Formation Of YBa2Cu3O7 Research Articles

Deposition of YBCO films on both sides of substrate by magnetron sputtering

We have studied features of the formation of YBa2Cu3O7 − δ (YBCO) films on both sides of sub-strates by magnetron sputtering in the on-axis geometry. During sputter deposition onto the first (front) side, a thin film is simultaneously formed on the second (rear) side, which can provide a high-quality sublayer for the final coating of preset thickness deposited at the subsequent stage. It is shown that, by monitoring the properties of a sublayer formed on the rear side of substrate during YBCO layer growth on the front side, it is possible to optimize technological parameters of the process.

The phase conversion of precursor powders for powder melting process YBa2Cu3O7−x superconductors

The effects of heating rate and holding time on the formation of YBa2Cu3O7−x phase in precursor powders for YBa2Cu3O7−x superconducting bulks prepared by powder melting process have been investigated. The phase conversion of the precursor powders is studied by X-ray diffraction and found to be different for different heating rates during heating. The YBa2Cu3O7−x phase is formed during heating to peritectic temperature at 100 and 400 °C/h, but not at 6,000 °C/h. The longer the holding time, the more the amount of YBa2Cu3O7−x phase between 880 °C and about 950 °C. The results are useful for understanding the mechanism of powder melting process and controlling the process conditions.

The degradation of novolak containing metal nitrates and the formation of YBCO

Polymers that form a complex with metal ions from nitrate salts can be used to prepare precursors for the production of high temperature superconductor (HTSC) ceramics that can be processed using advantageous polymer processing techniques and then pyrolyzed. This paper describes the production of HTSC from a precursor based on m-cresol formaldehyde novolak resin (mCFNR) that contains yttrium, barium and copper nitrate salts in the proportions needed for the formation of YBa2Cu3O7−x (YBCO). The degradation of the precursor and the effects of the pyrolysis process (temperature, time, environment, substrate) were studied in detail. The mechanisms of degradation for mCFNR and for the HTSC precursors were significantly different with the precursor degradation beginning at significantly lower temperatures. The optimal pyrolysis begins in an inert atmosphere to hinder BaCO3 formation and then continues in oxygen to 950 °C. A dense orthorhombic YBCO film with preferential [001] orientation results from topotaxial growth on SrTiO3.

Phase Transformations in the Systems Y2BaCuO5–“Ba3Cu5O8” and Y2BaCuO5–BaCuO2

Data are presented on the sequence of phase transformations leading to the formation of YBa2Cu3O7 – δ textured ceramics and single crystals in the systems Y2BaCuO5–“Ba3Cu5O8” and Y2BaCuO5–BaCuO2 . During cooling in the Y2BaCuO5–BaCuO2 system, YBa2Cu3O7 – δ crystallization in the range 1260–1210 K occurs through the intermediate phase YBa4Cu3O9 – δ , without an additional oxygen source. In the Y2BaCuO5–“Ba3Cu5O8” system between 1250 and 1210 K, YBa2Cu3O7 – δ crystallization is accompanied by oxygen absorption.

Preparation of YBa2Cu3O7− powders by the thermal decomposition of a heteronuclear complex, CuY1/3Ba2/3(dhbaen)(NO3)1/3(H2O)3

Abstract YBa2Cu3O7−δ powders were prepared by the thermal decomposition of a heteronuclear complex, CuY1/3Ba2/3(dhbaen)(NO3)1/3(H2O)3. The products of the complex thermal decomposition were analyzed by TG-DTA, XRD, SEM-Auger and XPS. The decomposition of the CuY1/3Ba2/3-complex was obtained at about 500°C and the product was a mixture of oxides and carbonates. The formation of YBa2Cu3O7−δ proceeded at 800°C, with a gradual decomposition of the carbonates. A homogeneous distribution of each element, Y, Ba, and Cu, was observed for the decomposed CuY1/3Ba2/3-complex by SEM-Auger analysis. The binding energy values of Ba3d5/2 and O1s photolines from Ba and O in the superconductive lattice did not shift during the sputtering period. Furthermore, the formation of Ba rich regions on the surface was depressed by using the complex as a starting material for homogeneous 123-oxide, YBa2Cu3O7−δ.

