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Estimation of maximum electrical resistivity of high Tc superconducting ceramics by the meissner effect
Solid State Communications, Printed in Great Britain.
ESTIMATION
pp.991-992,
Vo1.63,No.l1,
OF MAXIMUM ELECTRICAL
1987.
RESISTIVITY
S.MbszBrosX,
+Oepartment P.Ll.Oox ‘Institute Debrecen,
*Central
2.
of
Solid
State
EFFECT
G.Ha13szX,
K.Vadx, Physics,
Kossuth
+ .OO Ltd.
OF HIGH Tc SUPERCONDUCTING
CERAMICS DY THE MEISSNER F.J.Kedves+,
0038-1098/87 $3.00 Pereamon Journals
O.Keszei*, L.
University,
Hungarian
Academy
and L.MihBly’ H-4010
Oebrecen
Hungary of
Nuclear
P.O.Dox
Research
Research
51.
of
the
of
Sciences,
H-4001
Hungary
Insitute Received
for
Physics,
H-1525
Budapest,
P.O.Box
47.
Hungary
31 May 19fl7 by A.Zawadowski
The observation of oersistcnt current decay is one of the best Non-decaying persistent current probes of superconducting state. induced bv Meissner effect has been observed in an Y-Ba-Cu-0 ce/ 10M6s/. From the measurements ramic superconductor for_;; days cm can be given for the resistivity an upper limit of 7 x 10 of the ceramic superconductor at liquid nitrogen temperature. 2
function estimate culating and in sample,
of time will make possible to the decay time ((7) of the circurrent In the levitated sample this wav the resistance (R) of the too. 1 Flux creeping is known to be the major source of dissipation in a superccnThe magnetic force acting on the ductor. sample is proportional to the volume the flux repelled from, therefore the change in the sample position may serve as an for the motion of the vortices. indicator
1. INTROGL!CTION breakthrough in achieving superconductivity inthe La-Ba-Cu-0 system [l] has initiated a great number of investigations of L-K-C”-0 compounds, e.g. [Z]. The determination of the limit of the resistance in superconducting state is restricted, because measuring the R(T )/R(300K) resistance ratio a drop of four or five orders of magnitude can be detected by means of the conventional four points method. It is, in principle,impossible to achieve much lower limit in the resistance ratio because of thermal flucthermoelectric power in inhomogetuations neous maierials and the transition resistance of the potential leads. high
Last year’s temperature
2.
The
SAMPLE PREPARATION ANC RESISTANCE MEASUREMENT
YBa2Cu307_b
sample
was
prepared
from the appropriate mixture of Y2%; ;;; ground mixture and Cufl. The finely starting mater:als was heat-treated at 9C10°C for 12 hours in air. The resulting black product was reground, ccmpr&ssed into pellets and sintered at 950 C in oxygen atmosphere for 12 hours. The resistance vs. temperature was measured by four probe
The most sensitive method to set an upper limit for electrical resistivity of materials thought to be superconductors is to measure the decay of the average persistent current in the sample [3] . Persistent current can be generated, for examby the Meissner effect. If the strength pie, and the gradient of a magnetic field are appropriately chosen the superconducting sample can be levitated in a magnetic field. In a constant magnetic field the position of the sample depends on the magnitude of the circulating current, the decay of which causes the change of the sample position. So observing the sample position as a
Teih?dxo? ~da~~~~.“::“‘~~~‘~~~~~~~nduciing transition is relatively sharp, with set temperature of T = 94 K. 3. 15 991
an
on-
APPARATUS
Since the3magnetic x 15 x5 mm Co-Sm
fouce, magnet
produced by was not suffi-
a
ESTIElATION OF MAXIWM ELECTRICAL
992
super?onducting cecient to levitate the of size 7 x 7 x 1 mm we hung the ramics, sample on a pendulum during the measurement. The measuring apparatus is shown in Fig. 2. The pendulum is formed by a Be-Cu wire fastened to the axis by silk threads. A magnet is placed into the brass tube with its front plane under the pendulum axis. The the ed
megnet is in electrical brass tube. A tungsten to the Se-Cu wire. So
able
to
the
detect
samole.
wire is pendulum.
the
contact with needle is solderthat we may be
change of the position mm dia. enamled coooer to the Be-Cu wire of the
a 0.05
soldered
of
serves as one lead for This wire the electrical resistance measured between the magnet and the sample. The resistance can be monitored continuously. A Keithley Mod. 197 DMM has ben used for this purpose
in storage mode with a sampling rate of 1 in 10 minutes. The probe is submerged II? a commercial laboratcry liquid nitrogen dewar vessel (L'air Liqulde PC-25) in such a 'way tha: the whole probe is in the cryogenic liquio. The de:?ar is placed on a vibration isolated platform. 4 .MEASURE”E!lTS
Vol.
