Stabilizing the Tl-1223 phase by doping with tellurium

Te-doping of (Tl_0.54Pb_0.5−xTe_x)(Sr_0.85Ba_0.15)₂Ca₂Cu₃O_y superconductors with x ranging from 0 to 0.1 has been investigated. Small amounts of Te (x < 0.05) strongly favoured the formation of the Tl-1223 phase in bulk samples, leading to phase-pure material. The concentration of the Tl-1212 phase was below the detection limit of the x-ray diffraction. The critical temperatures of bulk phase Tl-1223 for x = 0.02 were 120 K. The transition widths narrowed and the critical current densities for bulk phase material increased upon addition of small amounts of Te. At higher doping levels, Ba₂CuTeO₆ appeared as a secondary phase but the remaining material was still high-purity Tl-1223 phase. (Tl_0.54Pb_0.48Te_0.02)(Sr_0.85Ba_0.15)₂Ca₂Cu₃O_y films on lanthanum aluminate substrates prepared by screen printing of the precursor and followed by ex situ thallination, lead to highly c-axis oriented and ab-aligned samples with critical temperatures T_c(0) of 117 K and transition widths ΔT_(90–10%) of 1 K. Critical current densities of 1.15 × 10¹⁰ A m⁻² were achieved for 1.5 µm thick films in self-field at 77 K. The critical current densities at 0.8 T and 77 K were 7.4 × 10⁹ A m⁻² for H||ab and 0.7 × 10⁻⁹ A m⁻² for H||c.