The discovery of superconducting MgB2 (39 K) draws attention to it as a new material for applications based on superconductivity. Many researchers successfully synthesized MgB2 using commercial boron and magnesium. In this study, elementary boron was obtained via an acid leaching process, after reacting B2O3, and Mg in an argon atmosphere at 800°C. Energy Dispersive X-ray Spectroscopy (EDX) results revealed that the powder obtained from the reaction was boron in 92% purity with magnesium as the major impurity. Superconducting MgB2 was produced from this boron and magnesium, in an argon atmosphere at 900°C, by a conventional solid-state reaction. Superconducting MgB2 powders were compressed in a dye to pellets by a hot pressing technique at 500°C and 1 GPa. The microstructural properties of the MgB2 were determined by X-ray Diffraction Spectroscopy, EDX, and Scanning Electron Microscopy techniques. The electrical properties of the fabricated MgB 2 were examined by resistivity measurements in a closed-cycle cryopump system, between 20 and 300 K. The critical temperature (Tc) of the MgB2 pellets was around 32 K

Eğilmez, Mehmet

Kalkancı, M.

Okur, Salih

Yavaş, Mert

Özyüzer, Lütfi

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Fabrication of superconducting MgB2 from boron oxide (B 2O3), and its microstructural and electrical characterization

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Journal of Optoelectronics and Advanced Materials Vol. 7, No. 1, February 2005, p. 407 - 410 
 
 
 
 
 
 
FABRICATION OF SUPERCONDUCTING MgB2 FROM BORON OXIDE (B2O3), 
AND ITS MICROSTRUCTURAL AND ELECTRICAL CHARACTERIZATION 
 
 
M. Yavas, S. Okur*, M. Egilmez, M. Kalkanci, L. Ozyuzer 
 
Department of Physics, Izmir Institute of Technology, Izmir, TR-35430, Turkey 
 
 
The discovery of superconducting MgB2 (39 K) draws attention to it as a new material for 
applications based on superconductivity. Many researchers successfully synthesized MgB2 
using commercial boron and magnesium.  In this study, elementary boron was obtained via 
an acid leaching process, after reacting B2O3, and Mg in an argon atmosphere at 800 oC. 
Energy Dispersive X-ray Spectroscopy (EDX) results revealed that the powder obtained 
from the reaction was boron in 92% purity with magnesium as the major impurity. 
Superconducting MgB2 was produced from this boron and magnesium, in an argon 
atmosphere at 900 °C, by a conventional solid-state reaction. Superconducting MgB2 
powders were compressed in a dye to pellets by a hot pressing technique at 500 °C and  
1 GPa. The microstructural properties of the MgB2 were determined by X-ray Diffraction 
Spectroscopy, EDX, and Scanning Electron Microscopy techniques. The electrical properties 
of the fabricated MgB2 were examined by resistivity measurements in a closed-cycle 
cryopump system, between 20 and 300 K. The critical temperature (Tc) of the MgB2 pellets 
was around 32 K.  
 
(Received December 9, 2004; accepted January 26, 2005) 
 
Keywords: Superconductivity, MgB2, Composites  
 
 
1. Introduction 
 
The discovery, in 2001 of superconductivity at 39 K in the intermetallic compound MgB2 
made this material a new alternative compound for superconductivity applications [1]. The transition 
temperature of 39 K means a higher operating temperature than commercially available 
superconductor like Nb3Sn (18 K) [2]. Mass production of MgB2 at a low cost is important, due to 
its great potential in the market for large and small scale applications. MgB2 has a low fracture 
toughness, like the Nb based conventional superconductors and high temperature superconductors. 
Therefore, it is not a suitable material for large-scale applications based on wire production. A 
commonly used method for manufacturing superconducting wire from a hard and brittle material is 
the powder in tube method (PIT). In this, the superconducting powder is filled into a ductile metal 
sheath and swaged into small diameters by a mechanical process for wire applications. The metal 
matrix composite (MMC) technique can be regarded as an alternative method to the PIT method [3]. 
Metal matrix composites consist of at least two constituents; the metal matrix and an intermetallic 
compound. The metal matrix improves the ductility, hardness and elastic modulus of the new 
compound. The MMC method is a new one for producing bulk superconductors, especially for target 
production for small-scale applications based on thin film production. This method has been used for 
the MgB2 superconductor by using an Al and Mg metal matrix [4,5]. For both the PIT and MMC 
techniques, production of high quality superconducting MgB2 powders in large amounts is essential 
and technologically important, since B2O3 is cheaper and easily available in large amounts than 
elementary boron. Many research groups have successfully fabricated MgB2 using commercial 
boron and magnesium [6].   
                                         
