Physica C: Superconductivity and its applications 548 (2018) 31–39

Contents lists available at ScienceDirect

Physica C: Superconductivity and its applications

journal homepage: www.elsevier.com/locate/physc

Enhancement in superconducting properties of Bi 2

Sr 2

Ca 1

Cu 2

O 8 + θ

(Bi-2212) by means of boron oxide additive

Hesam Fallah-Arani a , d , Saeid Baghshahi a , ∗, Arman Sedghi a , Daniela Stornaiuolo

b , c , Francesco Tafuri b , c , Nastaran Riahi-Noori d

a Department of Materials Engineering, Faculty of Engineering, Imam Khomeini International University, Qazvin, Iran b Dipartimento di Fisica “E. Pancini”, Università di Napoli “Federico II”, Complesso Universitario di Monte S. Angelo-Via Cintia, 80126 Napoli, Italy c CNR-SPIN UO, Napoli, Italy d Non-Metalic Materials Research Group, Niroo Research Institute (NRI), Tehran, Iran

a r t i c l e i n f o

Article history:

Received 16 October 2017

Revised 4 January 2018

Accepted 15 January 2018

Available online 31 January 2018

Keywords:

Bi-2212

B 2 O 3 Sintering temperature

Phase evolution mechanism

Superconducting properties

Grain morphology

a b s t r a c t

By using a solid state method, Bi 2 Sr 2 Ca 1 Cu 2 O 8 + θ (Bi-2212) polycrystalline samples were synthesized with

the addition of boron oxide additive, with the aim of improving the performance of this compound for

large scale applications. As the first step, the parameters for the solid state method, in particular sintering

temperature, were optimized in order to obtain pure Bi-2212 samples with an optimal microstructure.

Then, based on this optimization, the properties of the Bi 2 Sr 2 Ca 1 Cu 2 B x O y samples with x = 0.05, 0.1, and

0.2 were studied using several characterization techniques. It was found that the sample having x = 0.05

showed a magnetic hysteresis loop larger than that of the pure Bi-2212 sample and a critical current

density value of 3.71 × 10 5 A/cm

2 , comparable to the best results found in the literature for Bi-2212,

while preserving well-stacked and oriented grains.

© 2018 Elsevier B.V. All rights reserved.

1

h

o

o

t

t

b

(

m

b

p

2

t

A

b

B

l

i

p

m

s

c

p

p

f

i

o

t

t

t

(

m

m

[

i

h

0

. Introduction

The potential applications of high-T c superconducting ceramics

ave attracted numerous research activities. Extensive researches

n superconductor properties have been conducted, with the aim

f fabrication and optimization of superconductive properties of

hese materials. However, there are still difficulties in the fabrica-

ion process of such ceramics [1,2] .

Among all classes of superconductors, cuprates are still the

est candidate for different applications, because of their high T c above 77 K) and critical magnetic field (above 200 T). In the Bis-

uth Strontium Calcium Copper Oxide or BSCCO system, a mem-

er of cuprates family, three different superconducting phases are

resent, with Bi 2 Sr 2 Ca n–1 Cu n O 2n + 4 + θ general formula, where n = 1,

, and 3. The n value indicates the number of CuO 2 layers in

he unit cell, forming Bi-2201, Bi-2212 and Bi-2223 phases [3,4] .

mong these phases, Bi-2212, with critical transition temperatures

etween 80 and 96 K, is the most stable and easiest to fabricate.

i-2212 shows a large compositional stability region and exhibits

ayered structure with strong anisotropic properties. Therefore, it

∗ Corresponding author.

E-mail address: baghshahi@eng.ikiu.ac.ir (S. Baghshahi).

p

r

ttps://doi.org/10.1016/j.physc.2018.01.012

921-4534/© 2018 Elsevier B.V. All rights reserved.

s suitable in many applications such as high-field magnets, if it is

roperly processed to achieving good grain morphology [5–7] .

In the literature, the effect of substituting/adding several ele-

ents in Bi-based superconductors has been studied and as a con-

equence the improvement of critical temperature (T c ) and critical

urrent density (J c ) values have been observed [8–16] . The mor-

hological characteristics have a key role in determination of the

roperties of the superconductors. Grain alignment and coupling

acilitate formation of the superconducting phase and the increase

n the J c values. Therefore, a detailed study of grain morphology is

f paramount importance to optimize the superconducting proper-

ies of bulk polycrystalline tapes and wires [17,18] .

To improve the microstructure of Bi-system superconductor ma-

erials, various fabrication routes such as laser floating zone, elec-

rically assisted laser floating zone, solid-state reaction, sol–gel

micro-emulsion-based), co-precipitation, glass–ceramic and poly-

er matrix method have been used, by which highly oriented

aterials such as single crystals and rods have been produced

19–22] . Although, in recent years, highly oriented superconduct-

ng materials have attracted the attention of many scientists, yet

olycrystalline bulk materials still remain important for the prepa-

ation of superconducting tapes and wires [16,23–27] .

32 H. Fallah-Arani et al. / Physica C: Superconductivity and its applications 548 (2018) 31–39

0 200 400 600 800 1000

DTADDTA

)u.a(AT

D

Temperature (°C)

Exo

86

88

90

92

94

96

98

100

TG

TG (%

)

a

b

c

Fig. 1. TGA/DTA/DDTA curves for Bi-2212. a) DTA, b) TG and c) DDTA.

