Physica C 399 (2003) 171–177

www.elsevier.com/locate/physc

Growth of 1–2 lm thick biaxially textured Bi-2212 filmson (1 0 0) LaAlO3 single crystal substrates by electrodeposition

Jun Chen *, Raghu N. Bhattacharya

National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, CO 80401, USA

Received 23 January 2003; received in revised form 17 June 2003; accepted 26 June 2003

Abstract

High quality Bi2Sr2Ca1Cu2Ox (Bi-2212) films with thickness around 1–2 lm have been grown on (1 0 0) LaAlO3

single crystal substrates using an electrodeposition technique, followed by a melt quench and annealing process. X-ray

diffraction (XRD) measurements of the final films indicated that the films were almost pure biaxially textured Bi-2212

films. The full width at half maximum (FWHM) of omega and phi scans were about 1.7� and 1.1�, respectively. Inmagnetization measurements, Tc of 79 K and Jc of 0.58 MA/cm2 (4.2 K, 0 T) and 44 kA/cm2 (50 K, 0 T) were observed.

The mechanism of the convention of Bi-2201 phase to Bi-2212 phase during the annealing process was discussed, the

length scale for the current flow in Bi-2212 film was calculated from the differential susceptibility dm=dH during re-

penetration of magnetic field, and the residual stress in the films were estimated from XRD h–2h scans.

� 2003 Elsevier B.V. All rights reserved.

Keywords: Bi2Sr2Ca1Cu2Ox; Critical current density; Melt process

1. Introduction

High-Tc superconducting Bi2Sr2Ca1Cu2Oy (Bi-

2212) thick films have a huge potential application

in superconducting wires, magnets, and electronic

devices. So far, most of the literature concentrates

on growth of thick Bi-2212 films on Ag substrates.Bi-2212 precursor films are deposited on Ag sub-

strates by techniques such as doctor blade and dip

coating, and a melt-solidification process is applied

to achieve desired c-axis textured structure. The

melt-textured Bi-2212/Ag tapes exhibit excellent

* Corresponding author. Tel.: +1-303-3846674; fax: +1-303-

3846655.

E-mail address: jun_chen@nrel.gov (J. Chen).

0921-4534/$ - see front matter � 2003 Elsevier B.V. All rights reserv

doi:10.1016/S0921-4534(03)01309-1

performance at low temperature and high mag-

netic field, for example, Jc of 0.5 MA/cm2 at 4.2, 10

T has been reported in multilayered Bi-2212/Ag

tapes prepared by a combination of pre-annealing

and intermediate rolling (PAIR) process and

melt-solidification technique [1]. Thus, Bi-2212/Ag

tapes are regarded as one of the most viable can-didates for applications such as magnets and

power transmission.

For other applications such as power switching

and chip-to-chip interconnection, growth of thick

Bi-2212 films on insulating substrates is highly

desired. Both of the melt-solidification process and

melt quench and annealing technique have been

applied to grow thick Bi-2212 films on singlecrystalline and polycrystalline MgO, and YSZ

substrates [2–7]. Although c-axis textured Bi-2212

ed.

172 J. Chen, R.N. Bhattacharya / Physica C 399 (2003) 171–177

films have been obtained, Jc values were typically

about 14 kA/cm2 (55 K, 0 T) [2] and 3.5 kA/cm2

(77 K, 0 T) [3] on MgO single crystal substrates,

and 6 kA/cm2 (4.2 K, 0 T) on polycrystalline MgO

substrates [6], which were much lower than Jcvalues in Bi-2212/Ag tapes [8], indicating sub-strates have significant effect on growth and

properties of Bi-2212 superconductors.

Electrodeposition is a promising technique to

grow high-Tc superconducting films. Its advanta-

ges include low cost, the adaptability to large-scale

process, mixture of the constituent elements at the

atomic scale, which significantly decreases the

processing time, and the ability to form films on anon-planar surface. High quality biaxially textured

Tl-1223 films [9] and c-axis textured Bi-2212 [10]

films have been grown on (1 0 0) LaAlO3 single

crystal substrates and polycrystalline Ag sub-

strates by electrodeposition, respectively. How-

ever, so far there is no report of successful growth

of high-quality biaxially textured Bi-2212 films via

an electrodeposition process.In this paper we report our recent work on the

growth of 1–2 lm thick, high Jc biaxially textured

Bi-2212 films on (1 0 0) LaAlO3 single crystal

substrates using electrodeposited Bi-2212 precur-

sor films and a melt quench and annealing process.

