Physica C 335 Ž2000. 97–100
www.elsevier.nlrlocaterphysc
Thermal properties and applications of high-Tc
žNd,Eu,Gd/ Ba 2 Cu 3 O y bulk superconductors
K. Noto a,b,) , T. Itoh a , T. Abe a , A. Sugiyama a , M. Murakami c , M. Muralidhar c ,
J. Yoshioka c , T. Kikegawa d , N. Kobayashi d
b
a
Faculty of Engineering, Iwate UniÕersity, 4-3-5 Ueda, Morioka 020-8551, Japan
AdÕanced Science and Technology Instutute of Iwate(ASTII), Iioka Shinden 3-35-2, Morioka 020-0852, Japan
c
SRL-ISTEC, Iioka Shinden 3-35-2, Morioka 020-0852, Japan
d
IMR, Tohoku UniÕersity ,Katahira 2-1-1, Aobaku, Sendai 980-8577, Japan
Abstract
In the newly approved Joint Research Project for Regional Intensive in Iwate ; ‘‘Development of practical application of
magnetic field technology for use in the region and in everyday living’’, application of magnetic field environments realized
by high TC bulk superconductors is one of the main R & D subjects. Numerical analyses on scattering mechanisms in the
thermal conductivity of ŽNd,Eu,Gd.Ba 2 Cu 3 O y wNEGŽ123.x bulk superconductors with 10, 20, 30 mol% NEGŽ211. second
phase ŽSP. were performed. We found a strong correlation between amount of added second phase and scatterings by grain
boundary and Umklapp process. Performance of power leads made of wNEGŽ123. q 30 mol%SPx bulk superconductor for
strong stray magnetic field environment was also estimated. q 2000 Elsevier Science B.V. All rights reserved.
Keywords: High-Tc superconductor; wNEGŽ123. q SPx bulk material; Thermal conductivity; Scattering mechanisms
1. Introduction
In the newly approved Joint Research Project for
Regional Intensive in Iwate; ‘‘Development of Practical Application of Magnetic Field Technology for
use in the Region and in Everyday Living’’, application of various magnetic field environments realized
)
Corresponding author. Tel.: q81-19-621-6357; fax: q81-19621-6373.
E-mail address: noto@iwate-u.ac.jp ŽK. Noto..
by high-Tc bulk superconductors is one of the main
R & D projects. On the other hand, recently developed OCMG w1x processed LREŽ123. bulk superconductors with Ž211. second phase ŽSP. have a higher
Birr and very good performance w2x. Among them, a
very high performance has been proved in OCMG
processed NEGŽ123. bulk superconductors with
Ž211.SPw3x.
In the magnetizing study on Ž123. bulk materials,
Yanagi et al. w4x observed a significant temperature
rise of the material and much smaller magnetization
than the applied peak value of pulsed magnetic field.
Thus, it is very interesting to study the thermal
0921-4534r00r$ - see front matterq 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 9 2 1 - 4 5 3 4 Ž 0 0 . 0 0 1 5 1 - 9
K. Noto et al.r Physica C 335 (2000) 97–100
98
Table 1
Amount of second phase ŽSP. in prepared NEGŽ123. bulk samples
Sample
Composition Ž P O 2 s 0.1%.
Pt Žmol%.
SP10
SP20
SP30
ŽNd,Eu,Gd.123q10 mol% SP
ŽNd,Eu,Gd.123q20 mol% SP
ŽNd,Eu,Gd.123q30 mol% SP
0.5
0.5
0.5
properties and intercorrelation between thermal properties and added SP amount. We found a strong
correlation between magnitude of thermal conductivity or average SP size and added SP amount in the
previous work w5x.
In this paper, we tried numerical analyses of
scattering mechanisms in the thermal conductivity of
NEGŽ123. bulk samples with 10, 20, 30 mol% SP by
the Tewort–Wolkhausen theory. Characteristics as
power leads are also estimated for the NEGŽ123. q
SP30 mol% material using the thermal conductivity
data and Jc value calculated from SQUID magnetization.
fitting curves of numerical analysis performed this
time. Thermal conductivity is divided into electronic
part and phonon part, K s K e q K ph . Since the electrical resistivity at room temperature is larger than
0.048 V cm for all samples, the electronic part is
negligibly small: less than 0.1% of the total thermal
conductivity. Therefore, we tried numerical fitting of
total conductivity to the phonon thermal conductivity
expression by Tewordt and Wolkhausen w7x:
k ph s AT 3
Samples of NEGŽ123. were prepared by OCMG
process w3x, main parameters of which are shown in
Table 1. A good stoichiometry was obtained by the
OCMG process. NEGŽ211.SP was added as strong
pinning centers. Nd:Eu:Gds 1:1:1 for both 123 matrix phase and SP. Added SP amount is 10, 20, 30
mol%. Moreover, 0.5 mol%Pt is also added to get
fine dispersion of SP.