3

s

c

s

3

D

f

d

p

fi

t

d

C

t 2 2

0 200 400 600 800 1000

DTADDTA

Temperature (°C)

94

95

96

97

98

99

100

TG

)u.a(AT

D TG (%

)Exo b

a

c

Fig. 2. TGA/DTA/DDTA curves for calcined Bi-2212. a) DTA, b) TG, c) DDTA.

Among the mentioned techniques, the solid-state method has

several advantages such as: low cost of starting materials, good re-

peatability, easy availability of the reactants and simplicity. There-

fore, it is still one of the most used techniques for manufactur-

ing the BSCCO system [28] . The sintering temperature, calcination

condition, pelletization pressure, milling, oxygen pressure, degree

of texturing, synthesis atmosphere and grain boundary conditions

are essential factors in solid state route. Among these parameters,

the influence of sintering temperature is particularly significant for

improving of grains coupling and grains morphology, leading to en-

hancement of the superconducting properties [29–32] .

In the present work, the use of B 2 O 3 additive to promote super-

conductive properties of BSCCO system is reported. Small amounts

of B 2 O 3 heve been reported to promote growth of the Tl-2212 and

Tl-2223 phases in Tl-based superconductors [33] . B 2 O 3 is a sinter-

ing aid that has a melting point lower than the general sintering

temperature of BSCCO. It is effective in stability, grain growth and

grain alignment of Bi-2223 phase and can act as a catalyst to ac-

celerate formation of Bi-2223. Therefore, it can form more liquid

phase, which results in the creation of ion diffusion paths required

to form superconductor phases. However, a detailed analysis of the

influence of B 2 O 3 in phase formation and superconducting prop-

erties of Bi-2212 is missing in the literature. The present study is

aimed to investigate the effects of the sintering temperature and

optimum boron oxide content on the properties of Bi-2212 ceramic

materials were synthesized through the solid state reaction tech-

nique.

2. Experimental procedure

2.1. Materials and methods

In this study, the conventional solid state reaction method was

used to prepare both Bi-2212 samples and samples with the chem-

ical composition Bi 2 Sr 2 Ca 1 Cu 2 B x O y (x = 0.05, 0.1, and 0.2). To this

aim analytical grade Bi 2 O 3 , SrCO 3 , CaCO 3 , CuO and B 2 O 3 (all from

Sigma-Aldrich Chemicals with a purity > 99.9%) were used as the

starting powders. The homogeneous mixtures of powders were cal-

cined at 800 °C for 24 h in a box furnace with a 5 °C/min heating

rate. The powders were grinded after calcination. Then, the mix-

ture was pressed into pellets of 28 mm diameter and about 2 mm

thick under pressure of 5 ton/cm

2 and then sintered at 820, 830

and 840 °C for 100 h in air atmosphere.

2.2. Characterizations

The thermal behavior of the precursor mixtures was investi-

gated by differential and gravimetric thermal analysis (TGA/DTA)

between 25–10 0 0 °C with the heating rate of 10 °C/min

−1 under

static air atmosphere. Crystal structure and phases were studied

by X-ray diffraction (XRD) using an X’Pert Pro MPD (PANalyti-

cal) diffractometer equipped with Cu–K α radiation ( λ= 1. 5418 A).

The Rietveld analysis was performed on the diffraction patterns

by using Diffraction (MAUD) program. Crystal structures, quan-

tity phases, Lattice parameter, correct atoms placement, occupancy

number and average crystalline size were computed. Field emis-

sion scanning electron microscopy (FESEM, Tescan Mira3) equipped

with an Energy-dispersive X-ray spectroscopy (EDS) system were

employed for morphological and microstructural investigations. El-

emental mapping analysis was used to investigate the material

composition. The magnetic measurements were carried out on

samples using a SQUID magnetometer. The Bean’s equation was

used to calculate critical current density (J c ) of the samples from

the M-H hysteresis loops.

. Result and discussion

Firstly, the optimization of the process parameter for Bi2212

amples was carried out. After establishing the best preparation

onditions for this phase, additives were introduced to improve the

uperconducting properties of the compound.

.1. Optimization of the sintering temperature of Bi-2212 compound

Fig. 1 shows the TGA/DTA/DDTA profiles for the Bi2212 powder.

erivative differential thermal analysis (DDTA) curve was plotted

or easier detection of the peaks accompanying the DTA curve.

The DTA profile ( Fig. 1 (a)) of Bi2212 powder displays three en-

othermic peaks located at 384, 639 and 791 °C, and peaks ap-

eared centered at approximately 415, 795 and 838 °C, as con-

rmed from the DDTA profile.

The first endothermic peak near 384 °C may be attributed to

he crystallization of CaO or Cu 2 O [34] . The second broader en-

othermic peak implies that some intermediate phases including

a 2 CuO 3 and CuO starts to form at about 600 °C, and crystalliza-

ion of Bi Sr CuO x (Bi-2201 phase) occurs at about same tempera-

H. Fallah-Arani et al. / Physica C: Superconductivity and its applications 548 (2018) 31–39 33

Fig. 3. XRD patterns of the Bi-2212 sintered at different temperatures for 100 h.

