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The epitaxial growth of YBCO films both on (001) SrTiO3 (STO) and Ni-W biaxially textured metallic substrates prepared by metal-organic deposition (MOD) using a trifluoroacetic acid (TFA) solution is reported. The degree of epitaxy of the YBCO films was investigated by X-ray diffraction and scanning electron microscopy (SEM). The as deposited films exhibit good morphological and structural properties. The ω-scan of the YBCO films grown on (001) SrTiO3 single crystal substrate and on Pd/CeO2/YSZ/CeO2 buffered biaxially textured Ni-5at%W (Ni-W) tapes has a full width at half maximum (FWHM) of 0.12° and 3.4°, respectively. The -scan of (113) peak of YBCO film grown on Ni-W substrate has FWHM of 6.1°. The YBCO/STO film has a zero resistance critical temperature of Tc(R = 0) = 92 K and a critical current density Jc > 2 MA/cm2 at 77 K and in zero magnetic field.

In this paper we will describe the main results of the activity aimed to develop a prototype of superconducting receiver front-end (HTS RFE) for specific application in UMTS network. The system has been specifically designed to reach very low noise figure on the receiving channel to exploit the best performance in terms of sensitivity of the up-link channel.

The formation and characterization of MgB/sub 2/ thin films is explored, using room-temperature deposition of precursor layers and subsequent annealing in-situ. Precursors were deposited by means of pulsed laser deposition (PLD), electron beam (EB), and sputtering (SD) techniques. Best results were obtained for B/Mg multilayers deposited by EB and annealed at 630/spl deg/C for 10 minutes, showing typical T/sub Con/ and T/sub C0/ values of about 32-34 K and 31-32 K, respectively. Structural and morphological analyses were performed by x-ray diffraction and SEM. A comparison among the different growth techniques is presented. Results are explained taking into account the pressure-temperature phase diagram of the Mg-B system.

The microstructure of Ni-5at%W (Ni-W) and Ni-11at%V (Ni-V) biaxially textured substrates has been investigated using X-ray diffraction (XRD) and electron backscatter diffraction (EBSD). The correlation between the substrate microstructure and superconducting transport properties of YBa/sub 2/Cu/sub 3/O/sub 7-y/ (YBCO) film grown on it has been studied on the YBCO/CeO/sub 2//Ni-W and YBCO/CeO/sub 2//NiO/Ni-V architectures. Our study has ascertained that the in-plane texture of the substrates is one of the most important factors, limiting the critical current density. The Ni-V substrate has a lower percolation area due to the larger number of twinned grains and a broader in-plane angular distribution and, as a consequence, the YBa/sub 2/Cu/sub 3/O/sub 7-y/ (YBCO) film grown on it has a critical current density of 0.6 /spl times/ 10/sup 6/ A/cm/sup 2/, depressed by factor 2 with respect to YBCO grown on the Ni-W substrate. For the Ni-V substrate, another limiting factor is its low oxidation resistance. In contrast to Ni-V, the Ni-W substrate has a larger percolation area, mainly due to the absence of twinned grains, and a high oxidation resistance.

We report on the growth of MgB 2 thin films by means of Pulsed Laser Deposition (PLD) and Electron Beam (EB) deposition techniques. In order to develop an in-situ deposition procedure both techniques have been exploited following two approaches: the "as grown" procedure, where the superconducting phase is formed during the film growth, and no further process is performed, and the "annealing" procedure, where precursor layers are deposited and annealed in argon atmosphere. In the case of EB evaporated films, the "as grown" procedure revealed to be inadequate, because of the low reactivity of the thermally evaporated species and the high magnesium volatility. On the contrary, using PLD, the higher reactivity of the plasma species promotes the formation of the superconducting phase at deposition temperature as low as 350°C. In the "annealing" procedure, different kinds of precursor layers have been studied, in order to reduce and prevent the fast Mg evaporation at high temperature. Different annealing processes were investigated in order to promote the interdiffusion and reaction between Mg and B. The films were characterised by means of resistivity measurements and X-ray analyses. The surface morphology was observed by SEM microscopy.

