting transition temperature of the Tl1−xXx(Ba, Sr)CaCu2O7 (Tl-1212) phase. The selected elements belong to the groups of transition metal, post-transition metal, non-metal, and metalloid. The relationship between the transition temperature and ionic radius of the elements was also discussed. The samples were prepared by the solid-state reaction method. The XRD patterns showed a single Tl-1212 phase was formed in the non- and Cr-substituted (x = 0.15) samples. The Cr-substituted samples (x = 0.4) showed a plate-like structure with smaller voids. The highest superconducting transition temperatures (Tc onset, Tcχ′, and Tp) were also achieved by the Cr-substituted samples for x = 0.4 compositions. However, the substitution of Te suppressed the superconductivity of the Tl-1212 phase. Jc inter (Tp) for all samples was calculated to be in the range of 12–17 A/cm2. This work shows that substitution elements with a smaller ionic radius tend to be more favorable in improving the superconducting properties of the Tl-1212 phase. [ABSTRACT FROM AUTHOR]

In the present work, the effect of Nd/Sr partial replacement on the crystallographic, morphological, electrical, and superconducting properties of Bi1.8Pb0.35Sr1.9-yNdyCa2.2Cu3Ox materials is studied with the aid of powder X-ray diffraction (XRD), dc electrical resistivity versus temperature (ρ-T), scanning electron microscope (SEM), and electron dispersive X-ray (EDX) measurements. The crystal structure of new produced materials is defined in the tetragonal crystal system with the P4/mmm space group. According to the experimental results observed, the quantity of characteristic Bi-2223 superconducting phase is found to reduce regularly with the enhancement of Nd nanoparticles in the crystal system, confirming that the replacement of Nd impurity at the Sr site causes an increase in the characteristic Bi-2212 superconducting phase. Similarly, the reductions of average crystallite size and c-lattice cell parameter as well as the systematic increment in the a-axis length verify that the partial Nd/Sr substitution deteriorates the Bi-2223 superconducting phase. Moreover, the experimental results display that the offset superconducting transition temperature ( T c offset ) is observed to decrease dramatically with increasing the concentration level of Nd impurity. In this context, the maximum T c offset parameter is noticed to be about 104.3 K for the pure Bi-2223 superconducting ceramic sample. This may be related to the degradation in the strength quality of transcrystalline regions, intergrain boundary couplings, and especially crystallinity quality. Furthermore, the SEM images demonstrate that the increment of Nd foreign impurities in the bulk Bi-2223 superconducting materials damages the flaky layers of platelet-like shape for the superconducting grains. [ABSTRACT FROM AUTHOR]