Fig. 4. XRD patterns of Bi-2212 sintered at 840; (...) the Rietveld analysis, (__) ex-

perimental data, (-.-) subtracted pattern. (For interpretation of the references to

color in the text, the reader is referred to the web version of this article.)

t

t

T

2

t

B

b

a

o

w

w

a

s

o

7

D

i

a

Fig. 5. Crystal structure of Bi-2212 obtained from MAUD software.

b

t

2

p

t

o

2

w

s

a

c

b

d

a

o

s

p

a

ure [35] . The third endothermic peak near 800 °C is attributed to

he gradually transformation of the mentioned phases to Bi-2212.

he reaction is summarized by the following equation [36] :

Bi 2 Sr 2 CuO x + (Sr, Ca) CuO 2 → 2Bi 2 Sr 2 CaCu 2 O x (1)

This equation shows that the Bi-2212 phase may be formed via

he Bi-2201 phase by inserting Cu–O and CaO layers. Therefore,

i-2201 is thermodynamically and crystallographically more sta-

le than Bi-2212 phases. The mentioned endothermic peaks are

ccompanied by weight losses. Indeed the TGA curve ( Fig. 1 (b))

f Bi-2212 synthesized by solid state shows approximately 13%

eight loss with three weight loss stages. In the first stage, a small

eight loss ( ∼2%) is observed in the temperature range 25–440 °C,

ttributed to the decomposition of mixed carbonates. The second

tage ( ∼4.5% weight loss) from 440–760 °C is due to the formation

f Bi-2201 phase. Finally, the third stage ( ∼4.5% weight loss) above

60 °C, accompanied by endothermic peak recorded in DTA and

DTA curves, can be attributed Bi-2212 phase formation. As shown

n Fig. 2 (a), the thermal behavior of the Bi-2212 calcined powder

t 800 °C for 24 h was examined by DTA. From these data, it can

e concluded that some intermediate phases have been formed in

he calcined powder. It is noteworthy that the Ca-poor phase (Bi-

201) formed from the Bi-rich phase and CuO, as well as the Cu-

oor phase (Bi 2 Sr 3 −x Ca 1 + x O 7 ) remain detectable up to 800 °C. Be-

ween 820 and 840 °C, complete melting of the mentioned phases

ccurs to develop the final Bi-2212 phase. The middle of the Bi-

212 phase formation peak was measured from DTA curve and it

as occurred at about 830 °C. Therefore, to reach the optimum re-

ults, 820, 830 and 840 °C were selected as sintering temperatures.

Fig. 3 shows the XRD patterns of the Bi-2212 samples sintered

t 820, 830 and 840 °C for 100 h. In the present research, the main

rystallized phases (Bi-2212 and Bi-2201) and some weak peaks

elonging to Bi 14 Ca 5 Sr 7 O 33 , Bi 2 Ca 1 + x Sr 3 −X O 7 , CaCO 3 and SrCO 3 are

etected. Excellent agreement is observed between the intensity

nd peak positions of the Bi-2212 and Bi-2201 phases with those

f reported in the literature [1] . Moreover, a clear change in the

harpness of the peaks is observed by increasing the sintering tem-

erature from 820 to 840 °C, confirming that the sintering temper-

ture is an important factor in increasing the formation of Bi-2212.

34 H. Fallah-Arani et al. / Physica C: Superconductivity and its applications 548 (2018) 31–39

Table 1

T c values determined from M–T measurements, lattice parameters and volume of unit cell for all samples (x = 0.0–0.2).

Boron oxide content (x) T c (K) Volume fracture of Bi-2212

phase (%)

Unit-cell parameter of a–b

axes ( A)

Unit-cell parameter of

c-axis ( A)

Volume of unit cell ( A 3 )

x = 0.0 81.7 ∼86 5.397(4) 30.683(6) 893.872(3)

x = 0.05 83.2 ∼89 5.397(3) 30.683(5) 893. 836(3)

x = 0.1 80.6 ∼80 5.397(5) 30.683(5) 893. 902(5)

x = 0.2 79.3 ∼78 5.397(4) 30.683(4) 893.866(5)

Table 2

The refinement of atomic positions and occupancy

of atoms in the Bi-2212 (Sintered at 840 °C) phase.

Atoms X Y Z Occupancy

Bi 0.0 0.0 0.197 0.99

Sr 0.49 0.51 0.108 0.99

Ca 0.51 0.50 0.0 1.00

Cu 0.0 0.0 0.056 0.99

O(1) 0.0 0.50 0.049 0.98

O(2) 0.50 0.49 0.198 0.99

O(3) 0.0 0.0 0.120 1.00

s

e

m

s

e

c

b

i

t

g

w

B

a

t

t

B

B

t

I

i

o

p

p

d

t

m

r

B

s

H

s

s

B

t

g

a

m

w

c

t

m

s

N

m

t

e

g

The XRD result for the Bi-2212 sintered at 840 °C was refined

with the MAUD software, based on Rietveld’s method, for the

structural analysis, exact atom position, occupancy number and

lattice parameter calculations. Fig. 4 exhibits the measured and cal-

culated XRD patterns of Bi-2212 sintered at 840 °C and their dif-

ferences. There is little difference between the XRD pattern be-

fore and after refinement due to good compatibility between the

theoretical and experimental structures. Based on these results, it

can be deduced that sintering of Bi-2212 at 840 °C leads to forma-

tion of the Bi-2212 superconductor with reduced impurity phases.

The volume fraction of the desired phase is about 86% with space

group symmetry I4/mmm.

Moreover, after the Reitveld refinements, the lattice parame-

ters of a ≈b = 5.3974 A and c = 30.6836 with the unit cell volume of

V = 893.8723 A

3 are obtained, as listed in Table 1 . The listed values

are in agreement with data reported in Ref. [8,37] . Table 2 shows

the result of the refined atomic positions and occupancy in the Bi-

2212 sintered at 840 °C. It can be easily seen that all atoms are

located properly in the unit cell, as suggested in Ref. [38] . The re-

sulting structure is shown in Fig. 5 , which is in good agreement

with the theoretical structure.

