> 4MP6-04 <1

Thermal conductivity and dilatation of a
Bi-2223/Ag (DI-BSCCO) superconducting wire
laminated with various thin alloy tapes
Tomoyuki Naito, Hiroyuki Fujishiro, Yuichi Yamada

Abstract—A Bi-2223/Ag wire laminated with Ni-alloy tapes
offered the high critical tensile strength over 400 MPa withhigh critical current of about 200 A, which has just started tobe equipped in high-field facilities. To design such a practicalsuperconducting apparatus, we must know the heat leakage
through the wires and the elasticity among the constitutional
materials. In this paper, we report on the thermal conductivity
and dilatation of this new Bi-2223/Ag/Ni-alloy tape, compared tothose of other Bi-2223/Ag tapes, and discuss the contribution oflamination alloy to the thermal properties.
Index Terms—Bi-2223/Ag tape, thermal conductivity, thermal
dilatation

I. I NTRODUCTION
first
generation
superconducting
tape,
(Bi,
Pb)2 Sr2 Ca2 Cu3 O10+x sheathed with Ag (Bi-2223/Ag),
has been strenuously studied by many researchers andcompanies [1]. The controlled overpressure (CT-OP) sintering
technique enables us to fabricate the high quality Bi-2223/Ag
tape with low porosity, high Young’s modulus and highcritical current, Ic , over 200 A [2], [3]. Since the criticalcurrent was degraded by the tensile/compressive stress [4],the Bi-2223/Ag tapes are often reinforced by the laminationof various alloys to obtain the high yield stress. Although thestainless steel lamination offered the critical tensile strengthof about 270 MPa at 77 K, a high-field superconducting
magnet over 23.5 T, which corresponds to the 1 GHz-NMR
frequency, requires the higher strength of the tapes. Recently,
the critical tensile strength of 400 MPa was realized fora Bi-2223/Ag tape by laminating Ni alloy tapes [5]. The
Bi-2223/Ag tapes have already been used in the practicalsuperconducting applications such as AC [6] and DC [7]cables, high-field magnets [8], [9] and current leads [10],[11].
In addition to the critical current and mechanical strength,
the heat intrusion, Qin , is also an important parameter forthe thermal stability of the practical superconducting applications [11]. The thermal conductivity, κ(T ), allows us toestimate correctly the heat intrusion in the materials between

A

Manuscript received January 18, 2018. Corresponding author: T. Naito (email: tnaito@iwate-u.ac.jp).
T. Naito, and H. Fujishiro are with Faculty of Science and Engineering,
Iwate University, Morioka 020-8551, Japan (e-mail: tnaito@iwate-u.ac.jp;
fujishiro@iwate-u.ac.jp).
Y. Yamada is with Superconductivity Technology Division, Sumitomo Electric Industries, Ltd., Osaka 554-0024, Japan (e-mail: yamada-yuichi@sei.co.jp).

a low and high temperature sides, TL and TH , in the following
relation,
Z TH

S
Qin =
l

κ(T )dT,(1)

