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  • Articles  (63)
  • superconductivity  (28)
  • YBa2Cu3O7  (18)
  • Ultrasonics  (17)
  • 1990-1994  (36)
  • 1985-1989  (27)
  • 1960-1964
  • 1950-1954
  • Electrical Engineering, Measurement and Control Technology  (63)
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  • Articles  (63)
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  • 1
    Electronic Resource
    Electronic Resource
    Thermal expansion in the Ba1−x K x BiO3 system (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 427-428 
    Details
    ISSN: 1572-9605
    Keywords: Thermal expansion ; dielectric ; metal ; superconductivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract A negative thermal expansion was measured for Ba1−x K x BiO3. This anomaly decreases with increasingx, still exists atx=0.4, and disappears atx=0.5.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00724582
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  • 2
    Electronic Resource
    Electronic Resource
    Backscattered microstructural noise in ultrasonic toneburst inspections (1994)
    Springer
    Journal of nondestructive evaluation 13 (1994), S. 111-136 
    Details
    ISSN: 1573-4862
    Keywords: Ultrasonics ; backscattering ; noise ; backscatter coefficient ; figure-of-merit ; microstructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract A model is presented which relates the absolute backscattered noise level observed in an ultrasonic immersion inspection to details of the measurement system and properties of the metal specimen under study. The model assumes that the backscattered noise signal observed for a given transducer position is an incoherent superposition of echoes from many grains. The model applies to normal-incidence, pulse-echo inspections of weakly-scattering materials using toneburst pulses from either a planar or focused transducer. The model can be used in two distinct ways. Measured noise echoes can be analyzed to deduce a “Figure-of-Merit” (FOM) which is a property of the specimen alone, and which parameterizes the contribution of the microstructure to the observed noise. If the FOM is known, the model can be used to predict the absolute noise levels that would be observed under various inspection scenarios. Tests of the model are reported, using both synthetic noise echoes, and measured noise echoes from metal specimens having simple and complicated microstructures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00728250
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  • 3
    Electronic Resource
    Electronic Resource
    Phonon structures in tunneling conductance of superconducting YBa2Cu3O7 (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 367-369 
    Details
    ISSN: 1572-9605
    Keywords: Tunneling conductance ; second derivative ; phonon structure ; YBa2Cu3O7
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We report on measurements of the tunneling conductance structures above the superconducting gap energy using YBa2Cu3O7 polycrystalline junctions. The measured second derivative data are reproducible among the junctions, and the intensities of the common structures at the biases of 37–38, 47–53, 67–77, and 94–95 mV are strong enough to be assigned. These structures are in agreement with those in the neutron phonon density of states in whole energy regions when the energies are measured from the gap edge of 26±1 meV. This correspondence indicates that the electron-phonon interaction contributes to the pairing mechanism of this superconductor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00724570
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  • 4
    Electronic Resource
    Electronic Resource
    Raman scattering studies of ultrathin-layer YBa2Cu3O7/PrBa2Cu3O7 superlattices (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 213-216 
    Details
    ISSN: 1572-9605
    Keywords: Raman scattering ; superlattice ; YBa2Cu3O7 ; PrBa2Cu3O7 ; phonon renormalization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We present Raman scattering studies ofc-oriented ultrathin-layer superconducting (YBa2Cu3O7) m /(PrBa2Cu3O7) n superlattices. For the superlattice with (m=2,n=1) sequence, Raman spectra reveal a new line in the spectral region around 320 cm−1. It is interpreted as a mode representing a combination of IR optical phonons of the Y-sublayers with an admixture of aB 1g type Raman active vibration in the Pr sublayers. This new line, which is similar to those from the interior of the Brillouin zone of the original lattice, does not exhibit superconductivity-induced self-energy effects, although its counterpart in the pure substance does. No additional line is found in the (m=1,n=2) superlattice in the same region, supporting our interpretation for the (m=2,n=1) sample.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00730397
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  • 5
    Electronic Resource
    Electronic Resource
    Electronic specific heat of YBa2Cu3O6+x from 1.8 to 300 K (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 243-249 
    Details
    ISSN: 1572-9605
    Keywords: Electronic specific heat ; superconductivity ; pseudogap ; Fermi statistics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We have determined for the first time the electronic specific heatγ(x, T) of YBa2Cu3O6+x for 0.16≤x≤0.97 from 1.8 to 300 K. Weakly superconducting behavior betweenx=0.4 and 0.8 progresses rapidly to strong coupling BCS-like superconducting and metallic normal state behavior forx〉 0.9. However, the continuous development of the entropyS(x, T) withx andT across the entire series suggests a progressive modification of the low-energy spin spectrum with hole doping rather than a simple band model. Fermi statistics andk-space pairing for allx is indicated by the magnitude andT-dependence ofS(x, T). Pseudogap behavior inS(x, T) is observed over a temperature region aboveT c , which increases rapidly with oxygen depletion to around 200 K forx∼0.7. This loss of entropy reflects normal-state correlations apparently unrelated to the superconducting pairing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00730405
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  • 6
    Electronic Resource
    Electronic Resource
    High-quality YBa2Cu3O7 films on 4-in. Wafers of sapphire, gallium arsenide, and silicon (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 231-233 
    Details
    ISSN: 1572-9605
    Keywords: YBa2Cu3O7 ; thin films ; large-area deposition ; semiconductor substrates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Our technique of reactive thermal co-evaporation has been extended to fabricate large films (up to 4 in.) of YBa2Cu3O7 with high quality. A rotating substrate holder is used to separate the deposition and oxidation processes. This allows free access of the metal vapors. As large substrate wafers we use Al2O3, Si, and GaAs with buffer layers of CeO2, YSZ, and MgO, respectively. On all substrates, the uniformity of thickness and composition was better than 2%. Inductively measuredT c andj c (77 K) were 87.5±0.2 K and 〉1×106 A/cm2, respectively, across the full wafer area. This holds also for GaAs substrates due to a new procedure of capping by Si3N4.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00730401
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  • 7
    Electronic Resource
    Electronic Resource
    Temperature dependence of the infrared optical properties of YBa2Cu3O7: A plasmon damping model (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 481-483 
    Details
    ISSN: 1572-9605
    Keywords: High-T c superconductors ; YBa2Cu3O7 ; infrared ; plasmon ; resistivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The temperature dependence observed in the mid- and near-infrared optical properties of YBa2Cu3O7 is explained in terms of the Drude model for free charge carriers. In the Drude model, the linear temperature dependence of the dc resistivity arises from the free charge carriers having a temperature-dependent mean free path. This temperature dependence results in the plasmon contribution to the dielectric constant having a damping coefficient which also varies linearly with temperature. We find that the temperature dependence which is observed in the absorption and reflection spectra of YBa2Cu3O7 is consistent with this simple model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00724594
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  • 8
    Electronic Resource
    Electronic Resource
    High-T c superconductivity and electronic band structure (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 547-553 
    Details
    ISSN: 1572-9605
    Keywords: van Hove singularities ; superconductivity ; cuprates ; doped fullerenes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We review the main results of the van Hove scenario applied to superconducting cuprates. It is based on the assumption that in these materials, the Fermi level lies near a singularity in the density of states (DOS). This hypothesis has recently been confirmed experimentally. We show that this model explains many properties of the high-T c superconductors. We show that an anaogous model with a peak in the DOS may also be applied to the superconducting doped fullerenes. A general feature of the model is a very short coherence length.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00728457
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  • 9
    Electronic Resource
    Electronic Resource
    Two-band mechanism of superconductivity in dimeric hubbard models (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 589-591 
    Details
    ISSN: 1572-9605
    Keywords: Two-band ; pair transfer ; superconductivity ; dimer ; Hubbard model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract In the two-chain Hubbard model the on-site Coulomb repulsion generates a remarkably large pair-transfer coupling constant between bonding and antibonding orbitals of a dimer made of the two sites lying on the opposite chains and linked by a transfer energy. It leads to a pair-transfer interaction between two bands composed of these orbitals, promoting superconductivity (SC). Since it is found to be as large as intraband Coulomb coupling constants, our previous work suggests that SC can occur in this model. In fact we have obtained a clear indication of SC in restricted-size systems carrying out the exact-diagonalization with 6 electrons and a variational diagonalization with up to 14. The SC occurs in suitable band situations for a wide range of on-site Coulomb energies. We also obtained such an SC indication in a two-dimensional Hubbard model. We mention some candidate materials substantiating the present mechanism and suggest it to be quite general.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00728465
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  • 10
    Electronic Resource
    Electronic Resource
    The pressure-induced superconductivity of iodine (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 921-924 
    Details
    ISSN: 1572-9605
    Keywords: Iodine ; superconductivity ; high pressure ; low temperature ; monatomic phase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The superconductivity of metallic iodine is observed at temperatures below 1.2 K under pressures above 28 GPa by magnetization and electrical resistance measurements. The pressure dependence of the superconducting transition temperature is studied up to 74 GPa. This is the first observation of the superconductivity of the molecular-dissociated monatomic metal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00732272
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  • 11
    Electronic Resource
    Electronic Resource
    The long-range proximity effect: Pair echoes (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 175-180 
    Details
    ISSN: 1572-9605
    Keywords: Proximity effect ; superconductivity ; pair echoes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Recent experiments on N′-N-S junctions with high-temperature cuprate superconductors have shown that superconductivity can be induced in the adjacent, normal metal at distances many times greater than the few hundred Ångstroms range of the conventional proximity effect. We show that this arises in the particular geometry used in these experiments through the constructive interference of the tails of the de Gennes-Saint-James bound and quasi-bound states of the normal metal N that penetrate into the third metal, N′. This constructive interference results in the re-appearance of a pair amplitude in this metal which is analogous to the “spin echo” of NMR and which we name a “pair echo.”