RESISTIVITY
for 12 days. The sensitivity ratus has been determined 10 urn displacement of the ma 6 net due to tilting to give practicaily zero No
has
been
change
in
the
observed
No.
11
of the appaby the fact that the sample toward caused the contact resistance.
position
during
63,
of
12 days
the
sample
(about
109s
1. Since the small cnange in the poslis proportional to the small change current we can use i il the persistent for estimating the decay i=l,o exp (-t/T) tion
of the appatime, 7 . From the sensitivity ratus estimated above we can state ‘X 7 3 x 108 s. Assuming that the persistent current flows only on the periphery of the 7 x 7 x 1 mm3 sample we have an estimation for the inductance to be 60 nt!. The resistance of this path,gcan be calcun. The resislated as R = L/T Q 2 x 10 tivi.ty of this path with penetration depth of lUmf m [4] can be received as e ( 7 x 1O-23 Q.cm.
AND RESiJLTS
After mcunting the sample and cooling oown the system, the position of the needle tslative to the magnet was adjusted b\/ tilting tne apparat;lis in the delwar slightly Tne tilt was cncsen so that no electrical contact (infinite resistance) shoula have been between the needle ana the magnet. Tnis resistance was monitored continuously
0
6 Q
0 -0
Fig.2.
Fig.!.
The temperature resistance of
the
dependence YBa2Cu307
of the sample.
The measuring arrangement 1: sample; 2: Be-Cu wire (pendulum); 3: magnet; 4: pendulum axis; 5: 0.05 mm dia. enameled Cu wire; 6: silk threads; 7: tungsten needle; 8: brass tube; 9: stainless steel tube, distance of sample from magnesit: 7mm.
REFERENCES
1. 2.
3.
J.G. Bednorz and K.A. Miiller, Z. Phys. B 64, 189 (1966). M.K. \ir’u, J.P. Ashburn, C.J. Torng, P.H. Hor, R.L. Meng, L. Gao, Z.J. Huang, Y.0. I:lang and C.W. Chen, Phys. Kev. Letters Xl, 908 (1987). C. Kittel: Introduction to Solid
4.
State Physics, 5th edition, John Wiley Sons Inc. 197. R.J. Cava, B. Batlogg, R.B. Dover, D . w . Murphy, S. Sunshine, T. Siegrist, J.P. Remeika, E.A. Rietman, S. Zahurah, and G.P. Espinosa, Phys. Rev. Letters 58, 1676 (1987).
ESTIMATION
pp.991-992,
Vo1.63,No.l1,
OF MAXIMUM ELECTRICAL
1987.
RESISTIVITY
S.MbszBrosX,
+Oepartment P.Ll.Oox ‘Institute Debrecen,
*Central
2.
of
Solid
State
EFFECT
G.Ha13szX,
K.Vadx, Physics,
Kossuth
+ .OO Ltd.
OF HIGH Tc SUPERCONDUCTING
CERAMICS DY THE MEISSNER F.J.Kedves+,
0038-1098/87 $3.00 Pereamon Journals
O.Keszei*, L.
University,
Hungarian
Academy
and L.MihBly’ H-4010
Oebrecen
Hungary of
Nuclear
P.O.Dox
Research
Research
51.
of
the
of
Sciences,
H-4001
Hungary
Insitute Received
for
Physics,
H-1525
Budapest,
P.O.Box
47.
Hungary
31 May 19fl7 by A.Zawadowski
The observation of oersistcnt current decay is one of the best Non-decaying persistent current probes of superconducting state. induced bv Meissner effect has been observed in an Y-Ba-Cu-0 ce/ 10M6s/. From the measurements ramic superconductor for_;; days cm can be given for the resistivity an upper limit of 7 x 10 of the ceramic superconductor at liquid nitrogen temperature. 2
function estimate culating and in sample,
of time will make possible to the decay time ((7) of the circurrent In the levitated sample this wav the resistance (R) of the too. 1 Flux creeping is known to be the major source of dissipation in a superccnThe magnetic force acting on the ductor. sample is proportional to the volume the flux repelled from, therefore the change in the sample position may serve as an for the motion of the vortices. indicator
1. INTROGL!CTION breakthrough in achieving superconductivity inthe La-Ba-Cu-0 system [l] has initiated a great number of investigations of L-K-C”-0 compounds, e.g. [Z]. The determination of the limit of the resistance in superconducting state is restricted, because measuring the R(T )/R(300K) resistance ratio a drop of four or five orders of magnitude can be detected by means of the conventional four points method. It is, in principle,impossible to achieve much lower limit in the resistance ratio because of thermal flucthermoelectric power in inhomogetuations neous maierials and the transition resistance of the potential leads. high
Last year’s temperature
2.