A study on CeO 2 film growth on randomly oriented metallic substrate using lnclined Substrate Deposition (ISD) technique was performed in order to develop a biaxially aligned buffer layer for YBa 2 Cu 3 O 7-δ (YBCO) coated conductors. The influence of deposition parameters, as the substrate inclination angle α with respect to the CeO 2 vapor direction, deposition temperature and film thickness, on structural and morphological properties of the film was investigated. At substrate temperature between 200°C and 700°C a biaxial texture was observed for α ranging from 15° to 75°. The minimum value of the ϕ-scan full width at half maximum (FWHM) on (002) poles of about 13.5° was obtained for film 2 μm thick deposited at 200°C and α=55°. Morphological analyses on cross-sectioned samples revealed a columnar structure, typical for this deposition technique, with spaced grains and a tile like surface.

Reduction of AC losses for large-scale applications of superconductors is a critical issue. Therefore, the quantitative evaluation of AC losses is important for the development of superconductors and their applications to electrical power systems. The development of numerical models that simulate the electromagnetic phenomena inside superconductors allows to understand the electromagnetic behavior of superconductors and to evaluate the AC loss properties. Following an approach proposed by Brandt in several papers, a numerical model was developed in order to study the AC properties of superconducting tapes in different geometrical arrangements and with time dependent current and magnetic field. Here we show an example for simple single-layer model cables to show how this rather simple and versatile numerical approach allows optimizing configurations for actual operational conditions.

Biaxially aligned YBa2Cu3O7−δ (YBCO) thick films were deposited by pulsed laser ablation technique on cube textured non-magnetic Ni89V11 (Ni–V) substrate, using CeO2/YSZ/CeO2/NiO buffer layer architecture. The first NiO seed layer was formed by epitaxial oxidation of the Ni–V substrate. Structural analyses show typical full width at half maximum values of φ- and ω-scans less than 10° and 8°, respectively. The highest value obtained for the critical current density at 77 K and zero magnetic field was 6×105 A cm−2, which is close to that obtained for YBCO films grown on CeO2/NiO buffer layer architecture.

The epitaxial oxidation of the (0 0 1)[1 0 0] textured Ni100−xVx tapes was studied because of the practical interest of NiO as a first buffer layer for the YBCO based coated conductors. The study revealed that the oxidation of the Ni–V alloy is rather complex, the less noble V being internally oxidized, while Ni undergoes an external oxidation. Moreover, the formation of the NiVO3 and of Ni7V5O17 compounds have negative effects on the epitaxial oxidation and on the surface morphology, as well. The role of vanadium on the epitaxial oxidation of Ni–V alloy has not been fully understood yet. The optimum conditions for the epitaxial oxidation have been found to be: 700 ° C, t

Biaxial cube texturing and surface quality of the metallic substrate are key parameters for high J c coated conductors. Experiments have demonstrated that the sharp cube texture can be developed up to 11 at.% V, 12 at.% Cr and 5 at.% W alloys; the respective cube textured area fractions result to be 96%, 97% and 99%. For all the studied alloys, FWHM values of ω - and φ -scans are in the range of 5–6° and 6–8°, respectively. Microstructural analyses reveal smooth surfaces with grooves localized at the grain boundaries of twinned cube textured and misoriented grains.

A promising approach to improve the engineering current density of coated conductors is to increase the thickness of the YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) layer. In this framework, a study regarding the relationship between the thickness of the superconducting film and its critical current was performed on biaxially aligned YBCO films grown on epitaxial Ce/sub 2/O/NiO structure using Ni/sub 89/V/sub 11/ non-magnetic substrate. The critical current density (J/sub C/) was measured for a series of YBCO films with thickness ranging from 0.2 to 2 /spl mu/m, deposited at constant rate. J/sub C/ values up to 6.4/spl times/10/sup 5/ A/cm/sup 2/ at 77 K and zero magnetic field were obtained for thinner films decreasing three orders of magnitude for the 2 /spl mu/m thick YBCO film. X-ray diffraction and morphological analyses indicate a progressive structural deterioration with the increase of film thickness.