*
 Corresponding author: salihokur@iyte.edu.tr 
M. Yavas, S. Okur, M. Egilmez, M. Kalkanci, L. Ozyuzer 
 
 
408 
In this study, elementary boron was obtained using a solid-state reaction of B2O3 with Mg, 
in an argon atmosphere at 800 oC. The boron obtained, with 92% purity and with Mg as the major 
impurity, was used to produce MgB2. The superconducting and microstructural properties of the 
MgB2 were investigated after compressing in a dye to pellets, by a hot pressing technique at various 
temperatures and a pressure of 1 GPa, by the metal matrix composite method [7]. 
 
 
2. Experimental details 
 
 
 
 
 
 
 
 
 
 
 
                                                    
 
 
Fig. 1. (a) XRD patterns, before and after acid leaching of the powders obtained after the 
reaction of B2O3 and Mg at 800 °C  (b) Variation of  the B purity with  respect to the number  
                                                              of acid leaching steps. 
 
 
B2O3, reduced from H3BO3 with 98.5 % purity (Marmara Research Center, Turkey), and 
commercial Mg (99.999 % purity and - 44 µm mesh size, Alfa Aesar) were used in this study.  The 
B2O3 and Mg were subjected to a solid-state reaction at 800°C in an Ar atmosphere for 1 hour. The 
particle size of the resulted powder at the end of the reaction was reduced in a mortar. Powder XRD 
measurements revealed that the resulted powder consisted of MgO and B, as shown in Fig. 1. Acid 
leaching with 0.5 M hydrochloric acid was applied to the powder, to remove the MgO. High purity 
(93.05 %) B was obtained after such a repetitive process of acid leaching. This method is known as 
the simplest available [8], but less pure boron can be obtained. On the other hand, the major impurity 
is Mg, which is a constituent of MgB2. Although there are a number of methods to reduce B from 
B2O3, these do not provide as high a purity as in the acid leaching method. Superconducting MgB2 
powder was obtained after the produced elementary B and Mg were subjected to a solid-state 
reaction in an Ar atmosphere at 900°C for 2 hours. Pellets with diameter of 10 mm were produced 
by placing the MgB2 powder in a cylindrical metal die and heating at 500 °C at 1 GPa in air, to 
investigate the superconducting and microstructural properties. X-ray Diffraction (XRD), Scanning 
Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDX) techniques were 
used for the microstructural analysis and phase determination. The electrical properties of 
rectangular samples with dimensions 10 × 2 × 0.9 mm were analyzed by resistivity measurements, in 
a closed-cycle cryopump system.  
 
 
3. Results and discussion 
 
XRD patterns of the B + MgO powders after the reaction of B2O3 and Mg at 800°C for 1 h in 
Ar atmosphere, before and after acid leaching, are shown in Fig. 1a. The peaks before acid leaching 
were reduced to the noise level, showing only amorphous boron after the acid leaching process. This 
shows that all phases except MgO and B in the sediment disappeared. EDX analysis (Fig. 1b) was 
carried out in order to detect the amount and purity of the boron in the amorphous powder. This 
increased with the number of acid leaching steps, as shown. The amount of boron in the initial 
output product was 6.97 %. It increased to 16 % after the 1st acid leaching and was above 80 % after 
6th step. Finally, after the 13th step, a purity of 93% was reached,and the Mg impurity was around         
20 30 40 50 60 70 80
XR
D
 
