SESSION R5: PROCESSING OF DEPOSITS, BSCCO, AND NEW MATERIALS1:30 PM R5.1
Chairs: David K. Christen and Dean E. Peterson
Wednesday Afternoon, April 2, 1997
Salon 15
Ag/Bi-2223 COMPOSITE CONDUCTORS: THE IMPORTANCE OF
REACTION-INDUCED TEXTURE, Nazarali Merchant, Argonne
National Laboratory, Chemical Tech Division, Argonne, IL; Stephen E.
Dorris, Argonne National Laboratory, Dept of Energy Technology,
Argonne, IL; Victor A. Maroni, Albert K. Fischer, Argonne National
Laboratory, Chemical Technology Div, Argonne, IL. at 77 K and zero field. The
mechanisms producing this texture are still not fully elucidated.
Some researchers claim that deformation induced texture (DIT) is a key
contributor, while others have shown that reaction induced texture
(RIT) is the dominant mechanism. In this paper we intend to present
an assessment of existing literature on this subject which suggests
that both mechanisms may be important in obtaining good texture. Our
results indicate that the dominant mechanism of texturing is also a
function of the initial phase assemblage in the powder that goes into
the silver tube before deformation processing. Tapes that exhibit
appreciable RIT usually have the highest J's because the liquid
phase generated during heat treatment enhances grain growth and heals
cracks that form during deformation processing. 
Work
sponsored by the U.S. Department of Energy (DOE), Energy Efficiency
and Renewable Energy, as part of a DOE program to develop electric
power technology under Contract W-31-109-ENG-38.
SrCaCu
O
TAPES, Yuan
L. Wang, Lijun Wu, Yimei Zhu, M. Suonaga, Brookhaven National
Laboratory, Dept of Applied Science, Upton, NY; T. R. Thurston,
Brookhaven National Laboratory, Dept of Physics, Upton, NY.
750
C. Bi(2212)
developed texture rapidly for several hours, accompanied by rapid
grain growth, upon raising the temperature to typical processing
temperatures, and then slowed down dramatically, with much of the
texture developing before the formation of Bi(2223). The degree of
texture attained after long heating times was found to be temperature
dependent, with higher temperatures generally producing better texture
but not necessarily better transport properties. Briefly heating a
sample near the Bi(2212) melting point can dramatically increase the
texture, but such heating usually results in less Bi(2223) content.
Finally, cooling rate was found to be related to the phase content and
transport properties of a sample. These results and their
implications for improving processing conditions are discussed.
Research supported by the U.S. Department of Energy,
Division of Materials Sciences, and Office of Energy Efficiency and
Renewable Energy under Contract No.
DE-AC02-76CH00016.
Mg the oxygen exchange was
studied at various temperatures. The oxygen uptake is different with
regard to whether the oxygen exchanges through the open ends of the
tape where the superconductor is in direct contact with the
surrounding gas-phase or whether the exchange takes place via the
lateral faces of the tape which means through the sheath material.
Methods for a separated analysis of both processes are discussed. The
different exchange properties with different sheath material are
discussed as well as its effect on the phase formation and the final
critical currents in the tapes. 
80 of total grain boundaries in
c-axis aligned polycrystalline Bi/2212 tapes, which are one of the
most promising high temperature superconductors for large scale
applications to date. Systematic studies of these important [001]
twist boundaries were fabricated with a wide range of twist angles
(0-180). The resistance and current-voltage
characteristics were measured simultaneously at various temperatures
and magnetic fields. The boundary structures were then characterized
with TEM, using high-resolution imaging and image simulation
incorporating with charge distribution, nano-probe electron
energy-loss spectroscopy and energy dispersive x-ray spectroscopy, and
strain-field analysis. Contrary to the conventional wisdom, all these
twist boundaries, regardless of their twist angle, carried the same
critical current as their constituent single crystals at magnetic
field up to 9 tesla at low temperatures. The absence of the weak-link
behavior of the [001] twist boundaries can be attributed to the
variation of elastic properties of the (001) layers (the soft-bonding
of the BiO bilayer at the boundaries and the rigid interlayer-bonding
of the CuO layers across the boundaries), to the local Bi/2223
structure, and to stoichiometric chemical composition including
oxygen/hole concentration of the grain boundaries. Our recent work on
the structure and properties of various tilt boundaries in Bi/2212
bicrystals will also be presented.