We analyze the voltage–current characteristics of high quality c -axis oriented YBa 2 Cu 3 O 7− δ films with T c0 ≈91 K. The films were dc sputtered in a pure oxygen atmosphere on SrTiO 3 (1 0 0) substrates and then patterned in a shape of a long strip. The voltage–current characteristics are modeled with single or multiple Gaussian distributions of depinning currents. We derive the distribution features as a function of the applied magnetic field at different temperatures.

Y 2 O 3 and MgO-based buffer layer architectures on non-magnetic cube textured Ni-V substrates were studied for YBa 2 Cu 3 O 7-δ (YBCO) coated conductors fabrication using both pulsed laser deposition and electron beam evaporation. The Y 2 O 3 films exhibited a biaxial texture with φ and ω-scans full width at half maximum (FWHM) of about 11° and 7° and a smooth and continuous surface. YBCO thick films deposited on CeO 2/ Y 2 O 3/ Ni-V and CeO 2/ Y 2 O 3/ NiO/Ni-V architectures were mainly c-axis oriented showing a T C(R=0) above 85 K. MgO films were grown by electron beam evaporation both directly on metallic substrates and with a Pd intermediate layer. The MgO films grown on Ni-V substrates show a good texture and good surface morphological properties. The MgO deposition on Pd buffered Ni-V substrate leads to films with better structural properties with respect to MgO deposition on bare Ni-V substrate, showing φ and ω-scans FWHM up to 8° and 5°, respectively. In spite of the interdiffusion between Pd buffer layer and Ni-V substrate, the MgO films preserve their structural and morphological properties when annealed at typical YBCO deposition temperature.

A morphological study of on-axis NdBa2Cu3O7-δ (NBCO) and on-axis and off-axis YBa2Cu3O7-δ (YBCO) pulsed laser deposited films is presented. YBCO films deposited in on-axis geometry exhibit a high droplet density of about 107 cm-2 and three-dimensional features probably related to stoichiometric outgrowths. YBCO off-axis films present a surface with very low droplet density (about 105 cm-2) and the density of other defects like holes and stoichiometric outgrowths is less than 103 cm-2. In spite of a higher droplet density with respect to off-axis YBCO (about 106 cm-2), NBCO films have a surface without other defects. Moreover, the NBCO film morphology is almost insensitive to variation in the deposition conditions. Atomic force microscopy analysis revealed that YBCO off-axis deposited films grow in a spiral growth mode, while NBCO films exhibit a texture, probably due to an initial two-dimensional growth. The YBCO off-axis and NBCO films have a mean roughness in a 10×10 µm2 area of about 7.5 and 1.45 nm, respectively.

The paper presents the current status of Ente per le Nuove tecnologie, ĽEnergia e ĽAmbiente research on the processing of high-irreversibility-field superconductor YBa2Cu3O7-x. (YBCO) tapes, useful for power application. A major part of this review is concerned with buffer layer growth, because this is the most important stage in the YBCO thick-film fabrication on biaxially textured metallic substrates. Several architectures are presented: CeO2/Pd/Ni, CeO2/(Ni-V) and CeO2/NiO/(Ni-V). For all the buffer layer structures the top CeO2 film was deposited by pulsed-laser deposition, while the Pd film was grown by electron-beam evaporation. The observed epitaxial orientation is [001]. The properties of a new non-magnetic Ni-V alloy substrate, as well as the preliminary results on superconducting multilayer structures, are also presented. The YBCO film grown on the CeO2/NiO/(Ni-V) configuration has the critical temperature Tc onset of 90.9 K, zero resistance at 86 K and the critical current density Jc =...

This paper presents the development of the CeO/sub 2/ buffer layers on both the non magnetic Ni-V and the Pd-buffered Ni substrates by pulsed laser ablation (PLD). The CeO/sub 2/ films show strong in-plane and out-of-plane orientations. The SEM studies showed that the CeO/sub 2/ films are both smooth and continuous. The magnetic and structural properties of the new Ni-V substrate are also presented. The results demonstrate that Ni-V is an alternative substrate for the fabrication of textured YBCO conductors.

