SUPRAS in High Tc Update
According to a preprint by C. Hannay et al. (Liege), different thermal cycles
have been used to synthesize DyBa2Cu3O7-x superconducting ceramics in situ
under a 0.6 T applied magnetic field at low and high temperature. Much grain
texturing is found, and new features (pyramid-like growth from terrace stacking)
are illustrated. The resulting grain alignments, however, did not result
in improved levels of the critical-current density. [92APR15]
In a step toward the development of a model for the atom-by-atom growth
of magnetically textured high-Tc superconductors, M. Ausloos (Liege) et
al. have introduced a magnetic Eden model, which is the Eden model with
an extra degree of freedom. The authors use the new model to simulate the
growth of clusters in two dimensions and to discuss the transitions between
compact and lacunar clusters. [93NOV15]
Investigations of several chemical and physical routes for improving the
crystallographic and physical properties of various high-Tc superconducting
materials are reported in the Liege Ph.D. thesis of R. Cloots. Included
are discussions of the critical-current density in high-Tc superconducting
materials, texturing of DyBa2Cu3O7-d superconducting grains synthesized
in situ in a magnetic field, ionic substitutions and intergrain and intragrain
doping possibilities, and chemical procedures for the synthesis of single-phase
high-Jc Bi- based materials (180 references)[93DEC15].
The effect of sulfur substitution in YBCO, which results in an amorphous
YBCO-S layer between YBCO grains, has been studied by R. Cloots (Liege)
et al. using mu^+ spin rotation/relaxation techniques in zero and applied
magnetic fields. The authors find that the new phase acts as a magnetic
impurity. [94JAN01]
A brief review article on oxygen diffusion in YBa2Cu3O7-d has been prepared
by M. Ausloos (Liege) and A. Pekalski (Wroclaw). The authors discuss the
results and interpretations of various experiments, and they note that it
is essential to account for oxygen-vacancy next-nearest-neighbor (NNN) hopping
in the basal plane to reconcile theory and experiment. The authors also
discuss a newly found V-Delta transition in the tracer diffusion coefficient
as a function of oxygen concentration at low temperature (31 references).
[94OCT01]
A preprint by R. Cloots et al. (Liege) discusses the crystal-growth mechanism
of 123 superconducting ceramics using scanning electron micrographs of DyBa2Cu3O7-d
synthesized by peritectic recombination under a magnetic field of 0.6 T.
The authors introduce a growth model, do computer simulations, and find
that they can explain all the microstructural data reported for such textured
materials. [94NOV15]
The Liege Ph.D. thesis of H. Bougrine describes the method, experimental
set-up, and related measurements with a simultaneous data acquisition technique
on the thermal conductivity and thermoelectric power of the high-temperature
superconductors YBa2Cu3O7-d (Y-123, including samples doped with Fe), Bi2Sr2CaCu2O8+d
(Bi-2212), and (Bi,Pb)2Sr2Ca2Cu3O10 [(Bi,Pb)-2223]. The author found that
in Y-123 the magnetic-field-dependent thermal conductivity has a complicated
behavior with several crossovers between various mechanisms due to free
and pinned vortices and the interplay of various characteristic lengths
(grain size, coherence length, and penetration depth). [94NOV15]
Measurements of the magnetic-field dependence of the thermal conductivity
of an untwinned YBa2Cu3O7-d single crystal and YBa2Cu3O7-d and YBa2(Cu0.95Fe0.05)3O7-d
ceramics are reported by M. Ausloos and M. Houssa (Liege). The authors find
that the results can be understood by assuming that the main carriers of
heat are electrons scattered by the vortex cores. [95MAR15]
A kinetic growth model describing the details of melt-textured growth of
R-123 compounds is discussed in a preprint by N. Vandewalle et al. (Liege).