TL

where l the length and S the cross section of the material.
On the other hand, the thermal dilatation is also the important
physical property, because the different change in the length
among the constitutional materials in a device would givea mechanical stress which suppresses the superconducting
properties. In this paper, we report the temperature dependenceof the thermal conductivity, κ(T ), and thermal dilatation for
the new Bi-2223/Ag tape laminated by Ni alloy tapes.
II. E XPERIMENTAL
A. Fabrication of Bi-2223/Ag tapes
Bi-2223/Ag tapes were fabricated by the powder in tube
(PIT) method with the CT-OP sintering technique [2]. Table I
summarizes the specifications of five Bi-2223/Ag tapes studied
here. Type H is a standard silver sheathed tape. Three type HT
tapes with high yield stress were prepared, in which the type
H tape was laminated from both surfaces by thin alloy (nickel
alloy (NX), stainless steel (SS), copper alloy (CA)) tapes. To
achieve higher yield stress against for the hoop stress in theextremely high magnetic field over 23.5 T, the ‘pre-tension’process was applied for the type HT-NX tape. The Ni alloy(NX) tapes were expanded and soldered to the type H tape toapply the residual compressive stress to the type H tape. The
stainless steel (SS) and copper alloy (CA) tapes were soldered
without the pre-tension, because both type HT-SS and HTCA tapes are often used for the low-field magnets. We also
prepared the low thermal conductive Bi-2223/Ag tape sheathedwith an Ag-5.4wt%Au alloy, which was type G.
B. Method of measurements
Thermal conductivity, κ(T ), along the rolling direction, i.e.,parallel to the ab-planes of Bi-2223 filaments, was measured
by a steady-state heat flow method [12]. One end of the tape
was soldered to the copper-block (sample stage). A small metal
chip resistor of 1 kΩ as a heater was adhered to the other endof the tape by GE7031 varnish. κ is obtained by the relation,κ=

Qapp `
· ,
∆T S

(2)

> 4MP6-04 <2

TABLE IS PECIFICATIONS OF THE B I 2223/A G TAPES
Type
H
HT-NX
HT-SS
HT-CA
G

sheath and lamination materials
Ag + no lamination
Ag + nickel alloy
Ag + stainless steel
Ag + copper alloyAg-5.4wt%Au + no lamination

cross section (mm2 )
0.99
1.4
1.3
1.5
1.0

width (w) (mm)
4.3
4.5
4.5
4.5
4.3

total thickness (t) (mm)
0.23
0.31∗
0.29∗
0.34∗
0.24

thickness of lamination (mm)
–
0.03
0.02
0.05
–

∗ including the thickness of lamination tapes and solder layers (N.A.).

(3)

was measured by a standard strain-gauge method using acommercial strain-gauge (CFLA-1-350-11[the gauge length
was 1 mm, the gauge resistance was 350 Ω, and the gauge
factor was 2.09]; Tokyo Sokki Kenkyujo Co., Ltd.). Electricalresistivity, ρ(T ), was measured by a conventional dc fourprobe method with a typical current density of about 3 A/cm2 .
The temperature of sample stage was controlled between 6 and300 K using a Gifford-McMahon cycle helium refrigerator and
30 W heater. To minimize a radiation loss, κ(T ) was measured
below 200 K. dL(T )/L(300 K) was measured above 20 K
owing to the sensitivity of strain gauge.
III. R ESULTS AND D ISCUSSION

H
HT-NX
HT-SS
HT-CA

10

3

10

2

10

1

10

0

H [meas](W m-1K-1)(L(T ) − L(300 K))
dL(T )=,
L(300 K)
L(300 K)

1000

(W m-1K-1)

where Qapp is the applied heat flow, ∆T is the temperature difference and ` is the distance between two chromel-constantan
thermocouples, and S is the cross sectional area of tape. ∆T
was maintained to be 0.5–0.7 K by controlling the heater
power. Thermal dilatation normalized by the sample length,
L, at 300 K,

Solder [meas]
Bronze Ref.[15]500Ni-alloy [meas]
SS [meas]

-1

10 0
10

10

1

2

10

T(K)

0

0

100

200

T(K)

A. Thermal properties of the Bi-2223/Ag tapes laminated byvarious alloys

Fig. 1. Temperature dependence of the thermal conductivity, κ(T ), for various
Bi-2223/Ag tapes. Inset shows the κ(T ) curves for the solder and various
lamination alloys.