Finally, the microstructure and grain morphology of Bi-2212

samples were investigated using FESEM. Fig. 6 shows the FESEM

images of the fractured surface of Bi2212 samples sintered at dif-

ferent temperatures (820, 830 and 840 °C) for 100 h. All the pic-

tures show the typical microstructure of Bi-2212 superocductors,

with flaky layers of plate-like grains [39] . However, it is clear from

the micrographs that the small changes in the sintering tempera-

ture (20 °C) had widely influenced the microstructural evolution of

the samples, indeed microstructure, grain connectivity and grain

size of the samples tend to change with increasing the sintering

temperature. From Fig. 6 (a), it can be seen that the sintering tem-

perature of 820 °C is insufficient for the metal cations to diffuse

and form pure the Bi2212 phase. The grain size of Bi-2212 sintered

at this temperature is small and grains are poorly connected to

each other. On the other hand, comparing Fig. 6 (b) and (c), it is

obvious that the samples sintered at 840 °C have a smoother sur-

face with the fine connectivity between the superconducting grains

and larger plate-like grain sizes.

3.2. Effect of B 2 O 3 additive

Fig. 7 shows the XRD patterns of the samples with different

boron oxide content. The inset in the figure shows their corre-

ponding low angle XRD patterns (2 ≤ 2 θ ≤ 10 °), in which the pres-

nce of the Bi-2212 phase is clearly visible. From these patterns, it

ay be concluded that the major peaks belong to Bi-2212, while

ome peaks positioned at 2 θ≈29 °, 36 ° and 38 ° indicate the pres-

nce of Bi-2201. As seen in Table 1 , the amount of Bi-2212 phase

hanged with boron oxide content. It reached a maximum for

oron content x = 0.05 and then started to decrease (for boron ox-

de content x = 0.1 and 0.2). The maximum in the Bi-2212 con-

ent, in x = 0.05 sample, is probably due to the increasing of inter-

ranular contacts. B 2 O 3 aids in formation of a liquid phase, which

ill facilitate the transformation of Bi-2201 into Bi-2212 ( Eq. (2) )

i-2201 + (Sr, Ca) CuO 2 → Bi-2212 (2)

Hence, it can be inferred that the boron oxide interacts with the

lkaline earth elements from the original powder, producing stron-

ium and calcium borate. A further increase of boron content leads

o the formation of borates, which cantributes to decomposition of

i-2212:

i −2212 + B 2 O 3 → CaO. B 2 O 3 + SrO. B 2 O 3 + CuO + Bi −2201 (3)

Fig. 8 depicts our proposed mechanism for the phase evolu-

ion of Bi-2212, determined from STA, XRD and the literature [1] .

t is obvious that the Bi-(2212) formation process starts with ox-

de and carbonate powders. The low T c phase (Bi-2201) and sec-

ndary phases form first and are then transformed to the Bi-2212

hase. Above 700 °C, the decomposition and sintering of bismuth

hases (Bi 2 Sr 3 −x Ca 1 + x O 7 and Bi-2201) occur and Bi-2212 phase is

etected.

The crystal symmetry of the samples was recognized as pseudo-

etragonal, and the lattice parameters were determined by XRD

easurements and the MAUD software. These results are summa-

ized in Table 1 . It should be noted that the coupling between

iO–BiO layers in the crystallographic unit cell of Bi-2212 is weak,

o the lattice constant in the c axis in Bi-2212 can easily change.

owever, all the samples have nearly similar c lattice constants. As

hown in Table 1 , the lattice parameters “a” and “c” remain con-

tant when boron oxide content changes. Therefore, it seems that

3 + is not intercalated into the Bi-2212 crystal lattice.

Fig. 9 shows the FESEM micrograph of the fractured surface of

he x = 0.05 and x = 0.2 samples. The FESEM images show that the

rains in the samples with lower B 2 O 3 content are well stacked

long their a–b plane, are larger and have no porosity. Further-

ore, the crystallinity, grains connectivity and grain alignment are

orsened greatly in x = 0.2 sample. It should be noted that grains

onnectivity and grain alignment are very important in BSCCO sys-

em and other high-T c superconductors, having a key role in the

agnetic and electrical properties.

The local distribution of the elemental concentrations in the

amples was also studied using quantitative EDS analysis ( Table 3 ).

umerical result showed that all the elements (except for B) re-

ained approximately constant, confirming that B

3 + was not in-

ercalated into the Bi-2212 layered structure. Fig. 10 shows the el-

mental distribution mappings result obtained from the nano-scale

rains of the Bi 2 Sr 2 Ca 1 Cu 2 B 0.1 O θ sample, demonstrating that all

H. Fallah-Arani et al. / Physica C: Superconductivity and its applications 548 (2018) 31–39 35

2 μm

(a)

2 μm

(b)

2 μm

(c)

Voids

Fig. 6. FESEM images of the samples sintered at a) 820, b) 830, and c) 840 °C for 100 h .

Fig. 7. XRD patterns of the Bi 2 Sr 2 Ca 1 Cu 2 B X O δ with x = 0.05, 0.1 and 0.2. The inset shows the low-angle XRD patterns of the samples.

36 H. Fallah-Arani et al. / Physica C: Superconductivity and its applications 548 (2018) 31–39

Fig. 8. General mechanism of phase evolution in solid-state route.

