Preparation of YBCO and BSCCO superconducting thin films by a new chemical precursor method

Article abstract of DOI:10.1246/bcsj.78.187

Homogeneous YBa₂-Cu₃O_7-δ (YBCO) and Bi₂SrCa₂Cu₂O_8+y (BSCCO) precursors were prepared by the reaction of triethanolamine with ethyl acetoacetato complexes of Y, Ba, and Cu and those of Bi, Sr, Ca, and Cu, respectively. These precursors showed melt-spinnability and converted to ceramics on heating with the elimination and combustion of organic groups. Superconductive thin films were prepared by depositing a solution on a substrate by spin-coating, followed by calcination. Epitaxial growth of the YBCO phase, with c axis normal to the substrate, was observed. The critical temperature was 88.7 K and the critical current density at 77 K and O T was 5 × 10⁵ A/cm². On the other hand, the epitaxial growth of the c axis aligned BSCCO phase was observed: the critical temperature was 77 K and the critical current density at 5 K was 6 × 10⁴ A/cm².

Full text of DOI:10.1246/bcsj.78.187

ꢀ 2005 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 78, 187–191 (2005)
187
Preparation of YBCO and BSCCO Superconducting Thin Films
by a New Chemical Precursor Method
ꢀ
Takahiro Gunji, Mitsuo Unno, Koji Arimitsu, Yoshimoto Abe,
Nick Long,1 and Andrea Bubendorfer1
Department of Pure and Applied Chemistry, Faculty of Science and Technology, Tokyo University of Science,
2641 Yamazaki, Noda, Chiba 278-8510
1Industrial Research Ltd., PO Box 31-310, Lower Hutt, New Zealand
Received June 21, 2004; E-mail: gunji@rs.noda.tus.ac.jp
Homogeneous YBa2Cu3O7ꢁꢀ (YBCO) and Bi2SrCa2Cu2O8þy (BSCCO) precursors were prepared by the reaction
of triethanolamine with ethyl acetoacetato complexes of Y, Ba, and Cu and those of Bi, Sr, Ca, and Cu, respectively.
These precursors showed melt-spinnability and converted to ceramics on heating with the elimination and combustion
of organic groups. Superconductive thin films were prepared by depositing a solution on a substrate by spin-coating,
followed by calcination. Epitaxial growth of the YBCO phase, with c axis normal to the substrate, was observed.
The critical temperature was 88.7 K and the critical current density at 77 K and 0 T was 5 ꢂ 105 A/cm2. On the other
hand, the epitaxial growth of the c axis aligned BSCCO phase was observed: the critical temperature was 77 K and the
critical current density at 5 K was 6 ꢂ 104 A/cm2.
Since the superconducting ceramics were reported in 1986,1
many superconductors which have high critical temperatures
have been discovered. Oxide superconductors, such as
YBa2Cu3O7ꢁꢀ (YBCO) and Bi2SrCa2Cu2O8þy (BSCCO), are
expected to be applied to large current transport or electronic
devices because their critical temperatures (Tc) are higher than
the boiling point of liquid nitrogen. For example, for the fab-
rication of Josephson junction devices, which are known as ul-
tra high-speed circuits, the formation of superconductive thin
films with high Tc and critical current density (Jc) is strongly
demanded. However, the preparation of superconductive thin
films or fibers by the conventional solid phase method has lim-
itations as to the homogeneity and the shape of samples be-
cause YBCO and BSCCO superconductors are ceramics.2–4
As typical methods for the formation of superconductive ce-
ramic thin films, the following methods and processes are
mentioned:5–9 sputtering, physical vapor deposition, chemical
vapor deposition, metal organic chemical vapor deposition,
sol–gel process, and metal organic decomposition (MOD). Es-
pecially, the MOD method has been applied as a simple and
inexpensive method for the preparation of thin films. The prep-
aration of YBCO superconductive thin films by MOD method
can be summarized as follows: McIntyre, Cima, and co-au-
thors10 used trifluoroacetates to provide a thin film of the thick-
ness of 200–250 nm and Jc of 2{3 ꢂ 106 A/cm2. T. Kumagai
and co-authors11 prepared thin films with Jc of 1 ꢂ 106 A/cm2
using acetylacetonate precursors. Shibata and co-authors12,13
also made thin films with Jc of 1 ꢂ 106 A/cm2 from trifluoro-
acetate precursors on a substrate which is covered with a buffer
layer of CeO2/YSZ.