Jc values of 0.58 MA/cm2 (4.2 K, 0 T) and 44 kA/

cm2 (50 K, 0 T) were observed in our films in the

magnetization measurements, which are muchlarger than the Jc values reported before in the

literature [2–7].

2. Experimental

The electrodeposited Bi-2212 precursor films

were obtained by co-electrodeposition of the con-stituent metals using nitrate salts dissolved in

dimethyl sulfoxide (DMSO) solvent. A typical

electrolyte-bath composition for the Bi-2212 pre-

cursor films consisted 2.0 g Bi(NO3)3 Æ 5H2O, 1.0 g

Sr(NO3)2, 0.6 g Ca(NO3)2 Æ 4H2O, and 0.9 g

Cu(NO3)2 Æ 6H2O dissolved in 400 ml of DMSO

solvent. The electrodeposition was performed at

room temperature in a ‘‘vertical cell’’, in which theelectrodes (working, counter, and reference) were

suspended vertically from the top of the cell. The

precursor films were electroplated by using a

constant potential of )4 V. The substrates were

LaAlO3 single crystals coated with 30 nm Ag. The

detailed information has been reported elsewhere

[9]. A melt quench and annealing process was ap-

plied to grow Bi-2212 films. In the melt quenchstep, Bi-2212 precursor films were pushed in

a furnace preheated to 1000 �C. The temperature

of the furnace dropped about 100 �C and rose to

960 �C in one and a half minutes, then the samples

were rapidly quenched to room temperature. The

melt quenched samples consisted mainly of the Bi-

2201 phase. In the annealing step, the melt quen-

ched samples were annealed at temperaturesranging from 840 to 870 �C in air or oxygen to be

converted to biaxially aligned Bi-2212 films.

The crystal structure of the films was charac-

terized by XRD with CuKa radiation, including

h–2h scan, omega scan, phi scan, and pole figure.

The surface morphology was observed by scanning

electron microscopy (SEM), and the compositions

of Bi-2212 films were analyzed by inductivelycoupled plasma (ICP) spectrometry. A SQUID

magnetometer (Quantum Design) was used to

measure the superconducting properties of Bi-2212

films.

3. Results and discussion

Fig. 1(a) shows the XRD h–2h scan of a melt

quenched Bi-2212 film. All the major peaks were

identified as (00 l) peaks from Bi-2201 phase

(length of c-axis is 24.454 �AA), and some small

peaks from (Sr,Ca)CuO2 phase and Cu-free phase

were also observed. This indicates that the pre-

cursor film has completely melted. The melt

quenched samples were then annealed at temper-atures ranging from 840 to 870 �C in air or oxygen

to convert the Bi-2201 phase to the Bi-2212 phase,

then they were cooled to room temperature at

different cooling rates. The conversion from Bi-

2201 phase to Bi-2212 phase was very fast, after

annealing at 870 �C in less than 1 h almost no

residual peaks from the Bi-2201 phase could be

found in XRD h–2h scans, all the major peakswere indexed as (00 l) peaks from the Bi-2212

phase (length of c-axis is 30.719 �AA), and the

Fig. 1. (a) h–2h scan of a Bi-2212 film after the melt quench, (b) h–2h scan of a Bi-2212 film after melt quench and annealing, (c) omega

scan of a Bi-2212 film after melt quench and annealing, (d) phi scan of a Bi-2212 film after melt quench and annealing and (e) pole

figure of a Bi-2212 film after melt quench and annealing.

J. Chen, R.N. Bhattacharya / Physica C 399 (2003) 171–177 173

6

5

4

3

2

1

0

B*c

os(t

heta

)(x1

0-3 )

0.60.50.40.30.20.10.0sin(theta)

Fig. 2. The dependence of the broadening of the Bragg peaks B

on the Bragg angles h of Bi-2212 films. The relation B�cosðhÞ � 2� ðDc=cÞ sinðhÞ was observed. The dashed lines are

the linear fits to the experimental data. d: Bi-2212 film after

melt quench; j: Bi-2212 film after melt quench, annealing, and

quench to room temperature;r: Bi-2212 film after melt quench,

annealing, and furnace cooling to room temperature.