Fig. 9. FESEM images of the samples with different percentages of B 2 O 3 a) x = 0.05 and b) x = 0.2.

Fig. 10. Elemental distribution mappings for x = 0.1.

H. Fallah-Arani et al. / Physica C: Superconductivity and its applications 548 (2018) 31–39 37

Table 3

Local elemental distributions in the superconducting materials

studied in this work.

Component Line Concentration (wt%)

x = 0 x = 0.05 x = 0.1 x = 0.2

Bi M α 46.42 44.62 45.21 44.67

Sr L α 15.94 15.85 15.26 15.21

Ca K α 4.01 4.78 4.08 4.21

Cu K α 15.42 14.91 14.28 14.56

O k α 18.21 17.83 18.24 17.84

B k α – 2.01 2.93 3.51

Fig. 11. Temperature dependence of susceptibility for various samples in the ap-

plied field of 10 Oe.

t

[

a

p

p

o

n

w

s

i

c

c

s

o

o

g

1

c

o

l

p

b

s

[

a

T

o

Fig. 12. Magnetic hysteresis curves obtained for all samples at 10 K.

Fig. 13. Critical current densities of all samples at 10 K, as a function of the applied

field.

s

J

s

u

o

s

c

i

w

1

t

N

i

o

w

s

S

r

he elements were homogeneously distributed in the scanned area

39] .

The transport properties of the samples containing boron oxide

dditives were also investigated. Fig. 11 shows the temperature de-

endence of the real component of susceptibility for all of the sam-

les in the magnetic field of 10 Oe. For the sample with x = 0.2, the

nset of the critical temperature, T c , corresponding to the diamag-

etic transition, was around 80 K. The sharp drop in the samples

ith x = 0 and x = 0.05 indicates good quality and homogeneity of

amples. The T c values slightly changed as a function of boron ox-

de content. Initially, T c increased with increasing boron oxide con-

entration up to 0.05, and then further boron oxide addition de-

reased T c . The best T c value is 83.2 K for x = 0.05 sample. The re-

ults are in good agreement with the XRD pattern and the FESEM

bservations discussed previously, which indicated that 0.05 boron

xide sample possess the highest fraction of the Bi-2212 phase to-

ether with the best connectivity of grains.

Fig. 12 illustrates the magnetic hysteresis loops measured at

0 K and ±2 T applied magnetic fields for the studied samples. It

an be clearly seen that the magnetization values and the width

f the hysteresis curves depended on boron content. The M-H

oop obtained for x = 0.05 was larger than that obtained for the

ure sample. This general behavior of the hysteresis cycles can

e attributed to parameters such as grain size, grain morphology,

econdary phases and the amount of HTS phase in the samples

40] . In addition, similar symmetry in M-H loops shape can be

ttributed to similar superconducting phases in studied samples.

hese results are in good agreement with the previously discussed

bservations.

The Bean’s equation was used to determine critical current den-

ity (J c ) of the samples from the hysteresis loops at 10 K [41] :

c = 30

�M

d

(4)

Where J c is the magnetization current density in amperes per

quare centimeter. �M = M

+ −M

− is measured in electromagnetic

nits per cubic centimeter and d is the thickness of the sample.

Fig. 13 shows intragranular J c for all samples, as a function

f the applied magnetic field, at 10 K, obtained from the hystere-

is cycles. As seen in the graph, Jc values depended on the B 2 O 3

oncentration and the applied magnetic field. There is a decrease

n intra-granular J c values with an increase in the magnetic field,

hich is a typical behavior in HTSs. The highest J c was obtained at

0 K for the sample with x = 0.05, but J c decreased with increasing

he boron in the system in the samples with x = 0.1 and x = 0.2.

ote that, J c in BSCCO system depends the temperature of sinter-

ng, stoichiometry of oxygen, doping/substitution, grain morphol-

gy, etc [29,42] . The higher intragranular J c values for the sample

ith x = 0.05, compared with the sample with x = 0.0, are the re-

ult of the improvement of grain morphology observed in the FE-

EM images attributed to the presence of the secondary or impu-

ity phases which are formed due to boron addition in low con-

38 H. Fallah-Arani et al. / Physica C: Superconductivity and its applications 548 (2018) 31–39

Table 4

Comparison of superconducting properties in various investigations in Bi-2212.

Sample Additive Synthesis method T c (K) J c (10 5 A/cm

2) Ref.

Bi-2212 B 2 O 3 Solid state 83.2 3.71 Present work

Bi-2212 Ag Sol–gel 103.86 3.22 [11]

Bi-2212 Er Glass ceramic 84.0 1.29 [44]

Bi-2212 Without Solid state 72.3 8.20 [32]

Bi-2212 Without Sol–gel 89.8 1.33 [29]

Bi-2212 K–Na Solid state 94.1 9.50 [40]

tent. These phases can act as flux pinning centers, which results in

a strong increase in Jc values. In samples with low content of B 2 O 3 ,

the flux pinning was strong and fluxes penetrated to the samples

as vortices. As shown in Fig. 13 , J c values initially increased up to a

certain magnetic field ( ∼0.2 T) and then gradually decreased with

increasing the applied magnetic field, implying that 0.2 T is the

first penetration magnetic field. By the increasing of magnetic field,

vortex motion in the studied samples started, which resulted in a

deterioration in the magnetic configuration of fluxes [43] .