Results of computer modeling also are presented. [95MAR15]
The contributions to the electronic thermal conductivity of two types of
electron scatterers in type-II superconductors, free (unpinned) vortices
and pinned (via extended defects) vortices, are discussed by S. Sergeenkov
and M. Ausloos (Liege). The theoretical predictions are found to be in reasonable
agreement with experimental data on the thermal conductivity of twinned
and tweeded high-Tc superconductors in high magnetic fields. [95JUN01]
The transport properties of Na-doped, Ba-deficient YBa2Cu3O7-d thin films
have been studied by M. Pekala (Warsaw and Liege) et al. The films had small
grains with c axes oriented perpendicular to the MgO substrate. The electrical
resistivity and thermopower were studied as a function of temperature and
magnetic field. The results are explained in terms of weak links. [95JUL01]
As reported by M. Ausloos (U. Liege) et al., the resistive transition R(T)
between the Kosterlitz-Thouless (K-T) temperature and the Ginzburg-Landau
temperature was studied in spray-dried bulk Bi2Sr2CaCu2O8+d superconductors
for magnetic fields between 0 and 0.3 Tesla. The results are in quantitative
agreement with the two- dimensional (2D) K-T theory. This implies that the
R(T) behavior can be described within a picture of a highly 2D behavior
of macroscopic fluctuations of vortex-antivortex depairing type. The role
of defects or inhomogeneities on R(T) is discussed. [95JUL15]
Monte-Carlo simulations of the kinetics of growth of Y1Ba2Cu3O7-d grains
have been carried out by Cloots et al. (Liege). Using simple kinetic and
geometric arguments, they develop a computer model that simulates growth
in the a-b plane. Both chemical-bonding anisotropy and the presence of Y2Ba1Cu1O5-d
precipitates are considered. The anisotropy of the 211 phase trapping was
found to be an important ingredient in the development of some of the patterns
observed in the growth. [95AUG15]
The microstructure of magnetically melt-textured DyBa2Cu3O7-d samples as
observed by polarized-light metallography is reported by P. Diko (Kosice),
M. Ausloos and R. Cloots (Liège). The authors discuss phase dimensions,
morphology, orientation, nature, and distribution, and they characterize
the grains, twin-structure pattern, and grain boundaries. [95SEP15]
The temperature dependence of the thermal conductivity of high-Tc superconductors
with a superconducting energy gap of either s-wave or d_[x^2-y^2] symmetry
has been considered theoretically by M. Houssa and M. Ausloos (Liege). The
authors analyzed existing experimental results on the low-temperature behavior
of the thermal conductivity of La2-xSrxCuO4, YBa2Cu3O7-d, Bi2Sr2CaCu2O8+d,
and Tl2Ba2Ca2Cu3O10 compounds. The authors found that this behavior is inconsistent
with an isotropic s-wave gap parameter but that it can be explained by assuming
a gap of d_[x^2-y^2] symmetry. [95OCT01]
A model for the two-dimensional growth of a solid interface through a
liquid in the presence of particles that are pushed by the advancing front
is proposed in a preprint by N. Vandewalle and M. Ausloos (Liege). A transition
between growing clusters and frozen ones occurs for a critical particle
fraction x_c = 0.560+-0.005. At x_c, both percolating clusters and internal
patterns are fractal with the same fractal dimension D = 1.87+-0.03, which
is close to the classical percolation exponent 91/48. The authors discuss
this model in connection with the growth of YBa2Cu3O7-d (123) in the presence
of Y2BaCuO5 (211) particles.[95NOV15]
A preprint by M. Ausloos (Liege) et al. describes a kinetics mechanism that
gives rise to dendritic morphology in YBa2Cu3O7-d crystals. The authors
present results of Monte Carlo simulations that exhibit dendritic growth.[96
JAN 01]
The temperature dependence of the in-plane electronic contribution to the
thermal conductivity of a d-wave superconductor has been calculated by M.
Houssa and M. Ausloos (Liege) using a variational method. To account for
the layered structure of high-Tc compounds, the authors consider an anisotropic
Lawrence-Doniach energy spectrum for the electrons. The low-temperature
behavior of the thermal conductivity of most high-Tc superconductors and
the peak structure observed below Tc are quantitatively reproduced by this
model. These results suggest that the order parameter of the high-Tc superconductors
has d_[x^2-y^2] symmetry, and support the hypothesis that the peak observed
in the thermal conductivity of these materials has an electronic origin.[96
JAN 01]
The mixed-state resistive tail of sintered YBa2Cu3O7-d has been studied
by V. V. Gridin (Witwatersrand) et al. using a Corbino-disk sample geometry.
