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The influence of electron irradiation on superconductivity of YBa2Cu3Ox
PHYSICA
Physica C 185-189 (1991) 2183-2184 North-Holland
THE
I N F L U E N C E OF E L E C T R O N IRRADIATION O~ S U P E R C O N D U C T I V I T Y OF YBa2Cu30 x
Yukio KAZUMATA,
Satoru O K A Y A S U and T e r u o KATO
Japan Atomic Energy R e s e a r c h Institute, 319-11 Japan
Tokai-mura, Naka-gun,
Ibaraki-ken,
The change of superconductive property by electron irradiation was studied in YBa2Cu30., x=6.9, 6.6 and 6.4. By the irradiation the transition temperatures measurC~d ~ y electrical resistivity shift from 87 to 83 K, 58 to 36 K, and 22 to below 10 K for x=6.9, 6.6 and 6.4, respectively. The critical current densities increase in x=6.9 after irradiation, but a slight decrease is found in both x=6.6 and 6.4. Timedependent magnetic relaxations are measured and activation energies for flux motion are calculated as a function of temperature. The increase of J_ and activation energies for x=6.9 are attributed to the small defects produced by electron irradiation. I. INTRODUCTION Radiation e f f e c t s o f h i g h T c m a t e r i a l s a r e p r i n c i p a l l y concerned w i t h transition temperature (Tc) and critical current density (Jc). On the T c subject, the degree of the d e g r a d a t i o n by particle irradiation is formulated on the basis of experiments by Summers et al I. In contrast to this, the correlation betwee/]Jcand lattice defects is totally unresolved though many experiments have been already accumulated2"3. In this paper, the change of superconductive properties by electron irradiation is studied in sintered YBa2Cu3Ox, x=6.9, 6.6 and 6.4. With these specimens, the correlation among Tc, Jc and lattice defects can be persuited. For the purpose of total understand of radiation effects, measurements are done by electrical resisitivity, ac and dc magnetization, hysteresis loops and timedependent magnetic relaxation. 2. EXPERIMENTAL RESULTS AND DISCUSSION The specimens used in this experiment,YBa2Cu30 x (x=6.9, 6.6 and 6.4), were supplied by Mitsubishi Materica! Co= by courtesy of the Multicore-Project-Data Group conducted by the Ministry of Science and Technology. Before irradiation, the TcS are found to be 87, 58 and 22 K at the offset temperatures for x=6.9, 6.6 and 6.4, respectively, from resistivity measurements. Irradiation was carried out by 3 Mev electrons. Primary knockon atoms with several ten-eV by the electron
0921-4534D1/$03.50 © 1991 - Elsevier Science Publishe~ B.V.
irradiation will produce only a few displaced atoms. Therefore small size defects will be produced by the electrons. After the irradiations to a dose of 2x1018/cm2, their respective temperatures are reduced to 83, 36 and below I0 K. After the irradiation the real part of the ac magnetization, Z', for the three specimens s h o w s a s l i g h t c h a n g e at the onset temperature, but the foot of the X'temperature curve shifts to lower temperature in a gentle slope, namely, broadening of the Tc, as shown in Fig.1 together with the X". The imaginary part of the ac magnetization, ;~", after the irradiation behaves in the s i m i l a r w a y w i t h the c h a n g e of the resistivities. The peaks of the X"s shift to YBa2Cu30~ I
I
I
I
I
I
I
I
¢
x=6.9
.; ~;
/---
X '
~'l
/;
AFIEI I~IAO IATIOil
/
DEFORE II|ADIA'~IOI
~
Z '' - ' s ' ~ ~ .
/
O[FOl~ |I~I~ADIATI 0~ "~
0
!
I
I
I
|
I
I
!
10
20
30
40
50
~0
70
80
'
•
90 100
TEMPERATURE ( K )
Fig.l Temperature dependence of the ):' and X"- In the drawing the base line of the X' curve after the irradiation is moved up.
All fights reserved.