Table 4 reports a comparison between the results shown in

the present work and values of Tc and J c reported in the litera-

ture for several types of Bi-2212 based samples. From this table,

it is possible to conclude that the Bi-2212 samples with B 2 O 3 ad-

ditive (x = 0.05) prepared in this study exhibited values of T c and

J c which are comparable with the best data in the literature. We

point out that the high J c values reported in Ref. [32] are proba-

bly due to the very high pelletization pressure used in that work,

Moreover, although, the best T c and J c values for Bi-2212 samples

were obtained by addition of alkali elements, the weak intergran-

ular coupling resulting shown in Ref. [40] is likely to cause poor

mechanical properties of these samples.

4. Conclusion

In this study, the influence of sintering temperature and boron

oxide addition on the properties of Bi-2212 superconductors was

investigated and verified by both theoretical calculation and exper-

imental results. The XRD and FESEM/EDS analyses proved the for-

mation of the desired phase of Bi-2212, accompanied by relatively

low amounts of secondary phases, resulting in the improvement of

the intragranular J c values. The magnetic measurements revealed

that the highest T c and J c values corresponded to the sample with

the boron oxide content of x = 0.05. Furthermore, the hysteresis

loop obtained for the sample with x = 0.05 had the highest surface

area. By increasing the boron content the loops became narrower.

Therefore, the boron oxide content of x = 0.05 was the optimum

amount for obtaining the best superconductor properties.

Refrences

[1] D.C. Green, R. Boston, S. Glatzel, M.R. Lees, S.C. Wimbush, J. Potticary, W. Oga-sawara, S.R. Hall, On the mechanism of cuprate crystal growth : the role of

mixed metal carbonates, Adv. Funct. Mater. 25 (2015) 4700–4707, doi: 10.1002/adfm.201501058 .

[2] S.R. Foltyn, L. Civale, J.L. MacManus-Driscoll, Q.X. Jia, B. Maiorov, H. Wang,M. Maley, Materials science challenges for high-temperature superconducting

wire, Nat. Mater. 6 (2007) 631–642, doi: 10.1002/adma.201004625/full .

[3] M.A. Nane, O. Özçelik, B. Sotelo, A. Madre, Effect of Na substitution on su-perconducting properties of Bi-2212 ceramics prepared by Sinter-Forged pro-

cess, J. Eur. Ceram. Soc. 37 (2017) 1007–1012, doi: 10.1016/j.jeurceramsoc.2016.09.035 .

[4] H. Fallah-arani, S. Baghshahi, D. Stornaiuolo, F. Tafuri, D. Massarotti, N. Riahi-noori, The influence of heat treatment on the microstructure, flux pinning and

magnetic properties of bulk BSCCO samples prepared by sol–gel route, Ceram.Int. 44 (2018) 5209–5218, doi: 10.1016/j.ceramint.2017.12.128 .

[5] F.M. Costa, N.M. Ferreira, S. Rasekh, A.J.S. Fernandes, M.A. Torres, M.A. Madre,

J.C. Diez, A. Sotelo, Very large superconducting currents induced bygrowth tailoring, Cryst. Growth Des. 15 (2015) 2094–2101, doi: 10.1007/

978- 3- 642- 19971- 4 . [6] Y.-F. Lv, W.-L. Wang, H. Ding, Y. Wang, Y. Ding, R. Zhong, J. Schneeloch, G.D. Gu,

L. Wang, K. He, S.-H. Ji, L. Zhao, X.-J. Zhou, C.-L. Song, X.-C. Ma, Q.-K. Xue,

Electronic structure of the ingredient planes of the cuprate superconductor

Bi 2 Sr 2 CuO 6 + δ: a comparison study with Bi 2 Sr 2 CaCu 2 O 8 + δ , Phys. Rev. B. 93(2016) 140504, doi: 10.1103/PhysRevB.93.140504 .

[7] Y.-F. Lv, W.-L. Wang, J.-P. Peng, H. Ding, Y. Wang, L. Wang, K. He, S.-H. Ji,R. Zhong, J. Schneeloch, G.-D. Gu, C.-L. Song, X.-C. Ma, Q.-K. Xue, Mapping

the electronic structure of each ingredient oxide layer of high-tc cuprate su-

perconductor Bi 2 Sr 2 CaCu 2 O 8 + δ , Phys. Rev. Lett. 115 (2015) 237002, doi: 10.1103/PhysRevLett.115.237002 .

[8] B. Özçelik, O. Nane, A. Sotelo, M.A. Madre, Effect of Yttrium substitution on su-perconductivity in Bi-2212 textured rods prepared by a LFZ technique, Ceram.

Int. 42 (2016) 3418–3423, doi: 10.1016/j.ceramint.2015.10.137 . [9] S.H. Pan, E.W. Hudson, K.M. Lang, H. Eisaki, S. Uchida, J.C. Davis, Imag-

ing the effects of individual zinc impurity atoms on superconductivity in

Bi 2 Sr 2 CaCu 2 O 8 + x , Nature 403 (20 0 0) 746–750, doi: 10.1038/35001534 . [10] N.K. Saritekin, M. Pakdil, E. Bekiroglu, G. Yildirim, Examination of effective nu-

cleation centers for flux pinning of vortices and optimum diffusion annealingtemperature for Au-diffusion-doped Bi-2212 polycrystalline compound, J. Al-

loys Compd. 688 (2016) 637–646, doi: 10.1016/j.jallcom.2016.07.203 . [11] F. Kahraman, A. Sotelo, M.A. Madre, J.C. Diez, B. Ozkurt, S. Rasekh, Relation-

ship between microstructure and superconducting properties in hot-pressed

Bi-2212/Ag ceramic composites, Ceram. Int. 41 (2015) 14924–14929, doi: 10.1016/j.ceramint.2015.08.029 .