Fig. 1 shows the temperature dependence of the thermal
conductivity, κ(T ), of various Bi-2223/Ag tapes. κ(T ) of type
H tape decreased quite moderately with decreasing temperature from 300 K down to 100 K and showed a gentle increase
below 100 K. Subsequently, it began to increase rapidly below
60 K and took a maximum of about 780 W m−1 K−1 at
14 K. The low-temperature peak of κ(T ) is often observedin high-purity metals and insulators, and can be explainedby the relation of κ = (1/3)Cth vth lth , where Cth , vth andlth , respectively, are the specific heat, the velocity and themean free path of thermal carriers [13]. The lattice vibration
suppressed at low temperatures causes the steep increaseof lth ; the lth finally reaches to the sample size. On theother hand, the specific heat decreases monotonically withdecreasing temperature. The competition between the increase(and saturation) of lth (T ) and the decrease of Cth (T ) resultsin the κ(T )-peak. The κ(T ) of the type HT-NX, HT-SS andHT-CA tapes showed the similar shape, but smaller absolutevalue, compared to κ(T ) of the type H tape. The κ(T ) of thetype H, HT-SS, and HT-CA tapes is almost the same as thereported previously [12], [14]. We estimated the contributionof electrons to the total thermal conductivity, κe , from theelectrical resistivity, ρ(T ), using the Wiedemann-Franz law,κe =L0 T /ρ. Here, L0 is the Lorenz number. Fig. 2 shows thetemperature dependence of the electrical resistivity for various
Bi-2223/Ag tapes. All the tapes showed the sharp superconducting transition at the critical temperature, Tc , of 111 K anddemonstrated a good T -linear dependence in the normal state.
The κe values were estimated to be approximately 245, 167,
179, and 226 W m−1 K−1 for the type H, HT-NX, HT-SS, and
HT-CA tapes, respectively, which are nearly comparable to themeasured κ(T ) above Tc . The absolute value of ρ(T ) of thesheath metal and lamination alloy is generally rather smaller
than that of Bi-2223 filaments in the normal state, suggestingthat the applied heat mainly flows through both sheath andlamination alloys. Therefore, the small κ(T ) of the type HTNX tape seems to originate from the poor thermal conductive
lamination alloy, as found in the inset of Fig. 1, in which themeasured κ(T ) curves for the solder, SS and Ni alloy andthe reported for the typical Cu alloy, bronze (Cu:Sn=9:1) [15]are shown. The absolute value of κ(T ) of the Ni alloy wasapproximately one to two orders of magnitude smaller than

> 4MP6-04 <

3

5
0
H
HT-NX
HT-SS
HT-CA

2
H
HT-NX
HT-SS
HT-CA

0
100

200

-0.2
0

dL/L(300 K) (%)

3

1

-0.1

dL/L(300 K) (%)

 (cm)

4

-0.3

-0.4

-0.1
-0.2
-0.3

-0.5
0

-0.5

300

100

200

300

T(K)

0

100

200

300

T(K)

T (K)
Fig. 2. Temperature dependence of the electrical resistivity, ρ(T ), for various
Bi-2223/Ag tapes.

Hastelloy C
SS

-0.4

Fig. 3. Temperature dependence of the thermal dilatation, dL(T )/L(300 K),
for various Bi-2223/Ag tapes. Inset shows the dL(T )/L(300 K) curves for
the Ni-based alloy (Hastelloy C) and stainless steel (SS).

1000

Fig. 3 shows the temperature dependence of the thermal
dilatation, dL(T )/L(300 K), for various Bi-2223/Ag tapes.
dL(T )/L(300 K) of all the samples showed a similar temperature dependence. dL(T )/L(300 K) decreased monotonically with decreasing temperature from 300 K to 25 K, andsubsequently showed almost constant value below 25 K. The
dL(T )/L(300 K) of about -0.25% at 20 K for the type HT-NX
tape was about -0.04% smaller than that of the type H tape(-0.29%), in contrast to both type HT-SS (-0.3%) and HT-CA(-0.31%) tapes. Inset of Fig. 3 shows the dL(T )/L(300 K)of the typical Ni-based alloy (Hastelloy C) and stainless steel.
The small dL(T )/L(300 K) of the Hastelloy C compared tothat of the stainless steel prevented from shrinking the type H
tape embedded in the HT-NX tape.