Thermal conductivity was measured by a standard
steady-state heat flow method using a fully automatic thermal property measuring system w6x. Jc Ž B .
was calculated from the results of magnetization
hysteresis measured by SQUID magnetometor using
the following relation Žmodified Bean model.:
Jc Ž B . s
20D M
a Ž 1 y a . r Ž 3b . 4
Ž e x y 1.
2
tph Ž x . d x
Ž 2.
and
1
1
1
s
tph
q
tphyb
1
q
tphyUm
1
q
tphysh
1
q
tphyp
tphye
Ž 3.
These expressions can be rewritten as,
k ph s At 3
=
2. Experimental
x 4e x
urT
H0
H0urT
x4e x
Že y 1.2
x
1
1 q Bx exp Ž y Q ratT c . q C Ž tx . 2 q D Ž tx . 4 q E w g Ž t , x , y . x
d x,
Ž 4.
where parameter A corresponds to the scattering
time of boundary scattering and B, C, D and E
Ž 1.
3. Results and discussion
Fig. 1 shows the temperature dependence of previously reported thermal conductivity data w5x and
Fig. 1. The temperture dependence of thermal conductivity.
K. Noto et al.r Physica C 335 (2000) 97–100
99
Table 2
Best-fitted parameters in Eq. Ž4.
SP 10
SP 20
SP 30
A
B
C
D
E
55 000
31 000
17 500
200
400
700
25
10
45
1300
1500
1500
60
30
10
correspond to the strength of the Umklapp process,
sheetlike-fault scattering, point-defect scattering and
electron–phonon scattering, respectively. The bestfitted parameters are listed in Table 2 and best-fitted
curves are also shown in Fig. 1. We can see fairly
good fitting using parameters shown in Table 2.
These parameters are plotted against the added SP
amount in Fig. 2. One can see a strong correlation
between boundary scattering or Umklapp process
and the added SP amount. Judging from the scatter
of thermal conductivity data, we think that we cannot
discuss a distinct correlation to the other parameters.
We think that the main part of the grain boundary
scattering should be at the SP grain boundaries.
Fig. 3 shows thermal conductivity integration,Q˙ s
S T
H k ŽT .dT for S s 1 cm2 , L s 10 cm from data
L 4.2
for the sample with 30 mol% SP. Since there is
almost no magnetic field dependence in the thermal
conductivity for all samples w5x, and Jc P 5 = 10 4
Fig. 3. The temperature dependence of thermal conductivity integration.
Arcm2 up to 2.5 T for SP30 mol% sample, we can
estimate the specifications of power leads for relatively strong stray field environment for the SP30
mol% material as follows,
Cross-section
2 mm2
Length
10 cm
Upper and lower end temperature 80 K, 4.2 K
Specific thermal losses at 4.2 K O 160 m WrA
Operational current
1000 A
Critical current density
P 5 = 10 4 Arcm2
Stray field
up to 2.5 T
4. Summary
After numerical fitting analyses on the thermal
conductivity data of NEGŽ123. q 10, 20, 30 mol%
SP samples w5x by the Tewort–Wolkhausen theoryw7x,
it turned out that:
Fig. 2. SP amount dependence of fitted parameters.
1. we can get fairly good fitting using parameters
shown in Table 2,
2. there is a strong correlation between boundary
scattering or Umklapp process and the SP amount,
and
100
K. Noto et al.r Physica C 335 (2000) 97–100
3. we think the main part of the grain boundary
scattering should be at the SP grain boundaries.
We estimated specifications of power leads for a
strong stray field environment for the SP30 mol%
material, in which thermal losses are less than 1r6
of the conventional power leads.
Acknowledgements
The authors would like to thank Mr.S.Fujinuma
ŽIwate Univ.. for technical assistance. This work was
partly supported by New Energy and Industrial
Technology Development Organization ŽNEDO..
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