When the transport current passes radially from the rim of the sample to
its center, the authors argue that the voltage signal consists of two components:
one due to quasiparticles and the other due to vortex motion. The authors
claim that the quasiparticle contribution is comparable with that from vortex
motion. [96 JAN 15]
The electronic contribution to the thermal conductivity of a d_[x^2-y^2]
superconductor has been calculated by M. Houssa and M. Ausloos (Liege) using
a variational method. By accounting for the scattering of electrons by point
defects and acoustic phonons, the authors find that the temperature dependence
of the thermal conductivity of YBa2Cu3O7-d and Bi2Sr2CaCu2O8+d (Bi-2212)
single crystals can be well described with realistic values of the parameters.[96
MAY 01]
A paper by N. Vandewalle et al. (Liege) presents evidence for fractal grain
boundaries in melt-textured Y-123, Dy-123, and Er-123. A universal fractal
dimension close to 7/3 is found. The authors present a statistical model
that predicts this value of the fractal dimension. [96 JUN 01]
Circular and butterfly-like patterns in DyBa2Cu3O7-d (Dy-123) enriched with
Dy2O3 are reported and explained by N. Vandewalle (Liege) et al. from the
growth-condition hypotheses of nonseeded melt-textured growth. These hypotheses,
which are confirmed via model simulations, are particle trapping and displacement
along the surfaces of expanding pyramids or terraces. [96 JUN 15]
A preprint by M. Pekala (Warsaw) et al. reports magnetotransport measurements
of Bi1.84Pb0.34Sr1.91Ca2.03Cu3.06O10+d (Bi-2223) ceramics. The authors found
that the temperature percolation line depends upon whether the line is defined
from electrical-resistivity or thermoelectric-power data. The authors also
measured the field and temperature dependence of the electrothermal conductivity
(thermoelectric power divided by resistivity) and compared their results
at high temperatures (approaching Tc) with those expected for s-wave or
d-wave order parameters. The results agreed with the d-wave description.[96
JUN 15]
New synthesis processes for Bi-2212 and Bi-2223 high-Tc superconducting
ceramics are described in the Liege Ph.D. thesis of S. Stassen. Included
are discussions of general features about Bi-based superconducting ceramics,
magnetic grain alignment in 2212 materials, nonisovalent alkaline-metal
substitution in 2212 materials, 2223 materials prepared by the glassy-matrix-precursor
method, and nonisovalent rare-earth substitution in 2223 materials (352
refs.). [96 JUN 15]
The electronic contribution kappa_e to the thermal conductivity of a two-dimensional
superconductor with saddle points at the Fermi level in the band structure,
corresponding to logarithmic van Hove singularities in the density of states,
has been calculated by M. Houssa and M. Ausloos (Liege) using a variational
method. The authors compare the theoretical results obtained for both isotropic
s-wave and anisotropic d_[x^2-y^2]-wave gap parameters. Although the peak
structure observed just below Tc in the thermal conductivity of a Bi-2212
single crystal can be reproduced by both gap-parameter symmetries, the low-temperature
behavior of kappa can be explained only by a d-wave gap parameter. [96 JUL
01]
The dynamic epidemic model has been investigated by N. Vandewalle and M.
Ausloos (Liege) for the evolution of an advancing interface through a medium
containing mobile impurities. The approach should apply to melt- texturing
of YBa2Cu3O7-d and related materials. [96 JUL 01]
The electronic contribution to the thermal conductivity of a two- dimensional
d_[x^2-y^2] superconductor with logarithmic van Hove singularities (vHs)
in the density of states has been calculated by M. Houssa (Liege) et al.
The authors explain the behavior of the thermal
conductivity maximum in YBa2Cu3O7-d as a function of oxygen doping in terms
of the vHs scenario. They also conclude that this effect is of electronic
origin. However, since the experiments near Tc do not distinguish between
d-wave and s-wave superconductivity, the authors urge that thermal conductivity
measurements be made at very low temperatures. [96 JUL 15]
A preprint by M. Houssa et al. (Liege) reports the determination of the
superconducting fluctuation contribution kappa_[fl] from measurements of
the thermal conductivity of a Bi2Sr1.8Ca1.2Cu2O8+d (Bi-2212) polycrystal.
A crossover from 2D to 3D behavior theoretically predicted by A. A. Varlamov
and D. V. Livanov [Sov. Phys. JETP 71, 325 (1990)] was observed. The crossover
temperature and the amplitude of the fluctuation contribution lead to realistic
values for the interlayer coupling energy and the transport relaxation time
near Tc.[96 AUG15]
A preprint by H. Houssa (Liege) et al. reports a calculation of the magnetic-field
dependence of the electrothermal conductivity P of high- Tc superconductors
with either s-wave or d-wave gap parameters. The authors analyze the field
dependence of P in Bi2Sr2CaCu2O8+d (Bi-2212), (Bi,Pb)2Sr2Ca2Cu3O10+d [(Bi,Pb)-2223],
and Tl2Ba2CaCu2O8+d (Tl-2212) and conclude that the observed behavior excludes
s-wave symmetry but is consistent with a d_[x^2-y^2]-wave gap parameter.