2184
E Kazumata et aL
/ Electron
irradiation on superconductivity of YBa~Cu~Ox
lower temperature with increases of their widUls. The dc magnetizations show the similar behavior as the X's. The pronounced change of the magnetization is o b s e r v e d n e a r t h e T c as a radiation-induced gentle slope of the magnetization vstemperaturecurve, especially in x=6.6 and6.4. The change of the slope will be attributed to the distribution of the regions with a slight different T c, which is caused by the displacement of oxygen ions in the chain sites• The critical current densities (Jc) are calculated from the hysteresis loops by using the formula, Jc=15 ~M/R, where R is thegrain size and is a s s u m e d to be 5 ~ m for all specimens. The Jcs in x=6.9 after the irradiation increase in the temperatures below 25 K as shown in Fig.2. The increment at 5 K amounts to 1.2 times as large as that of before the irradiation• The change of Jc s above 50 K is small. For x=6.6 and 6.4 the Jc s decrease by the irradiation. In these two specimerL~ large decreases of TcS are caused by the irradiation as mentioned above. These decreases will be one of the reason of the decrease of Jc" in order to study the origin of the change of the Jc by the irradiation, the magnetic relaxation is measured as a function of time• From the logalithmic time decay of the remanent magnitization ~ using the formula, -1/M0(dM/dln(t/t0))=kT/U, activation energies are obtained. As shown in Fig.3, activation energies at low temperatures increase after the irradiation and this fact corresponds the increase of Jc" Small size defects will be produced by 3 MeV electrons as mentioned above. These defects will be effective for the flux pinning only at low temperatures because of their weak pinning forces. Consequently the increase of Jc s and activation energies will be attributed to the defects. In summary, distribution o f th e regions with different Tc will be produced by the electron irradiation and the distribution causes the broadening of T c. The increase of Jc at low temperatures corresponds to the increase of the activation energy. This fact will result from the samll size defects produced b y t h e
irradiation. 10' YBozCu30 x ; X ,, 6.9 IIoee e O
Oo oil ,1.1 •
Oo
• l, ~ l= A
SIloded symbols (I,,l~,l.l[b) : After irrod, Open symbols { o,~,o, ~ ) : Belore irred.
Oo o
o
•
5K
¢+
• O
• O
•
o O
•
O
O
a
, •
e• 8
a
15K A
a
& A
a
g
e
Io2 -$
&
•
a
, 25K •
u
=
"**%
4
A
8
• •
b
•
u e
I
a o
5O K #
I i I I 2,0 3.0 Mo~ne|i¢ field ( Teslo I
t.O
I
!
5.0
4.0
Fig.2 Magnetizahion critical current density vs applied magnetic field for x=6.9 before and after irradiation. xiO-Z
80 YB%Cu30x : X : 6.9
70
o.~ ~.001 K6 G ] Before irrad. O
>=
:,KG500G
]Afterirrod.
40
2
zo
& o
2O 10
o ! ,,
o_, ~
"
1
I
l
I
I
10
,/0
30
40
50
.
I
60
I
I
70
80
.
90
Temper~iure {K}
Fig.3 Activation energies calculated frola the magnetic relaxation before and after the irradiation. REFERF~CES 1. C.P. Summers et al, Appl.Phys.Lett. 55(I 989) 1 469. 2. F.M. Sauerzopf et al, Physica C162-164 (1989) 731. 3. A.E. White et alw Appl,Phys.lett. 533(1988) 1010
Physica C 185-189 (1991) 2183-2184 North-Holland
THE
I N F L U E N C E OF E L E C T R O N IRRADIATION O~ S U P E R C O N D U C T I V I T Y OF YBa2Cu30 x
Yukio KAZUMATA,
Satoru O K A Y A S U and T e r u o KATO
Japan Atomic Energy R e s e a r c h Institute, 319-11 Japan
Tokai-mura, Naka-gun,
Ibaraki-ken,
The change of superconductive property by electron irradiation was studied in YBa2Cu30., x=6.9, 6.6 and 6.4. By the irradiation the transition temperatures measurC~d ~ y electrical resistivity shift from 87 to 83 K, 58 to 36 K, and 22 to below 10 K for x=6.9, 6.6 and 6.4, respectively. The critical current densities increase in x=6.9 after irradiation, but a slight decrease is found in both x=6.6 and 6.4. Timedependent magnetic relaxations are measured and activation energies for flux motion are calculated as a function of temperature. The increase of J_ and activation energies for x=6.9 are attributed to the small defects produced by electron irradiation. I. INTRODUCTION Radiation e f f e c t s o f h i g h T c m a t e r i a l s a r e p r i n c i p a l l y concerned w i t h transition temperature (Tc) and critical current density (Jc). On the T c subject, the degree of the d e g r a d a t i o n by particle irradiation is formulated on the basis of experiments by Summers et al I. In contrast to this, the correlation betwee/]Jcand lattice defects is totally unresolved though many experiments have been already accumulated2"3. In this paper, the change of superconductive properties by electron irradiation is studied in sintered YBa2Cu3Ox, x=6.9, 6.6 and 6.4. With these specimens, the correlation among Tc, Jc and lattice defects can be persuited. For the purpose of total understand of radiation effects, measurements are done by electrical resisitivity, ac and dc magnetization, hysteresis loops and timedependent magnetic relaxation. 2. EXPERIMENTAL RESULTS AND DISCUSSION The specimens used in this experiment,YBa2Cu30 x (x=6.9, 6.6 and 6.4), were supplied by Mitsubishi Materica! Co= by courtesy of the Multicore-Project-Data Group conducted by the Ministry of Science and Technology. Before irradiation, the TcS are found to be 87, 58 and 22 K at the offset temperatures for x=6.9, 6.6 and 6.4, respectively, from resistivity measurements. Irradiation was carried out by 3 Mev electrons. Primary knockon atoms with several ten-eV by the electron
0921-4534D1/$03.50 © 1991 - Elsevier Science Publishe~ B.V.
