Properties and structure of (Tl_0.5Pb_0.5)Sr₂(Ca_1−xNd_x)Cu₂O_z(Tl-1212) superconductors

Abstract

Bulk material of Nd-doped Tl-1212 superconductors was prepared via a two-step procedure based on a wet chemical method to prepare precursor material followed by heat-treatment at 895 °C for 10 h. The samples with Nd stoichiometry of x = 0.05, 0.1, 0.15, 0.20 0.25 and 0.30 were characterized by XRD, electron microscopy and by resistance measurements. Oxygen stoichiometry of the specimens was analyzed. Lattice parameters were derived from x-ray diffraction and neutron diffraction measurements. The increase of the a-axis and the decrease of the c-axis as a function of the Nd content are discussed.

Effects of low-level La doping and ageing on TlPb-1223 high T c superconductors

“…It can be assumed that the weak improvement of T c of Ladoped samples in comparison to the sample without La is caused by higher overall oxygen content of La-doped samples as discussed before. This is in accordance with the observed results of the rare earth substitutions in the Ca position in Tl-1223 superconductors [22].…”

“…From the height of the first magnetization peak of M vs. H a curves near zero values of H a , it can be inferred that La improves inter-grain critical current density and/or intragrain pinning of all doped samples in this field range at The (Tl,Pb)-0.04La sample shows the best magnetization hysteresis and thus highest value of J c (77 K, 0 Am −1 ) for all treatments. It has been reported recently [22] that the substitution of rare-earths into the Ca site in Tl-based superconductors improves superconducting properties for low substitution level and deteriorates the superconductivity for higher substitution levels. The decreasing of the slope of the curves at x 0.07 (Fig.…”

Properties, magnetic susceptibility, critical currents and irreversibility fields of (Tl0.5Pb0.5)Sr2(Ca1−xGdx)Cu2Ozbulk superconductors

“…The oxygen content was analyzed by an iodometric titration as described in the literature [25,32,33]. For the estimation of the 'Cu valency' the following formal oxidation states of the cations in the sintered superconductor were assumed: Pb: 4+, Gd and Tl: 3+, Sr and Ca: 2+.…”