We report a study of the resistive transitions in Bi2Sr2CaCu2O8+x in presence of an applied magnetic field (up to 12 tesla) at various field orientations. We focus our attention on the results obtained with orientations parallel and perpendicular to the (a,b) planes. We show that scaling arguments, typical of dissipative regimes independent of oriented defects, can explain the experimental findings, provided a 3D-2D crossover is assumed as the temperature is lowered, due to the variation of the out of plane coherence length.

The problem of developing non magnetic cube textured metallic substrates other than pure Ni, to be used for epitaxial deposition of Y-123 superconducting film (with an intermediate oxide buffer layer) is being tackled since three years by several laboratories. As reported in this paper, we have developed a new substrate, based on Ni-V 10 wt % alloy, which exhibits a cube texture comparable to Ni, but has a Curie temperature < 4.2 K; in addition, it has a hardness which is more than twice higher and a comparable oxidation resistance.

Biaxially aligned YBCO thick films on oxide buffered metallic substrates is a promising route toward the fabrication of superconducting tapes operating at liquid nitrogen temperature. The role of buffer layer is to reduce the lattice mismatch between the substrate and the YBCO film, to adapt the thermal expansion coefficient, to hamper the diffusion of Ni in YBCO film and to prevent the oxidation of the metallic substrate surface. This paper presents a study regarding CeO 2 buffer layer deposition on a new nonmagnetic (001)[100] textured Ni-V alloy substrates. The deposition of CeO 2 was performed by both pulsed laser ablation and e-beam evaporation techniques. The θ-2θ X-ray diffraction pattern mainly exhibits the (00l) peaks of CeO 2, indicating that the films are epitaxially grown with the c axis perpendicular to the substrate. Rocking curved through the CeO 2 (002) peak have a FWHM of about 6°. The SEM studies have shown that the surface is smooth, continuos and free of cracks. Texture analysis reveals a good in-plane orientation for the ablated CeO 2 film, whereas the electron beam evaporated CeO 2 shows two textures in the growth plane. Further efforts are focused on the deposition of YBCO thick film on the as buffered nonmagnetic metallic substrate.

The paper presents the structural and magnetic properties of a new non-magnetic biaxially textured substrate based on Ni 100-x V x solid-solution for YBa 2 Cu 3 O 7-y tape fabrication. The effective atomic magnetic moment monotonously decreases with the vanadium concentration, causing a corresponding decrease of Curie temperature. The Curie temperature reaches the zero value at about 11.5. % of vanadium. The texturing studies revealed that (100)[001] cube texture can be easily developed up to x=11 at. %, by a cold rolling process followed by a recrystallization thermal treatment. The X-ray ω and ϕ scans have demonstrated that the samples have a good out-of-plane and in-plane texture for the whole solubility range, with FWHM of 7° and 11°, respectively. The correlation between the magnetic and structural anisotropy was also studied.

In order to fabricate high temperature superconducting tapes for power applications, we have analysed different buffer layer architectures grown on textured Ni substrates suitable for YBCO deposition. Due to its optimal lattice matching the studied structures present as top layer a CeO 2 film. The deposition of CeO 2 on Ni substrates was performed by pulsed laser ablation and by e-beam evaporation at different temperatures. The films obtained by the two deposition techniques have not optimal structural properties, having a polycrystalline component. The misorientation of CeO 2 is probably due to the formation of NiO at the interface between the film and the substrate during the deposition process even if no oxygen is introduced. In order to prevent Ni oxidation an intermediate 2000 Å Pd thick film was deposited by e-beam. Furthermore, the lattice mismatch between Pd and CeO 2 is smaller than that between Ni and CeO 2. The Pd layer inhibits nickel oxide formation and improves the CeO 2 epitaxial growth: the XRD pattern contains only the (001) peaks of Pd and CeO 2. SEM analysis on CeO 2/Pd/Ni shows a smooth surface free of cracks, contrary to that observed for CeO 2/Ni structure.

