Tc Zero Research Articles

Orientation control of ex situ (Hg1−xRex)Ba2CaCu2Oy (x≈0.1) thin films on LaAlO3

( Hg 1−x Re x ) Ba 2 CaCu 2 O y (x≈0.1) thin films have been prepared ex situ on LaAlO3 substrates by a two-step process in which an HgO/Re0.1Ba2CaCu2Oy multilayer precursor film is annealed in a quartz tube using an unreacted monoxide pellet containing HgO as an Hg vapor source. By varying the composition of the monoxide pellet, the film orientation can be changed from c-axis to the predominantly a-axis one. The a-axis growth of the grains directly on the substrate is confirmed by x-ray diffraction and transmission electron microscopic observation, although the grains are twinned with 90° orientation. The a-axis films exhibit a Tc onset and Tc zero of approximately 110–127 and 55 K, respectively, suggesting substantial influence of weak links at the grain boundaries on their transport properties.

Noise characteristics and detectivity of YBa2Cu3O7 superconducting bolometers: Bias current, frequency, and temperature dependence

Meander line patterned infrared detectors, with values of resistance Ronset at the onset temperature Tc onset of 3–5 kΩ, were fabricated from YBa2Cu3O7−x superconducting material on MgO and SrTiO3 crystalline substrates. Noise voltages from the samples were measured versus bias current, radiation modulation frequency, and temperature, in both the normal and superconducting states. Four major types of voltage noise were identified according to where they occurred in temperature relative to Tconset and the zero resistance temperature Tc zero, and their dependence on frequency and bias current. They were also associated with the granularity of the superconducting film, which is related to the substrate material used. From these observations a specific cause for each type of noise is suggested. The results are as follows. (i) In the normal state with temperature T≳Tc onset, noise with a magnitude that is consistent with thermal (Johnson) noise is seen, but it depends linearly on bias current above a threshold value, at low frequencies. The suggested noise source is conductivity fluctuations due to Cooper pairs. (ii) Noise was found to occur below Tc zero in granular films. With increasing bias current its magnitude increases, and it shifts to a lower temperature range; however, the noise magnitude becomes constant as the current goes to zero. It is weakly dependent on frequency above 400 Hz. Suggested cause is voltage fluctuations in superconductor–normal–superconductor junctions at grain boundaries. (iii) This noise also occurs below Tc zero with peaks at various temperatures. With increasing bias current the peaked noise spreads to lower temperatures, but the noise goes to zero as the bias current goes to zero. Its suggested cause is magnetic flux tube motion. (iv) This noise occurs between Tc onset and Tc zero and is present in all samples, but lowest on samples prepared on SrTiO3 substrates. Its suggested cause is fluctuations in the volume fraction of the superconducting phase along the current path. While the measured detectivity D* of our samples at a wavelength of 20 μm was only 106 cm Hz1/2/W, engineering changes can be expected to raise the value to above 1010 cm Hz1/2/W.

Electrodeposition of DyBaCu alloyed films from aqueous bath

Electrodeposition of DyBaCu alloyed films from aqueous bath was carried out onto fluorine doped tin oxide (FTO) coated MgO substrates and stainless steel substrates. Black coloured deposits of DyBaCu alloy with thickness of 3–4 μm were obtained for deposition period of 30 minutes. The nature of deposits has been studied by varying different preparative parameters such as deposition potentials and bath composition. The alloyed films were oxidised and tested for their superconducting properties. The oxidised films shows superconductivity with Tc onset of 100 K and Tc zero at 67 K.