Formation of YBa2Cu3O7−δ superconducting films by electrodeposition

M. S. Martín-González, J. García-Jaca, E. Morán and M. Á. Alario-Franco, J. Mater. Chem., 1999, 9, 1293 DOI: 10.1039/A809172B

Influence of an electric current on the crystallization of YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} in BaO/CuO/CuO{sub 0.5} flux melts

The influence of an electric current on the ternary BaO/CuO/CuO0.5system and the quaternary YO1.5/BaO/CuO/CuO0.5system has been investigated by modified differential thermal analysis. Increasing the current in the ternary system leads to the crystallization of an additional phase. In the quaternary system we find a splitting of the solidification of the residual melt BaO/CuO/CuO0.5indicating the formation of two different eutectics. In both systems we find a preferential deposition of material at the positive electrode. Crystal growth experiments including electric current show a preferential formation of Yba2Cu3O7−xcrystals at the positive electrode.

Partial melting during formation of YBa2Cu3O7−x

Partial melting during formation of YBa2Cu3O7−x

Formation of YBa2Cu3O7−y/BaTiO3 multistructures by pulsed laser deposition for high-temperature superconducting device applications

The formation of YBa2Cu3O7−y(YBCO)/BaTiO3(BTO)//SrTiO3(STO) (100) and BTO/ YBCO//STO(100) bilayer structures is demonstrated for the construction of a superconductor ferroelectric field transistor. The resulting films of the bilayers have highly c-axis oriented structure. Epitaxial YBCO films formed on the BTO//STO(100) have a zero resistance temperature of 88.9 K. The surface morphology of the epitaxial BTO films on the YBCO//STO is very smooth with a mean surface roughness of 32 Å. Moreover, the Au/BTO/YBCO structures have been fabricated, and the dielectric constant and remanent polarization of BTO layer are obtained to be 180 and 3.5 μC/cm2 at 77 K, respectively.

Comparison of the catalysed decomposition of hydrogen peroxide over superconducting and insulating barium cuprates—kinetics of decomposition over Y2BaCuO5

AbstractCatalytic activities of two non‐conducting cuprates (Ba2Cu3O5, Y2BaCuO5) and a superconducting cuprate YBa2Cu3O7–δ, prepared by two different methods, were compared using H2O2 solution. The two non‐conducting barium cuprates were found to be about two orders of magnitude more active than the superconducting perovskite‐like YBa2Cu3O7–δ. The near coincidence of the kinetic curves for the catalysed decomposition of H2O2 over YBa2Cu3O7–δ, prepared either from the perovskite‐like Ba2Cu3O5 and Y2O3 or from its components, proves that Ba2Cu3O5 is essential in the formation of YBa2Cu3O7–δ. First‐order kinetics were observed for the catalysed decomposition of H2O2 solution over the non‐perovskite Y2BaCuO5 at the initial stages of the reaction, similar to that of the superconducting perovskite catalyst. A tentative scheme of the possible catalytic reactions for the decomposition of H2O2 solution over the insulator Y2BaCuO5 is given.

Temperature-dependent mobility of a GaAs/AlGaAs heterostructure after deposition of MgO and superconducting YBa2Cu3O7−x

High quality YBa2Cu3O7−x films have been grown on MgO epitaxial buffer layers deposited onto a GaAs/AlGaAs heterostructure incorporating a two-dimensional electron gas (2DEG). The critical temperature of the YBa2Cu3O7−x, Tc(0) was ≳80 K, and Jc≳2×104 A/cm2 at 77 K. Electron mobilities and concentrations of 2DEG substrates were measured at different stages in the formation of YBa2Cu3O7−x/MgO/2DEG structure. Room-temperature mobilities and concentrations were unchanged after YBa2Cu3O7−x/MgO deposition, while low-temperature mobilities were slightly degraded. It is found that the degradation of electron mobility is correlated to the high growth temperature of YBa2Cu3O7−x. Since the 2DEG is only 1200 Å from the substrate surface, this constitutes a sensitive demonstration of the viability of the semiconductor substrate under these growth conditions.

