Effect of 3d metal ion doping on the structure and superconductivity of (Tl0.5Pb0.5)Sr2CaCu2O7 (original) (raw)

Superconductivity at 124 K in (Tl, Pb)Sr2Ca2Cu3O9

Physica C Superconductivity, 1992

We report the preparation of almost phase pure (T10.sPbo.s)Sr2Ca2Cu3Og, which is characterized by high temperature superconductivity with T¢onset= 130 K, Tcmidpoint= 124 K, Tczero= 122.5 K as measured by electrical resistance, and a diamagnetic onset temperature, Tcm~ of 124 K determined by DC magnetic susceptibility. The new procedure involves synthesizing a material with nominal stoichiometry (Tlo.sPbo.5)Srl.6Ca2.4Cu3Og, which is encapsulated in gold foil and sintered at 950°C for 3 h in oxygen, then sealed in an evacuated quartz tube and finally annealed at 700~ 750°C for 5 ~ l0 days. From the results of X-ray diffraction and energy-dispersive X-ray spectrometry (EDS), we have identified the phase responsible for the superconductivity in the annealed sample to be Tlo.sa(3)Pbo.3s(2)Srt.9t2)Ca2.~ o)Cu309. No superlattice and intergrowth along the a* and c* directions were observed but streaks along the c*-axis were found from microcrystallites of the annealed sample.

Characterization of superconducting (Tl,Bi)Sr2CaCu2Oy

Physica C: Superconductivity, 1996

The superconducting phase with mixed TI and Bi, namely (Tlo.55Bio.45)Sr2CaCu20y, was synthesized and characterized. Synthesis conditions were studied, and this phase, (TI,Bi)-1212, was found to form preferentially to (TI,Bi)-1223 when Sr was present with no Ba present. X-ray powder diffraction with Rietveld refinement provided structural data. The phase is tetragonal with a = 3.7988(4) A and c = 12.076(1) A, with space group symmetry P4/mmm, and with a platelet crystal morphology. Magnetic-susceptibility data gave an onset of superconductivity T c at 94.9 + 1.3 K with a T c mid of 86.0 + 1.1 K. Magnetic-hysteresis measurements showed that substantial flux pinning occurs in this phase at high temperatures.

Structural characterization and superconducting properties of (Tl0.5Pb0.5)(Sr2−xBax)Ca2Cu3O9−δ

Physica C: Superconductivity, 1996

Samples of nominal composition (Tlo.sPbo.sXSr2_xBax)Ca2Cu309_~, 0 < x < 0.6, and (Tlo.6Pbo.2Bio.2)(Srt.8Bao.2)-Ca2Cu309_~5 were characterized by X-ray powder diffraction, scanning electron microscopy and AC susceptibility measurements. In the Bi-free samples, the highest weight fraction of the 1223 phase, 91.3%, was observed for x = 0.4. Above this Ba content, BaPbO 3 perovskite appeared as main impurity phase. In the Bi-containing sample the weight fraction was even higher, 92.6%. The Ba content of the 1223 phase, as determined from X-ray diffraction data, was in agreement with the nominal composition of the samples. The unit cell parameters increased when the Sr atoms were progressively replaced by the larger Ba atoms. The refinement of the crystal structure of the 1223 phase revealed a significant off-centering of the TI site. The distance from the splitted site to the ideal position on the four-fold axis was found to be ~ 0.26 ,~ for the Ba-containing samples, but only 0.07 ,~ for the Ba-free sample. The distance from the Cu atom to the apical atom of the square pyramid formed by the oxygen atoms increased from 2.29 to 2.50 ,~ as the Ba content was raised. The critical temperature remained between 116 and 120.5 K and was not significantly affected by changes in composition or structure.