tion of (ethyl acetoacetato)metal complexes with triethanol-
amine (H3tea).14 These superconductive fibers are, however,
so brittle that the superconductive properties have not been
fully evaluated. In this study, therefore, the preparation of
superconductive films from YBCO and BSCCO precursors
by the reaction of (ethyl acetoacetato)metal complexes
([M(etac)n]: M ¼ Y, Ba, Cu, Bi, Sr, Ca) with H3tea according
to Eq. 1 will be reported. Such films have high homogeneity,
stability against condensation, solubility in organic solvents,
and melt-spinnability. Furthermore, evaluation of supercon-
ductive properties and surface properties was performed for
the superconductive thin films prepared by spin-coating and
calcination.
M(etac)n + m N(CH2CH2OH)3
ð1Þ
CH2CH2OH
(etac)n-m
M
OCH2CH2N
+ m Hetac
CH2CH2OH
m
Results and Discussion
Preparation of YBCO and BSCCO Precursors. The
reaction of H3tea with ethyl acetoacetato complexes was
followed by the determination of the amount of Hetac formed,
using gas chromatography on the reaction of H3tea with metal
chelate in the molar ratio of 1:1. The results are summarized in
Table 1. On the reaction of [Bi(etac)3] with H3tea, 3 equivalent
amounts of Hetac was recovered. Similarly, [Y(etac)3] pro-
duced 2 equivalent amounts of Hetac. [Cu(etac)2], [Sr(etac)2],
and [Ca(etac)2] produced 1 equivalent amount of Hetac. On
the other hand, Hetac was not formed when the reaction was
with [Ba(etac)2]. These results suggest the formation of YBCO
and BSCCO precursors by the reaction of H3tea with ethyl
On the other hand, superconductive fibers and bulk bodies
with the critical temperature of 88.2 K for YBa2Cu3O7ꢁꢀ were
prepared by the calcination of precursors obtained by the reac-
Published on the web January 13, 2005; DOI 10.1246/bcsj.78.187

188 Bull. Chem. Soc. Jpn., 78, No. 1 (2005)
YBCO and BSCCO Superconducting Thin Films
Table 1. Results of the Reaction of Chelate with H3teaaÞ
Figs. 1 and 2. These traces showed exothermic peaks with
ꢃ
ꢃ
weight losses at 450 C (YBCO) and 400 C (BSCCO). The
ceramic yields were calculated based on the residual weight af-
ter the DTA-TG analysis at 800 ꢃC, which decreased gradually
with increasing molar amount of H3tea. The YBCO and
BSCCO precursors were soluble in acetone, tetrahydrofuran,
methanol, and ethanol, while they were less soluble in chloro-
form, carbon tetrachloride, and benzene.
As [Y(etac)3], [Ba(etac)2], and [Cu(etac)2] behave as di-
functional, inert, and monofunctional, against H3tea, respec-
tively, a plausible structure of YBCO precursor is shown in
Scheme 1. Yttrium and copper are connected by means of a li-
gand exchange reaction between H3tea and etac. The coordina-
tion of the oxygen and nitrogen atoms in H3tea to Ba atom in
[Ba(etac)2] can be postulated, because no precipitation was ob-
served on mixing [Ba(etac)2] and H3tea. Moreover, the
BSCCO precursors are considered to be formed by the same
systems.
Chelate
Molar ratio of Hetac formedbÞ
Hetac/chelate
[Y(etac)3]
[Ba(etac)2]
[Cu(etac)2]
[Bi(etac)3]
[Sr(etac)2]
[Ca(etac)2]
2.0
0.0
1.0
3.0
1.0
1.0
a) Reaction condition: reflux 1 h in ethanol. Molar ratio of
H3tea/chelate: 1.0. b) Calculated from the amount of Hetac
in the reaction mixture by gas chromatography.
acetoacetato complexes based on a ligand exchange reaction
between H3tea and Hetac.
