YBaCuO Thick Films Research Articles

Characterisation of the magnetic shielding properties of YBaCuO thick films prepared by electrophoretic deposition on silver substrates

This communication reports experimental results on the superconducting properties of YBaCuO thick films prepared by electrophoretic deposition on silver substrates. The magnetic shielding properties of the coatings were characterised by various methods. First, the electrical resistance and the transport critical current density, Jc, were determined. Our coatings exhibit a superconducting transition at a temperature of 90 K. Next, shielding characterisations were carried out at 77 K for samples having either a slab or a cylindrical geometry. In both cases, the frequency of the applied magnetic field was 103 Hz; the field behind the shielding wall was measured by a pick-up coil connected to a lock-in amplifier. In the case of cylindrical samples and for an applied induction lower than 1 G, the field inside the shielding enclosure is reduced by a factor greater than 106 (i.e. 120 dB) with respect to the applied field.

Fabrication of High Tc Superconducting Films by CVD Process

YBaCuO thick films were fabricated by plasma enhanced chemical vapor deposition, and the crystallinity and the superconducting properties were investigated. The growth temperature to obtain the thick films was decreased by around 150<TEX>$^{\circ}C$</TEX> due to plasma enhancement. The zero resistivity temperatures for films grown at 590<TEX>$^{\circ}C$</TEX> and 620<TEX>$^{\circ}C$</TEX> were 55 and 80 K, respectively.

Directional solidification of YBaCuO thick films deposited by screen printing on Ag and Ag–Pd tapes

Textured tapes of Ag{1 1 0} and polycrystalline tapes of Ag–Pd(0.5–12.5%) alloys have been prepared by cold rolling as possible substrates for deposition of high critical current density YBCO films. The Ag{1 1 0} texture with some twins was promoted by recrystallization after cold rolling from ingots prepared by melting and solidification of Ag powders. Nevertheless, no textured tapes were obtained by cold rolling from Ag–Pd alloys with Pd>0.5%. YBCO thick films (10–30 μm) were deposited on the metallic tapes by screen printing using organic inks. Biaxially textured superconducting thick films were observed on the Ag{1 1 0} substrates at low solidification rates. Nevertheless, uniaxial texture with some biaxial colonies of YBCO grains were found on Ag–Pd alloys when the superconducting phase was solidified at high rate.

Self-field effects on critical current density and current-voltage characteristics in superconducting YBaCuO thick films

The self-field and percolative influences on transport measurements of polycrystalline bridges engraved on YBaCuO thick film have been investigated. A maximum in the dependence of the critical current density on cross-sectional area of the bridge (A = 0.003 mm2-0.3 mm2) has been found experimentally, in samples with low critical current densities (Jc<50 A cm-2). The result of the measurements are in agreement with Mulet and coworkers, who have predicted that, under certain conditions, the self-field effects on transport measurements are negligible and the Jc dependence on the sample dimensions is determined by the percolative character of the transport current. Self-field influences have also been observed in current-voltage characteristics, which have been analysed using the Ambegaokar-Halperin phase-slip theory. By allowing the noise parameter () to change with temperature, magnetic field and transport current, adequate agreement between theoretical and experimental current-voltage characteristics has been obtained. The dependence of the noise parameter with the transport current is demonstrated to be related with the self-field.

YBaCuO thick films on planar and curved technical substrates

For high-current applications, homogeneous well-textured high-temperature-superconducting Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBaCuO) films on technical ceramic or metallic substrates are required. The ion-beam-assisted deposition (IBAD) of yttria-stabilized zirconia (YSZ) buffer layers, which serve as templates for the YBaCuO, was extended to large planar areas (20 cm/spl times/20 cm) as well as curved or cylindrical (diameter /spl les/15 mm) substrates. For both types of substrates a pronounced in-plane alignment is observed. A deposition equipment is developed to grow high-quality YBaCuO films also on tubes by pulsed laser deposition (PLD), which is characterized by a high long-term stability both of the deposition rate and of the surface temperature of the growing film. Current densities up to 0.9/spl times/10/sup 6/ A cm/sup -2/ at 77 K in self fields are observed in films on planar Ni foils with biaxially aligned YSZ buffers (bi-YSZ). For the coating of long lengths of tubes and tapes a translation and a rotation of the samples are incorporated both in the buffer as well as in the YBaCuO-deposition process. Furthermore, the dependence of the critical transport current densities, J/sub c/, of the HTS layer on magnetic fields and on mechanical stresses are investigated.