174 J. Chen, R.N. Bhattacharya / Physica C 399 (2003) 171–177

Bi-2212 grains were biaxially textured. However,

the superconducting properties of the films an-

nealed for less than 1 h are quite poor, longer

annealing up to 8–10 h is necessary to optimize Tcand Jc. Fig. 1(b)–(e) shows the h–2h, omega scan,

phi scan and pole figure of a typical Bi-2212 filmsafter being annealing at 870 �C for 10 h. FWHM

of omega scan and phi san were around 1.1� and

1.7�, respectively. The film thickness after anneal-

ing was around 1–2 lm from the ICP measure-

ments.

The fast formation of the Bi-2212 phase and

improvement of superconducting properties with

longer annealing time indicates that the Bi-2212phase may form via two different processes: in the

initial stage of the annealing process, the solid/

liquid reaction Bi-2201+ (Sr,Ca)CuO2 +LfiBi-

2212 was the dominant process, which led to high

cation diffusion rates and fast formation of Bi-

2212 phase. After the consumption of the liquid

phase, the reaction mechanism changes to a solid

state reaction, Bi-2201+ (Sr,Ca)CuO2 fiBi-2212,which is a much slower process. As observed by

transmission electron microscopy (TEM) mea-

surements [11], although there were no Bi-2201

grains observed in samples which were melt

quenched and annealed for a shorter time, there

were many 2201 intergrowths inside Bi-2212

grains. The solid/solid reaction in prolonged an-

nealing led to a decrease of the amount of Bi-2201intergrowths inside Bi-2212 grains. Bi-2201 inter-

growths have been considered as strong current-

limiting defects due to its lower Tc (0–20 K) and

lower Bc2 (4.2 K) (0–15 T). Thus the decrease of

the amount of Bi-2201 intergrowths could signifi-

cantly improve the superconducting properties of

Bi-2212 films. In transmission electron microscopy

(TEM) measurements of our Bi-2212 films only 3%Bi-2201 intergrowth was observed, indicating high

quality Bi-2212 films have been grown with the

melt quench and annealing process.

In some practical applications such as magnets

and cables, uncontrollable thermal stresses in-

duced by quenching could affect the mechanical

properties of the final products. Indeed in XRD

h–2h scans of the Bi-2212 films after meltquenching and annealing, the broadening of the

Bragg peaks B satisfied the relation B� cosðhÞ �

2� ðDc=cÞ sinðhÞ as shown in Fig. 2, indicating

some stress existed in the films [12]. The curve

fittings gave a residual strain (Dc=c) of 4.3 · 10�3 in

a Bi-2201 film after melt quench; a residual strain

(Dc=c) of 4.1 · 10�3 in a Bi-2212 film after melt

quench and annealing then quenched to room

temperature; a residual strain (Dc=c) of 3.1 · 10�3

in a Bi-2212 film after melt quench and annealingthen furnace cooled to room temperature. It

seemed the residual strain could be relieved a little

bit by annealing and slower cooling to room

temperature, but it could not be eliminated com-

pletely. However, no cracks due to thermal stress

were observed in SEM measurements. How the

stress would affect the mechanical properties of Bi-

2212 films will be studied in the future.Fig. 3 shows the SEM picture for the surface of

a typical Bi-2212 film prepared by melt quench and

annealing process. A dense and melted plate like

structure has developed in the Bi-2212 films from

amorphous/polycrystalline, small grain electrode-

posited precursor films. Although the surface

roughness was rather large, the Bi-2212 grains

appeared to coalesce well, suggesting good grain-boundary properties between Bi-2212 grains.

It was observed that the annealing temperature

at which the Bi-2201 phase was converted to Bi-

2212 phase, and the rate at which the samples were

cooled to room temperature had significant effect

on the superconducting properties of the final

Fig. 3. SEM micrograph of a Bi-2212 film on LaAlO3 single

crystal substrate prepared by electrodeposition and a melt

quenching and annealing process.

-20

-15

-10

-5

0

5

Mag

neti

c M

omen

t (10

-6em

u)

120100806040200

Temperature (K)

103

2468

104

2

468105

2

468

106

J c m

agne

tiza

tion

(A/c

m2)

706050403020100

Temperature (K)

H=0

(a)

(b)

Fig. 4. (a) Temperature dependence of magnetization of a Bi-

2212 film on LaAlO3 single crystal substrate. The applied

magnetic field was 1 mT. (b) Temperature dependence of the

critical current density of a Bi-2212 film measured by magne-

tization curves.