The results on the preparation of YBCO and BSCCO pre-
cursors are shown in Table 2. When the molar ratio of H3tea
to [Cu(etac)2] was lower than 1.3 (for YBCO) or 4.5 (for
BSCCO), a copper compound precipitated during the concen-
tration process and a heterogeneous precursor was formed. The
YBCO precursors showed spinnability on melting at 70–80 ꢃC.
The YBCO and BSCCO precursors decomposed on heating
above the temperatures of 90 ꢃC and 60 ꢃC, respectively.
The DTA-TG analyses of these precursors are shown in
Superconductive Properties of YBCO Superconductive
ꢀ
Thin Films.
In this study, SrTiO3 (a ¼ 3:905 A), MgO
ꢀ
ꢀ
(a ¼ 4:203 A), and LaAlO3 (a ¼ 3:792 A) were used as sub-
strates for the epitaxial growth of a superconductive phase
because the lattice constants are close to YBa2Cu3O7ꢁꢀ
ꢀ
(a ¼ 3:82 and b ¼ 3:89 A). The X-ray diffraction pattern of
YBCO superconductive thin film, which was formed on the
Table 2. Preparation Condition and Properties of Precursors
Molar ratio
H3tea/[Cu(etac)2]
Softening
point/ꢃC
Spinnꢃability
at 90 C/cm
Decomposition
point/ꢃC
Ceramic
yieldaÞ/%
No.
Composition
YBCObÞ
1
2
3
4
1.3
1.5
1.7
2.0
70–80
2–3
20–30
120–150
150–200
>90
36
34
32
31
5
6
7
8
9
BSCCOcÞ
4.5
4.7
5.0
5.5
6.0
58–68
0
5
15
30
60
>60
33
27
20
18
15
a) Calculated based on the remaining weight at 800 ꢃC by thermogravimetry. b) Scale in operation (g
(mmol)): [Y(etac)3], 1.9918 (4.182); [Ba(etac)2], 3.3080 (8.363); [Cu(etac)2], 4.0366 (12.55). Solvent:
EtOH, 180 mL. Time and temp.: 1 h under reflux. c) Scale in operation (g (mmol)): [Bi(etac)3], 5.23
(8.78); [Sr(etac)2], 2.7095 (7.8979); [Ca(etꢃac)2], 1.3079 (4.3877); [Cu(etac)2], 3.1038 (9.653). Solvent:
EtOH, 200 mL. Time and temp.: 2 h at 50 C.
100
80
100
80
60
40
60
40
TG
TG
20
0
20
DTA
DTA
0
200
400
Temprature/ oC
600
800
1000
200
400
600
800
1000
Temprature/ oC
Fig. 1. DTA-TG traces of YBCO precursor (Y:Ba:Cu =
1:2:3; H3tea/[Cu(etac)2] = 2.0).
Fig. 2. DTA-TG traces of BSCCO precursor (Bi:Sr:Ca:
Cu = 2:1.8:1.0:2.2; H3tea/[Cu(etac)2] = 4.5).

T. Gunji et al.
Bull. Chem. Soc. Jpn., 78, No. 1 (2005)
189
HO
O
O
Cu(etac)
OH
N
N
Ba(etac)2
HO
OH
O
Y(etac)
N
O
OH
O
HO
N
Cu(etac)
O
10 µm
Cu(etac)
N
OH
Ba(etac)2
OH
Fig. 4. SEM image of YBCO film prepared from the precursor.
HO
HO
N
OH
OH
20
15
Scheme 1. A possible structure of YBCO precursor.
10
3
2
1
[ 003 ]
[ 002 ]
[ 006 ]
[ 005 ]
5
0
[ 001 ]
[ 007 ]
124
60
50
60
70
80
90
100
110
120
130 140
150
[ 004 ]
124
Temperature/ K
Fig. 5. Temperature dependence of the resistivity of YBCO film.
0
0
10
20
30
40
50
70
80
2
θ
(CuKα)/ o
30
Fig. 3. X-ray diffractogram of YBCO superconducting thin film.
MgO
ꢃ
20
SrTiO3 substrate by calcination at 850 C, is shown in Fig. 3.
