Physica C 426–431 (2005) 699–704
www.elsevier.com/locate/physc

Database for thermal and mechanical properties
of REBaCuO bulks
Hiroyuki Fujishiro a,*, Kazumune Katagiri a, Akira Murakami b,
Yasuhiro Yoshino a, Koshichi Noto a,caFaculty of Engineering, Iwate University, 3-4-5 Ueda, Morioka 020-8551, Japanb
Hirosaki University, 3 Bunkyo-cho, Hirosaki 036-8561, Japanc
Iwate Industrial Promotion Center, 3-35-2 Iiokashinden, Morioka 020-0852, Japan
Received 23 November 2004; accepted 24 January 2005
Available online 14 July 2005

Abstract
The thermal properties (thermal conductivity, thermal diﬀusivity, thermoelectric power, thermal dilatation, etc.) andthe mechanical properties (YoungÕs modulus, strength, hardness, fracture toughness, etc.) have been measured at low
temperatures (4–300 K) and under a high magnetic ﬁeld (0–10 T) for about 50 REBaCuO bulks (RE = Y, Gd, Nd, Sm,Dy, etc.). We have constructed the database of these properties and opened it on the Web site (thermal properties:
http://ikebehp.mat.iwate-u.ac.jp/database.html and mechanical properties: http://paris.mech.iwate-u.ac.jp/sc-bulk/
database.html). The inﬂuence of the species of RE ions, the content, size and dispersion of the RE211 (or Nd422) phaseand Ag particles and the defects distribution on these properties is characterized.
 2005 Elsevier B.V. All rights reserved.
PACS: 74.72. h; 51.20.+d; 74.70; 62.20.Mk
Keywords: REBaCuO bulk; Thermal properties; Mechanical properties; Database; Low temperature; Applied ﬁeld

1. Introduction
For the practical applications and fundamental
researches of the melt-processed REBaCuO superconductors (RE: rare earth elements), thermal*

Corresponding author. Tel./fax: +81 19 621 6363.
E-mail address: fujishiro@iwate-u.ac.jp (H. Fujishiro).

properties such as the thermal conductivity, thermal dilatation, etc. and the mechanical properties
such as the YoungÕs modulus, strength, hardness,
etc. are valuable parameters besides the electromagnetic properties such as the critical current
density Jc and the trapped magnetic ﬁeld BT. The
REBaCuO bulk material is an anisotropic andcomplex material, which consists of RE123,
RE211, Ag and Pt. The thermal and mechanical0921-4534/$ - see front matter  2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.physc.2005.01.045

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H. Fujishiro et al. / Physica C 426–431 (2005) 699–704

properties depend on the quality and alignment of
the RE123 superconducting phase, and the content, size and dispersion of the RE211 phase andadded metals. Defects such as voids and cracks
are also the inﬂuencing factors, especially, for themechanical properties. We have measured thethermal and mechanical properties at low temperatures (4–300 K) and under a high magnetic ﬁeld
(0–10 T) for REBaCuO bulks, which were fabricated by several companies and institutes. We haveconstructed the database of these properties andopened it on the Web site. In a conventional database for materials, the numerical data and ﬁgures
are aligned boringly for each sample. In order tomake the origin of these properties clear and to
elucidate the relation between the samples, wehave constructed the new type database, which isnamed as the ‘‘advanced database’’, together withthe data for each sample with a conventional style.
In this paper, we introduce the database for thermal and mechanical properties of HTSC bulks.
The typical origin of these properties is discussed.

2. Experimental
The REBaCuO superconducting bulk samples(RE = Y, Sm, Nd, Gd, Dy, Ho and (Nd, Eu, Gd))
were fabricated at DOWA Mining Co. Ltd.
(DOWA), Nippon Steel Co. Ltd. (NSC) and International Superconductivity Technology Center,
Superconductivity Research Laboratory (ISTEC).

Table 1 summarizes the speciﬁcations of the bulk
samples investigated in this study. The content of
the RE211 phase (or Nd422 phase) to the RE123
phase was expressed as RE123:RE211 = 100:X.
The Pt powder of 0.4–0.5 wt.% was added in all
the samples.
The thermal conductivity j(T) and thermoelectric power S(T) were measured by a steady-stateheat ﬂow method and the thermal diﬀusivity a(T)was measured by an arbitrary heating method under an identical experimental setup with the j andS measurements [1]. The speciﬁc heat C(T) was
estimated from the relation C = j/a. The thermal
dilatation DL(T)/L(300 K) was measured using astrain-gage method [2]. All the thermal properties
were measured in the ab-plane and along the c-axis
using a Giﬀord–McMahon (GM) cycle helium
refrigerator as a cryostat between 4 and 300 K.
The magnetic ﬁeld of up to 10 T was applied using
a cryocooler-cooled superconducting magnet [3].
Tensile, bending and compressive tests werecarried out at the cross-head speed of 0.15 mm/
min by using the 2 kN Shimadzu Servopulser orthe 5 kN Shimadzu Autograph testing machine
equipped with loading jigs. The tensile test specimen, 3 · 3 · 4 mm3in size, glued to the aluminumalloy rods were loaded through the universal
joints. The bending test was carried out using
three-point bending specimen, 4 · 3 · 36 mm3 insize with the fulcrum span 30 mm. The dimensionsof the compressive test specimen were 3 · 3 · (8 or
12) mm3. The fracture toughness tests wereTable 1
Speciﬁcations of the bulk samples investigated in this study
Company and InstituteRE element (123):(211) = 100:X Ag content (wt.%) Atmosphere during growth Measuring direction