[12] M.A . Madre, A . Sotelo, J.C. Diez, Effect of Yb substitution in Bi-2212 ceram-ics prepared by laser floating zone technique, J Mater. Sci. Mater. Electron. 26

(2015) 5761–5766, doi: 10.1007/s10854-015-3134-9 . [13] N.A .P.V. V Zhghamadze, D.I.D.V.A . Aliyev, Enhancement of (Bi, Pb)-

2223 HTS formation by boron-doping, (2010) 1241–1243. doi: 10.1007/

s10948-010-0808-7 . [14] S. Yu , Y. Okuda , T. Hashimoto , Y. Suemune , Effect of B 2 O 3 addition on the for-

mation of single high-T c phase in the (Bi, Pb) 2 Sr 2 Ca 2 Cu 3 O y superconductor,Phys. C. 224 (1994) 363–367 .

[15] E.A . Eremina, A .V Kravchenko, P.E. Kazin, Y.D. Tretyakov, M. Jansen, Influenceof boron-containing dopants on the formation of superconducting phase in the

system Bi(Pb)-Sr-Ca-Cu-O, Supercond. Sci. Technol. 11 (1998) 223–226, doi: 10.

1088/0953-2048/11/2/009 . [16] X.L. Wang, H.K. Liu, S.X. Dou, J. Horvat, D. Millikon, G. Heine, W. Lang,

H.M. Luo, S.Y. Ding, Superconductivity and flux pinning in Y and heavily Pbcodoped Bi-2212 single crystals, J. Appl. Phys. 89 (2001) 7669–7671, doi: 10.

1063/1.1356055 . [17] R. Jayavel, T. Mochiku, S. Ooi, K. Hirata, Vapour–liquid–solid (VLS) growth

mechanism of superconducting Bi-Sr-Ca-Cu-O whiskers, J. Cryst. Growth. 229(2001) 339–342, doi: 10.1016/S0022- 0248(01)01177- 0 .

[18] E. Cecchetti, P.J. Ferreira, J.B. Vander Sande, A model for the texture develop-

ment in BSCCO high- T c superconductors, Supercond. Sci. Technol. 13 (20 0 0)1270–1278, doi: 10.1557/JMR.1999.0368 .

[19] M. Suzuki, S. Shimakage, H. Kawakami, A. Saito, A. Takeda, Characteristics ofMOD Bi-2212 thin films on r-cut sapphire with CeO 2 buffer layer, IEEE Trans.

Appl. Supercond. 23 (2013) 7501404–7501404, doi: 10.1109/TASC.2013.2248191 .[20] M.A. Diez, J.C. Sotelo, A. Rasekh, S. Amaveda, H. Torres, M.A. Bosque,

P. Chocarro, C. Madre, Composite Bi-2212/Ag superconductors grown by laser

travelling floating zone at low rates, J. Supercond. Nov. Magn. 28 (2015) 415–418, doi: 10.1007/s10948- 014- 2758- y .

[21] M.F. Carrasco, V.S. Amaral, R.F. Silva, F.M. Costa, Electrical assisted laser float-ing zone (EALFZ) growth of BSCCO-2212 superconducting fibres, Appl. Surf. Sci.

257 (2011) 5283–5286, doi: 10.1016/j.apsusc.2010.11.068 . [22] A.J. Stollenwerk, N. Hurley, B. Beck, K. Spurgeon, T.E. Kidd, G. Gu, Manipula-

tion of subsurface carbon nanoparticles in Bi 2 Sr 2 CaCu 2 O 8 + δ using a scanning

tunneling microscope, Phys. Rev. B. 91 (2015) 1–5, doi: 10.1103/PhysRevB.91.125425 .

[23] S. Safran, E. K, H. Ozturk, M. Alp, M. Akdogan, E. Asikuzun, Superconductingand mechanical properties of the bulk Bi(Pb)SCCO system prepared via solid

state and ammonium nitrate precipitation methods, Phys. B. 472 (2015) 34–40, doi: 10.1016/j.physb.2015.05.006 .

[24] H. Yang, M.B. Shahzad, X. Yu, Y. Qi, Influence mechanism of secondary gel

technique on Bi-2212 superconducting phase : gel model simulation and verifi cation, Mater. Des. 99 (2016) 115–119, doi: 10.1016/j.matdes.2016.03.051 .

[25] X. Lu, T. Wang, Y. Qi, Crystalline characteristics and superconducting proper-ties of Bi2212 thin films by Pechini sol–gel method : effect of heating rate

on the film growth, J. Sol–Gel Sci. Technol. 77 (2016) 100–108, doi: 10.1007/s10971-015-3834-x .

[26] I. Hamadneh, System prepared via conventional solid state and coprecipitation

methods, 465 (2007) 207–210. doi: 10.1016/j.physc.2007.03.445 .

H. Fallah-Arani et al. / Physica C: Superconductivity and its applications 548 (2018) 31–39 39

[

[

[

[

[

[

[

[

[

[

[

[

[27] A. Tampieri, G. Celotti, S. Lesca, G. Bezzi, T.M.G La Torretta, G. Mag-nani, Bi(Pb)-Sr-Ca-Cu-O-2223-superconductor-prepared-by-improved-sol–gel-

technique, J. Eur. Ceram. Soc. 20 (20 0 0) 119–126, doi: 10.1016/S0955-2219(99)00158-2 .