The epitaxial growth of YBa 2 Cu 3 O 7-x (YBCO) films on biaxially textured substrates is one of the most promising technique for the fabrication of high current superconducting tapes operating at high temperature. Ni is very attractive as substrate because it easily develops a (100)[001] cubic texture. The low oxidation resistance represents the main drawback of the Ni substrate. In order to better assess the role of oxygen on the Ni substrates, a surface physics technique as Auger spectroscopy has been used. It has allowed to evaluate the amount of impurities for different Ni processing and exposure to the air. The results demonstrate that the surface contamination can be efficiently removed by RF sputtering before buffer layer deposition. This procedure allows to obtain CeO 2/Pd/Ni architecture by laser ablation with a good epitaxy both of Pd and CeO 2 films. On the contrary, when CeO 2 is directly deposited on Ni a low epitaxy is obtained. The Auger analysis confirms that the formation of (111) NiO at the Ni - CeO 2 interface hampers the epitaxial growth of the ceria film.

We have investigated the possibility of improving the weak link properties of Tl-1223 tape by melt processing, and also studied the technical limitations of coil fabrication using multimeter lengths of PIT tape. We conclude that melt processing does offer some potential for grain growth, but that grain alignment is only achieved in some places at the Ag/1223 interface. Until we can establish more control of the local grain alignment by altering the geometry of the samples, the properties of coils in high fields remains rather poor.

We have studied the superconducting and structural properties of YBCO thin films and YBCO/STO/YBCO trilayers deposited on (100) SrTiO3 substrates by off-axis PLD technique. The as-obtainedc-axis oriented YBCO films show an excellent surface free of droplets or other irregularities as well as good structural and superconducting properties with Tc (R=0)=89 K, Jc=3×106 A/cm2 (at 77 K and zero magnetic field) and the Full Width at Half Maximum (FWHM) of the (005) YBCO rocking curve of about 0.2°. These structural and electrical properties are very close to those of the YBCO films deposited by the conventional PLD on-axis geometry. The TEM cross-sectional image shows that the YBCO/STO/YBCO heterostructure has smooth interfaces and no short-circuits or pinholes were observed. The electron diffraction analysis has revealed that both YBCO top and bottom layer as well as STO interlayer are epitaxially grown withc-axis perpendicular to the substrate.

In order to improve the surface quality of the pulsed laser deposited YBCO thin films an off-axis deposition geometiy is proposed. Using this new PLD geometry, YBCO thin films have been grown on SrTi03 substrates. These films were found to have a good surface morphology without droplets or other particulates, and good supelrconducting and structural properties. We have obtained Tc(R=0)=89 K, R(300)/R(100)=2.6, ΔT=1.5 K, Jc=2×106 A/cm2 (at 77 K and zero magnetic field), and the FWHM of the rocking curve of (005) YBCO peak is about 0.12°. A study regairding the influence of the deposition parameters on the film quality is also presented.

YBCO was synthesized by the co-precipitation of stoichiometric amounts of nitrate solutions of Y, Ba and Cu using a mixture of NaOH, Na 2 CO 3 and H 2 C 2 O 4 in a molar ratio of 5:1:1 as a precipitation agent. Even after prolonged thermal treatment at 950 °C the samples exhibit a zero-resistance critical temperature of about 87 K. This fact indicates a copper deficiency of about 0.1, more reduced than in the case of hydroxycarbonate co-precipitation. The as-synthesized samples have a high density, reaching 94% of the theoretical density. The SEM analyses show a large grain distribution from microns to tens of microns, favourable for good stacking.

Epitaxial YBCO superconducting thin films have been grown in-situ by XeCl excimer laser ablation using an off-axis deposition geometry. This PLD geometry allows to obtain films with an excellent surface morphology without droplets or other particulates. The as-obtained YBCO films exhibit good structural and superconducting properties with T c( R = 0) =89.5 K, R (300) / R (100) =2.8, ΔT = 1.3 K, J c = 2 × 10 6 A/cm 2 (at 77 K and zero magnetic field) and full width half maximum of the rocking curve of the (005) YBCO peak of about 0.16°. These structural and electrical properties are very close to those of the YBCO films deposited by the conventional PLD on-axis geometry.