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00730390
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  • 12
    Electronic Resource
    Electronic Resource
    Inelastic neutron scattering results on pure and doped fullerenes (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 643-645 
    Details
    ISSN: 1572-9605
    Keywords: Pure and doped C60 ; inelastic neutron scattering ; superconductivity ; phonon density of states
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Via inelastic neutron scattering (INS) generalized phonon densities of states are obtained for C60 and superconducting A3C60 (A=K, Rb). Changes in the intramolecular modes agree with and augment recent Raman (RA), infrared (IR), and INS measurements, i.e., in the vicinity of the high-frequency modes of C60 [H g (8),A g (2),H g (7)] we find a pronounced shift of about 10 meV toward smaller energy transfers upon intercalating with potassium. Separated from these vibrations by a gap are the intermolecular spectra which for the doped samples display well-defined optic modes at 11 and 14 meV due to the vibrations of Rb and K ions. Indications of a weak anomalous temperature dependence of low-energy phonons (ħω 〈3 meV) nearT c are observed for K3C60.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00728477
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  • 13
    Electronic Resource
    Electronic Resource
    Normal-state transport properties of fullerene superconductors (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 639-642 
    Details
    ISSN: 1572-9605
    Keywords: Alkali-metal-doped fullerenes ; normal-state transport ; superconductivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The normal-state transport properties of alkali-metal-doped fullerene crystals are explored. The Hall effect has been measured in KxC60 from room temperature toT c . The electrical resistivityρ for K3C60 and Rb3C60 has been measured over a wide temperature range (20–650 K), and notable differences are observed for the materials at both low and high temperatures. The electrical resistivity of Rb3C60 has been measured in hydrostatic pressures up to 9 kbar. The resistivity is highly pressure sensitive. The transport results give an insight into the normal-state conduction mechanism and thus have consequences for the superconductivity mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00728476
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  • 14
    Electronic Resource
    Electronic Resource
    Theoretical study of isotope effect in La-doped Y-123 (1993)
    Springer
    Journal of superconductivity 6 (1993), S. 19-25 
    Details
    ISSN: 1572-9605
    Keywords: Isotope effects ; YBa2Cu3O7 ; Cooper pairing interaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The recent oxygen isotope effect measurement made in the system YBa2-x La x Cu3O7 (0≤x≤0.5) is analyzed using the “two-carrier” model which describes a superconducting system as a mass anisotropic system consisting of charge carriers with two different masses as a result of lattice defects or oxygen deficiency. The extent to which Ba, Cu, and O atoms participate in the phonon-mediated Cooper pairing interaction is elucidated. The relationship between the theoretically deduced mass anisotropic factor andT c agrees closely with the experimental results of Uemuraet al. [28]. Furthermore, the superconducting energy gap toT c ratio is found to be close to 3.5. Excellent agreement is also achieved between the theoretically calculated oxygen isotopic constant and the experimental results of Bornemann and Morris [12].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00618501
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  • 15
    Electronic Resource
    Electronic Resource
    Film thickness dependence of critical current density for YBa2Cu3O7 films post-annealed at a low oxygen partial pressure (1993)
    Springer
    Journal of superconductivity 6 (1993), S. 37-41 
    Details
    ISSN: 1572-9605
    Keywords: Superconducting films ; YBa2Cu3O7 ; critical current density
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The variation of critical current density at 77 K as a function of film thickness was studied for YBa2Cu3O7 films on (100) LaAlO3 substrates. Film thicknesses were in the range 0.2–1.6μm. The films were deposited by co-evaporation and post-annealed under conditions which have previously resulted in high-quality films (750°C and an oxygen partial pressure of 29 Pa). The critical current density at 77 K exceeds 1 MA cm−2 for the thinner films, and decreases with increasing film thickness in excess of about 0.4μm. The decrease is in rough agreement with a switch fromc-axis toa-axis growth at about this critical thickness. A good anticorrelation was found between room temperature resistivity and critical current density at 77 K. The results are compared to those obtained before by post-annealing at 850°C in 1 atm of oxygen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00618503
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  • 16
    Electronic Resource
    Electronic Resource
    Effect of codoping Sb and V to the BiPbSrCaCuO system (1993)
    Springer
    Journal of superconductivity 6 (1993), S. 107-109 
    Details
    ISSN: 1572-9605
    Keywords: BiSrCaCuO ; superconductivity ; phase structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract With XRD,R-T curves, and a.cϰ measurements, the doping and codoping effects of Sb and V to a Cu-deficient Pb-doped Bi system have been studied. A sample singly doped with V possesses aT c about 2 K lower than that of a sample singly doped with Sb. This is attributed to the different sites of their substitution. It was observed that for promoting 2223 phase formation, Sb and V works cooperatively, and the codoping of Sb may enhance the 2223 phase formed. With a low doping level of Sb, the optimum doping amount of V is 0.3, i.e., with a nominal composition of Bi1.5Pb0.3Sb0.06Sr2Ca2Cu2.4V0.3O y . A sample in which the 2223 phase is the dominant phase and which has a zero resistance transition temperature of 105 K has been obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00617809
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  • 17
    Electronic Resource
    Electronic Resource
    Asymmetry between flux penetration and flux expulsion in Tl-2212 superconductors (1993)
    Springer
    Journal of superconductivity 6 (1993), S. 185-189 
    Details
    ISSN: 1572-9605
    Keywords: Thallium cuprates ; superconductivity ; magnetic hysteresis ; irreversibility ; flux pinning
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract dc magnetic hysteresis as well as flux penetration and flux expulsion were investigated in Tl2−y Ba2CaCu2O8−x polycrystals and monocrystals. All measurements were performed at 35 K and in the 0–5 T field range. Hysteresis measurements revealed an irreversibility field of about 2 T. Existing models predict identical field-cooled (fc) and zero-field-cooled (zfc) magnetizations and vanishing time dependence above this field. Although the identical fc and zfc magnetizations are in fact observed, the time dependence vanishes only for flux penetration after zero-field cooling; a remanence is preserved after field cooling and decays with a finite relaxation rate. Activation energies calculated on the basis of the thermal activation model display a pronounced field dependence, and arelower for flux penetration than for flux expulsion in high fields (H≥3 T) for all orientations. This behavior of extreme layered superconductors contradicts classical theoretical models and questions the original definition of the irreversibility line as well. All of our results are consistent with the recent theory of lock-in transition, and can be well interpreted by using those principles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00625745
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  • 18
    Electronic Resource
    Electronic Resource
    Utilization of prior flaw information in ultrasonic NDE: An analysis of flaw scattering amplitude as a random variable (1992)
    Springer
    Journal of nondestructive evaluation 11 (1992), S. 57-67 
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    ISSN: 1573-4862
    Keywords: Ultrasonics ; digital signal processing ; flaw scattering amplitude ; prior information ; random variable analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Probabilistic approaches to flaw detection, classification, or characterization often assume prior knowledge of the flaw distribution. It is implicit that there is a scattering amplitude distribution associated with the flaw distribution. In a number of previously published probabilistic analyses, it has been assumed that scattering amplitude is an uncorrelated, Gaussian random variable with zero mean and known variance. In the work reported here, these assumptions are evaluated for the case of a lognormal distribution of spherical flaws. The correlation, mean, variance, and nature of the scattering amplitude distribution are considered as a function of frequency and as a function of the breadth of the assumed flaw distribution. It is shown for the assumed flaw distributions that scattering amplitude is not uncorrelated and does not have zero mean. It is shown that errors in estimating the flaw distribution variance affect both the scattering amplitude mean and variance. Using both analytical and numerical procedures, the scattering amplitude distribution is shown to be lognormal at long wavelength for a lognormal distribution of spherical scatterers. At high frequency, the distribution is shown to have a bimodal character.
