Tl, Pb)(Ba, Sr)-1223 superconducting films with a thickness of about 1 µm were prepared on highly polished, untextured silver as substrate. Excellent c-axis orientation of the superconducting material was obtained. The transition temperature (T c(0) ) was 116 K with a very narrow transition range (T 90−10% ) of 2 K. Critical current densities of 80 kA cm −2 at 77 K in self-field were obtained.
A thin film of a (Tl 0.5 Pb 0.5 )(Sr 0.85 Ba 0.15 ) 2 Ca 2 Cu 3 O z superconductor was prepared on highly polished silver substrates. Its superconducting transition temperature (T c,50% ) is 114.7 ± 0.3 K and the critical current density is 11.4 × 10 3 A cm −2 at 77 K in the self-field. The transport critical currents densities were measured as a function of temperature for several applied magnetic fields. The magnetization versus the dc applied magnetic field and temperature were also measured and the critical current densities were calculated. The temperature dependence of the critical currents obeys the Ginzburg-Landau power-law. Reasons for this behaviour were discussed taking into account the pinning force and anisotropy of the critical currents associated with the c-axis grain orientation of the film. The magnetization as a function of the angle between the applied magnetic field and the a-b plane showed a periodic dependence due to changes of the demagnetizing field.
Te-doping of (Tl 0.54 Pb 0.5−x Te x )(Sr 0.85 Ba 0.15 ) 2 Ca 2 Cu 3 O 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, Ba 2 CuTeO 6 appeared as a secondary phase but the remaining material was still high-purity Tl-1223 phase. (Tl 0.54 Pb 0.48 Te 0.02 )(Sr 0.85 Ba 0.15 ) 2 Ca 2 Cu 3 O 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 T (90-10%) of 1 K. Critical current densities of 1.15 × 10 10 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 × 10 9 A m −2 for H ab and 0.7 × 10 −9 A m −2 for H c.
The interface between a screen-printed (Tl0.5Pb0.5)(Sr0.85Ba0.15)2Ca2Cu3Oy (Tl-1223) superconducting film and an untextured Ag substrate is analyzed by transmission electron microscopy (TEM). Preferential orientation between the Tl-1223 grains and the Ag substrate is found. The (001) plane of Tl-1223 grains is parallel to and the {113} plane of Ag is almost parallel to the interface. High-resolution TEM images show that CuO2 planes contact the faceted {113} planes of Ag substrate at the interface. A mechanism for the preferential growth of the Tl-1223 (001) film on untextured Ag substrate is proposed.
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