Stabilising the Tl-1223 phase by doping with tellurium

Te-doping of (Tl0.54Pb0.5-xTex)(Sr0.85Ba0.15)2Ca2Cu3Oy 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. (Tl0.54Pb0.48Te0.02)(Sr0.85Ba0.15)2Ca2Cu3Oy 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 Tc(0) of 117 K and transition widths &#916;T(90-10%) of 1 K. Critical current densities of 1.15 x 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 x 109 A m 2 for H || ab and 0.7 x 10-9 A m 2 for H || c.