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    URL: http://dx.doi.org/10.1007/BF00568289
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  • 19
    Electronic Resource
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    Self-calibrating ultrasonic technique for crack depth measurement (1992)
    Springer
    Journal of nondestructive evaluation 11 (1992), S. 103-108 
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    ISSN: 1573-4862
    Keywords: Ultrasonics ; surface breaking cracks ; self-calibrating ; crack depths
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract A configuration of transducers together with a self-calibrating measurement technique is proposed to investigate the reflection and transmission of surface waves by a surface-breaking or near surface defect. By means of this technique, the ratio of the reflection and transmission coefficients (R/T and/orT/R) can be obtained in a reliable and accurate manner. The reflection and transmission of surface waves for oblique incidence on a surface breaking crack is investigated in detail. Information onT/R for the latter case can be used to determine the depth of the crack. The experimental measurements ofT/R show excellent agreement with theoretical results.
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    URL: http://dx.doi.org/10.1007/BF00568293
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  • 20
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    Reflection of ultrasonic waves from imperfect interfaces: A combined boundary element method and independent scattering model approach (1992)
    Springer
    Journal of nondestructive evaluation 11 (1992), S. 141-149 
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    ISSN: 1573-4862
    Keywords: Ultrasonics ; imperfect interfaces ; quasi-static ; reflection coefficients ; spring constants ; independent scattering ; boundary element
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract A numerical technique for obtaining interface reflection coefficients for imperfect bonds between similar materials for a wide range of distributed defects is developed. A numerical boundary element method is utilized to find the far-field scattering amplitudes of a single defect for a normally incident plane wave. Then, the normal incidence reflection coefficient for a planar distribution of such defects is obtained from the independent scattering model. As a validation, the reflection coefficients are compared to the quasi-static model results where the latter are available. This establishes the basis for one application of the new model, the determination of spring constants which are not available. Other applications of the model, including studies of the response at frequencies beyond the quasi-static limit, the ratio of longitudinal to transverse wave reflectivities, and the effects of selected multiple scattering are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00566405
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  • 21
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    The relationship among oxygen content, defect distribution and superconductivity in BiSrCaCuO systems (1992)
    Springer
    Journal of superconductivity 5 (1992), S. 1-3 
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    ISSN: 1572-9605
    Keywords: Bi-Sr-Ca-Cu-O ; superconductivity ; phase structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The effect of oxygen content on superconductivity of the 2212 and 2223 phase has been studied. By comparing the excess oxygen, the modulation vector, the XRD patterns, and the electric resistivity of 2212 and 2223 phase samples obtained with different post-annealing conditions, i.e., annealing at 600°C or quenching from 860°C, it was found that the super-conductivity is markedly influenced by both the defect distribution in non-Bi layers and the interstitial oxygens incorporated in the Bi-O layers. A tentative explanation for this is given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00617988
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  • 22
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    60-Hz AC losses in Ag-doped high-temperature superconductors (1992)
    Springer
    Journal of superconductivity 5 (1992), S. 25-27 
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    ISSN: 1572-9605
    Keywords: YBa2Cu3O7(Ag) ; superconductivity ; ac losses
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract 60-Hz ac lossesP were measured at temperature 77 K for sintered powder (YBa2Cu3O7)1-x Ag x samples as a function of applied magnetic fieldh. Rod-shaped samples were cut from pellets forx= 0 and 0.05. The losses were measured in a uniform ac magnetic fieldh applied parallel to the sample surface. Measurements were made in fields up toh= 1000 A/cm rms at temperature 4.2 K and up toh=600 A/cm rms at temperature 77 K. The results may indicate an increase of the intergranular current density and are discussed in relation to the grain size.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00617992
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  • 23
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    Vapor pressures of Y, Ba, Cu precursors for the growth of YBa2Cu3O7 by MOVPE (1992)
    Springer
    Journal of superconductivity 5 (1992), S. 119-125 
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    ISSN: 1572-9605
    Keywords: YBa2Cu3O7 ; MOVPE ; vapor pressures ; β-diketonates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The vapor pressures of theβ-diketonates Y(THD), Ba(THD), and Cu(THD), commonly used as precursors for MOVPE of YBa2Cu3O7, and Y(MCP) were measured at different temperatures. A time-resolved static method recording the pressure vs. time at constant temperature was used, permitting us to deduce the vapor pressure even if the materials tend to decompose. The values of the constants of the Clausius-Clapeyron equation log10p(T)/p 0=A-B/T are,A=11.7, 8.7, 8.27, 16.6 andB=4359, 2654, 3602, and 6453 K for Y(THD), Y(MCP), Ba(THD), and Cu(THD), respectively withp 0= 1 Pa and temperatureT in K. The thermal stability of the sources was measured and are discussed.
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    Effects of silver on the phase formation of the Bi-Pb-Sr-Ca-Cu-O superconductors (1992)
    Springer
    Journal of superconductivity 5 (1992), S. 301-311 
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    ISSN: 1572-9605
    Keywords: Ag substitution ; BPSCCO ; bismuth ; Raman spectroscopy ; superconductivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The effects of Ag substitution on the formation of the superconducting phases in the BPSCCO system have been investigated by Raman spectroscopy and XRD. The silver was found either to accelerate the formation of the 2212 phase or to reduce the formation temperature of the 2212 phase. Moreover, addition of even a small amount of silver (Bi∶Pb∶Ag=8∶2∶1) poisons or inhibits the formation of the 2223 phase. However, there is no apparent effect on theT c of both the 2212 and 2223 phases. In addition, the presence of silver does not alter the mechanism for the formation of the PBSCCO superconducting phases.
