Yttrium Barium Copper Oxide Superconductor Research Articles

New Liquid Precursors for Chemical Vapor Deposition

ABSTRACTNew precursors have been found for chemical vapor deposition (CVD) of many metal oxides. Each precursor is a mixture formed by randomly attaching a selected set of organic groups, such as the isomers of the butyl group, to a metal 2,4-pentanedionate (also known as acetylacetonate) in place of the methyl groups of the 2,4-pentanedionate ligand. Most of these new mixed metal beta-diketonates are liquids at room temperature, whereas the corresponding metal 2,4-pentanedionates are solids. In the cases where they were solids or viscous liquids, small amounts of organic solvents were added to reduce the viscosity. We have so far prepared mixed beta-diketonate precursors for barium, strontium, calcium, magnesium, aluminum, indium, tin, lead, bismuth, titanium, zirconium, vanadium, niobium, tantalum, chromium, molybdenum, manganese, iron, ruthenium, cobalt, nickel, copper, zinc, yttrium, lanthanum and cerium.Liquid sources are much more convenient for CVD than solid sources. These liquid mixtures or solutions were vaporized by ultrasonically nebulizing the liquid into a flow of hot nitrogen carrier gas preheated to 150–250 °C. These vapor mixtures were mixed with air or oxygen and flowed over substrates heated typically to 350–450 °C. Films of the corresponding metal oxide (or carbonate, in the case of barium, strontium and calcium) were deposited on substrates of silicon or glass. Gas pressures from 20–760 Torr were used.Because a common set of ligands is used for each of these metal precursors, they can be mixed as liquids or vapors without any precipitation due to ligand exchange reactions. To demonstrate their use in forming mixed metal oxides, we have prepared films of ferroelectric barium titanate. This method should be applicable to other mixed metal oxides of current interest, such as high dielectric constant strontium titanate, ferroelectric bismuth strontium tantalate, superconducting yttrium barium copper oxide, refractory yttrium zirconium oxide, second-harmonic generating barium borate, metallic lanthanum strontium cobalt oxide and magnetoresistive lanthanum strontium manganate.

Processing yttrium barium copper oxide superconductor in near-zero gravity

The effects of processing YBa 2Cu 3O x (Y123) superconductor in the near-zero gravity (0 g) environment provided by the NASA KC-135 airplane flying on parabolic trajectories were studied. A new sheet float zone furnace, designed for this study, enabled fast temperature ramps. Up to an 18 g sample was processed with each parabola. Samples of Y123 were processed as bulk sheets and composites containing Ag and Pd. The 0 g processed samples were multi-phase yet retained a localized Y123 stoichiometry where a single ground-based (1 g) oxygen anneal at temperatures of 800°C recovered nearly 100 vol% superconducting Y123. The 1 g processed control samples remained multi-phase after the same ground-based anneal with less than 45 vol% as superconducting Y123. The superconducting transition temperature was 91 K for both 0 g and 1 g processed samples. Melt texturing of bulk Y123 in 0 g produced aligned grains about a factor of three larger than in analogous 1 g samples. Transport-critical current densities were at or below 18 A/cm 2, due to the formation of cracks caused by the rapid heating rates required by the short time at 0 g.

YBa/sub 2/Cu/sub 3/O/sub 7/

Some background information on superconducting ceramics is given, and the history of yttrium barium copper oxide (YBCO) is discussed. The crystal structure of superconducting YBCO is described. The production and extraction methods of bulk samples of YBCO are detailed. Different theories of superconductivity in YBCO are addressed, and applications of YBCO superconductors are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Preparation of a calcium-substituted copper-rich yttrium barium copper oxide superconductor from a spray-dried nitrate precursor

A calcium-substituted YBa 2Cu 4O 8 (1–2–4) high-temperature superconductor is synthesized from a precursor obtained by spray-drying of a nitrate solution containing the corresponding metals in a stoichiometric ratio. The synthesis takes place during one-stage heat-treatment of the precursor at 800°C in an oxygen flow under a pressure of 1 atm within a relatively short period of time, additives as well as intermediate grinding and pressing of the products being not needed. Measurements of the a.c. susceptibility have revealed a very sharp superconducting transition which is comparable with that of samples prepared under a high pressure. The transition in Ca-substituted YBa 2Cu 4O 8 occurs at a temperature by about 8 K higher than T c of the Ca-free phase. Raman spectra suggest that during the substitution calcium does not occupy barium positions in the YBa 2Cu 4O 8 lattice.

ChemInform Abstract: Comparing Yttrium Barium Copper Oxide Superconductors by Copper, Oxygen and Barium NMR/NQR

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Microwave Preparation of the YBa2Cu3O7-δSuperconductor

Several attempts at microwave calcination and sintering of the yttrium barium copper oxide superconductor have been reportedinthe literature. Some of the findings ofthese reports are explained in terms of the theory behind the interaction of microwaves with conductive substances and the behaviour of this material at elevated temperatures.

Anisotropic thermal expansion of the 1:2:4 yttrium barium copper oxide superconductor

The 1:2:4 yttrium barium copper oxide superconductor has been prepared and sintered to high density by high pressure techniques. This material is phase pure and shows a sharp transition temperature of 80 K. High temperature X-ray powder diffraction of the 1:2:4 material shows a small anisotropy in thermal expansion. This is compared to the anisotropy in thermal expansion of the 1:2:4 superconductor. A critical grain size, above which thermal expansion anisotropy causes cracking, is calculated for 1:2:4 and compared to that for 1:2:3. The results predict that the critical grain size is over twice as large for the 1:2:4 material. This should result in less microcracking in polycrystalline materials due to thermal expansion anisotropy in devices based on 1:2:4.