We measure resistive transitions in YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} for several orientations and strength of the applied magnetic field. Experiments show that an angular scaling takes place in the upper part of the transition, for all angles, down to a field-dependent temperature T{sub f}(H). The fluctuations theory is shown to fully describe the experimental findings for T{gt}T{sub f}, including the angular scaling and the detailed temperature behavior of the resistivity. The scaling breakdown at T{sub f}(H) is argued to be due to pinning effects on vortex lines that become relevant at low temperatures. {copyright} {ital 1997} {ital The American Physical Society}

NbN superconducting thin films have been grown by using pulsed laser ablation in a N 2 pure atmosphere. The X-ray spectra indicate that highly oriented superconducting NbN films having a FWHM of the 002 reflection narrower than 0.5°, has been obtained. Critical zero resistance temperature T c higher than 16.3 K and resistivity ratio ≈ 1.3 were measured as well as critical field of 12 T at LHe temperature on the high quality films. Transport critical current density J c , measured on a patterned film with a 50 μV cm criteria, gave an extrapolated value of J c0 higher than 1 × 10 7 A/cm 2 computed by using a Kim Andersen model. Preliminary photoemission spectroscopy measurements in the presence of N 2 background gas indicate some reactivity in the plume region.

Epitaxial YBa 2 Cu 3 O 7− y films were grown by pulsed-laser ablation on SrTiO 3 buffered (100) MgO substrate without any pre- or postannealing of the substrate or STO buffer layer. The role of the SrTiO 3 layer is to provide a better lattice mach to the YBCO film and to prevent the interaction between YBCO and MgO. The as-obtained YBCO films exhibit excellent structural and superconducting properties with T c (R = 0) = 90 K , R(300) R(100) = 2.8, Δ T = 0.8 K , J c ≈ 10 6 A/cm 2 (at 77 K and zero magnetic field) and a full width half maximum of the (005) YBCO peak of about 0.18°. These characteristics are very close to those of the YBCO film deposited on SrTiO 3 single crystal.

We have measured the properties of a large number of Tl-1223 tapes as part of a programme to optimise the fabrication procedures. During this work we have noticed that the highest I c values are not proportionally dependent on the cross-sectional geometry of the tapes. There seems to be a limiting I c value of around 10–13 A in our samples (and those of many other groups). We have performed a series of experiments on self-field effects in Tl-1223 tapes and compared the results with calculated field distributions in tape-shaped conductors in different configurations. We conclude that the I c are self-field limited in these tapes when the currents being carried are around 10 A.

YBa 2 Cu 3 O 7−δ was synthesised using a solution method. The coprecipitation of the stoichiometric amounts of nitrate solution of yttrium, barium and copper was performed using a mixture of NaOH, Na 2 CO 3 and H 2 C 2 O 4 in a molar ratio 5:1:1 as precipitation agent. The as-obtained precursors have a copper deficiency of 0.1 with respect to the nominal stoichiometry of the starting solution. The mechanistic study of the product formation has revealed that in these atomically mixed precursors the individual components have a different behaviour with respect to those in a mechanical mixture. The final products was obtained after heat treatment at 950°C for 6 h in oxygen atmosphere. The product was analyzed by XRD, SEM, EDXS and four probe DC resistivity measurements. The as-synthesised YBCO has shown good superconducting properties T c ( R = 0) = 90.5 K and ΔT = 1 K. This method was used with success in the fabrication of YBCO target for laser ablation.

An accurate determination of the optical conductivity σ(ν) of high-Tc materials at low frequencies (ν

We measured reflectance spectra R(v) of oxygen deficient Y1Ba2Cu3O7−x (YBCO) films of different thickness, with critical temperatures between 85 and 87 K. Measurements were made at room temperature between 15 and 25000 cm−1. The measured R(v) have a maximum below 100 cm−1 and then decrease for v → 0. This low frequency behaviour of R(v) can be accounted for by considering a relevant extra-Drude contribution to the far infrared optical conductivity of YBCO.