The
SAMPLE PREPARATION ANC RESISTANCE MEASUREMENT
YBa2Cu307_b
sample
was
prepared
from the appropriate mixture of Y2%; ;;; ground mixture and Cufl. The finely starting mater:als was heat-treated at 9C10°C for 12 hours in air. The resulting black product was reground, ccmpr&ssed into pellets and sintered at 950 C in oxygen atmosphere for 12 hours. The resistance vs. temperature was measured by four probe
The most sensitive method to set an upper limit for electrical resistivity of materials thought to be superconductors is to measure the decay of the average persistent current in the sample [3] . Persistent current can be generated, for examby the Meissner effect. If the strength pie, and the gradient of a magnetic field are appropriately chosen the superconducting sample can be levitated in a magnetic field. In a constant magnetic field the position of the sample depends on the magnitude of the circulating current, the decay of which causes the change of the sample position. So observing the sample position as a
Teih?dxo? ~da~~~~.“::“‘~~~‘~~~~~~~nduciing transition is relatively sharp, with set temperature of T = 94 K. 3. 15 991
an
on-
APPARATUS
Since the3magnetic x 15 x5 mm Co-Sm
fouce, magnet
produced by was not suffi-
a
ESTIElATION OF MAXIWM ELECTRICAL
992
super?onducting cecient to levitate the of size 7 x 7 x 1 mm we hung the ramics, sample on a pendulum during the measurement. The measuring apparatus is shown in Fig. 2. The pendulum is formed by a Be-Cu wire fastened to the axis by silk threads. A magnet is placed into the brass tube with its front plane under the pendulum axis. The the ed
megnet is in electrical brass tube. A tungsten to the Se-Cu wire. So
able
to
the
detect
samole.
wire is pendulum.
the
contact with needle is solderthat we may be
change of the position mm dia. enamled coooer to the Be-Cu wire of the
a 0.05
soldered
of
serves as one lead for This wire the electrical resistance measured between the magnet and the sample. The resistance can be monitored continuously. A Keithley Mod. 197 DMM has ben used for this purpose
in storage mode with a sampling rate of 1 in 10 minutes. The probe is submerged II? a commercial laboratcry liquid nitrogen dewar vessel (L'air Liqulde PC-25) in such a 'way tha: the whole probe is in the cryogenic liquio. The de:?ar is placed on a vibration isolated platform. 4 .MEASURE”E!lTS
Vol.
RESISTIVITY
for 12 days. The sensitivity ratus has been determined 10 urn displacement of the ma 6 net due to tilting to give practicaily zero No
has
been
change
in
the
observed
No.
11
of the appaby the fact that the sample toward caused the contact resistance.
position
during
63,
of
12 days
the
sample
(about
109s
1. Since the small cnange in the poslis proportional to the small change current we can use i il the persistent for estimating the decay i=l,o exp (-t/T) tion
of the appatime, 7 . From the sensitivity ratus estimated above we can state ‘X 7 3 x 108 s. Assuming that the persistent current flows only on the periphery of the 7 x 7 x 1 mm3 sample we have an estimation for the inductance to be 60 nt!. The resistance of this path,gcan be calcun. The resislated as R = L/T Q 2 x 10 tivi.ty of this path with penetration depth of lUmf m [4] can be received as e ( 7 x 1O-23 Q.cm.
AND RESiJLTS
After mcunting the sample and cooling oown the system, the position of the needle tslative to the magnet was adjusted b\/ tilting tne apparat;lis in the delwar slightly Tne tilt was cncsen so that no electrical contact (infinite resistance) shoula have been between the needle ana the magnet. Tnis resistance was monitored continuously
0
6 Q
0 -0
Fig.2.
Fig.!.
The temperature resistance of
the
dependence YBa2Cu307
of the sample.
The measuring arrangement 1: sample; 2: Be-Cu wire (pendulum); 3: magnet; 4: pendulum axis; 5: 0.05 mm dia. enameled Cu wire; 6: silk threads; 7: tungsten needle; 8: brass tube; 9: stainless steel tube, distance of sample from magnesit: 7mm.
REFERENCES
1. 2.
3.
J.G. Bednorz and K.A. Miiller, Z. Phys. B 64, 189 (1966). M.K. \ir’u, J.P. Ashburn, C.J. Torng, P.H. Hor, R.L. Meng, L. Gao, Z.J. Huang, Y.0. I:lang and C.W. Chen, Phys. Kev. Letters Xl, 908 (1987). C. Kittel: Introduction to Solid
4.
State Physics, 5th edition, John Wiley Sons Inc. 197. R.J. Cava, B. Batlogg, R.B. Dover, D . w . Murphy, S. Sunshine, T. Siegrist, J.P. Remeika, E.A. Rietman, S. Zahurah, and G.P. Espinosa, Phys. Rev. Letters 58, 1676 (1987).