DOWA

Y
Sm
Gd

X = 33–40
X = 10–40
X = 40

0–15
0–20
10–15

In airIn airIn airab and c
ab and c
ab and c

NSC

Y
Gd
Dy

X = 0–33
X = 33–50
X = 330
100

In airIn airIn airab and c
ab and c
ab and c

ISTEC

Nd
Gd
Dy
Ho
(Nd,Eu,Gd)X(422) = 20–30
X = 50
X = 5–40
X = 40
X = 11–43

0–10
0–30
0–10
10
0–20

Reduced O2
Reduced O2
In airIn airReduced O2

ab
ab
ab
ab
ab

H. Fujishiro et al. / Physica C 426–431 (2005) 699–704

conducted using three-point bending specimens
4 · 3 · 18 mm3 in size containing single edge Vnotch. Indentation tests were carried out by using
the Vickers hardness testing machine equippedwith the GM cryocooler [4].

3. Results and discussion
The database for each sample can be accessedfrom the following Web sites: (http://ikebehp.mat.
iwate-u.ac.jp/database.html) and (http://paris.
mech.iwate-u.ac.jp/sc-bulk/database.html). In thissection, we introduce the characteristic ‘‘advanced
database’’ in which the origin of these properties
can be clariﬁed.
3.1. Thermal properties [1–3,5–9]
Fig. 1 shows the temperature dependence of theab-plane thermal conductivity jab(T) for various
kinds of bulks with the RE211 contents of
X = 40, adding the Ag2O of 10 wt.%. The thermal
conductivity jc(T) along the c-axis for the Gd- andSm-system is also shown. In the previous paper, it
was conﬁrmed for all the RE systems that theabsolute value of jab(T) decreased with increasing
X and increased with increasing content of thehigh-thermal-conductive Ag [3,9]. The anisotropy(jab/jc) in the thermal conductivity can be seen,Fig. 1. The ab-plane thermal conductivity jab(T) for various
kinds of bulks with the RE211 contents of X = 40, adding the
Ag metal of 10 wt.%.

701

which is reduced with increasing Ag contents [3].
The temperature dependence and the absolute value of jab change depending on the species of RE
ion; for the Sm- and Dy-systems, the jab(T)enhancement below the superconducting transition temperature Tc and the absolute value above
Tc is fairly small. For the light RE (LRE) element
such as Sm and Nd, a part of the LRE ionsis substituted for the Ba site, thus forming theLRE1+yBa2 yCu3Oz-type solid solution. The
migration of Sm and Ba decreases in oxygenreduced atmosphere but a small amount of the
migration remains. The migration enhances thephonon scattering in the Sm123 phase, working
as a kind of point-defect-type phonon scattering
centers. On the other hand, for the RE = Y and
Gd systems, jab(T) shows a large enhancement below Tc. The absolute jab(T) value is large with thenegative djab/dT slope which suggests that no
migration of RE and Ba takes place and a good
crystalline RE123 phase can be conﬁrmed fromthe heat transport. It should be noticed that, for
the Dy-system, a very small jab(T) can be observed
comparable with the Sm-system. The Dy-system
has been considered to be the non-substituted system of Dy ions for the Ba site because the ionicradius of Dy3+ is large comparable with Y3+. A
sizable amount of the migration of Dy and Ba
may take place or other powerful phonon scattering centers may be introduced. A detailed investigation is in progress.
Fig. 2 shows the temperature dependence of theab-plane thermoelectric power Sab(T) for the samebulks shown in Fig. 1. In the normal state, theSab(T) value for the Y-system is negative, but thatfor the Sm-system is positive. Quantitatively, S is
expected to increase in materials with some kindsof defects because of increasing resistivity q values.
In the YBa2Cu3O7 d phase, the S value continuously changes from negative to positive withincreasing oxygen deﬁciency d, which also reﬂects
the q values [10]. In the Sm system, the observed
Sab increases positively with increasing X [3],which may partly be attributable to the qab(T) increase in the Sm123 phase caused by the migrationeﬀect and/or the increase of the oxygen deﬁciency
d. The large negative Sab value of the Y-systemsuggests that no substitution of Y3+ for the Ba2+

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H. Fujishiro et al. / Physica C 426–431 (2005) 699–704

Fig. 2. The ab-plane thermoelectric power Sab(T) for the samebulks shown in Fig. 1.