The epitaxial growth toward the c axis of YBa2Cu3O7ꢁꢀ phase
was observed because all peaks observed were ascribed to
(00l) peaks, while a slight contamination of YBa2Cu4O8 phase
was observed. A relatively narrow peak width suggests an ex-
cellent orientation and good crystallinity of this thin film. The
peaks at 2ꢁ ¼ 44, 49, and 52ꢃ are ascribed to the diffraction
pattern of the substrate. The main diffraction peaks of the sub-
strate have overlapped with the peaks of the YBa2Cu3O7ꢁꢀ
phase due to (003) and (006) diffractions. A similar c axis ori-
entation was observed when MgO and LaAlO3 were used as
substrates.
The SEM image of the surface of a YBCO superconductive
thin film, which was prepared by calcination at 850 ꢃC on
SrTiO3 substrate with the film thickness of 10 mm, is shown
in Fig. 4. A flat and smooth surface consisting of crystal grains
of 1–2 mm size was observed. The white portion would reflect
the high electric conductivity, which, in turn, is ascribed to the
crystal grain of CuO due to the incomplete calcination to form
YBa2Cu3O7ꢁꢀ phase.
The temperature dependency of the electric resistance of
YBCO superconductive thin film, which was prepared on
SrTiO3 substrate by calcination at 850 ꢃC and pO2 ¼
2:7 ꢂ 102 Pa, is shown in Fig. 5. The resistivity decreased rap-
idly at 90.0 K (Tc(onset)) and decreased to zero at 88.7 K
(Tc(zero)). The difference between Tc(onset) and Tc(zero) was very
small, 1.3 K. The Jc of YBCO superconductive thin film was
5 ꢂ 105 A/cm2 at 77 K and 0 T.
10
0
0
10
20
30
40
50
60
2
θ
(CuKα)/ o
Fig. 6. X-ray diffractogram of the BSCCO superconducting
film.
Superconductive Properties of BSCCO Superconductive
Thin Films. During the preparation of BSCCO superconduc-
tive thin films, MgO was used as a substrate for the epitaxial
growth of a superconductive phase. The X-ray diffraction pat-
tern of BSCCO superconductive thin film is shown in Fig. 6.
The epitaxial growth toward the c axis of Bi2SrCa2Cu2O8þy
phase was observed because all peaks observed were due to
(00l) peaks. The peak due to the substrate was observed at
2ꢁ ¼ 43ꢃ. Moreover, the diffraction peaks at 2ꢁ ¼ 17 and
22ꢃ are considered to be from the Bi2SrCa2Cu2O8þy phase.
The observation of the surface of a film by the laser beam
microscope is shown in Fig. 7. The white portions have swol-
len up and the black portions serve as holes. Moreover, the
measurement of the surface profile of the section from points
A to B showed that the largest hole within the measured area
was 1.1 mm with a radius of 0.9 mm. Since the difference of
peaks and troughs on the film surface was about 1 mm and film

190 Bull. Chem. Soc. Jpn., 78, No. 1 (2005)
YBCO and BSCCO Superconducting Thin Films
mL of benzene and isopropyl alcohol were added. This procedure
was repeated 4 times. Tetrahydrofuran 250 mL, ethyl acetoacetate
13.0 g (0.11 mol), and triethylamine 11.0 g (0.11 mol) were added
at the temperature of 5–10 ꢃC; then stirring was continued for 5 h
at room temperature. After filtration of triethylamine hydrochlo-
ride followed by concentration, the residual solid was subjected
to recrystallization using carbon tetrachloride. White pellet-like
crystals were obtained by drying under reduced pressure. The
yield was 54%.
Synthesis of Bis(ethyl acetoacetato)barium(II) ([Ba(etac)2]).
Barium, 10.80 g (0.079 mol), was put into the mixture of 200 mL
of cyclohexane, and ethyl acetoacetate, 61.40 g (0.472 mol); then
the mixture was stirred in an ice bath until the barium disappeared.
The white precipitate was washed with hexane and dried under re-
duced pressure. The solid was dissolved in 250 mL of tetrahydro-
furan and then subjected to hot filtration and condensation. White
pellet-like crystals were obtained by recrystallization with ethanol.
The yield was 57%.
Synthesis of Bis(ethyl acetoacetato)copper(II) ([Cu(etac)2]).