irradiation will produce only a few displaced atoms. Therefore small size defects will be produced by the electrons. After the irradiations to a dose of 2x1018/cm2, their respective temperatures are reduced to 83, 36 and below I0 K. After the irradiation the real part of the ac magnetization, Z', for the three specimens s h o w s a s l i g h t c h a n g e at the onset temperature, but the foot of the X'temperature curve shifts to lower temperature in a gentle slope, namely, broadening of the Tc, as shown in Fig.1 together with the X". The imaginary part of the ac magnetization, ;~", after the irradiation behaves in the s i m i l a r w a y w i t h the c h a n g e of the resistivities. The peaks of the X"s shift to YBa2Cu30~ I
I
I
I
I
I
I
I
¢
x=6.9
.; ~;
/---
X '
~'l
/;
AFIEI I~IAO IATIOil
/
DEFORE II|ADIA'~IOI
~
Z '' - ' s ' ~ ~ .
/
O[FOl~ |I~I~ADIATI 0~ "~
0
!
I
I
I
|
I
I
!
10
20
30
40
50
~0
70
80
'
•
90 100
TEMPERATURE ( K )
Fig.l Temperature dependence of the ):' and X"- In the drawing the base line of the X' curve after the irradiation is moved up.
All fights reserved.
2184
E Kazumata et aL
/ Electron
irradiation on superconductivity of YBa~Cu~Ox
lower temperature with increases of their widUls. The dc magnetizations show the similar behavior as the X's. The pronounced change of the magnetization is o b s e r v e d n e a r t h e T c as a radiation-induced gentle slope of the magnetization vstemperaturecurve, especially in x=6.6 and6.4. The change of the slope will be attributed to the distribution of the regions with a slight different T c, which is caused by the displacement of oxygen ions in the chain sites• The critical current densities (Jc) are calculated from the hysteresis loops by using the formula, Jc=15 ~M/R, where R is thegrain size and is a s s u m e d to be 5 ~ m for all specimens. The Jcs in x=6.9 after the irradiation increase in the temperatures below 25 K as shown in Fig.2. The increment at 5 K amounts to 1.2 times as large as that of before the irradiation• The change of Jc s above 50 K is small. For x=6.6 and 6.4 the Jc s decrease by the irradiation. In these two specimerL~ large decreases of TcS are caused by the irradiation as mentioned above. These decreases will be one of the reason of the decrease of Jc" in order to study the origin of the change of the Jc by the irradiation, the magnetic relaxation is measured as a function of time• From the logalithmic time decay of the remanent magnitization ~ using the formula, -1/M0(dM/dln(t/t0))=kT/U, activation energies are obtained. As shown in Fig.3, activation energies at low temperatures increase after the irradiation and this fact corresponds the increase of Jc" Small size defects will be produced by 3 MeV electrons as mentioned above. These defects will be effective for the flux pinning only at low temperatures because of their weak pinning forces. Consequently the increase of Jc s and activation energies will be attributed to the defects. In summary, distribution o f th e regions with different Tc will be produced by the electron irradiation and the distribution causes the broadening of T c. The increase of Jc at low temperatures corresponds to the increase of the activation energy. This fact will result from the samll size defects produced b y t h e
irradiation. 10' YBozCu30 x ; X ,, 6.9 IIoee e O
Oo oil ,1.1 •
Oo
• l, ~ l= A
SIloded symbols (I,,l~,l.l[b) : After irrod, Open symbols { o,~,o, ~ ) : Belore irred.
Oo o
o
•
5K
¢+
• O
• O
•
o O
•
O
O
a
, •
e• 8
a
15K A
a
& A
a
g
e
Io2 -$
&
•
a
, 25K •
u
=
"**%
4
A
8
• •
b
•
u e
I
a o
5O K #
I i I I 2,0 3.0 Mo~ne|i¢ field ( Teslo I
t.O
I
!
5.0
4.0
Fig.2 Magnetizahion critical current density vs applied magnetic field for x=6.9 before and after irradiation. xiO-Z
80 YB%Cu30x : X : 6.9
70
o.~ ~.001 K6 G ] Before irrad. O
>=
:,KG500G
]Afterirrod.
40
2
zo
& o
2O 10
o ! ,,
o_, ~
"
1
I
l
I
I
10
,/0
30
40
50
.
I
60
I
I
70
80
.
90
Temper~iure {K}
Fig.3 Activation energies calculated frola the magnetic relaxation before and after the irradiation. REFERF~CES 1. C.P. Summers et al, Appl.Phys.Lett. 55(I 989) 1 469. 2. F.M. Sauerzopf et al, Physica C162-164 (1989) 731. 3. A.E. White et alw Appl,Phys.lett. 533(1988) 1010