SESSION R6: POSTER SESSION: BSCCO AND TBCCO CONDUCTORS AND BULK{ R6.1
Chair: Dominic F. Lee
Wednesday Evening, April 2, 1997
8:00 P.M.
Salon 7
and the phase formation of 2223-phase
in Ag-sheathed Bi-2223 tapes. For variations of the copper-, lead-,
and bismuth-content, the relative effect on the critical currents was
studied. Varying the copper content between 3.0 and 3.4 in
Bi
Pb
Sr
Ca
Cu
O
, we observed
a distinct effect on the critical current. A maximum critical current
was observed for values at x = 3.2. This result was found for
annealing temperatures lower than 822
C. For higher
temperatures, samples with lower Cu contents achieved higher critical
currents. Different results were found for the variation of the Pb
content with a plateau-like region between x = 0.25 and 0.35 for a
variation of x between 0.2 and 0.4 in
BiPbSrCaCu
O. This turns
out to be strongly temperature dependent and was modified for T <
812 C and T > 821C. In the region with T <
812C, tapes with high Pb-contents gave lower critical
currents whereas in the T-region above 821C, the samples
with x(Pb) = 0.4 achieved high lc values. A variation of the Bi
content between 1.65 and 1.95 indicated a decrease of critical
currents towards low Bi contents with an optimum at x(Bi) = 1.85.
Finally a combined variation of Bi and Pb content had nearly no
influence on the final critical currents which improved at T
>818C with lower bismuth and higher lead contents.
Furthermore the dependence of the phase formation on the Cu- Pb- and
Bi- content was investigated. It is also shown that the stoichiometry
variations strongly affect the kinetics of phase formation and the
formation of critical transport current densities in the
tapes.
SrCaCuO WITH NANOSCALE OXIDE ADDITIVES, Y.
Xu, Mankato State Univ, Mankato, MN; Ken C. Goretta, L.
R. Feng, M. Jiang, P. Kostic, Argonne National Laboratory, Energy
Tech Div, Argonne, IL. O
, TiO, SnO, or ZrO particles
to BiSrCaCuO (Bi-2212) were examined. Powder compacts
were blended and heat treated by a variety of methods, including
solid-state sintering and partial-melt processing. Melting response,
microstructural development, and superconducting properties were
studied, and the processing routes most likely to be successful in
enhancing flux pinning were identified. 
,/2 and rocking curve
were made during heating and cooling of the samples. Melting and
solidification temperatures showed monotonic decrease in
semi-logarithmic scale as a function of oxygen partial pressure.
Melting point of the Bi-2212 on Ag plate at 100
oxygen pressure
is 879C and melting point at 1 oxygen pressure
827C, and solidification temperatures are 5 -10C
lower than the melting points for each oxygen pressure, indicating
that melting and solidification points are strongly dependent on
oxygen partial pressure. On heating we observed, for all oxygen
partial pressures used, melting point gap of 5 - 6C in
which Bi-2212 and liquid phases coexist, and the fact was attributed
to the effect of Ag diffused from substrate. In addition, we observed
the strong grain alignment of the Bi-2212 compound along c-axis at
the initial stage of melting as well as strong grain alignment along
c-axis during solidification of the compound. The best c-axis
alignment of grains was obtained for the samples cooled down slowly
under 20 oxygen partial pressure.
BSCCO SUPERCONDUCTOR TAPES, HanJin Lim,
Stanford Univ, Center for Materials Research, Stanford, CA; J. Gerald
Byrne, Univ of Utah, Dept of Metallurgical Engr, Salt Lake City, UT.
BSCCO superconductor tapes were
prepared by the conventional powder-in-tube method.Some tapes
involved partial melting and some involved solid state processing
only.X-ray diffraction (XRD) showed the presence of both BSCCO 2223
(T = 105 K) and BSCCO 2212 (T = 80 K) phases in all the
materials. For the mostly BSCCO 2212 phase samples, X-ray studies
indicated that tape#1 which involved partial melting at
850C for 0.3 h had a higher degree of basal orientation than
a tape#2 which involved partial melting at 855 C for 0.5
h. For the mostly BSCCO 2223 phase samples, however, a comparison of
a tape #3 (solid state processing at 840C), tapes #5 and
#6 (another solid state processing followed by repeated short
annealing), and tape #4 (partial melting at 865C for 0.5h),
showed that the solid state processed tape (#3) had the highest
degree of basal orientation. Direct current magnetic susceptibility
measurements were used to follow the transition at T. Critical
current density, J, values were estimated from DC magnetic
hysteresis loops for all tape samples. OF COMMERCIAL HTS CONDUCTORS, Yusuf
S. Hascicek, Lee-Ye Xiao, Beatrice Boutemy, Steven W. Van Sciver,
Florida State Univ, Natl High Magnetic Field Lab, Tallahassee, FL.
PbSr
Ca
CuO
(x = 0,3-0,4; y
= 0-0,2) ceramics have been studied. The ceramic samples were formed
from synthesized powders by an ordinary static pressing at pressures
100-1500 MPa, by a dynamic explosive compacting at pressures 1,5-4
Gpa, by a hot-press method at pressures 30-60 MPa and temperatures
800-860C with using of carbon heating elements, by
high-pressure technique and technology at pressures 2-7 GPa and
temperatures up to 900C in an oxidizing atmosphere and by a
sedimentation from suspensions with following static pressing. The
texture factor, F, was determined from relationship of x-ray
intensities of reflections (115) and (0010). The texture factor in
very thin surface layer of pressed ceramic samples was in 1,5-2 times
higher than in their volumes. At compacting pressure about 100 MPas,
its values ran already up to 97-98 in perpendicular direction
of pressing and F was decreased up to 80-90 in other
directions. The ceramic's density was increased up to
85-90 at increase of compacting pressures up to
1000-1500 MPa. The critical current density (j) was determined
by levels of texture, density, and by conditions of heat treatment of
ceramics. 