Ethyl acetoacetate, 32 g (0.26 mol), was added to anhydrous cop-
per(II) acetate, 10.0 g (0.55 mol), dissolved into ethanol (450 mL),
and then the mixture was subjected to reflux and cooling to obtain
crystals of crude product. Green needle-like crystals were isolated
by recrystallization using ethanol; decantation and drying under
reduced pressure followed. The yield was 91%.
1
0
0
2
4
6
8
Length from the point A/ µm
Fig. 7. Surface depth profile of BSCCO thin film.
End = 5.0 K
6
5
4
3
2
Synthesis of Tris(ethyl acetoacetato)bismuth(III) ([Bi-
Into a refluxing solution of bismuth trichloride,
(etac)3]).
14.85 g (0.047 mol) in 45 mL of ethanol, a solution of sodium eth-
oxide 9.61 g (0.14 mol) in 120 mL of ethanol was added, followed
by addition of 28 mL of benzene. The solution was refluxed for 5
h under dark condition. The white solid thus formed was separated
by hot filtration. Bismuth(III) triethoxide was isolated by recrys-
tallization of the filtrate as colorless pillar-like crystals in the yield
of 5.55 g (0.016 mol).
1
0
0
100
200
300
Temperature / K
Into bismuth(III) triethoxide 5.55 g (0.016 mol) suspended in
60 mL of benzene, 6.28 g (0.0483 mol) of ethyl acetoacetate
was added. After stirring for 2 h at room temperature, insoluble
material was filtered and then concentrated. Colorless pillar-like
crystals were obtained by recrystallization from the mixed sol-
vents of hexane and benzene in 4/1 volume ratio. The yield
was 85%.
Synthesis of Bis(ethyl acetoacetato)strontium(II) ([Sr-
(etac)2]). A mixture of 40 mL of hexane, 74.10 g (0.57 mol)
of ethyl acetoacetate, and 25.00 g (0.29 mol) of strontium was stir-
red at room temperature for 20 h. After concentration and dissolv-
ing in ethanol, insoluble matter was separated by hot filtration.
The filtrate was subjected to concentration and recrystallization
from ethanol. White pellet-like crystals were obtained by washing
the precipitate with hexane and drying. The yield was 24%.
Synthesis of Bis(ethyl acetoacetato)calcium(II) ([Ca(etac)2]).
A mixture of 5 mL of tetrahydrofuran, 167.50 g (1.3 mol) of ethyl
acetoacetate, and 5.48 g (0.14 mol) of calcium was stirred at room
temperature until the calcium totally disappeared. After concentra-
tion and dissolving in ethanol, insoluble matter was separated by
hot filtration. The filtrate was subjected to concentration and re-
crystallization from ethanol. White pellet-like crystals were ob-
tained by washing the precipitate with hexane and drying. The
yield was 55%.
Fig. 8. Temperature dependence of the resistivity of the
BSCCO film.
thickness was 10 mm, the Bi2SrCa2Cu2O8þy superconductive
thin film had a relatively flat and smooth surface.
The temperature dependence of the resistance of the
BSCCO superconductive thin film is shown in Fig. 8. The
Tc(onset) was 92 K and the Tc(zero) was 77 K. The relatively
big difference between Tc(onset) and Tc(zero) is considered to
be due to the low degree of orientation toward the c axis
and the degradation of the superconductive property due to
contamination by impurity phases, which are understood from
the relatively broad peaks in X-ray diffraction pattern. The
Jc at 5 K was 6 ꢂ 104 A/cm2.
Experimental
Reagents. Reagent grade yttrium(III) trichloride hexahydrate,
barium, copper(II) acetate anhydride, bismuth(III) chloride, calci-
um, and sodium (Wako Pure Chemical) were used as purchased.
Reagent grade strontium (Soekawa Chemical) was used as pur-
chased. Other reagents (Wako Pure Chemical) were purified by
conventional methods.
Synthesis of Tris(ethyl acetoacetato)yttrium(III) ([Y-
Yttrium(III) trichloride hexahydrate 9.1 g (0.030
(etac)3]).
Preparation of YBCO and BSCCO Precursors. All reac-
tions were performed under a dry nitrogen atmosphere.