J. Chen, R.N. Bhattacharya / Physica C 399 (2003) 171–177 175

Bi-2212 films. The best Tc and Jc at 4.2 K were

observed in Bi-2212 films annealed at 870 �C for

10 h in and then quenched to room temperature.

Fig. 4(a) shows the temperature dependence ofmagnetization for one of our typical Bi-2212 films,

the superconducting transition temperature Tc is

around 79 K. The critical current density Jc was

measured from the magnetization curves with

Hkc-axis. According to Bean model [13] and for a

sample with orthorhombic shape, the critical cur-

rent density Jc (A/cm2) can be derived using

Jc ¼ 20DM=½að1� a=3bÞ�, where M (emu/cm3) isthe width of the hysteresis loop, a and b (b > a)(cm) are the width and the length of the cross

section of the film perpendicular to the applied

magnetic field, respectively. Jc of 5.8 · 105 A/cm2 at

4.2 K, 0 T, and 44 kA/cm2 at 50 K, 0 T were ob-

served, as shown in Fig. 4(b). Due to strong flux

creep in Bi-2212 superconductors, Jc measured by

magnetization curve is generally 2 or 3 timessmaller than Jc measured by transport measure-

ment. Compared with Jc values previously re-

ported in the literature for thick Bi-2212 films

prepared by non-vacuum techniques on oxides

substrates, our Bi-2212 films showed much im-

proved superconducting properties [2–7].

For many applications, the critical temperature

Tc of Bi-2212 superconductor is a very important

parameter. It is well known that in Bi-2212 su-

perconductor the oxygen excess is not the only

factor which contributes to the optimization ofcritical temperature Tc, and that the cationic

composition also plays a role [14]. The oxygen

content depends on the annealing temperature

T , and the oxygen partial pressure. Normally

quenching technique optimize the oxygen content

and gives higher Tc in Bi-2212 superconductor. Tccould be 94 K in Bi-2212/Ag tapes quenched from

850 �C in air [15]. However, with the nearly samequenching technique, the typical Tc values in our

Bi-2212 films were about 79 K, so we believe the

cationic compositions in our Bi-2212 films were

not optimized. The ICP measurements indicated

-10

-8

-6

-4

-2

0

2

4

6

Mag

neti

c M

omen

t (10

-3em

u)

90 92 96 98 10094H (mT)

Fig. 5. Magnetic field re-penetration loop of a Bi-2212 film at

4.2 K.

176 J. Chen, R.N. Bhattacharya / Physica C 399 (2003) 171–177

that the cationic compositions were about Bi2:11-

Sr2:05Ca1Cu2:12Ox, which is a little off-stoichiome-

try. Further work is now under way to optimize

the cationic composition.

In high-Tc superconductors, the current does

not necessarily circulate the entire sample due to

the weak links at high-angle grain boundaries. The

current-carrying length scale can be estimatedfrom the differential susceptibility dm=dH during

re-penetration of magnetic field [16], which follows

the equation (SI units)

dm=dH ¼ �ðp2RK3Þ=H ð1Þwhere m is the magnetic moment, H is the applied

magnetic field, K is the length scale for current

flow, and H is a geometry factor which is around

11 for a thin film. The differential susceptibility

dm=dH curves in a typical Bi-2212 film at 4.2 K

was measured, as shown in Fig. 5. The calculated

length scale for the current flow was about 2.38

mm, which agreed very well with the sample di-mension. This indicated that the current circulated

through the entire sample, and confirmed the ab-

sence of weak links in the sample.

The improved Jc values in our Bi-2212 films can

be due to several factors. First, the Bi-2212 grains

in our Bi-2212 films are well biaxially aligned,

which eliminates weak link problem in the films.

Although some experiments suggested that in Bi-2212 superconductor which is characterized by

plate-like grains, the current could flow in a ‘‘brick

wall’’ [17] or a ‘‘railway switch’’ [18] pattern to

come around the weak link problem, it is expected

that the critical current density Jc will be improved

if Bi-2212 grains are biaxially aligned. Second, the

SEM pictures showed the Bi-2212 films were very

dense and XRD h–2h scans showed very clean Bi-

2212 peaks, which implied there were very fewporosity and non-superconducting phases existent

in the films to limit current flow. Meanwhile it is

also known that LaAlO3 substrates are heavily

twinned, they may induce twining in Bi-2212 films

and improve the vortex pinning. All of these fac-

tors could significantly improve the Jc value.