[96 NOV15]
April 27 - 29, 1997: Free Boundary Problems in Superconductivity: Device
& Process Modeling, SPA, Belgium. For information, contact Marcel Ausloos,
Chair, S.U.P.R.A.S. Institut de Physique B5, Universite de Liege, Sart Tilman,
B-4000 Liege, Belgium, telephone +32 4 366 37 52 ; telefax +32 4 366 29
90 ; web site http://www.phe.ulg.ac.be/supras.html.
June 26 - 28, 1997: Superconducting Materials Aspects : Research & Technology
(SMART 97), Liege, Belgium. A satellite to the Third European Conference
on Applied Superconductivity (EUCAS'97) to be held at Veldhoven, The Netherlands
(June 30 - July 3, 1997). Topics will include phase chemistry, synthesis,
crystal growth, thermal stability, pinning, texturing, applications, modeling,
properties, and HTS materials. For information, contact Chantal Lacrosse,
Conference Secretary, A.I.M. rue St. Gilles 31, B-4000 Liege, Belgium; telephone
+32 4 222 2946; telefax +32 4 222 23 82; e-mail aimulg@misc.ulg.ac.be.
The Ph.D. thesis of M. Houssa (Liege) is devoted to the theory of the thermal
conductivity of high-Tc superconductors. The author analyzes the magnetic-field
dependence of the thermal conductivity and finds, in comparing with experiment,
that the peak in the in-plane thermal conductivity below Tc is of electronic
origin. The author also finds strong support in the data for an energy-gap
parameter with d_[x^2-y^2]- wave symmetry (278 refs.) [97 JAN15].
A physico-chemical model for the growth of melt-textured YBa2Cu3O7-d/Y2BaCuO5
(123/211) composites under isothermal conditions, taking into account the
effect of repulsion between the front and 211 particles, is proposed in
a paper by N. Vandewalle et al. (Liege). The results are in good agreement
with experimental observations. [97 FEB 01].
A brief review of the state of the art of transport in the high-Tc superconductors,
including electrical resistivity, thermoelectric power (Seebeck effect),
and thermal conductivity has been prepared by M. Ausloos (Liege). The author
focuses on the interpretation of magnetic- field-induced changes in the
corresponding transport coefficients (18 refs.).[97 FEB 01].
As reported by M. Houssa and M. Ausloos (Liege), the electronic contribution
to the in-plane electronic thermal conductivity of high-Tc superconductors
leads to a T^2 dependence of the electron-impurity contribution, not a T
dependence.[97 JUN 15]
The effect of both oxygen stoichiometry and zinc doping on the thermal conductivity
of YBCO has been studied by M. Houssa et al. (Liege). An electronic model
which considers the effect of the position of the Fermi level with respect
to the energy of the Van Hove singularities describes many aspects of the
data. The data shows that the Cu(2) valence and thus the charge density
in the planes is closely related to the critical temperature. [97 AUG 1]
Measurements of the temperature dependence (20-300 K) of the resistivity,
thermopower, and thermal conductivity of polycrystalline Hg-1223 with nominal
composition Hg1.4Ba2Ca2Cu3O8+d are reported by H. Bougrine (Liege) et al.
The authors also focus attention on the fluctuation contributions to these
transport properties. [97 AUG 15]
Formulas for the temperature dependence of 3D paraconductivity near the
superconducting transition have been derived by P. Konsin (Tartu) et al.
using the Kubo formalism and the linearized Ginzburg-Landau equations for
a two-band model with interband scattering of pairs. The authors find that
the Aslamasov-Larkin formulas are modified in this model. [97 AUG 15]
A preprint by S. Dorbolo et al. (Liege) reports a theoretical analysis of
the specific heats of single-crystal YBa2Cu3O7-d and HgBa2Ca2Cu3O8+d (Hg-1223)
in a magnetic field. The authors take into account critical XY and Gaussian
fluctuation regimes.[97 SEPT 15]
The information to be gained from magneto-thermoelectric studies of high-temperature
superconductors (electrical resistivity, thermoelectric power, electrothermal
conductivity, Nernst effect, transport entropy, Hall effect) is discussed
in a preprint by M. Pekala (Warsaw) and M. Ausloos (Liege). [97 OCT 15]
A review of the melt-texturing and modeling of YBa2Cu3O7-d/Y2BaCuO5 (123/211)
composites under isothermal conditions has been prepared by N. Vandewalle
(Liege). The author reports that a multigrain growth model gives a good
account of the development of 123/211 composites (50 refs.). [97 OCT 15]
From digitized micrographs of melt-textured YBa2Cu3O7-d/Y2BaCuO5 (123/211)
composites, N. Vandewalle et al. (Liege) have found that the spatial distribution
of the 211 particles is highly inhomogeneous. The authors how that the
distribution differences can be explained only by the partial dissolution
of the 211 particles during the growth process [98 JAN 15]
A preprint by S. Dorbolo et al. (Liege) reports calculations of the mean-field
electronic specific heat of a superconductor in the presence of a magnetic
field. The authors assume an energy spectrum with saddle points in the band
structure, corresponding to Van Hove singularities in the density of states.