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    URL: http://dx.doi.org/10.1007/BF00617631
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    Theory of superconductivity. II. Excited Cooper pairs. Why does sodium remain normal down to 0 K? (1992)
    Springer
    Journal of superconductivity 5 (1992), S. 83-94 
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    ISSN: 1572-9605
    Keywords: Theory ; superconductivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Based on a generalized BCS Hamiltonian in which the interaction strengths (V 11,V 22,V 12) among and between “electron” (1) and “hole” (2) Cooper pairs are differentiated, the thermodynamic properties of a type-I superconductor below the critical temperatureT c are investigated. An expression for the ground-state energy,W-W 0, relative to the unperturbed Bloch system is obtained:W-W 0=−1/4[N 1(0)Δ 1 2 +N 2(0)Δ 2 2 ], whereN j(0) represent the electron and hole densities of states at the Fermi energy εF, and Δj are the solutions of the simultaneous equations, $$\Delta _j = \tfrac{1}{2}V_{j1} N_1 (0)\Delta _1 {\text{ sinh}}^{ - {\text{1}}} (\hbar \omega _D /\Delta _1 ) + \tfrac{1}{2}V_{j2} N_2 (0)\Delta 2_2 {\text{ sinh}}^{ - {\text{1}}} (\hbar \omega _D /\Delta _2 )$$ with ωD denoting the Debye frequency. The usual BCS formulas are obtained in the limits: (all)V jl=V0,N 1(0) =N 2(0). Any excitations generated through the BCS interaction Hamiltonian containingV jl must involve Cooper pairs of antiparallel spins and nearly opposite momenta. The nonzero momentum orexcited Cooper pairs belowT c are shown to have an excitation energy band minimum lower than the quasi-electrons, which were regarded as the elementary excitations in the original BCS theory. The energy gapε g(T) defined relative to excited and zero-momentum Cooper pairs (whenV jl〉0) decreases fromε g(0) to 0 as the temperatureT is raised from 0 toT c. If “electrons” only are available as in a monovalent metal like sodium (V 12=0), the energy constant Δ1 is finite but the energy gap vanishes identically for allT. In agreement with the BCS theory, the present theory predicts that a pure nonmagnetic metal in any dimensions should have a Cooper-pair ground state whose energy is lower than that of the Bloch ground state. Additionally it predicts that a monovalent metal should remain normal down to 0K, and that there should be no strictly one-dimensional superconductor.
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    Critical current density and microstructure of YBa2Cu3O7 thin films post-annealed at a low oxygen partial pressure (1992)
    Springer
    Journal of superconductivity 5 (1992), S. 143-147 
    Details
    ISSN: 1572-9605
    Keywords: Superconducting films ; YBa2Cu3O7 ; critical current density ; microstructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Post-annealing of thin films of YBa2Cu3O7 (YBCO) has been performed at 29 Pa and 750°C. For films 0.6 μm thick, a critical current density 〉1 MA cm−2 is obtained at 77 K, with a sharp eddy current response at 25 MHz. Microstructural investigation of these films by crosssectional and planar transmission electron microscopy reveals that the YBCO film has thec-axis normal to the plane of the substrate in a continuous sheet of varying thickness, frequently covering the entire thickness of the film. Mutually perpendicular rods with thec-axis in the plane of the LaAlO3 substrate are also seen. The microstructure and critical current density of these films are compared with those of previously reported films post-annealed in atmosphericpressure oxygen.
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    Process monitoring during post-annealing of YBa2Cu3O7 thin films containing fluorine (1992)
    Springer
    Journal of superconductivity 5 (1992), S. 167-170 
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    ISSN: 1572-9605
    Keywords: Superconducting films ; YBa2Cu3O7 ; post-annealing ; process monitoring
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The post-annealing method of producing thin films of YBa2Cu3O7 (YBCO) has taken on a new impetus due to the recent work showing that films of the highest quality can be made by using low partial pressures of oxygen during the annealing cycle. Here it is shown that for films produced by using BaF2 as a source material, the post-annealing procedure can be closely controlled by monitoring the F that evolves due to the water vapor reaction with BaF2. The use of an ion-sensitive electrode allowed small F evolution rates (about 1 ng s−1) to be detected above background, sufficient to measure the F evolution rate from even the smallest samples used. The time interval during which F evolves was found to increase with increasing YBCO film area being annealed.
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    How to optimize high-Tc superconductive cuprates (1992)
    Springer
    Journal of superconductivity 5 (1992), S. 203-217 
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    ISSN: 1572-9605
    Keywords: Cuprates ; superconductivity ; review
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Different ways to optimizeT c 's and the magnetic properties of high-T c superconductive cuprates are described and discussed. Oxygen intercalation-desintercalation phenomena and cationic substitutions (M3+ for M2+ or vice versa) lead to a variation of the hole carrier density and can have a drastic influence onT c 's, as shown for bismuth, thallium, and lead-based cuprates, as well as for La2CuO4 and “123”-type superconductors. In the former, the role of hole reservoirs for the rock salt type layers is outlined. The modification of the hybridization of orbitals can also explain the variations ofT c 's observed in some systems like Y1−x Ca x Ba2Cu3−x :Fe x O7 in which the oxidation state of copper remains constant. A critical current density enhancement can be realized by irradiating high-T c materials by high-energy heavy ions because of the peculiar columnar structure of the heavy ion-induced tracks. The effects of such columnar defects, 70 Å in diameter, on flux pinning, magnetic relaxation, and location of the irreversibility line of bismuth-based 2212 crystals irradiated by 6-GeV Pb ions are reported. We observe a strong shift of the irreversibility line toward high fields and temperatures, indicating that pinning effects must be taken into account in the vortex lattice motion. Such induced changes are accompanied by a strong enhancement of the critical current density and a significant enlargement of the irreversibility region in theH,T plane.
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    Far-field radiation of a vibrating point source in anisotropic media (1991)
    Springer
    Journal of nondestructive evaluation 10 (1991), S. 71-78 
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    ISSN: 1573-4862
    Keywords: Ultrasonics ; far-field radiation ; anisotropic media ; directivity pattern
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract In this paper, Lamb's technique,(1) which was used to study acoustic radiation due to an external force acting in an infinite isotropic solid or over the surface of an isotropic solid, has been extended to the case of general anisotropic media. The far-field radiation is numerically calculated for a vibrating point source in an infinite anisotropic solid or on the free surface of a semi-infinite anisotropic solid. The directivity patterns of a point source are obtained for the three different elastic modes, and a brief discussion of the main features of the numerical results is presented.
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    Monitoring phase formation of Pb-substituted Bi-Sr-Ca-Cu-O superconducting samples at different preparative stages using Raman spectroscopy and X-ray diffraction (1991)
    Springer
    Journal of superconductivity 4 (1991), S. 179-188 
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    ISSN: 1572-9605
    Keywords: Bismuth ; lead substitution ; superconductivity ; Raman spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Raman spectroscopy and X-ray diffraction were used to follow structure and phase formation at various stages in order to study the effect of Pb substitution in (Bi1−x Pb x Sr3Ca3Cu4O y samples. We found that major reactions involving Bi2O3 occurred at around 700°C and that reactions with Ca, Cu, and Pb started at a lower temperature. The amount of Ca2PbO4 formed increases as a function of lead concentration and annealing temperature (up to 800°C), but excess lead substitution (50%) destroys the superconductivity. The high-temperature superconducting phase (2223) is only observed in the 15% and 20% leaded samples. These two samples exhibit a higher amount of Ca2PbO4 during intermediate processing stages, which suggests that the presence of the Ca2PbO4 is important for the formation of the high-T c phase. It was found that theT c increases with lead concentration (up to 20% Pb).