Screw dislocation mediated growth of sputtered and laser-ablated YBa2Cu3O7-? films

By imaging the as-grown surfaces of sputtered and laserablated YBa2Cu3O7−δ films with scanning tunneling microscopy (STM), we have directly observed spiral-shaped growth terraces which emanate from screw dislocations. The density of screw dislocations was observed to decrease with increasing growth temperature and substrate misorientation. The surface structures observed by STM together with cross-sectional transmission electron microscope (TEM) images provide insights into the mechanisms of crystal growth operative during the formation of YBa2Cu3O7−δ films grown using these two widespread techniques.

Grain orientation studies in YBCO superconductors by molten salt synthesis

The molten salt or the flux method is utilized in this study to fabricate a grainoriented YBa2Cu3O7−x superconductor. The formation of YBa2Cu3O7−x in the presence of molten salts of Na, K, Li belonging to chloride and iodide systems does not appear feasible due to the instability of the superconducting phase in these salt systems. Studies using the “green phase,” Y2BaCuO5, as seed crystals suggest a two-stage approach in the formation of YBa2Cu3O7−x . The process uses Y2BaCuO5 formed by molten salt synthesis which has been observed to be stable in water and against most of the salts. The 211 crystals can be mixed with oxides and converted to 123. Analysis of X-ray data and SEM micrographs indicates a certain degree of grain orientation, which can be further enhanced by tape-casting or not-forging.

Processing and properties of superconducting YBa2Cu3O7?x powder by single-step calcining in air

The preparation of orthorhombic YBa2Cu3O7−x powder using only one calcination step is described. Yttrium and copper nitrates and barium carbonate were used as precursor materials. The use of an appropriate precipitant agent leading to a complete coprecipitation of the Y3+ and Cu2+ cations, promoted the rapid low temperature formation of YBa2Cu3O7−x (900‡C for 4 h) with no secondary phases. X-ray diffraction patterns of the obtained powder showed the presence of the only one phase with the orthorhombic structure, and lattice parameters ofa=0.3824 nm,b=0.3893 nm,c=1.1676 nm and σ=1.775 which correspond to a superconducting YBa2Cu3O6.95 phase. Sintering compacted samples at 940‡C several times led to highly dense (⩾ 96% theoretical density) superconductor bodies, and a value ofT c as high as 94 K was measured. Although AES depth profiles in fracture surfaces evidenced good grain boundaries of the superconducting YBa2Cu3O6.95 samples, however, theJ c measured was never greater than 15 A cm−2, which could be due to a weak-link region between highJ c grains. Slow degradation of the YBa2Cu3O6.95 ceramics seems to take place by the formation of Ba(OH)2 and YO(OH) at the superconductor surface in contact with the moisture of the air.

Microwave absorption investigation on the formation of YBa2Cu3O7−σ by a binary metal oxide route involving interaction of BaCuO2 and Y2Cu2O5

Low-field microwave absorption has been used to discriminate between the YBa2Cu3O7−σ high temperature superconductor synthesized by reacting the binary metal oxides, BaCuO2 and Y2Cu2O5, versus synthesis with a single metal oxide route. This discrimination is more clearly seen by microwave absorption than by resistance measurements. Supplementary data was obtained by electron spin resonance in the g=2 region, scanning electron microscopy, thermal analysis and x-ray diffraction techniques. The scanning electron micrographs indicate a more separated granular structure for the material synthesized from the binary oxides. The low field non-resonant microwave absorption, which is characteristic of the superconducting phase, is twice as intense for the binary metal oxide preparation as compared to the single metal oxide preparation. Also, the superconducting transition temperature seems to be several degrees higher for the binary oxide preparation.

Control of YBa2Cu3Oy Sol-Gel Solution Structure by Chemical Modification of Organic Acid and its Effects

2-ethylhexanoic acid (2EHA) has been applied to control the YBa2Cu3O7−x sol-gel solution. The experimental results prove that 2EHA functions as a sol-gel solution structure controlling and precipitation-prevention agent. The structure of the solution can be one, two or three dimensions of the network by using different concentration of 2EHA to modify the metal alkoxides. With decreasing 2EHA concentration, the homogeneity is improved due to increasing the network connectivity. This results in: (1) ease of the formation of YBa2Cu3O7−x; (2) denser microstructure with fine grains; and (3) narrower but lower superconducting transition.