High T c Oxide Solid State Reaction Kinetics Via Complex Impedance Spectroscopy
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HIGH Tc OXIDE SOLID STATE REACTION KINETICS VIA COMPLEX IMPEDANCE SPECTROSCOPY KULLBERGt§ N .L E.A OPR E. A. COOPER ,T. 0. MASON U. BALACHANDRANt, AND M. L. * Northwestern University, Department of Materials Science and Engineering, Evanston IL 60208 Components and Technology t Argonne National Laboratory, Materials Division, Argonne, IL 60439 § On leave from Amoco Chemical Co., Naperville, IL 60566 ABSTRACT Impedance reaction
spectra (5Hz
- 13MHz)
of YBa2 Cu3 06+3 from
were collected during the solid state
large monosized
finely divided Y203/BaCO3 matrix.
CuO particles
No particle size
imbedded
effect was
in
a
observed,
but a large temperature effect was observed corresponding to an activation energy of approximately 1.8eV (175kJ/mol)
0
over the range 700-900 C.
INTRODUCTION In recent work [1], be
used
to
follow
superconductors
we demonstrated that impedance spectroscopy could
the kinetics
of
solid
state
from oxide or other precursors.
reaction
of
cuprate
Mechanical mixtures of
high purity La203 and CuO were reacted in situ with or without SrCO3 to form La 2xSr.CuO4 (x-0, 0.12). The spectra typically consisted of a semicircle dramatically
passing as
through
the
time increased.
origin,
whose
diameter
decreased
This behavior was
interpreted using an
equivalent circuit consisting of a 70-100pF capacitor
(consistent with bulk
capacitance) with
in
increasing
resistance) vs.
parallel with a time.
resistor whose
Linear behavior was
log (time)
plot.
value
obtained
decreased
steadily
on
(inverse
a
log
A parallel X-ray diffraction experiment
confirmed that the increase in effective conductivity correlated well with the increase in the fraction of product phase. The present study focused on the solid state reaction of YBa2 Cu3 06+y from relatively large, monosized CuO particles of varying sizes imbedded in a finely divided Y203 and BaCO3 matrix. approximate,
as closely as possible,
This
strategy was undertaken
to
a three-phase analogy to the existing
two-phase solid state powder reaction models [2-4].
Both particle size and
temperature effects were considered.
EXPERIMENTAL Monosized fractions of CuO were separated from coarsened high purity
Mat. Res. Soc. Symp. Proc. Vol. 169. ©1990 Materials Research Society
266
powders via sieving.
The three size ranges employed in
were 35-50 pm, 75-I00lm,
and 120-140pm.
the present study
A submicron mechanical mixture of
high purity Y2 0 3 and BaCO3 was prepared by ball milling with alumina media. The CuO particles were mixed by hand into the Y20 /BaCO3
matrix material
under methanol
Pellets
prior to drying and
diameter
by
1-2mm
rapidly
inserted
pressing
thickness)
were
into
experimental
the
(150MPa).
held between
Pt
foil
furnace
in
(0.75cm
electrodes
air.
A
thermocouple attached to one electrode recorded the temperature.
and Pt/Rh
Pt leads
from the two electrodes were connected via coaxial cable to a PC-controlled HP-4192A impedance analyzer. are
shown
spectrum,
in
Fig.
wit
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