We describe the fabrication and testing of dc SQUIDs (Superconducting QUantum Interference Devices) obtained by photolithographic patterning of YBa2Cu3O7−x thin films deposited both on SrTiO3 and MgO substrates. The Josephson junctions in the superconducting loop are of the “step-edge” type, where the weak link is obtained through the growth of grains with different orientations across suitably prepared steps previously etched on the substrate surface. TheI−V characteristics of the devices tested show multiple branches and instabilities having a weak dependence on the external magnetic field, probably due to formation of junction clusters on the substrate step. The SQUID devices showed quantum interference behavior and an easily detectable voltage modulation with the applied magnetic field at a temperature of 77 K.

The fabrication by sputtering of Nb/sub 0.75/Zr/sub 0.25/ thin films that showed critical temperature as high as 10.5 K is described. Transport critical current measurements on Nb/sub 0.75/Zr/sub 0.25/ films whose geometries were photolithographically defined in the micrometer range are reported. The measurements were performed as a function both of the temperature and of the magnetic field up to 6 T. The temperature behavior is compared with the Kim-Anderson model, and the magnetic field behavior of the resulting pinning force is compared with existing models. >

The superconducting YBa2Cu3O7-δ/CeO2/NiO multilayer structure was grown in situ by pulsed-laser deposition on biaxially textured Ni89V11 non-magnetic alloy. The role of vanadium is to decrease the Curie temperature of Ni and to favour the formation of oriented NiO. The (00l)NiO buffer layer has been formed by the controlled oxidation of the Ni-V substrate under 10 mTorr oxygen pressure and at 700 °C. The critical current density of 0.6 MA cm-2, at 77 K and zero magnetic field, was obtained for 0.7 µm thick YBa2Cu3O7-δ films.

Thin films of YBa 2 Cu 3 O y have been grown in situ on (100) SrTiO 3 and (100)MgO, by pulsed excimer laser evaporation from a stoichiometric target. The substrate temperature was adjusted at 750°C by using a CO 2 laser as the heating source and the oxygen partial pressure during the deposition was about 0.3 mbar. The samples have been patterned in the shape of lines 0.2 mm long and of widths between 5μm and 20μm. DC transport critical currents have been investigated as a function of temperature and of applied magnetic field up to 6T.

We study the transport critical current of c-axis YBCO films grown on low angle [001] tilt bicrystals of 2.5/spl deg/, 5/spl deg/, and 7.5/spl deg/. The influence of low magnetic fields on each single grain boundary has been studied at different temperatures by varying the field direction in the plane of the boundary with the magnetic field always perpendicular to the bias current. The tilt angle, /spl theta/, between the magnetic field direction and the normal to the film surface has been varied from -110/spl deg/ to +110/spl deg/, where 0/spl deg/ corresponds to the field direction parallel to the c-axis of the film. We find that the angular dependence of the critical current density Jc shows a hysteretic behavior for applied magnetic fields below 1 T. Maxima of Jc are observed at different angles depending on the rotation direction of the applied magnetic field. We notice that the angular difference between the critical current peaks is a function of the external magnetic field, so that for strong fields only the /spl plusmn/90/spl deg/ maxima are observed. We relate these observations to the intrinsic pinning between CuO layers, and to trapped flux in the superconducting film.

We analyze the voltage–current ( V – I ) characteristics of the YBCO films grown above the CeO 2 /NiO/Ni 89 V 11 structure to study the dissipative mechanisms limiting the critical current in these structures. The analysis is performed on the shape of the V – I characteristics, emphasizing the voltage behavior as a function of the bias current. The complex behavior of the fluxon dynamics is described in connection to the reduced pinning force measured on the YBCO films grown on these metallic flexible substrates.

This article analyzes the magnetic field dependence of the Fiske steps in a small Josephson junction having a peaked critical current density distribution along the direction orthogonal to the field. The maximum current of the resonant states is computed in the case of a periodic and a nonperiodic distribution of the peaks in the current density along the junction. It is observed that the maximum amplitude of the Fiske steps and the magnetic field at which they occur are affected by the nonperiodic peak distribution. These results are discussed in connection with parallel networks of junctions coupled by negligible inductances.

