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Thallium-based high-temperature superconductors exhibit excellent superconductivity performance (Tc, Jc). Formation of the Tl-based superconducting materials critically depends on the used precursor and synthesis conditions. In the present investigation, we used the in situ polymerization method for synthesizing high-purity and reaction-ability precursors. We find the critical dependence of Tl-based superconductor phase formation on the quantity of applied oxygen pressure. The experimental results showed that the Tl-1223 phase formed at an oxygen gas pressure at 1 to 2 atm, Tl-2223 phase at 3 atm, and Tl-2212 phase at 4 to 8 atm. [ABSTRACT FROM AUTHOR]

This paper presents sol-gel (SG) and solid-state reaction (SSR) pathways to produce multiphase ceramic precursors of BCCO and then the superconducting phase of Tl-1223. The heat treatments showed that to obtain high-purity precursors prepared by SG and SSR methods are sufficient to heat treatments at 915 and 945 °C, respectively. Furthermore, the diamagnetic onset temperature of the superconducting transition for the Tl-1223 samples prepared by precursors SG at 915 °C and SSR at 945 °C is approximately 120 K, and complete screening of applied ac magnetic fields observed at T ≈ 102 and ≈ 94 K, respectively. In addition, the value of the transport critical current density Jc for SSR was 128 A/cm2, whereas for the SG sample it was precisely 174 A/cm2. Thus, we could conclude that using wet chemistry offers some advantages over classical solid-state ceramic processing, significantly better chemical homogeneity, and higher reactivity of the precursor powder. [ABSTRACT FROM AUTHOR]

This research carried out experiments on the Chevrel-phase Mo6S6I2 polycrystalline superconductor. The behavior of harmonic generation in the dc magnetic fields, the dependence of the high harmonics on the ac magnetic field amplitude, the dc magnetic field, and the temperature are investigated. The experimental results are well described by the classical Bean critical state model, when the current does not depend on the dc field and even harmonics are not observed. [ABSTRACT FROM AUTHOR]