From an analysis of the electronic specific heat in YBa2Cu3O7-d, HgBa2Ca2Cu3O8+d
(Hg-1223), and Tl2Ba2CuO6+d (Tl-2201) near Tc, the authors find confirmation
of the existence of d-wave symmetry of the energy gap parameter, and they
find evidence for the presence of Van Hove singularities. [98 JAN 15]
As reported by R. A. Doyle (Cambridge) et al., artificial bulk zero- angle
grain boundaries parallel to the c axis have been engineered between large
melt-processed YBa2Cu3O7-d grains and observed to carry a transport supercurrent
at fields up to at least 5 T at 77 K. The temperature and angular dependencies
of the boundary resistance have exactly the same form as those of the grains,
which is evidence that the grains are intimately coupled. The current transfer
across the grain boundary is thus not that of a weak link or a weak Josephson
junction. [98 MAY15]
A related paper describing investigations by electrical resistivity, current-voltage
characteristics, magnetic-moment measurements, and Hall-probe mapping techniques
of natural high-angle and artificial low-angle grain boundaries parallel
to the CuO2 layers has been prepared by Ph. Vanderbemden (Liege and Cambridge)
et al. The authors note that artificial boundaries engineered by joining
two YBCO single domains display a remarkably weak magnetic-field dependence.
The authors thus suggest that such boundaries have significant potential
for applications inhigh fields at 77 K. [98 MAY15]
The electronic contribution to the specific heat and thermal conductivity
of high-Tc superconductors has been calculated by S. Dorbolo et al. (Liege)
et al. using a 3D band structure including saddle points and a Lawrence-Doniach
coupling between the CuO2 planes. The authors deduce the electronic thermal
diffusivity for s- and d-wave symmetry of the order parameter. The authors
find that the theory and data on DyBa2Cu3O7-d and Y0.9Ca0.1Ba2Cu3O7-d are
in good agreement with respect to the change of slope near Tc. [98 MAY15]
A review of the magnetic field dependence of the electrical and thermal
transport properties (electrical resistivity, thermoelectric power, Nernst
effect, and magneto-thermal conductivity) in the high-Tc superconductors
has been prepared by M. Ausloos (Liege). The author emphasizes the role
of anisotropy (66 refs.)[98 JULY15].
The excess electrical resistivity, excess thermoelectric power, Nernst effect,
and excess magneto-thermal conductivity arising when a magnetic field is
applied to a superconducting sample are the subject of a brief review by
M. Ausloos (Liege) et al. The authors examine several Bi- based 2212 and
2223 superconducting ceramics. They also report a linear relationship between
the Ginzburg-Landau parameter kappa and the vortex viscous drag coefficient
eta (18 refs.)[98 JULY15].
The effects of Van Hove singularities on the thermal properties of high-
temperature superconductors is reported by S. Dorbolo et al. (U. Liege).
Specific heat, thermal conductivity and thermal diffusivity are calculated
within a phenomenological model that includes both s-wave and d-wave gap
symmetries. A relation between the doping level and the oxygenation rate
is found. [98 AUG15].
A preprint by M. Ausloos (Liege) presents a theoretical discussion of the
intrinsic effects of a dc magnetic field B upon the real (R_s) and imaginary
(X_s) parts of the microwave surface impedance of superconductors. The author
presents predicted power-law dependencies of R_s and X_s upon B for s- and
d-wave superconductors. Since the published data are not always in agreement
with the predicted power laws, the author suggests that this indicates the
presence of extrinsic effects, such as granularity and weak links. [98 DEC15].