We present some experimental facts which suggest that fluctuational phenomena dictate the dissipative behaviour in a wide region of fields and temperatures across the critical temperatureT c. In particular, we discuss resistivity data on an YBCO thin film as a function of the field orientation ϑ with respect to the crystallographic axes of the sample. We also compare our data with those taken on an untwinned single crystal. Both analyses define a temperatureT f(H) marking the onset of extrinsic effects on the dissipation. Finally, the comparison of the data with the predictions of the interacting fluctuations theory and with the Bardeen-Stephen flux-flow expression is used to clarify whether the intrinsic behaviour is due to fluctuations of the order parameter or to the free motion of vortex lines.

We report the manufacturing and the properties of two types of step-edge Josephson junctions: YBCO-YBCO (SEJ) and YBCO-Au-YBCO (SNS-SEJ), respectively. The junctions were prepared on step shaped SrTiO3 substrates using in-situ pulsed laser deposition technology for film deposition and ion-etching patterning. The YBCO films used for this purpose have zero resistance transition temperature Tc(R=0) in the range (89–91) K and a critical current density Jc(B=0)>106 A/cm2 at 77 K in zero applied magnetic field. For both types of junction the I-V characteristics can be well described in the limit of the resistively shunted junction (RSJ) model.

We report on resistive transitions in YBCO films as a function of strength and orientation of the applied magnetic field. Angular behaviour is found to be markedly different in the upper and lower part of the transition. At high dissipation level, an angular scaling behaviour is observed, following the anisotropic Lawrence-Doniach expression for the upper critical field. The scaling breaks down at the midpoint of the transition. No scaling is observed at lower temperatures, even if different angular scaling functions are used. The results are very well interpreted in terms of superconducting fluctuations above rho/rho(n)=0.5 and pinning phenomena below.

The potential applications of high- T c ceramic superconducting materials is a subject of intensive investigation in many laboratories worldwide. In this paper, results concerning devices based on Josephson junctions, SQUIDs and arrays are presented.

Static and dynamical states in one‐dimensional parallel arrays of small, all refractory Josephson tunnel junctions, are experimentally investigated at 4.2 K. The dependence of the maximum Josephson current on the applied magnetic field in parallel arrays shows asymmetric behavior around secondary maxima which are discussed in terms of a nonuniform applied magnetic field. Current steps and linear branches induced by the applied magnetic field are observed together in the current‐voltage characteristics for the first time in the strongly underdamped regime. The resonant structures appearing in the current‐voltage characteristics of the arrays show features similar to high‐order Fiske modes in a long Josephson junction.

The current status of the electronic applications of high-T c Josephson junctions is briefly reviewed. Recent results obtained by the authors on devices employing step-edge junctions are reported. In particular the design of a microwave oscillator based on a parallel array of junctions is discussed and preliminary experimental results are presented.

We have observed anomalous voltage vs. magnetic flux modulations in YBCO dc-SQUIDs employing step-edge junctions. The anomaly consists inphase inversion and frequency doubling of the voltage modulations in a restricted range of bias currents. We ascribe this phenomenon to the non-negligible capacitance of the junctions in the SQUID, as confirmed by numerical simulations.

A study regarding the epitaxial growth of Y 2 O 3 -based buffer layer architectures on (001)[100] textured Ni-V metallic substrates using both PLD and e-beam evaporation is presented. The as deposited films exhibit good structural and morphological properties indicating that the Y 2 O 3 is a suitable layer for epitaxial growth of YBCO superconducting films for power applications. Mainly, YBCO/CeO 2 /Y 2 O 3 /Ni-V and YBCO/CeO 2 /Y 2 O 3 /NiO/Ni-V architectures have been studied.

Biaxially aligned YBa 2 Cu 3 O 7−y thick films were obtained by Pulsed Laser Deposition on cube textured non-magnetic Ni-V metallic substrates, with NiO as a first buffer layer. The critical temperature and critical current density at 77K and self field of the YBCO thick film grown on an epitaxial CeO 2 /NiO buffer layer architecture are 90.5K and 0.6 MA/cm 2 , respectively.