This work was supported by the U.S. Dept. of Energy, Division
of Materials Sciences, Office of Basic Energy Science, under Contract
No. DE-AC02-76CH00016.
superconducting tapes, a two
step cooling procedure was developed. Monolithic and wire-in-tube
tapes at 825C in 8 O (balance N) in two 50-h
cycles, for a total of 100 h, with one intermediate pressing at 1 GPa
for 5 s. Subsequently, the tapes were cooled by the two-step cooling
procedure. The first cooling step was used to control the
solidification of the partial melt to produce a dense microstructure
with large grains, while the second cooling step maintained phase
purity. The results indicate a pronounced effect of cooling rate on
2223 content during the first 50 h of sintering. At longer sintering
times, the effect of cooling rate on 2223 content was minimal. On the
other hand, the effect of cooling rate on critical current (I) is
quite pronounced even after 100 h of sintering. This strong influence
of cooling rate on I is attributed to microstructural changes that
occur during cooling. Work at Argonne National
Laboratory is supported by the U.S. Department of Energy, Pittsburgh
Energy Technology Center, under Contract
W-31-109-Eng-38. of (Cu,C)-1234 is about 117K, and that of (Cu,C) 1223 can be
raised from 67K to 120K, which is not far away from that of
the new superconducting phase, their annealing effects and
thermostability are quite different from the new phase. For example,
after annealed at 300C in Ar, the T of the 126K-phase
can be suppressed to 80K, while the T of (Cu,C)-1223
increases to 70K and that of (Cu,C)1234 barely changes. T
variations are systematically studied under different
thermo-equilibrium conditions. While no significant decomposition was
observed in (Cu,C)-1223 anal (Cu,C)-I234 when annealing temperature
is lower than 600C, the new superconducting phase is not
even stable at room temperature, especially with moisture. It can
decay into another superconducting phase with T
90K,
while significant change in x-ray diffraction pattern appears at the
same time.
Re
BaCaCuO
CERAMICS AND THICK
FILMS, S. Pinol, CSIC, Inst de Ciencia de Matls de
Barcelona, Bellaterra, SPAIN; Agustin Sin, Albert Calleja, CSIC, Inst
de Ciencia de Materials de Barcelona, Bellaterra, SPAIN; Xavier
Obradors, CSIC, Inst de Ciencia de Matls de Barcelona, Bellaterra,
SPAIN; Josep Fontcuberta, CSIC, Inst de Ciencia de Materials de
Barcelona, Bellaterra, SPAIN; Ferran Espiell, Univ de Barcelona, Dept
of Engr Quinica i Metallurgia, Barcelona, SPAIN.
Re
BaCaCuO
with a critical temperature onset of 138 K and zero resistance at 130
K. The superconductors were prepared using precursor powders of
BaCaCuO
mixed with stoichiometric additions of ReO2
and HgO. We have utilized these ceramics for the preparation of thick
film superconductors by the vacuum-sealed quartz technique. Ceramic
pellets were obtained by solid state reaction of the precursors inside
a quartz tube at 900C. We have studied the influence of
different thermal treatments in the kinetics of the reaction.
Different Re compositions were explored in order to optimize the
purity of the 1223 phase. Only a very narrow Re composition was found
to be appropriate to obtain single phases. Cell parameters and
composition were characterized using a SQUID magnetometer, and AC
susceptometer and electrical resistivity. We have studied the
vapor-solid reaction of the Hg-vapors with a
ReBaCaCuO
thick films precursor (
m thickness) deposited by spray techniques on different metallic
and ceramic substrates (Cr, AlO, SrTiO). We have placed
the samples in a sealed quartz tube together with stoichiometric
Hg-Re-Ba Ca-Cu-O pellets in order to maintain an appropriate Hg-vapor
pressure. Then the tubes were introduced rapidly into a preheated
furnace at 900C for a few minutes and quickly cooled at
room temperature by quenching in air. Superconducting Hg-1223 grains
with c-axis oriented perpendicular to the substrate were identified
by Scanning Electron Microscopy and EDX analysis. Homogeneity and
composition of the thick film grains depend strongly on the time
thermal treatment.CuO
COATED CONDUCTORS ON ROLLED-Ni SUBSTRATES,
Mariappan Paranthaman, Oak Ridge National Laboratory,
Dept of Chemical & Analytical Science, Oak Ridge, TN; F. A. List,
Oak Ridge National Laboratory, Solid State Div, Oak Ridge, TN; David
P. Norton, Oak Ridge National Laboratory, Oak Ridge, TN; Amit Goyal,
Oak Ridge National Laboratory, Metals & Ceramics Div, Oak Ridge, TN;
E. D. Specht, David K. Christen, D. M. Kroeger, John D. Budai,
Qing He, Oak Ridge National Laboratory, Solid State Div, Oak Ridge,
TN; Dominic F. Lee, Oak Ridge National Laboratory, Metals & Ceramics
Div, Oak Ridge, TN; P. M. Martin, Oak Ridge National Laboratory, Oak
Ridge, TN. 