Superconducting Characteristics of Metal-YBa2Cu3O7-xComposites

Metal powder such as Au or Ag was mixed a Y-Ba-Cu-O superconductor so as to improve its critical current density, Jc. The metals were uniformly dispersed into the superconductor without reaction. The Jc for YBa 2 Cu 3 O 7−x mixed with Au(5 wt%) or Ag(3 wt%) was magnified by a factor of four or two in comparison with that for the YBa 2 Cu 3 O 7−x superconductor without the metal mixing, respectively. The metal addition into YBa 2 Cu 3 O 7−x influenced little to Tc zero . The decrease of Tc zero under the magnetic flux application was considerably inhibited by the metals mixing

Effect of chemical substitution and oxide additives on theTcbehaviour of the oxide superconductor, Bi4Sr3Ca3Cu4O16

Abstract Studies on the superconductivity behaviour of pure and doped (Pb,TI) Bi4Sr3Ca3Cu4O16 phases are reported. Effect of oxide additives PbO, BaPbO3 and BaBiO3 has also been examined. Results show that an oxygen treatment at 600°C for 12 h during the final stages of the synthesis has the beneficial effect of sharpening the Tc zero of the 4334 Bi-composition. Pb and TI substitution has only a marginally beneficial effect on the Tc , though it is not definitely known whether substitution is actually occurring in the system. PbO as an additive raises the Tc zero to 89 K, whereas other additives do not basically affect the properties of the 4334 system.

Effect of processing geometry in oxygen incorporation and i n s i t u formation of YBa2Cu3O7 superconducting thin films by pulsed laser evaporation technique

I n situ formation of YBa2 Cu3 O7 superconducting thin films by the pulsed laser evaporation technique is critically dependent on the processing conditions (substrate temperature, oxygen partial pressure, subsequent annealing, etc.) and on the deposition setup, including the nozzle geometry required for the incorporation of oxygen. We have studied the recovery of the superconducting properties as a function of location of the oxygen jet relative to a fixed substrate-target setup at a substrate temperature of 550 °C and an oxygen partial pressure of 200 mTorr. Several experiments were performed with the oxygen jet directed on the target and/or on the substrate. During the deposition process, a dc bias voltage of +300 V was applied on an interposing ring, which has resulted in formation of superconducting thin films at a low temperature of 500 °C. Excellent superconducting properties with the Tc zero of 88 K were obtained on films fabricated at 550 °C with the nozzle directed onto the substrate. In contrast, films formed with the oxygen jet directed at the target showed poor superconducting properties, with a Tc0 of approximately 50 K. The x-ray diffraction studies on these films showed much sharper Bragg peaks and higher oxygen content for films fabricated with the oxygen jet directed on the substrate compared to that of the target.

Structure and superconductivity studies on (Y1-xLax)Ba2Cu3O7(0 ≤x ≤1)

Abstract Studies on (Y1 - xLa X )Ba2Cu3O7, x = 0.0 - 1.0, in steps of 0.1, have been carried out. Results show that for x ≤ 0.4, orthorhombicity and high Tc of 90 K are retained. Tc decreases gradually for x ≥ 0.4. Pure LaBa2Cu3O7 shows a TC ZERO of 73 K. XRD data do not reveal any clearcut orthorhombic distortion for pure LaBa2CuO7 after annealing at 350°C for 4 days.

Growth of high Tc-superconducting Y-Ba-Cu-O thin films by a chemical spray pyrolysis method

A chemical spray pyrolysis method has been applied to grow high Tc Y-Ba-Cu-O thin films on SiO 2 , (001)SrTiO 3 and (001)MgO substrates. The best results were obtained for films deposited on (001)SrTiO 3 and (001)MgO substrates with Tc onset at 95 and 82 and Tc zero at 82 and 76 K, respectively. For films deposited on MgO, X-ray diffraction pattern revealed that the films are highly preferentially oriented with respect to MgO substrates with the C-axis parallel to the normal of the substrate surface. Both planview and cross-sectional transmission electron microscopy have been applied to characterize the 6pitaxia1 films. The orientation relationships between the epitaxial films and the substrate were analyzed to be [001]YBCO//[001]MgO and (110)YBCO//(200)MgO. Twins, which may be preceived as domains that are rotated 900 along the C-axis of the thin films with respect to the substrate, were found to be copiously present.