G

(W m-1K-1)

that of the type H tape. The κ(T ) value of the HT-NX tape issomewhat smaller than that of the HT-SS tape, although theabsolute κ(T ) values of SS and Ni alloy were nearly identical.
This might originate from the difference in the laminatingprocess, as described in Sec. II-A. The large compressive stressdue to the pre-tension process for the type HT-NX tape causes
the lattice distortion in the Ag sheath, which should create thedislocations. The dislocations are known to scatter the mobile
electrons as well as the phonons, which suppresses naturally
the thermal conductivity [13]. The absolute value κ(T ) of thetype HT-CA tape was comparable with that of the type H tapein the normal state, however the low-temperature peak wasstrongly suppressed. This suggests that the unignorable amountof applied heat flows through the Cu alloy lamination [14].

H

500

0

0

100

200

T(K)
Fig. 4. Temperature dependence of the thermal conductivity, κ(T ), for the
Bi-2223/Ag tape sheathed with Ag-5.4wt%Au alloy; the κ(T ) of the type H
tape is also shown as a reference.

B. Thermal conductivity of the Bi-2223/Ag tapes sheathedwith Ag-Au alloy
Fig. 4 shows the temperature dependence of the thermal
conductivity, κ(T ), for the Bi-2223/Ag tape sheathed with Ag5.4wt%Au alloy, type G tape. The κ(T ) decreased monotonically with decreasing temperature. The absolute value of κ(T )> 4MP6-04 <4

was quite smaller than that of the type H tape, and the lowtemperature peak was fully suppressed. The κ(T ) of the type G
tape resembles to that of low-purity metals and alloys, in which
the electrons are scattered by the substituted impurity atoms.
The obtained result agreed well with the reported data [12],and will be used to estimate the heat leakage through thecurrent leads for ITER.
IV. S UMMARY
We have measured the thermal conductivity, κ(T ), anddilatation, dL(T )/L(300 K), of a new type Bi-2223/Ag tapelaminated with the Ni alloy (NX), Bi-2223/Ag-NX. The measured κ(T )of the Bi-2223/Ag-NX tape was smaller than theestimated from those of the constitutional components, suchas the bare Bi-2223/Ag and NX tapes. We considered that
residual compression stress in the tape, which was introduced
during the lamination process, deteriorated the thermal conductivity. The dL(T )/L(300 K) of the Bi-2223/Ag-NX tape
was found to be about -0.04% smaller than that of the bare
Bi-2223/Ag tape, which is contrast to other Bi-2223/Ag tapes
laminated by the stainless steel and copper alloy. This canbe explained by the small dL(T )/L(300 K) of the Ni alloy.
We believe that the obtained results are useful information for
designing a practical superconducting application. The κ(T )was also measured for a Bi-2223/Ag tape sheathed with Ag5.4wt%Au alloy and the quite low κ(T ) was confirmed. The
heat leakage through the current leads consisting of the stacked
tapes can be estimated correctly by using the κ(T ) measured
here.
R EFERENCES[1] K. Sato, Ed., Research, Fabrication and Applications of Bi-2223 HTS
Wires. World Scientific Publishing Co. Pte. Ltd., 2016, vol. 1.
[2] S. Kobayashi, K. Yamazaki, T. Kato, K. Ohkura, E. Ueno, K. Fujino,
J. Fujikami, N. Ayai, M. Kikuchi, K. Hayashi, K. Sato, and R. Hata,“Controlled over-pressure sintering process of Bi2223 wires,” Physica
C, vol. 426-431, no. 2, pp. 1132–1137, 2005.
[3] G. Osabe, N. Ayai, M. Kikuchi, K. Tatamidani, T. Nakashima,
J. Fujikami, T. Kagiyama, K. Yamazaki, S. Yamade, E. Shizuya,
S. Kobayashi, K. Hayashi, K. Sato, J. Shimoyama, H. Kitaguchi,
and H. Kumakura, “Recent progress of high performance Ag-sheathed
Bi2223 wire,” Physica C, vol. 470, no. 20, pp. 1365–1368, 2010.
[4] K. Osamura, S. Machiya, H. Suzuki, S. Ochiai, H. Adachi, N. Ayai,
K. Hayashi, and K. Sato, “Mechanical behavior and strain dependenceof the critical current of DI-BSCCO tapes,” Supercond. Sci. Technol.,vol. 21, no. 5, p. 054010, 2008.
[5] T. Nakashima, K. Yamazaki, S. Kobayashi, T. Kagiyama, M. Kikuchi,
S. Takeda, G. Osabe, J. Fujikami, and K. Osamura, “Drastic improvement in mechanical properties of DI-BSCCO wire with novel laminationmaterial,” IEEE Trans. Appl. Supercond., vol. 25, no. 3, pp. 1–5, 2015.
[6] H. Yumura, Y. Ashibe, M. Ohya, H. Itoh, M. Watanabe, K. Yatsuka,
T. Masuda, S. Honjo, T. Mimura, Y. Kitoh, and Y. Noguchi, “Test resultsof a 30-m HTS cable pre-demonstration system in Yokohama project,”
Physica C, vol. 470, no. 20, pp. 1558–1562, 2010.
[7] S. Yamaguchi, Y. Ivanov, J. Sun, H. Watanabe, M. Hamabe, T. Kawahara, A. Iiyoshi, M. Sugino, and H. Yamada, “Experiment of the
200-meter superconducting DC transmission power cable in chubu
university,” Physics Procedia, vol. 36, no. Supplement C, pp. 1131–
1136, 2012.
[8] S. Hanai, M. Kyoto, M. Takahashi, K. Tasaki, T. Kurusu, H. Takigami,
M. Urata, G. Nishijima, S. Awaji, and K. Watanabe, “Design andtest results of 18.1 T cryocooled superconducting magnet with Bi2223
insert,” IEEE Trans. Appl. Supercond., vol. 17, no. 2, pp. 1422–1425,
2007.

