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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]

Two coordination polymers [Cu(BIM)(suc)]n (1) and [Cd(BIM)(ox)(H2O)]n (2) (where BIM = bis(imidazol-1-yl)methane, suc = succinic dianion, and ox = oxalic dianion) have been solvothermally synthesized and characterized by single-crystal X-ray diffraction. Complex 1 crystallizes in the monoclinic space group C2/c with a = 12.2302(8) Å, b = 11.4007(6) Å, c = 10.1791(6) Å, β = 118.4090(10)°, V = 1248.38(13) Å3, and Z = 4. Cu(II) is square planar with nitrogen from BIM ligand and oxygen from the suc in the trans arrangement. Each BIM is bidentate bridging two Cu(II)s to generate a 1-D zigzag chain; the suc bridges two Cu(II)s in a monodentate gauche conformation, which results in the formation of wavy 2-D (4, 4) grid arrays. Complex 2 crystallizes in the monoclinic space group P2(1)/n with a = 10.8042(3) Å, b = 9.1053(2) Å, c = 12.0134(6) Å, β = 96.394(1)°, V = 1174.47(7) Å3, and Z = 4. Cd(II) is coordinated in a distorted decahedral geometry. Each BIM is bidentate bridging two Cd(II)s to form a 1-D infinite zigzag chain; each ox bridges two neighboring Cd(II)s in a distinct zigzag chain in a chelating/chelating coordination mode, which extends the 1-D chain to a 2-D supramolecular network. [ABSTRACT FROM AUTHOR]

Two cadmium(II) coordination polymers, [Cd(2-mBIM)(NCS)(SCN)]n (1) and [Cd2(2-mBIM)2(NO3)2(C4H4O4)(H2O)5]n (2) (2-mBIM = bis(2-methylimidazo-1-yl)methane, C4H4O4= succinate), have been synthesized and characterized by X-ray diffraction. Complex 1 crystallizes in the triclinic space group P1 with a = 9.0770(5) Å, b = 9.4043(4) Å, c = 19.8720(9) Å, α = 101.551(1)°, β = 93.498(1)°, γ = 108.484(1)°, V = 1562.02(13) Å3, and Z = 2. Each Cd(II) is octahedrally coordinated and connected with two adjacent Cd(II)'s by double end-to-end thiocyanate bridges, resulting in the formation of 1-D zigzag chains, linked to each other via bridging 2-mBIM giving a 2-D supramolecular framework. Complex 2 crystallizes in the monoclinic space group P2(1)/n with a = 12.6543(6) Å, b = 7.7128(4) Å, c = 17.3089(9) Å, β = 109.3980(10)°, V = 1593.45(14) Å3, and Z = 2. Cd(II) is coordinated with oxygen and nitrogens from two independent 2-mBIM, in a cis-configuration to form a 1-D helical structure. A 3-D supramolecular network comprised of succinate anion bridged 1-D helical chains, and weak hydrogen bonds between dimer waters gave 2-D layers. [ABSTRACT FROM AUTHOR]