(Ethyl acetoacetato)metal complexes were mixed in the stoi-
chiometric molar ratio Y:Ba:Cu = 1:2:3 for YBCO and Bi:Sr:
mol) was mixed with 50 mL of benzene and 50 mL of isopropyl
alcohol. The mixture was heated to evaporate water by azeotropic
distillation. When almost all of the liquid was distilled, another 50

T. Gunji et al.
Bull. Chem. Soc. Jpn., 78, No. 1 (2005)
191
Ca:Cu = 2.0:1.8:1.0:2.2 for BSCCO. The stated amount of H3tea
was added and the mixture was refluxed for a certain period. High-
ly viscous liquid was obtained by condensation under reduced
pressure, and then foamed and solidified by further heating. The
precursor was obtained by grinding this solid. The spinnability
was evaluated by measuring the length of a fiber drawn by pulling
a glass rod up from the solution.
Preparation of YBCO Superconductive Thin Films. The
YBCO precursor, which was prepared by adding 2.0 equivalent
moles of H3tea compared to copper, was dissolved in ethanol to
provide a 16 wt % solution. This solution was dropped on the sub-
strate of SrTiO3, MgO, or LaAlO3 (10 mm ꢂ 10 mm) and spun at
3000 rpm for 30 s and then heated at 150 ꢃC for 10 min. This
procedure was repeated 10 times. The YBCO superconductive
thin film was obtained by the calcination of the coating film under
the following conditions: the film was placed under low oxygen
pressure (2:7 ꢂ 102 Pa) and the temperature was raised quickly
to 850 ꢃC and then held there for 2 h. The atmosphere was
changed to pure oxygen and the film was heated at 450 ꢃC for
48 h then cooled to room temperature.
Preparation of BSCCO Superconductive Thin Films. The
BSCCO precursor, which was prepared by adding 4.0 equivalent
moles of H3tea compared to copper, was dissolved in ethanol
to provide a 20 wt % solution. Spin-coating on the substrate
of MgO (10 mm ꢂ 10 mm) was carried out by the following
process: dropping the solution and spinning at 1000 rpm for 5 s,
dropping the solution and spinning at 4000 rpm for 5 s, and then
heating for 15 min at 500 ꢃC. This procedure was repeated 10
times. The BSCCO superconductive thin film was obtained by
the calcination of the coating film at 810 ꢃC for 10 min under
air atmosphere.
respectively. These precursors were considered to be polymers
in which the metals are connected by bridges of triethanol-
amine with the elimination of ethyl acetoacetate. These precur-
sors were highly stable against self-condensation and showed
high solubility in organic solvents.
Superconductive thin films were prepared simply by dis-
solving the precursor in an organic solvent, spin-coating the
precursor solution on a substrate, and then calcining the spun
film. The epitaxial growth, with the c axis normal to the sub-
strate surface, of YBa2Cu3O7ꢁꢀ and Bi2SrCa2Cu2O8þy phases
was observed. The critical temperature of YBCO superconduc-
tive thin film was 90.0 K (Tc(onset)) and 88.7 K (Tc(zero)) and the
critical current density at 77 K and 0 T was 5 ꢂ 105 A/cm2.
The Tc(onset) and Tc(zero) of BSCCO superconductive thin film
were 92 K and 77 K, respectively. The Jc at 5 K was 6 ꢂ
104 A/cm2.
The authors thank Mr. Yohei Tsunochi for his helpful guid-
ance and cooperation on the preparation and characterization
of superconductive thin films.
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.
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every 4 s. The critical current (Ic) was obtained using a voltage
criterion of 1 mV/cm. The film thickness was measured by SEM
for the cross-section of the films. Jc was calculated based on the
distance between two patterned bridges and the film thickness.
13 H. Fuji, T. Honjo, Y. Nakamura, T. Izumi, T. Araki, I.
Hirabayashi, Y. Shiohara, Y. Iijima, and K. Takeda, Physica C,
357–360, 1011 (2001).
14 Y. Abe, K. Hara, K. Hirai, T. Gunji, Y. Nagao, and T.
Misono, J. Ceram. Soc. Jpn., 102, 765 (1994).
Conclusion
Homogeneous YBCO and BSCCO precursors were pre-
pared by the reaction of triethanolamine with ethyl acetoaceta-
to complexes of Y, Ba, and Cu and those of Bi, Sr, Ca, and Cu,