Pb
SrCaCuO
: A
KINETICALLY FASTER ROUTE TO TEXTURED BSCCO, Matthew J.
Kramer, L. Margulies, Iowa State Univ, Ames Laboratory, Ames, IA;
K. W. Dennis, R. W. McCallum, Iowa State Univ, Ames Lab, Ames, IA.
SrCaCu2O8 (Bi2212) could be rapidly converted
into a highly c-axis textured tape with the application of uniaxial
pressure during crystallization. Unfortunately these materials were
weak-linked even though the density was high and the concentration of
second phases was < 5%. Attempts to demonstrate this process route
in the (BiPbSrCaCuO) Bi2223
system were stymied by the considerably higher liquidus temperature
and the low vapor pressure of Pb. A new high temperature furnace with
controllable atmosphere has now been constructed. We have learned how
to control the loss of Pb and can now routinely produce nearly
amorphous Bi2223. Unlike the amorphous Bi2212, the amorphous Bi2223
is not deficient in oxygen. Flash annealing of the amorphous Bi2223
glass in 7.5% O2 (balance N2) shows that greater than 80% of the
glass converts to Bi2223 in less than 24 hrs. The presence of Ag
appears to improve the kinetics. The purpose of flash annealing is to
suppress the formation of intermediate phases such as
CaPb
by jumping over the stability field for this
compound. CaPb produces a liquid phase below the Bi2223
processing temperature leading to significant second phase coarsening
and long processing times. Preliminary magnetization measurements
suggest that the Bi2223 is not as weak-linked as the Bi2212 was. Work
is underway to crystallize the amorphous Bi2223 under uniaxial load to
induce texture during crystallization.
Pb
Sr
Ca
CuO was
sandwiched between two MgO plates, and was sinter-forged in air at 850
C, 1.96 MPa for 5 h in the first stage and at 850C, 9.8 MPa
for 50 h in the second stage. The size of Bi-2223 body was 60 mm
long, 10 mm wide and 1.2 mm thick. The critical current was 300 A at
77 K, O T. The flexural strength of the sinter-forged Bi-2223 body
was 170 MPa at room temperature. This value was higher than that of a
sample prepared by CIP normal sintering technique by more than 2
times. The flexural strength of the composite of Bi-2223 body and MgO
plate was 210 MPa at room temperature. This result shows that the
current lead with a high mechanical strength can be prepared by
joining an engineering ceramics to an oxide
superconductor.
This world is
performed at Sandia National Laboratories, Albuquerque, NM, and
supported in part by the U.S. Department of Energy, Office of Basic
Energy Sciences, under contract no.
DE-AC04-94AL85000.
,
Chuan-bing Cai, Shanghai Inst of Metallurgy, Dept of
Special Metallic Matl Lab, Shanghai, CHINA. CuO(Nd123) was synthesized by melt growth method in
various oxygen partial pressures. Measurement of ac susceptibility
showed that the onset superconding transition temperature(Tc) for all
samples depended on the oxygenating temperature(Ta). Within the
tested Ta, the oxygen content and Tc decrease with Ta. It implies
that oxygen content accounts for the difference of Tc. Those samples
which grown in the lower P(O), have higher oxygen content. We
assume that more second phases and porosities in them maybe provide
more passages for oxygen diffusion, especially for those oxygenated
at low Tature oxygen treatment. The post oxygenation at
250C seems to be most effective process to obtain high
onset Tc, while for Y123, a higher temperature (about 400)
may be best. The fact may result from the lower repulsive energy of
oxygen atoms between O(1) and O(5) sites for Nd123 and the lower
orthorhombic-tetragonal transition temperature.. The increase in the J property seems to
be due to mainly an improved texture of Bi-2223 grain alignment as
well as electric connectivity and also to a some kind of finer
defects introduced into the Bi-2223 microstructure. Anisotropy in
the J properties have been measured by a resistive transport and
magnetic hysteresis methods. The flux pinning force parameter for
the Hf doped tape sample, calculated form the hysteresis loops by
SQUID measurement and assuming the Bean's critical state model, has
shown almost identical curves for two applied magnetic field
directions, parallel and normal, to the tape wide surface. This
feature seems to be responsible for pinning centers which are
effective and equivalent for the two field directions.
Microstructures on the Hf doped Bi-2223 samples have also been
observed by high resolution transmission electron microscopy and
scanning electron microscopy. 37 core multifilamentary wires are
being fabricated to study workability of the AgCu sheathed composite
materials and to measure the superconducting
properties
demonstrates that this surface has almost perfect
C-orientation. The study of the reflection in <116> direction from
the same surface shows the presence of four narrow peaks of the pole
figure. It means that 
-directions are parallel in all
blocks, therefore the cleaved surface has the structure close to
single crystalline. The pole figure <200> demonstrates a pack of
single-crystalline layers over the whole volume of the sample. That
means that misorientations of -axes are small,
(
)8 in different layers, and
within each layer
3, ()
2. The reflection (006) is present, because the inter-plane
distances d
= d
. For the best MTG samples of Y-based
material the critical current I (77K)10
A/cm
.
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