Physica C 162-164 (1989) 737-738
North-Holland
ELECTRICAL PROPERTIES
E.N. van EENIGE,
Natuurkundig
AND T c OF Bi2CaSr2Cu208
R.J. WIJNGAARDEN,
Laboratorium,
H. HEMMES,
UP TO PRESSURES
J.J. SCHOLTZ,
VriJe Universiteit,
Amsterdam,
OF 15 GPA
J.J. de KLEUVER,
R. GRIESSEN
The Netherlands.
By means of four-point resistivity measurement the critical temperature of Bi2CaSr2Cu208 was
studied under high pressure. Evidence for three phases, one non-superconducting and two
superconducting with Tc'S of 80 and Ii0 K is found. Both Tc'S are only weakly pressure dependent. The non-superconducting background increases with pressure and with measurement current
indicating the presence of weak links and a "weakening" of these links with pressure.
i. INTRODUCTION
4. RESULTS
Since the beginning
superconductor
of high temperature
research,
A typical curve for resistivity versus
pressure has played an
important role in identifying possible new materials and mechanisms I. Our efforts 2'3 were
concentrated
in a diamond anvil cell. In this contribution we
Bi2CaSr2Cu208
dependence
of T c of
and we also investigate
non-superconducting
this we conclude
T c was determined
For the midpoint
SAMPLE PREPARATION
We describe
three experiments
sintering
a weak pressure
(ll0K-phase),
110
x
were done in a diamond anvil
x
^
x
100"
Bi 2 Ca 1Sr'2Cu208
90
t l Sample 1
Trn x Sample 2a
[3 Sample 2b
,_u
corrected for temperature.
The
samples were small grains taken from a crushed
Each grain was checked separately
superconducting
properties
by levitation.
surements
Four-point
8C
for
No
pressure medium was used, hence the pressure was
quasi-hydrostatic.
(80K-phase)
see fig. i.
cell 3. Pressure was measured using ruby
pellet.
dependence
1 Io_
3. EXPERIMENTAL
fluorescence,
phase.
subtraction.
on samples from
prepared by a standard
technique 3'4
Experiments
after background
-0.7 K/CPa and -1.6 K/GPa
-0.1K/GPa
resistivity mea-
7C
CoC
p(GPa )
and I-V curves were obtained using gold
or copper wires as shown in fig. 1 of ref. 3.
0921-4534/89/$03.50 © Elsevier Science Publishers B.V.
(North-Holland)
From
phases with T c = 80 K and
T c = II0 K and a non superconducting
the
background.
two different batches,
background was observed.
that samples 2a and 2b consisted
of two superconducting
found:
2.
showed one jump for sample I and two
jumps for sample 2a and 2b. For all samples a
non-superconducting
on ultrahigh pressure as obtainable
look at the pressure
temperature
FIGURE i
The midpoint of the resistive
Bi2CaSr2Cu208 •
transition for
is
and
738
E.N. van Eenige et al. / Electrical properties and T c o f Bi2CaSr2Cu208
This result follows the general trend I that high
rely similar behaviour was observed in granular
T c superconductors
aluminium 5 and thin films 6. The correspondence
with a high T c have a very
small pressure dependence
superconductors
8Tc/ap, whereas high T c
with a low T c generally
show a
very strong increase of T c with pressure
n-type superconductors
(the
as (Ndl.yCey)2CuO 4 seem to
be an exception).
We now address
between those results and Lal.8Sr0.2CuO 4 was
discussed by Markiewicz 7. He suggests
behaviour
behaves
that this
is a strong indication that the sample
as a Josephson coupled array.
The observed values for T c (after background
the non superconducting
phase.
subtraction ) did not seem to depend on the measu-
At ambient pressure our resistivity measurements
rement current,
did not show such a phase. However this may have
In conclusion,
been masked by the fact that the metallic/super-
interesting weak-linked
conducting phase was connected through a perco-
with the possibility
lation path. Upon pressurization
coupling strength of the links by changing pres-
ducting background
pressure.
a non supercon-
developped with increasing
We speculate
that the grain edges lost
as expected.
using pressure we have created an
sure. The pressure
to confirm existing
superconducting
array
to change continuously
dependence
the
of the Tc'S seems
ideas.
part of their oxygen due to highly anisotropic
stress and became semiconducting.
the superconducting
vable indicated
that this is not a bulk effect
and that a superconducting
Apparently
The fact that
transition was still obser-
phase still coexists.
the non-superconducting
regions acted
as weak links between superconducting
We thank Dr. A.A. Menovsky
ble the samples.
for making availa-
The financial
Stichting voor Fundamenteel
support of the
Onderzoek der Materie
is greatfully acknowledged.
particles.
With increasing current the insulating behaviour
became more dominant
ACKNOWLEDGEMENT
(see fig. 2). A qualitati-
REFERENCES
i. R.J. Wijngaarden and R. Griessen, "High
Pressure Studies" in "Studies of high
temperature superconductors". Ed A.V.
Narlikar, NOVA Science Publ., New York,
1989 and R. Griessen, Phys. Rev. B36
(1987)5284
2. A. Driessen, R. Griessen, N. Koeman, E.
Salomons, R. Brouwer, D.G. de Groot, K.
Heeck, H. Hemmes and J. Rector, Phys. Rev.
B36(1987)5602
D
15
3. R.J. Wijngaarden, H.K. Hemmes, E.N. van
E.N. van Eenige, R. Griessen, A.A. Menovsky
and M.J.V. Menken, Physica C152(1988)140
4. Y.K. Huang et al., A.A. Menovsky,
Menken et al. to be published
0
0
510
I
100
150
T(K)
FIGURE 2
The resistivity of sample 2b at - 4 gPa as a
function of temperature for different values of
the current.
M.J.V.
5. M. Kunchur, Y.Z. Zhang, P. Lindenfeld, W.L.
McLean and J.S. Brooks, Phys. Rev.
B36(1987)4062 and W.L. McLean, M. Kunchur,
P. Lindenfeld and Y.Z. Zhang, Physica
B152(1988)230
6. H.M. Jaeger, D.B. Haviland, A.M. Goldman,
B.G. Orr, Phys. Rev. B3___44(1986)4920
7. R.S. Markiewicz, Solid State
Comm.67(1988)I175