28] M. Pakdil, E. Bekiroglu, M. Oz, N.K. Saritekin, G. Yildirim, Role of preparationconditions of Bi-2223 ceramic materials and optimization of Bi-2223 phase in

bulk materials with experimental and statistical approaches, J. Alloys Compd.673 (2016) 205–214, doi: 10.1016/j.jallcom.2016.02.232 .

29] D. Sharma, R. Kumar, V.P.S. Awana, DC and AC susceptibility study of sol–gel

synthesized Bi 2 Sr 2 CaCu 2 O 8 + d superconductor, Ceram. Int. 39 (2013) 1143–1152,doi: 10.1016/j.ceramint.2012.07.038 .

30] R. Chen, Y.L. Stevens, 2223 phase formation in Bi(Pb)-Sr-Ca-Cu-0: II, the roleof temperature- reaction mechanism, J. Am. Ceram. Soc. 75 (1992) 1150–1159,

doi: 10.1111/j.1151-2916.1992.tb05552.x . [31] O. Ozturk, D. Yegen, M. Yilmazlar, A. Varilci, C. Terzioglu, The effect of cool-

ing rates on properties of Bi 1.7 Pb 0.35 Sr 1.9 Ca 2.1 Cu 3 O y superconductors produced

by solid-state reaction method, Phys. C Supercond. Appl. 451 (2007) 113–117,doi: 10.1016/j.physc.20 06.11.0 03 .

32] I.S. Aytekin, M. Ersin, B. Özkurt, Physical, magnetic and mechanical propertiesof Bi-2212 superconductors prepared by high pelletization pressure, J. Mater.

Sci. Mater. Electron. 26 (2015) 1799–1805, doi: 10.1007/s10854- 014- 2613- 8 . [33] H. Topal, U. Ozkan, Effects of B 2 O 3 addition on the properties of melt-

processed YBa 2 Cu 3 O 7 −δ , Supercond. Sci. Technol. 18 (2005) 82–86, doi: 10.1088/

0953-2048/18/1/013 . 34] E. Stojanovic, D. Biljana, V.V. Skorokhod, M. Nikolic, Advanced Science and

Technology of Sintering, Springer Science & Business Media, 2011, doi: 10.1007/978- 1- 4419- 8666-5 .

[35] F.H. Chen, H.S. Koo, T.Y. Tseng, Effect of Ca 2 PbO 4 additions on the formationof the 110 K phase in Bi-Pb-Sr-Ca-Cu-O superconducting ceramics, Appl. Phys.

Lett. 58 (1991) 637–639, doi: 10.1063/1.104553 .

36] R. Wesche, Physical Properties of High-Temperature Superconductors, Wiley,2015, doi: 10.1002/9781118696644 .

[37] B. Özçelik, O. Nane, A. Sotelo, H. Amaveda, M.A. Madre, Effect of Na substitu-tion and Ag addition on the superconducting properties of Bi-2212 textured

materials, J. Mater. Sci. Mater. Electron. 28 (2017) 6278–6283, doi: 10.1007/s10854- 016- 6309- 0 .

38] D.A. Cardwell, D.S. Ginley (Eds.), Handbook of Superconducting Materials, Tay-lor & Francis, 2002, doi: 10.1201/9781420034202 .

39] R. Siavash, S. Masudy-panah, M. Jalali, G. Kia, L. Goh, A. Dolati, M. Ghorbani,

Sunlight driven photoelectrochemical light-to-electricity conversion of screen-printed surface nanostructured TiO 2 decorated with plasmonic Au nanopar-

ticles, Electrochim. Acta. 219 (2016) 386–393, doi: 10.1016/j.electacta.2016.10.022 .

40] M.E. Kir, B. Özkurt, M.E. Aytekin, The effect of K-Na co-doping on the formationand particle size of Bi-2212 phase, Phys. B Condens. Matter. 490 (2016) 79–85,

doi: 10.1016/j.physb.2016.03.016 .

[41] O. Kizilaslan, G. Kirat, M.A. Aksan, Magnetic relaxation behavior in theBi 2 Sr 2 Ca 2 Cu 3 −x Mo x O 10 + δ system fabricated by glass-ceramic technique, J.

Magn. Magn. Mater. 384 (2015) 186–191, doi: 10.1016/j.jmmm.2015.02.045 . 42] B. Özkurt, Enhancement in superconducting transition temperature and J c

values in Na-doped Bi 2 Sr 2 Ca 1 Cu 2x Na x O y superconductors, J. Mater. Sci. Mater.Electron. 24 (2013) 2426–2431, doi: 10.1007/s10854- 013- 1113-6 .

43] K. Murai, Õ. Jun, Y. Fujii, J. Shaver, G. Kozlowski, Magnetic flux pinning and

flux jumps in polycrystalline MgB 2 , Cryogenics (Guildf). 45 (2005) 415–420,doi: 10.1016/j.cryogenics.20 05.03.0 01 .

44] G. Kirat, O. Kizilaslan, M.A. Aksan, Effect of the Er-substitution on critical cur-rent density in glass-ceramic Bi 2 Sr 2 Ca 2 Cu 3 −x Er x O 10 + δ superconducting system,

Ceram. Int. 42 (2016) 15072–15076, doi: 10.1016/j.ceramint.2016.06.171 .