site and the suﬃcient oxidation (d = 0) should takeplace during the fabrication processes [10]. On theother hand, for the Gd- and Dy-systems, Sab value
is nearly zero. Since the present bulk materials are
a composite system, we cannot analyze Sab(T) at
the present stage. However, it is worth while tonote that the migration eﬀect can be detected by
the Sab(T) measurements, if the oxygen content isnearly equal.
3.2. Mechanical properties [4,11–20]
Typical stress–strain curves for the Gd-systemwith diﬀerent Gd211 contents (X = 33, 40, 50) and
10 wt.% Ag2O loaded in the c-axis direction or perpendicular to it at room temperature (RT) are
shown in Fig. 3 [11,12]. The latter was almost linear until the fracture, while the former was not.
This anisotropy is mainly ascribed to the openingof the pre-existing micro-cracks perpendicular tothe c-axis formed during the fabrication process.
The YoungÕs modulus (E) for the latter was 100–
130 GPa and that for the former was 35–45 GPa.
It increased with increase of the Gd211 contents
X. The tensile strength in the direction perpendicular to the c-axis was 20–55 MPa and that in thec-axis was about 10 MPa. The former decreased
with increase of X. The fracture surface observations clariﬁed that the crack initiates from voids
or sub-grains [13,14]. There was a signiﬁcantanisotropy in the PoisonÕs ratio due to the micro-

Fig. 3. The eﬀects of Gd211 contents X on tensile stress–strain
behavior of Gd-bulk (NSC) by stressing (r) in c-axis andperpendicular to c-axis at RT. Symbols indicate fracture points.

cracks; the value for loading perpendicular to thec-axis were 0.15 for the transverse strain in thec-axis, and 0.30–0.36 for that perpendicular to it[11]. The specimen length dependence of the elastic
constants observed was ascribed to the constraints
near the interfaces between the specimen and thealuminum alloy rods [11].
The compressive stress–strain curves in perpendicular to the c-axis were almost linear, while thosein the c-axis were non-linear; increasing with increase of the applied stress [15]. This can be
ascribed to the closure of the pre-existing microcracks. The E deﬁned from the region of the almost linear part of the stress–strain curves (after
the closure of the pre-existing micro-cracks) inthe c-axis was smaller than those in perpendicular
to the c-axis. This is considered to be originatedfrom the intrinsic anisotropy of the bulk. The compressive strength in the c-axis was higher than thatin the perpendicular to the c-axis. This is ascribedto the buckling fracture associated with the preexisting micro-cracks perpendicular to the c-axis
in the loading perpendicular to the c-axis. Bothof the E and the fracture strength by compressive
test were higher than those by tensile test [15].
The E and strength rf by bending tests of the Yand Gd-bulks at RT and liquid nitrogen temperature (LNT) are shown in Fig. 4 [16,17]. The Y-bulk(X = 33, Ag: 0, NSC), Y-bulk (X = 40, Ag:
15 wt.%, DOWA) and Gd-bulk (X = 33, Ag:

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703

has been constructed and opened on the Web site.
The inﬂuence of the species of RE ions, the content, size and dispersion of the RE211 phase andAg metals and defects distribution on these properties is characterized in the database. We expectthat the database will be widely used for the practical application and the basic research for the
REBaCuO bulks.

Acknowledgements
Fig. 4. The bending mechanical properties of Y33-, Y40-Agand Gd33-Ag-bulks at RT and LNT (see text).

10 wt.%, NSC) are denoted as Y33, Y40-Ag andGd33-Ag, respectively. The E of Y33 and Y40Ag at LNT, 148 and 143 GPa were higher thanthose at RT, 132 and 136 GPa, respectively. Thistemperature dependence coincides with theoreticalones [11] associated with the inter-atomic distance.
The E at RT was higher than that by tensile test[12]. This can be ascribed to the behavior of thecompressive stress region induced in a half of thevolume of the bending test specimens. The rf ofY33, Y40-Ag and Gd33-Ag at LNT, 90, 122 and96 MPa, were higher than those at RT, 74, 104
and 71 MPa, respectively. The bending fatigue
endurance limits of the Y33 and that of theGd33-Ag for 5 · 104 stress cycles at LNT wereabout 80% and 70% of rf, respectively [16,17].
The fracture toughness KIc for the bulks ranged
from 1.0 to 2.0 MPa m1/2 [4,18–20]. Although, theKIc obtained from bending tests and tensile tests
coincided fairly well, those from indentation test
gave underestimation [18]. While the Vickers hardness increased with lowering temperature, the KIc
from indentation decreased and those fromnotched specimen increased [4,18,20].

4. Summary
The thermal properties and mechanical properties have been measured at low temperatures andunder a high magnetic ﬁeld for about 50 REBaCuO bulks. The database of these properties

The authors greatly thank Dr. S. Kohayashi of
Dowa Mining Co., Ltd., Dr. H. Teshima of Nippon Steel Co., Ltd., Dr. S. Nariki and Dr. N.
Sakai of ISTEC for the sample preparation andvaluable discussion. We also thank Prof. M.
Murakami of Shibaura Institute of Technology
for the technical support and valuable suggestion.
This work is partially supported by Japan Scienceand Technology Corporation under the Jointresearch Project for Regional Intensive in the
Iwate Prefecture on ‘‘development of practicalapplications of magnetic ﬁeld technology for use
in the region and in everyday living’’.

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