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    Reproducibility of transition temperature and critical current density of thin films of YBa2Cu3O7 on (100) LaAlO3 (1991)
    Springer
    Journal of superconductivity 4 (1991), S. 61-65 
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    ISSN: 1572-9605
    Keywords: Superconducting films ; YBa2Cu3O7 ; critical current ; LaAlO3
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Submicrometer epitaxial films of YBa2Cu3O7(YBCO) on (100) LaAlO3 were made by coevaporation and furnace annealing. Samples from more than a dozen runs are used in this study. The zero resistance transition temperature (T c) is high (89 or 90 K) if the film composition is phase pure (Ba/Y=2, Cu/Y=3) or if it is enriched in Ba and Cu. For these compositions the critical current density (J c) at 77 K has an average value of 2×105 A cm−2, with a tendency for decreasingJ c with increasing film thickness (0.2 to 0.8μm). Variations inJ c are not correlated with deviations from ideal stoichiometry. Steeper slopes of the resistance-temperature curves above 100 K and lower values of the room-temperature resistivity are associated with high values ofJ c. If the film composition is enriched in Y relative to Ba and Cu,T c decreases by several degrees.
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    The search for an excitonic mechanism: A recollection of John Bardeen (1991)
    Springer
    Journal of superconductivity 4 (1991), S. 357-360 
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    ISSN: 1572-9605
    Keywords: Excitonic mechanism ; superconductivity ; John Bardeen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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    URL: http://dx.doi.org/10.1007/BF00618216
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    Microwave properties of highly oriented YBa2Cu3O7-δ superconducting thin films (1991)
    Springer
    Journal of superconductivity 4 (1991), S. 253-257 
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    ISSN: 1572-9605
    Keywords: YBa2Cu3O7 ; microwave properties ; R s
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We have performed millimeter-wave frequency (94 GHz) measurements on high-quality YBa2Cu3O7-δ superconducting films on yttrium-stabilized (100) ZrO2 and MgO substrates. The ∼0.2μm thin films fabricated by magnetron sputteringin situ with the YBa2Cu3O7-δ powders as target exhibit superconducting transition temperatures up to 88 K. The critical current density of 6×105 A/cm2 at 77 K and the X-ray diffraction spectrum as well as scanning electron microscope photographs indicate these thin films are fullyc-axis oriented, extremely high in density, and universally homogeneous. Millimeter-wave surface resistances have been measured on a hemisphere open resonator in the temperature range of 20 K toT c and beyond. The surface resistance at 94 GHz and 77 K for these films is found to be about 30 mΩ, nearly 1/4 that for copper, and a drop of two orders in the surface resistance within 4 K is observed, which indicates that these films are good materials for applications in the millimeter-wave range, especially for fabricating microwave devices. We observed such low surface resistance in these thin films due to the near absence of grain and phase boundaries coupled with a high degree of crystalline orientation.
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    Optimization of annealing temperature for YBa2Cu3O7 thin films post-annealed at a low oxygen partial pressure (1991)
    Springer
    Journal of superconductivity 4 (1991), S. 279-282 
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    ISSN: 1572-9605
    Keywords: Superconducting films ; YBa2Cu3O7 ; annealing temperature ; LaAlO3
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Post-annealing of YBa2Cu3O7 (YBCO) thin films is usually performed at 850–900°C in atmospheric-pressure oxygen. In this study, coevaporated YBCO films on LaAlO3 were post-annealed in an oxygen partial pressure of 29 Pa at temperatures in the range 700–825°C. Zero resistance transition temperatures were 89–90 K. Both d.c. (room-temperature resistance and critical-current density) and a.c. parameters (extracted from eddy-current response measurements at 25 MHz) were monitored. The optimum temperature is close to 750°C, which is on the YBCO thermodynamic stability line at this low oxygen partial pressure.
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    Application of the boundary element method to elastic wave scattering by irregular defects (1990)
    Springer
    Journal of nondestructive evaluation 9 (1990), S. 113-127 
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    ISSN: 1573-4862
    Keywords: Ultrasonics ; modeling ; scattering ; boundary element method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract A time-harmonic boundary element formulation for elastic wave scattering in 3D is adapted to ultrasonic NDE. Defect classes addressed are volumetric voids and inclusions, and crack-like elliptical voids. For axisymmetric flaws, comparisons are made with method of optimal truncation (MOOT) and transition-matrix calculations. Comparison to experiment is made for more general shapes. For crack-like voids, comparisons are made with the Kirchhoff, geometric theory of diffraction (GTD), and quasistatic asymptotic approximations. The efficiency and usefulness of the boundary element method (BEM) in finding the bounds of applicability of these approximate theories are demonstrated. An example of a flaw characterization technique based on intermediate frequency scattering data simulated by BEM is given. The ability of BEM to handle nonplanar incident fields, as described by a transducer beam model, is shown. Other computational and modeling efficiencies of the BEM are noted.
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    Computer simulation of ultrasonics and its applications (1990)
    Springer
    Journal of nondestructive evaluation 9 (1990), S. 81-99 
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    ISSN: 1573-4862
    Keywords: Ultrasonics ; visualization ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Numerical calculations have been carried out for about 20 years, and the results are demonstrated graphically by vector or lattice representations. These results are now being used mainly for clarifying the mechanisms of ultrasonic interaction with material and defects and checking and improving the experimental results. Parts of this paper review results, many involving cracktip diffraction in various geometries, which have been published mainly in conference proceedings and have not appeared in journals. Other parts, dealing with focused fields, focal lenses, and radiation in an anisotropic medium are new, and have not appeared even as conference papers.
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    Color indicator of cuprate superconductivity observed by polarized light microscopy (1989)
    Springer
    Journal of superconductivity 2 (1989), S. 351-359 
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    ISSN: 1572-9605
    Keywords: Cuprates ; superconductivity ; optical microscopy ; phase differentiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract A common mineralogical technique for identifying individual crystals in a heterogeneous, polycrystalline sample involves the observation at room temperature of their colors in reflected polarized light (colors of polarization). Here we present the observation that a brownish yellow (golden) color of polarization is not only characteristic of the YBa2Cu3O7 superconductor, but of the cuprate superconductors in general and is correlated with the occurrence of superconductivity.
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    Studies of magnetic flux penetration in a chemically synthesized Bi(Pb)SrCaCuO superconductor (1989)
    Springer
    Journal of superconductivity 2 (1989), S. 273-279 
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    ISSN: 1572-9605
    Keywords: superconductivity ; flux penetration ; bismuth-lead ; hysteresis loops ; a.c. susceptibility
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Magnetic measurements were conducted on a sample of chemically synthesized Bi1.5Pb0.5Sr1.5Ca1.75Cu2O x using an a.c. susceptometer and a vibrating sample magnetometer. The sample showed a large fraction of the phase with a superconducting onset temperature of 110K. This high-temperature superconducting phase appears to have extremely narrow hysteresis loops above liquid-nitrogen temperatures, showing a small number of eflective flux pinning sites. Below 40 K, a dimpling can be observed in the hysteresis loop under certain conditions.
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    Thermoelectric effects in superconductors (1989)
    Springer
    Journal of superconductivity 2 (1989), S. 323-328 
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    ISSN: 1572-9605
    Keywords: superconductivity ; theory ; thermoelectric effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The possibility of observing thermoelectric effects in high-temperature superconductors (HTS) is discussed.
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    Zero resistance at 117 K in Bi1.6Pb0.4Sr2Ca2Cu2+xOy compounds (1989)
    Springer
    Journal of superconductivity 2 (1989), S. 329-335 
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    ISSN: 1572-9605
    Keywords: superconductivity ; Bi1.6Pb0.4Sr2Ca2Cu2+x O y ; microstructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract In the Pb-doped Bi-Sr-Ca-Cu-O system, optimization of the composition and heat treatment conditions at which a greater amount of the high-T c phase forms has been reported in our early paper [1], where the temperature of zero resistance was 107K. Recently, we have achieved zero resistance at 117 K and observed an a.c. susceptibility step at around 150 K by changing the Cu composition in the Bi1.6Pb0.4Sr2Ca2Cu2+x O y system (x=0, 0.4, 0.8, 1.2, and 1.6).