Measurements of the Nernst effect (flux-flow voltage induced by a temperature
gradient) in magnetic fields up to 4 T along the c axis in textured Bi-2223
have been used by M. Pekala (Warsaw) and M. Ausloos (Liege) to determine
the vortex-lattice melting line B_M(T). The authors measured the Nernst
voltage N vs. temperature T at different fields B, and obtained the melting
line from the temperatures at which changes in the slope dN/dT occurred.
[98 DEC15].
The phase-dependent differential thermopower of s-wave superconductor /
normal-metal / d-wave superconductor (S/N/D) junctions has been calculated
by S. Sergeenkov and M. Ausloos (Liege). The authors discuss the
experimental conditions under which predicted behavior could be measured
[99 APR 01].
Proceedings: Symmetry and Pairing in Superconductors -- Proceedings of the
NATO Advanced Research Workshop, Yalta, Ukraine, April 29-May 2, 1998,
edited by Marcel Ausloos and Sergei Kruchinin. Contains latest findings
of
leading researchers on high-Tc superconductivity, including considerations
of the order parameter and the pairing conditions. Both theoretical and
advanced experimental results are outlined. Considerations of d-, s-, or
more complicated order-parameter symmetry are discussed at length, serving
as a benchmark for an overall view of the field. Details of experiments
on
junctions and fluctuations, both in the presence and absence of a magnetic
field are presented. Electronic, optical, magnetic, and transport
properties are discussed. Publ. 1999; 424 pp.; price $192 (hardbound) or
$84 (PB); ISBN 0-7923- 5520-2 (HB) or 0-7923-5521-0 (PB). Contact Kluwer
Academic Publishers, Customer Service Department, P.O. Box 358, Accord
Station, Hingham, MA 02018-0358; telephone (781) 871-6600; telefax (781)
871-9045; e-mail kluwer@wkap.com. Outside the Americas, contact Kluwer
Academic Publishers, Customer Service Department, P.O. Box 989, 3300 AZ
Dordrecht, The Netherlands; telephone +31 78 639 23 92; telefax +31 78 639
22 54; e-mail services@wkap.nl.
The magnetic-field dependence of the magneto-thermopower DeltaS(T,H) in
textured Bi2Sr2CaCu2O8+d (Bi-2212) is theoretically explained by S.
Sergeenkov and M. Ausloos (Liege) by introducing a field-dependent chemical
potential of holes mu(H) into the Ginzburg-Landau theory [99 APR 15].
Experimental data and theoretical aspects of the thermal conductivity kappa
and magneto-thermal conductivity kappa(B) of high-Tc superconductors and
heavy fermions are treated in a review by M. Ausloos and M. Houssa (Liege).
The authors show how the experiments reveal the order-parameter symmetry.
For the high-Tc cuprates, the experimental results in YBa2Cu3O7-d (Y-123)
and Bi2Sr2CaCu2O8+d (Bi-2212) are inconsistent with an isotropic s-wave
energy gap but are well described by an anisotropic d_[x^2-y^2] gap with
nodes (100 refs.) [99 APR 15].
The evidence for 2D and 3D effective dimensionality of the high-Tc
superconductors as seen in the electrical resistivity, thermal
conductivity, and specific heat is considered in a preprint by M. Ausloos
(Liege). [99 OCT 01].
The Ph.D. thesis of P. Vanderbemden (Liege) reports studies of the critical
current density in bulk high-temperature superconductors as determined by
magnetic-flux-profile measuring methods. The author presents (a) a
theoretical discussion of flux-profile methods, (b) a description of a
practical realization of an experimental set-up intended for measuring such
flux profiles, and (c) a discussion of flux- profile measurements in
several bulk high-temperature superconductors, including Y-123, Bi-2212,
and Bi-2223 sintered ceramics and polycrystalline textured Bi-2212 and
Dy-123 (207 refs.). [99 NOV 01].
A new, simple, low-cost experimental technique designed for investigating
the electrical properties of disk-shaped superconducting samples is
described in a preprint by Ph. Vanderbemden (Liege) et al. In response to
two neighboring, 90 degrees out-of-phase ac magnetic fields applied
perpendicular to the disk, the material experiences an electromagnetic
torque, which depends on its electrical properties. [99 NOV 15]
The mixed-state resistivity of polycrystalline (Bi,Pb)2Sr2Ca2Cu3O10+d
[(Bi,Pb)-2223] has been analyzed by M. Pekala (Warsaw) et al. to locate
the
percolation line in the phase diagram. The authors also calculated the
magnetic-field and temperature variations of the vortex liquid viscosity
and determined the activation energies. [00 JAN 15]
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