[9] S. Hanai, T. Tsuchihashi, S. Ioka, K. Watanabe, S. Awaji, and H. Oguro,“Development of an 11 T BSCCO insert coil for a 25 T cryogen-freesuperconducting magnet,” IEEE Trans. Appl. Supercond., vol. 27, no. 4,
pp. 1–6, 2017.
[10] K. Ding, Y. Bi, H. Feng, X. Huang, C. Liu, X. Lin, Q. Ni, G. Shen,
Y. Song, J. Tang, H. Wu, J. Yu, and T. Zhou, “Development of ITERHTS current lead at ASIPP,” Physics Procedia, vol. 36, no. Supplement
C, pp. 931–936, 2012.
[11] T. Tsurudome, J. Yoshida, H. Ookubo, Y. Mikami, H. Mitsubori,T. Kato, J. Sakuraba, and K. Watazawa, “Reliability of Bi-2223/AgAu
current leads for cryocooled superconducting magnet,” IEEE Trans.
Appl. Supercond., vol. 23, no. 3, p. 4802204, 2013.
[12] T. Naito, H. Fujishiro, and Y. Yamada, “Thermal conductivity of single
and multi-stacked DI-BSCCO tapes,” Cryogenics, vol. 49, no. 8, pp.
429–432, 2009.
[13] R. Berman, Thermal conduction in solid. Oxford University Press,
1977.
[14] T. Naito, H. Fujishiro, and Y. Yamada, “Thermal conductivity of DIBSCCO tapes with stacked or sandwiched structure,” J. Phys.: Conf.
Ser., vol. 234, no. 2, p. 022025, 2010.
[15] Y. Touloukian, R. Powell, C. Ho, and P. Klemens, Thermophysical
Properties of Matter. IFI/Plenum, New York-Washington, 1970, vol. 1.