Surface Resistance at Microwave Frequencies in Transition Metal Ion Substituted Yttrium Barium Copper Oxide Superconductors

The temperature dependence of the surface resistance is investigated in polycrystalline yttrium barium copper oxide samples in which 2% of Cu is replaced with Fe, Mn, Co, or Ni. The superconducting transition temperature, determined from ac susceptibility measurements, varies from a maximum of 93K for the undoped sample to a minimum of 89.5K for the sample with Ni. A resonant cavity technique is used to determine the surface resistance at x-band frequencies over the temperature range 77 to 100 K. The data show a relatively large microwave resistance in the normal and superconducting states for samples containing Fe and Co. The superconducting energy gap is determined from the high frequency resistance data. Es wird die Temperaturabhangigkeit des Oberflachenwiderstands in polykristallinen Yttrium–Batrium–Kupferoxidproben, bei denen 2% des Cu durch Fe, Mn, Co oder Ni ersetzt ist, untersucht. Die aus Wechselstromsuszeptibilitatsmessungen bestimmte Supraleitungsubergangstemperatur andert sich von einem Maximum von 93 K fur die undotierte Probe zu einem Minimum von 89,5 K fur die Probe mit Ni. Es wird eine Resonatortechnik benutzt, um den Oberflachenwiderstand bei X-Bandfrequenzen im Temperaturbereich 77 bis 100 K zu bestimmen. Die Werte zeigen einen relativ grosen Mikrowellenwiderstand im normalen und supraleitenden Zustand fur Fe- und Co-haltige Proben. Aus den Hochfrequenzwiderstandswerten wird die Supraleitungsenergielucke bestimmt.

Fe(III)/Fe(II) separation by solvent extraction for the determination of oxygen stoichiometry in yttrium barium copper oxide superconductor materials

Oxygen stoichiometry is a critical parameter defining the Tc of cuprate superconductors (e.g. YBa2Cu3O7). On dissolution excess or deficiency of oxygen can be converted into shifts of the Fe(II)/Fe(III) concentration ratio of an aqueous solution. For small samples a solvent extraction technique for the separation of Fe(III) from Fe(II) was developed, to make use of the superior sensitivity of atomic spectrometry (AAS, ICP-AES). The system n-benzoylphenylhydroxylamine (BPHA)/CHCl3 was chosen because it is relatively inactive as a redox partner. Despite the catalytic effect of Cu(II) on the oxidation of Fe(II), oxidation blanks can be kept down at negligible levels. Less than 0.55% of residual Fe(II) is converted to Fe(III) during the extraction procedure (argon atmosphere). In the presence of air, oxidation levels are still practical (≤3%). Extraction is from 0.3 mol/l HBr providing excellent recovery of Fe(III) (e.g. 98.8%). All Fe(II), Y, Ba (including BaSO4 precipitate) and 99.4% of the Cu remain in the aqueous phase. Fe(III) is rapidly back-extracted into an aqueous phase by 6 mol/l HCl for dilution and aspiration into the flame or ICP. Recovery of Fe(III) after the two extraction steps is still 98.3%.

Resistivity, thermopower and single-particle tunneling studies on some zinc-doped yttrium barium copper oxide superconductors

Abstract Resistance and thermopower measurements have been made on a series of compounds, YBa2Cu3- x Zn x O7-y, with x = 0.025, 0.05, 0.1, 0.15 and 0.2. The superconducting transition temperature decreases as the zinc concentration increases. In a range of temperatures below TM , the mid point of the transition, the resistance shows an exponential temperature dependence fitting the phenomenological formula proposed by Ausloos et al. From the plot of logarithm of resistivity vs. (TM ‒ T) 1/2/T, one deduces a value of the average dimension of the Josephson junction to be a few tens of A, suggesting the microtwin boundaries to be the location of the junctions. The thermopower shows a peak always just above Tc . This conclusively shows that phonon drag is not the cause of the peak. The temperature dependence of the thermopower appears to resemble closely the earlier observations of Srinivasan et al. on yttrium barium copper oxide. Single-particle tunneling measurements carried out for two concentrations, x = ...

Determination of the magnetic field penetration depth in superconducting yttrium barium copper oxide: Deviations from the Bardeen-Cooper-Schrieffer laws.

We have measured the low-field magnetization for a number of fine powders of ${\mathrm{Y}}_{1}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ and applied a standard formula to determine the magnetic field penetration depth $\ensuremath{\lambda}(T)$ in the superconducting state. Consistent values of $\ensuremath{\lambda}(0)$ and similar temperature dependences $\ensuremath{\lambda}(T)$ are obtained for average particle diameters ranging from 1.1 to 9 \ensuremath{\mu}m. At low temperatures $\ensuremath{\lambda}(T)$ is not Bardeen-Cooper-Schrieffer-like, instead a ${T}^{2}$ law is observed. The implications of this result are discussed.

Oxygen content and site distribution in high-Tc superconducting yttrium barium copper oxide (YBa2Cu3Oy) ceramics

It is suggested here that accurate determination of the unit cell length for a given preparation of the superconducting ceramic YBa/sub 2/Cu/sub 3/O/sub y/ can give a good estimation of the total oxygen content (y) and the distribution of oxygen between two different sites. Cell parameters for a large number of preparations of YBa/sub 2/Cu/sub 3/O/sub y/ are tabulated herein. Accurate cell constants may be determined from x-ray, neutron, and electron diffraction of the prepared YBa/sub 2/Cu/sub 3/O/sub y/. 16 references, 2 tables.