Pinning in Al doped YBCO bulk superconductors

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15 Νοε 2013 (πριν από 3 χρόνια και 6 μήνες)

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Pinning in Al doped YBCO

bulk superconductors


V. Antal
1,2
, M. Ka
ňuchová

1
, M. Šefčiková

1
, P.
Diko

1,3



M. Eisterer

2
,

N. Hörhager
2
, M. Zehetmayer
2
,
H. W. Weber
2



X. Chaud

3


1
Material Physics Laboratory,
Institute of Experimental Physics, SAS,



Košice, Slovakia


2
Atomic Institute of the Austrian Universities, Vienna, Austria


3

CNRS/CRETA, 25, Avenue des Martyrs, 38042 Grenoble Cedex 9, France










Motivation

:


Cu
substitutions

in TSMG YBCO

bulk superconductors


Zn

Krabbes

et al.,

Physica

C, 2000


Li

Shlyk

et al., Appl. Phys.
Lett
., 2002

Pd, Ni
Shlyk

et al.,
Physica C
,

2002

Fe

Shlyk

et al., Journal of Physics, 2006

Zn, Ni, Co,
Ga

Zhou, Scruggs,
Salama

SUST, 2006

Ag

T
.

Nakashima
, Journal of Physics, 2008



Al substitution was not studied

in YBCO bulks
so far


Al

Al substitutes in CuO chains (Re = Y)

Al
-

doped TSMG YBCO bulk

Preparation of Al


doped

YBCO bulk

superconductors

Time
-

temperature program for the top

seeded melt growth (TSMG) process

Samples:

YBa
2
Cu
3
O
7

+ 0.25Y
2
O
3

+ 0.5 wt. % CeO
2

+ Al
2
O
3


YBa
2
(Cu
3
-
x
Al
x
)O
7
, (x = 0.0025, 0.005, 0.01, 0.02, 0.05)


TSMG:


pellets
f

㴠㈰2浭Ⱐ卭‱㈳獥敤sⰠ捨慭扥爠晵牮慣攠楮i慩a

The

samples

were

heated

to

800

°
C

in

flowing

O
2

atmosphere

and

kept

there

for

2

hrs,

then

cooled

to

400

°
C

and

held

at

this

temperature

for

240

hrs,

then

cooled

down

to

room

temperature
.



1) Standard oxygenation (SO)

2) Annealing in flowing argon

The samples were heated to 800
°
C in flowing Ar atmosphere and annealed
there for 2 hrs, then cooled to room temperature. After annealing in Ar the
samples were heated to 400
°
C in flowing O
2

atmosphere and held there for
240 hrs, then cooled down to room temperature.


3) High pressure oxygenation (HPO)

The

samples

were

oxygenated

under

an

oxygen

pressure

of

160

bars

at


750

°
C

for

24

hrs

with

progressively

increasing

oxygen

pressure
.


Different methods of oxygenation

Typical dimensions of the samples for
oxygenation and magnetization measurements

c
-

axis

Magnetization measurements:

VSM with magnetic fields of up to 5 Tesla

at a constant sweep rate of 0.25 T/min,

applied field parallel to the c
-
axis

)
3
1
(
4
)
(
)
(
a
b
b
B
m
B
J
i
c



)
(
2
1




m
m
m
i
c
b
a




,

,

b
a

Bean model

Magnetization measurements

Checking samples for homogeneity

by trapped field scanning

Critical current densities in samples treated by SO and annealing in argon

Annealed in argon

Standard oxygenation

x = 0.0025 (SO), x = 0.05 (Ar)

J
c

≈ 1.8·10
4

A/cm
2
,
μ
0
H = 1 T

Effect of Al


doping and HPO on critical current density

HPO

HPO, T = 77 K

x = 0.0025

J
c

peak
≈ 5.3·10
4

A/cm
2
,
μ
0
H
p

≈ 1.37 T

SO, T = 77 K

x = 0.0025

J
c

peak
≈ 1.8·10
4

A/cm
2
,
μ
0
H
p

≈ 0.89 T

(55 ~80 K)

Suppression of oxygenation cracks by high pressure oxygenation

c

a/b

c

a/b

c
-

and a/b
-
macrocracks formed

in TSMG YBa
2
(Cu
3
-
x
Al
x
)O
7

during
standard oxygenation at 400
°
C (SO)


a/b
-
microcracks

in

TSMG

YBa
2
(Cu
3
-
x
Al
x
)O
7


oxygenated

at

750

°
C

under

an

oxygen


pressure

of

160

bars

(HPO)

c
-
MAC

a/b
-
MAC

c
-
MAC

Pinning force density

HPO

HPO
:

1
.
58



p



2
.
11
;

7
.
10



q



8
.
28

SO
:

1
.
07



p



1
.
38
;

2
.
86



q



4
.
51

for

SO

x

=

0
.
0025

p

=

1
.
86
,

q

=

3
.
44

Argon: 1.12 ≤ p ≤ 1.25; 0.63 ≤ q ≤ 0.93

for x = 0.05 p = 1.83; q = 3.44

[
E.J. Kramer, J. Appl. Phys. 44, 1360 (1973)
]

p
p
r
c
b
b
B
B
F
)
1
(
)
(
2


2
/
c
B
B
b



q
fp
p
fp
n
b
q
p
b
F









1
1
p, q > 0
;

b
fp
=H
max

/H
a

F
n
=F
p
/
F
max

[
M. Jirsa et al., Physica C 338, 235 (2000)
]

77 K

Magnetization relaxation measurements

t
d
dM
M
S
ln
1
0

at
μ
0
H

= 1 T and
T

= 77 K

S (SO) = 0.0911 ≈ 9.11%

S (HPO) = 0.0568 ≈ 5.68%

Conclusions

-

Al

substitution

induces

a

peak

effect

in

TSMG

YBCO

b
ulks


-

Annealing

in

Ar

caused

significant

changes

in

both

T
c

and



pinning

behaviour


-

High

pressure

oxygenation

preserves

the

peak

effect



caused

by

Al

substitution


-

Oxygenation

cracks

are

eliminated

by

high

pressure



oxygenation

J
c

increases

by

a

factor

of

~

3


The results were presented at :

P. Diko

et al.,

“International Conference on Superconductivity and Magnetism (ICSM 2008)

25
-
29 August 2008, Side

Antalya
,
T
urkey


V. Antal

et al.,

2
nd

NESPA
meeting
, 2
-

4.10.2008 Rus
t
, Austria.


Publication accepted in
Journal of Physics: Conference Series (200
9
)
.

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