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    A numerical integration Green's function model for ultrasonic field profiles in mildly anisotropic media (1989)
    Springer
    Journal of nondestructive evaluation 8 (1989), S. 165-179 
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    ISSN: 1573-4862
    Keywords: Ultrasonics ; Green's function ; anisotropic media ; field profiles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract A numerical integration technique utilizing a point source Green's function is introduced to analyze the wave behavior in transversely isotropic-type anisotropic media allowing us to make fast and accurate computations of the acoustic field. The centrifugally cast stainless steel (CCSS) used in nuclear power plants is chosen as a sample medium because of its columnar grain character leading to material anisotropy. A representative number of field profiles are computed and plotted to illustrate the quasi-longitudinal, quasi-transverse, and horizontally-polarized shear wave propagation in a transversely-isotropic medium. Phenomena such as beam skewing, beam splitting, beam focusing, unsymmetrical beams, and other anisotropic effects, some of which are already known from earlier experimental observations, emerge as a computational result of the introduced technique.
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    CO2 laser annealing of plasma-deposited high-T c superconducting thick films (1989)
    Springer
    Journal of superconductivity 2 (1989), S. 293-304 
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    ISSN: 1572-9605
    Keywords: laser annealing ; Y-Ba-Cu-O ; plasma spray ; thick films ; superconductivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Recent advances in the fabrication of high-T c superconducting thick films demand processing techniques which can eliminate film/substrate interdifiusion that occurs during subsequent post-annealing heat treatment after the film is deposited, thereby limiting the application of the thick films for devices. The present study evaluates laser annealing techniques for plasma-deposited Y-Ba-Cu-O thick films using a high-energy CO2 laser (10.6Μm) in a continuous wave mode. The results are compared with those obtained by conventional furnace annealing techniques necessary for post-heat treatment of as-deposited superconducting thick films. The high-T c superconducting phase is recovered by cationic diffusion during subsequent post-annealing heat treatment. Crystallographic phases and microstructural characterization have been performed using XRD, SEM, and EPMA analytical techniques. The significance of the technology lies in the elimination of film/substrate interdiffusion problems, thereby resulting in high-quality superconducting thick films. The technology will significantly reduce the post-annealing times usually required by conventional furnace annealing techniques.
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    Substitution of Cu by Fe in the superconducting ceramic oxide EuBa2Cu3Oy: Structure, electrical conductivity, and microwave response (1989)
    Springer
    Journal of superconductivity 2 (1989), S. 305-316 
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    ISSN: 1572-9605
    Keywords: superconductivity ; EuBa2Cu3Oy ; iron substitution ; oxygen stoichiometry ; conductivity ; microwave response ; cell constants
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract A series of EuBa2(Cu1−x Fe x )3Oy (0.0⩽x⩽0.15) ceramics were prepared and examined by thermogravimetric analysis, X-ray powder diffraction, electrical resistance measurements, and a magnetically modulated microwave absorption technique. The oxygen content (y=6.98±0.03), determined by thermogravimetric analysis in a reducing atmosphere, was independent of the iron concentration forx⩽0.12. The introduction of iron into the EuBa2Cu3O y lattice, via substitution into copper sites, effects a progressive decrease in the superconducting transition temperature with increasing iron concentration. Normal-state conductivity similarly progresses from a low resistivity and negative temperature coefficient behavior, to a semiconducting-like response at the high iron concentrations. X-ray powder diffraction measurements indicate that material containing 6% iron and above is tetragonal, yet it remains superconducting with up to at least 12% iron.
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    The low magnetic field properties of superconducting bulk yttrium barium copper oxide-sintered versus partially melted material (1989)
    Springer
    Journal of superconductivity 2 (1989), S. 427-461 
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    ISSN: 1572-9605
    Keywords: YBa2Cu3O7 ; a.c. susceptibility ; magnetic field effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract A comparison of the low magnetic field properties of sintered (990°C) and partially melted samples (1050°C) has been performed. Changes in the microstructure produced by recrystallization from the melt result in a significant increase in flux pinning at 77 K. Low-frequency (10–100 Hz), low-a.c. magnetic field (0.01–9.0 Oe) a.c. susceptibility data show that gross changes in the a.c. loss component accompanies the observed changes in microstructure. The effects of applied d.c. magnetic fields (10–220 Oe) on the a.c. responses of these microstructures have also been probed. Data are analyzed and critically discussed in terms of current models appropriate for granular superconductors and in terms of older models appropriate for metallic alloys and compounds. Particular attention is given to published interpretations of the in-phase or loss component of the a.c. magnetic susceptibility and to the possible roles which minority phases and sample inhomogeneities may play in determining the detailed a.c. responses of these high-T coxides.
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    Analysis of electronic structure and charge density of the high-temperature superconductor YBa2Cu3O7 (1988)
    Springer
    Journal of superconductivity 1 (1988), S. 111-141 
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    ISSN: 1572-9605
    Keywords: YBa2Cu3O7 ; electronic band structure ; LAPW method ; density of states ; Fermi surface ; Coulomb potential ; charge density ; electron-phonon interaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Self-consistent linearized augmented plane wave (LAPW) method calculations of the band structure, density of states, Fermi surface, Coulomb potential, charge density, core-level shifts, and electron-phonon interaction are presented for Y1Ba2Cu3O7. The calculated Sommerfield parameterγ is 4.35 mJ(mole Cu)−1 K−2, roughly about a factor of 2 smaller than experimentally deduced values of the enhanced valueγ=(1 + λ)γ0, suggesting that the Fermi surface mass enhancement is of the order of unity. The crystal charge density is best represented by overlapping spherical ionic densities when the Cu and O ions are assigned charges of +1.62 and −1.69, respectively, corresponding to about 0.3 holes per oxygen atom. Core-level energies for the inequivalent atoms differ by as much as 0.45 eV for Cu and 0.7 eV for O, amounts which may be detectable by core-level spectroscopies. These results provide important information on the character and magnitude of ionic contributions to bonding in these materials. Within the rigid muffin-tin approximation, calculated McMillan-Hopfield parameters yield estimates for the electron-phonon strength λ that appear to be too small to account for the observedT c. We point out an unusual band of oxygen-derived chain states below, but within 0.1 eV of, the Fermi level.
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    URL: http://dx.doi.org/10.1007/BF00617955
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    Growth and characterization of evaporated thin films of Y1Ba2Cu3Ox (1988)
    Springer
    Journal of superconductivity 1 (1988), S. 303-311 
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    ISSN: 1572-9605
    Keywords: YBa2Cu3Ox ; evaporation ; films ; superconductivity ; elastic backscattering spectroscopy (EBS)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We have prepared thin films of Y-Ba-Cu-O by coevaporation in the presence of oxygen onto room-temperature substrates, followed by postannealing in oxygen. Films have been grown on (100) SrTiO3, (100) MgO, and LiNbO3. The films have been characterized by electrical resistivity, X-ray diffraction, and elastic backscattering (EBS) measurements.
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    URL: http://dx.doi.org/10.1007/BF00617719
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    The interminable adolescence of superconductivity (1988)
    Springer
    Journal of superconductivity 1 (1988), S. 339-348 
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    ISSN: 1572-9605
    Keywords: superconductivity ; magnetic separation ; magnetic levitation ; supercritical helium ; magneplane ; maglev ; technology crisis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Seventy-seven years after its discovery, superconductivity has failed to mature into a practical technology because we in America have lacked the curiosity to understand it, the imagination to appreciate it, and the spirit of enterprise to develop it. We are about to miss our last chance to regain technical leadership and economic security if we continue to pretend that higher-T c materials alone will change the situation.