The fishtail effect in irradiated YBaCuO thick films

The fishtail effect in irradiated YBaCuO thick films

Critical current enhancement and flux creep in irradiated YBaCuO thick films

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Microwave Surface Resistance of Plasma-Sprayed YBaCuO Thick Films on Large-Area Metallic Substrates

The microwave surface resistance of YBaCuO thick films was measured using a demountable copper cavity operated at 3 GHz in the TE011 mode over a temperature range from 4.2 K to 300 K. The films were deposited onto end plates and cylinder walls of silver substrates or nickel-buffered copper substrates by a low-pressure plasma-spraying technique combined with a melt-reaction method. The area of the end plate was 177 cm2 and that of the cylinder wall was 396 cm2. The surface resistance was obtained from the Q values measured before and after substituting either the end plate or the cylinder wall for one covered with the film. The ratio of the surface resistance of the film to that of the copper was lower than 0.08 at 5.2 K and 0.65 at 77.3 K for the end plate and was 0.15 at 5.1 K and 1.91 at 77.3 K for the cylinder wall.

Current-induced decoupling of superconducting planes in oriented YBaCuO thick films

The critical current of decoupling of superconducting CuO 2 planes is extracted from resistive data obtained on oriented YBaCuO films. Distinctive 3D—2D crossover in dissipation takes place at a temperature dependent current j c( T) that exhibits a clear tendency to vanish at T KT (Kosterlitz—Thouless transition temperature) of individual superconducting layers. That confirms the idea of full suppression of interlayer coupling due to 2D-vortex fluctuations close to T KT.

Preparation of screen-printed YBCO thick films on an alumina substrate under flowing argon

Y-Ba-Cu-O (YBCO) thick films of 10–15 μm thickness were prepared on bare alumina substrates by the screen-printing technique. The films, which were heated at 850–900 °C in argon atmosphere and then exposed to oxygen, showed zero resistance at 79–84 K.

Evolution of the microarchitecture of YBaCuO thick films through dissolution

The mechanism of formation of the YBaCuO thick film layered structure on Y-TZP substrates has been studied by selective dissolution with a weak acid solution. The role of the compositional gradient established in the liquid phase during the peritectic reaction as well as the mechanism of 1-2-3 texturing are discussed.

Preparation and sintering behaviour of YBaCuO thick films prepared by tape casting

Abstract A composition of cyclic hydrocarbon as solvent, an acrylic binder and a plasticizer was used for tape casting of superconducting YBa2Cu3O7-δ. A small-particle-size superconducting powders, ≈ 1μm, with two different degree of agglomeration were added to adequate amount of the organic mixture for obtaining slips. Thick films of several thickness were prepared. The sintering was performed in the 920–940°C temperature range. The organic compounds were burnout at 500°C. High density values were obtained for tape fired at 940°C. SEM analysis revealed a rather homogeneous microstructure for samples made from the weak agglomerated powders. Tc and Jc at 77K were measured on Ag-electroded samples.

Magnetic properties of YBaCuO thick films prepared by LPE method

Single-crystalline YBaCuO thick films have been grown on NdGaO 3 substrates by liquid phase epitaxial technique. With the magnetic field H parallel to the c-axis, critical currents of up to 5 MA.cm −2 at 4,2K from magnetization measurements are obtained. With H perpendicular to the c-axis, various magnetization measurements with field cooling in 30 kOe indicated strong pinning effect with critical currents more much higher than that observed in the parallel field geometry.

Performance of YBaCuO thick film rf SQUIDs at 77 K

RF SQUID behaviour has been observed at 77 K in YBaCuO thick films prepared by screen printing technique. A hole shunted with a microbridge type of geometry is patterned manually for observing rf SQUID behaviour. Flux noise spectrum is also studied and it is found to depend on the quality of the film. The spectral density of the flux noise in the white noise region is 1.7×10−3 Φ0/√Hz at 77 K.