Further work needs to be done to clarify which

factor is dominant in improving Jc in our Bi-2212films.

4. Conclusions

Using an electrodeposition technique followed

by a melt quench and annealing process, 1–2 lmthick biaxially textured Bi-2212 films have beengrown on (1 0 0) LaAlO3 single crystal substrates.

The FWHM of omega and phi scan were about

1.7� and 1.1�, respectively. In magnetization mea-

surements, typical Bi-2212 films exhibited Tc around79 K and Jc about 0.58 MA/cm2 (4.2 K, 0 T) and

44 kA/cm2 (50 K, 0 T).

Acknowledgements

This work was supported by the Department of

Energy Superconductivity Program for ElectricPower Systems under contract no. DE-AC36-

996010337. The authors would like to thank Dr.

Philip Parilla for helpful discussions.

References

[1] H. Miao, H. Kitaguchi, H. Kumakura, K. Togano, T.

Hasegawa, T. Koizumi, Physica C 303 (1998) 81.

[2] H.M. Hsu, I. Yee, J. Deluca, C. Hilbert, R.F. Miracky,

L.N. Smith, Appl. Phys. Lett. 54 (1989) 957.

[3] M.J. Naylor, C.R.M. Grovenor, IEEE. Trans. Appl.

Supercond. 9 (1998) 1860.

[4] M. Levinson, S.S.P. Shah, D.Y. Wang, Appl. Phys. Lett.

55 (1989) 1683.

J. Chen, R.N. Bhattacharya / Physica C 399 (2003) 171–177 177

[5] X.L. Wang, P.L. Steger, A. Ritzer, B. Hellebrand, S.

Proyer, E. Stangl, X.Z. Wang, Supercond. Sci. Technol. 8

(1995) 229.

[6] J.R. Spann, L.E. Toth, I.K. Lloyd, M. Kahn, M. Chase,

B.N. Das, T.L. Francavilla, M.S. Osofsky, J. Mater. Res. 5

(1990) 1163.

[7] S. Chen, S. Patel, E. Narumi, D.T. Shaw, D.S. Julien, T.D.

Ketcham, Physica C 218 (1993) 191.

[8] H. Kitaguchi, K. Itoh, T. Takeuchi, H. Kumakura, H.

Miao, H. Wada, K. Togano, T. Hasegawa, T. Koizumi,

Physica C 320 (1999) 253.

[9] R.N. Bhattacharya, M. Paranthaman, Physica C 251

(1995) 105.

[10] J. Chen, R.N. Bhattacharya, R. Padmanabhan, R.D.

Blaugher, Mat. Res. Soc. Symp. Proc. 689 (2002) 113.

[11] B. Heeb, I.J. Gauckler, H. Heinrich, G. Kostorz, J. Mater.

Res. 8 (1993) 2170.

[12] B.D. Cullity, S.R. Stock, Elements of X-ray Diffraction,

Prentice Hall, 2001.

[13] C.P. Bean, Rev. Mod. Phys. 36 (1964) 31.

[14] A.Q. Pham, M. Hervieu, A. Maignan, C. Michel, J.

Provost, B. Raveau, Physica C 194 (1992) 243.

[15] H. Noji, W. Zhou, B.A. Glowacki, A. Oota, Appl. Phys.

Lett. 63 (1993) 833.

[16] M.A. Angadi, A.D. Caplin, J.R. Laverty, Z.X. Shen,

Physica C 177 (1991) 479.

[17] M. Kawasaki, E. Sarnell, P. Chaudhari, A. Gupta, A.

Kussmaul, J. Lacey, W. Lee, Appl. Phys. Lett. 62 (1993)

417;

J.L. Wang, X.Y. Lin, R.J. Kelley, S.E. Babcock,

D.C. Larbalestier, M.D. Vaudin, Physica C 230 (1994)

189.

[18] L.N. Bulaevskii, J.R. Clem, L.I. Glazman, A.P. Malozem-

off, Phys. Rev. B 45 (1992) 2545.