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    A self-calibrating technique for the ultrasonic discrimination of solid-state welds (1988)
    Springer
    Journal of nondestructive evaluation 7 (1988), S. 191-197 
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    ISSN: 1573-4862
    Keywords: Ultrasonics ; solid-state welds ; calibration ; discrimination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract This paper presents the description and application of a self-calibrating technique for ultrasonic weld discrimination. A broad-band ultrasonic transducer is bonded to one side of the component containing the weld. The transducer transmits and receives short pulses in the pulse-echo mode. The received short pulses are processed to provide data on weld quality. The technique is self-calibrating in the sense that the capture of two waveforms in a single measurement provides enough information to remove the transducer transfer function and transducer bond losses. A key feature of the technique is the elimination of the deleterious effects of ultrasonic bond variability, which was found to be the major limitation for the materials investigated in this study. Another feature is the requirement of access to one side of the weld only. The technique is applied to solid-state welds involving two types of steel, i.e., martensitic and austenitic steel. For the martensitic steels, substantial improvement over previous studies was seen and first- and fourth-class welds could be discriminated. On the other hand, the austenitic steel welds are examples which demonstrate the need for still further improvements, since the discrimination between first- and fourth-class welds was only marginal.
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    URL: http://dx.doi.org/10.1007/BF00566002
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    Ultrasonic evaluation of solid-state welds (1988)
    Springer
    Journal of nondestructive evaluation 7 (1988), S. 227-235 
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    ISSN: 1573-4862
    Keywords: Ultrasonics ; solid-state welding ; pattern recognition ; feature extraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Ultrasonic techniques for evaluating the quality of solid-state weld interfaces have been investigated over the past several years. Promising results have been obtained on a variety of solid-state welds by extracting features from the ultrasonic wave forms and applying pattern recognition algorithms to separate acceptable from unacceptable welds. The general conclusion is that the ultrasonic features most sensitive to interfacial bonding are those dependent on high frequencies. However, no single feature has been discovered that is adequate to yield separation of good vs. poor welds, since the microstructural response is also frequency dependent. Given the increase in sensitivity and resolution with high-frequency ultrasonic evaluation, selected specimens have been examined with acoustic microscopy. These specially prepared samples were inspected with focused transducers at frequencies in the 35–75 MHz range. The reflections observed indicated bond quality to vary in discrete regions with good and poor regions distributed across the diameter. Corresponding variations in the degree of bonding have been observed on the fracture surfaces of mechanically-tested specimens. The development of both low- and high-frequency acoustic microscopy has led to the possibility of sensing and imaging subtle changes in the reflection coefficient of the bond line. These acoustic images will improve our understanding of the mechanisms involved in evaluating solid-state bonds.
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    URL: http://dx.doi.org/10.1007/BF00566005
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    Interfacial spring model for ultrasonic interactions with imperfect interfaces: Theory of oblique incidence and application to diffusion-bonded butt joints (1988)
    Springer
    Journal of nondestructive evaluation 7 (1988), S. 131-152 
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    ISSN: 1573-4862
    Keywords: Ultrasonics ; diffusion bonds ; oblique incidence ; spring model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract The quasi-static distributed spring model is used to derive the ultrasonic reflectivity of an imperfectly-bonded interface as a function of frequency and angle of incidence. The results are then incorporated in a model for the corner reflection from a diffusion-bonded joint between two abutting plates, the corner being defined by the bond plane and the common lower surface plane of the plates. An immersion-inspection geometry is assumed, and seven categories of corner reflections are identified and examined in detail. These fall into two classes: those having parallel incident and exiting rays in water (φ′=φ), and those having nonparallel water rays (φ′ ≠ φ). The φ′ = φ categories are suitable for single probe (pulse-echo) inspections of the joint. Based on the amplitude of the outgoing corner-reflected signal, two φ = φ′ geometries appear promising. These employ, respectively, a corner reflection involving only longitudinal waves with the interface illuminated at near-grazing incidence (LLL), and a corner reflection involving only transverse waves with the interface illuminated at near 45° incidence (TTT). In addition, two practical φ′ ≠ φ geometries are indicated; these both involve mode conversion upon reflection from the interface, with the incident or outgoing longitudinal wave traveling nearly parallel to the interface. Model predictions for LLL and TTT reflections are compared to measurements on diffusion-bonded Inconel specimens, and techniques for applying the model results to more complicated bond geometries are discussed.
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    URL: http://dx.doi.org/10.1007/BF00565998
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    Ultrasonic characterization of tubing pinch welds (1988)
    Springer
    Journal of nondestructive evaluation 7 (1988), S. 217-225 
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    ISSN: 1573-4862
    Keywords: Ultrasonics ; pinch welds ; solid-state bonds ; grain scattering
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Spatially-focused, high-frequency ultrasonic pulses have been used in the evaluation of the quality of stainless steel tubing pinch welds. Experimentally, echoes from the bond plane were generally too weak to observe, except in bond planes with macrocracking. Correlations were therefore sought between bond quality and the amplitude and spectral features of the back-surface echo that has passed through the bond plane twice. Linear scans of the back-surface echo parallel and perpendicular to the tubing axis were made on pinch welds of four classes of bond quality. Trends, with scatter, were observed between the ultrasonic parameters and bond quality. These experimental results were interpreted using the Stanke-Kino theory of ultrasonic attenuation due to grain scattering to relate the microstructural changes caused by the pinch-weld process to the observed ultrasonic signals. The results illustrate the importance of process-related changes in near-bond microstructure in attempts to nondestructively determine bond strength.
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    Interfacial phenomena and microstructural connectivity in explosively fabricated Y-Ba-Cu-O superconductors (1988)
    Springer
    Journal of superconductivity 1 (1988), S. 3-19 
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    ISSN: 1572-9605
    Keywords: YBa2Cu3O7 ; explosive consolidation ; SEM ; TEM
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Measurements of supercurrent transport and current density in explosively fabricated superconducting prototypes have been erratic, with current densities measured to be in excess of 103 A/cm2. This erratic behavior appears to be related to the degree of consolidation achieved for Y-Ba-Cu-O powders and, more specifically, to the connectivity or interfacial structure at individual, contacting, superconducting particles. We have used SEM and TEM to characterize and illustrate some of these features in preliminary superconducting prototypes composed of Y-Ba-Cu-O powder channels consolidated and encapsulated in copper and aluminum matrices by explosively generated shock waves. Observations of grain boundaries and interface phase regions cast some light on the prospects for producing good connectivity through optimizing the consolidation process and process parameters as well as the elimination of surface reactions on particles prior to consolidation, or thermal effects during consolidation.
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    Optical differentiation of orthorhombic superconductors such as YBa2Cu3O7 from their tetragonal precursor material (1988)
    Springer
    Journal of superconductivity 1 (1988), S. 35-44 
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    ISSN: 1572-9605
    Keywords: ErBa2Cu3O7 ; superconductivity ; optical microscopy ; phase differentiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The orthorhombic superconducting phase of YBa2Cu3O7 is shown to be differentiable from its tetragonal precursor by optical microscopy. Individual grains 1 μm in diameter or larger are found to either exhibit the color of the compensator in reflected polarized light (tetragonal material) or to change colors from the compensator (orthorhombic material). By using color differences, retained tetragonal material and the orthorhombic nature of untwinned areas of grains are identified. The advantage to producing better superconducting single crystals and sintered polycrystalline materials is discussed.
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    Processing of single-phase ceramic 123 YBaCu-oxide superconductor by hot pressing (1988)
    Springer
    Journal of superconductivity 1 (1988), S. 45-52 
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    ISSN: 1572-9605
    Keywords: YBa2Cu3O7 ; hot pressing ; electrical resistivity ; critical current density
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract High-quality, single-phase, polycrystalline samples of high-temperature superconducting 123 YBaCu-oxide have been processed by hot pressing of specially prepared charge material at elevated temperatures. The samples are orthorhombic with unit cell dimensionsa = 3.824(1) Å,b = 3.888(1) Å, andc = 11.679(2) Å. They exhibit: (i) densities up to 82% of the theoretical value; (2) a sharp phase transition between the normal and superconducting states at 91.6 K; (3) a reduced dependence on thermal cycling effects and on excitation currents in resistivity measurements; and (4) a reduction in surface deterioration due to water, air, and acid attack. The hot-pressed samples supported current densities at least two orders of magnitude greater than those found in cold-pressed samples measured under similar conditions.