(referred to as YBCO) Coated Conductors were fabricated with a layer
sequence of YBCO/YSZ/CeO/Ni. The cube (100) texture in the
starting Ni substrates was obtained by cold-rolling followed by
recrystallization. The CeO and YSZ films were grown epitaxially
on the textured Ni substrates using electron beam evaporation and rf
magnetron sputtering techniques. The YBCO films were then grown by
pulsed laser deposition. The biaxial texture in the YBCO layer is
over 90. A high transport critical current density of 7.8 x 105
/cm
at 77 K was obtained on 0.7 
m thick YBCO films in
zero field. The effect of buffer layer thicknesses will be discussed.
We also recently demonstrated that over 6 cm long buffered substrates
with good biaxial texture can be obtained using the electron beam
evaporation technique. Research was sponsored by the Division of
Materials Sciences, Office of Basic Energy Sciences and Office of
Energy Efficiency and Renewable Energy, Office of Utility
Technology-Superconductivity Program, performed at ORNL, managed by
Lockheed Martin Energy Research Corporation for the U.S. Department
of Energy under contract DE-AC05-96OR22464.O pressure of 10
Torr while they were tilted at
approximately 70 from the horizontal plane and at a
target-to-substrate distance of approximately 2 cm. Substrates of
Hastelloy C276 were polished to a mirror finish using aluminum oxide
lapping powders. To characterize the in-plane texturing of the YSZ
buffer layers, x-ray polo figure measurements using the Schultz
reflection method were carried out. The full width at the
half-maximum (FWHM) of the YSZ (111) peak, as a measure of the
alignment of the YSZ grains, wa about 25 at best. Next,
YBaCuO
(YBCO) films deposited on YSZ/Hastelloy C276 by
laser ablation or MOCVD technique. The x-ray rocking curve FWHM for
the YBCO (013) peak was 13 on a YSZ buffer layer which was
considerably less well textured than the best result noted above. The
superconducting properties of the YBCO films will be discussed as a
function of sputtering parameters. CuO (YBCO) films with homogeneous superconducting
properties. Pulsed Laser Deposition (PLD) is used to deposit YBCO on
two different kinds of substrates (CeO-buffered sapphire and
biaxial textured YSZ buffer on polycrystalline YSZ) with a size up to
7 x 20 cm. YBCO films with constant thickness are produced by a
special PLD setup with a 8 cm line-focus on a cylindrical target and
substrate scanning perpendicular to it. The spatial variation of the
critical current density j (77 K) and the transition temperature
T over the area of 7 x 20 cm was investigated by an inductive
method. Small samples (1 x 1 cm) were used to study the influence
of activated oxygen provided by an ion source during YBCO deposition.
CuO
COATED
CONDUCTORS BY LIQUID PHASE EPITAXY USING BaF-ADDED OXIDE
SOLUTION, Yasuji Yamada, ISTEC, Superconductivity
Research Lab, Nagoya, JAPAN; Junichi Kawashima, Yusuke Niiori,
Izumi Hirabayashi, Shoji Tanaka, ISTEC, Nagoya, JAPAN.
(STO) single crystalline fibers of 0.4 mm in
diameter have been formed by low temperature liquid phase epitaxy
using BaF added oxide flux. Since BaF addition make the
crystallization temperature lower down to 920C, reaction
between the substrate material and the flux is suppressed enough to
steadily form YBCO film coating the fibers. YBCO coated conductors
were prepared by dipping the fiber that had been pre-coated by a YBCO
thin film by laser ablation as a seed layer of the solution growth.
The growth temperature and time were 925C for 5 min. The
thickness of the film was about 5 m. Although the YSZ fibers
grown along [100] are almost cylindrical, c-axis oriented YBCO film
grows on the round face the c-axis parallel to the <100> direction
of the base fiber. The films grown on the STO fiber have rather
smooth surface maybe due to the facet faces formed on the surface of
the fiber. |
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