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    Effects of the structure of the Fermi surface on the normal and superconducting parameters of the high-Tc oxide superconductors (1988)
    Springer
    Journal of superconductivity 1 (1988), S. 143-151 
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    ISSN: 1572-9605
    Keywords: La1.8Sr0.2CuO4 ; YBa2Cu3O7 ; Fermi surface ; multiband structure ; coherence length ; effective mass ; Fermi energy ; Fermi velocity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We have described the major features of the Fermi surfaces of the high-Tc cuprates. The description in momentum space and use of Fermiology allows us to analyze the large anisotropy and multiband structure of the new materials. These properties are crucial because of the extremely small values of the coherence length. The Fermi surface can be reconstructed with the use of experimental data. Based on this method, we have evaluated the parameters such as effective mass, Fermi energy, Fermi velocity, and coherence length and estimated them for La1.8Sr0.2CuO4 and Y1Ba2Cu3O7 with the use of heat capacity and Hall effect measurements.
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    Microwave absorption in high-T c superconductors (1988)
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    Journal of superconductivity 1 (1988), S. 165-174 
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    ISSN: 1572-9605
    Keywords: microwave ; surface impedance ; highT c ; La2CuO4 ; YBa2Cu3O7
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We have investigated the 9- and 10-GHz microwave properties of bulk samples of strontium and barium substituted La2CuO4 and YBa2Cu3O7 and one YBa2Cu3O7 MBE film on SrTiO3. Anomalous microwave absorption is seen especially for poorly compacted bulk ceramic samples. Transitions were generally broadened nearT c and the residual losses were high. The real part of the surface impedance could be fit belowT c to the empirical equation with an added term linear in temperature. The microwave response of the film was masked by paraelectric absorption and acoustic resonances in the substrate.
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    Band structure and electron-phonon interaction of LaAgO3 (1988)
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    Journal of superconductivity 1 (1988), S. 175-180 
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    ISSN: 1572-9605
    Keywords: band structure ; electron-phonon interaction ; superconductivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract A comparison is made between the band structure of LaAgO3 and LaCuO3, which is the cubic counterpart of the high-T c superconducting oxides. The electron-phonon parameterη is also calculated and is found to be larger for Ag and O in LaAgO3 than for Cu and O in LaCuO3.
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    Novel technique for crystal growth of superconducting ErBa2Cu3O7 (1988)
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    Journal of superconductivity 1 (1988), S. 181-190 
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    ISSN: 1572-9605
    Keywords: ErBa2Cu3O7 ; crystal growth ; microscopy ; superconductivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Millimeter-sized crystals of ErBa2Cu3O7 were fortuitously grown while sintering a flat disk. It was possible to separate individual crystals from the sintered mass and measure their properties. The resistive transition and onset of magnetic transition of a single crystal was 93 K and the resistive transition width was 〈 1 K. Flux expulsion was observed and individual crystals could be levitated by a magnetic field. Crystals showed unusual growth features. They were heavily corrugated along the part of the crystal that grew parallel to the top surface of the disk and that coincided with thec axis of the unit cell. Crystals were characterized by X-rays, electron microscopy, and optical microscopy.
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    Fiber optic sensing for ultrasonic NDE (1987)
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    Journal of nondestructive evaluation 6 (1987), S. 135-146 
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    ISSN: 1573-4862
    Keywords: Ultrasonics ; fiber optics ; lasers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract An innovative approach to nondestructive evaluation (NDE) using noncontacting optical sensors has demonstrated. In this effort a single mode optical fiber interferometer (OFI) was used to sense the presence and form of Rayleigh waves traveling along the surface of a steel test bar at a velocity of nearly 3mm/µs. Acousto-optic time-domain data was successfully used to detect the presence and locate the position of a test “flaw” (a machined slot) in the bar, and spectrum analysis was used to estimate its geometry and size. This approach has many potential applications in the ultrasonic evaluation of real flaws in structures with complex geometries. Coupled with the authors' earlier work demonstrating the feasibility of generating acoustic waves in metals using laser light pulses transmitted through the fiber optic probes, this latest achievement points to the development of a fully noncontacting, fiber optic based thermal-acousto-photonic (TAP) NDE system, with potential applications to the reliability testing of many important structures where composition, scale, geometry, or restricted access preclude the use of conventional NDE techniques.
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    Separation and characterization of stress levels and texture in metal sheet and plate. II. Rolled copper sheet experiment (1987)
    Springer
    Journal of nondestructive evaluation 6 (1987), S. 33-45 
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    ISSN: 1573-4862
    Keywords: Ultrasonics ; texture ; metals ; EMATs ; nondestructive evaluation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract In this paper, we compared elastic shear moduli determined by EMAT techniques to x-ray pole figure measurements for three lots of rolled copper sheet. All moduli (C′44,C′55,C′66) decreased with rolling reduction to more than −10% for a 90% rolling reduction and the difference betweenC 44 andC 55 increased with developing in-plane anisotropy as predicted in Part 1. Pole figures of (111) and (200) planes revealed various initial textures for the starting annealed plates, and (111) pole rotation toward a single well-defined preferred orientation at large rolling reductions. Stress relief annealing of a heavily cold rolled plate produced no significant changes in elastic moduli while hardness decreased, thus indicating that textural changes were responsible for the observed moduli changes.
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    Laser excitation through fiber optics for NDE (1987)
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    Journal of nondestructive evaluation 6 (1987), S. 57-64 
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    ISSN: 1573-4862
    Keywords: Ultrasonics ; fiber optics ; lasers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract This paper describes experiments designed to generate acoustic waves by using a laser pulse, transmitted through fiber optics, to thermally shock the surface of a steel specimen. The purpose of this effort was to explore the noncontacting generation of Rayleigh surface waves appropriate to the interrogation of structures for the detection of subcritical defects, with the ultimate goal of developing an efficient laser-based nondestructive evaluation technique utilizing flexible fiber optics.
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    Nondestructive detection of flaws in material using transducer arrays (1987)
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    Journal of nondestructive evaluation 6 (1987), S. 47-55 
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    ISSN: 1573-4862
    Keywords: Ultrasonics ; transducer array ; flaw detection ; signal processing ; NDE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract In this paper, we describe a system which uses array filters for processing the recordings of an array of transducers for the purpose of locating possible flaws in the material being tested nondestructively. When applied, in order to focus the array outputs at a point inside the material, these filters are able to attenuate, very effectively, interfering residual energy scattered from adjacent flaws, as well as random noise. If there is a flaw at the point of focus, the summed output of the filters will have a large signal at a delay time corresponding to the total travel time for this point; otherwise the output will consist mainly of residual random noise. Thus, the location of flaws or even microflaws in material may be achieved by simple threshold detection.
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    Diffraction of elastic waves by defects in plates: Calculated arrival strengths for point force and thermoelastic sources of ultrasound (1986)
    Springer
    Journal of nondestructive evaluation 5 (1986), S. 145-156 
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    ISSN: 1573-4862
    Keywords: Ultrasonics ; elastic waves ; diffraction ; defects ; time-of-flight technique ; thermoelastic
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract This paper applies geometrical ray theory to the calculation of the surface displacements generated by point force and thermoelastic sources of ultrasound in plates containing planar defects. The calculation includes direct wave arrivals, waves undergoing back-wall reflection with or without mode conversion, and waves diffracted by the crack-tip. Ultrasonic B-scan data are also simulated so that comparison can be made with experimental data. It is shown that the thermoelastic source, which can be generated by a pulsed laser, is particularly well suited to defect detection by the ultrasonic time-of-flight technique.
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    URL: http://dx.doi.org/10.1007/BF00570623
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