Co
u
n
ts
 2θ
Before Acid Leaching
After Acid Leaching
(a)
0
20
40
60
80
100
0 5 10 15
B K
O K
Mg K
W
ei
gh
t P
er
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n
ta
ge
Acid Leaching Steps
(b)
W
ei
gh
t P
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Fabrication of superconducting MgB2 from boron oxide (B2O3), and its microstructural and electrical… 
 
 
409
5 %. The 5% Mg impurity is not important, since the final goal was to obtain superconducting MgB2 
using another solid-state reaction of the amorphous boron powder with high purity commercial Mg. 
Reducing the amount of Mg by 5% in the solid-state reaction compensated for the impurity.  
For the production of MgB2, elemental boron was reacted with pure Mg of 325 mesh at          
900 °C in an Ar atmosphere, for 2 hours. Since Mg vaporizes at this temperature, mixing Mg and B 
in a stoichiometric ratio would cause the amount of Mg in resulting MgB2 to be less than its 
stoichiometric value. This situation may degrade the superconducting properties [9]. For this reason, 
10% of excess Mg was added to conserve the stoichiometry after the reaction.  
 
0
1
2
3
4
20 30 40 50 60 70 80
No
rm
.
 
XR
D
 
In
te
n
si
ty
2 θ
MgB
2
 - produced at IYTE
MgB
2
- Alfa Aesar
Mg - Alfa Aesar
 
   Fig. 2. Normalized XRD patterns of the produced MgB2.    
 
 
The normalized XRD patterns of commercial Mg, MgB2 and the produced MgB2 are shown 
in Fig. 2. The patterns for the commercial MgB2 and the produced MgB2 are normalized to 1 and 
shifted vertically. The produced and commercial MgB2 peaks match exactly, except for a Mg peak 
present at 2θ = 63.6 as an impurity.  
 
 
 
 
 
 
 
 
 
 
   
 
 
 
 Fig. 3. SEM images of the produced MgB2 (a) as a powder, (b) as a pellet. 
 
 
SEM images of the produced MgB2 in powder form and in a pellet compressed at 1 GPa at 
500 °C for 2 hours are shown in Figs. 3a and 3b respectively. The average particle size was smaller 
for the pellet material, due to pressure and annealing. The small particle size increases the number of 
grain boundaries, to increase the critical current density. This is also an important superconducting 
parameter of the material, to improve the pinning properties [10]. 
(a) 
500 nm 
4.00 kV 3.0   50000x  Magn 
 
(b) 
500 nm 
4.00 kV 3.0   50000x  Magn 
 
M. Yavas, S. Okur, M. Egilmez, M. Kalkanci, L. Ozyuzer 
 
 
410 
Rectangular samples were cut from the pellets, to measure the resistivity between 20 and 
300 K. A resistivity versus temperature plot is given in Fig. 4, with the resistivity value normalized 
to that at 50 K. The superconducting transition occurs at 32 K. The measured density of the 
superconducting MgB2 pellet was 1.99 g/cm3, which is smaller than the theoretical value of  
2.62 g/cm3. This shows that a large amount of voids is present in the material. This high porosity 
ratio causes a low connectivity between the MgB2 grains. The low transition temperature and 
broadened transition interval indicate the low grain connectivity due to the porosity. 
 
  
 
 
 
 
 
 
 
 
 
 
 
 
Fig. 4. Temperature dependence of the resistivity of the produced MgB2. 
 
 
4. Conclusions 
 
The XRD, EDX, SEM and temperature dependent resistivity results revealed that 
superconducting MgB2 is successfully produced from the reaction of Mg and B reduced from B2O3. 
The produced MgB2 pellet showed a superconducting transition at about 32 K.  
 
 
Acknowledgement 
 
This research is supported by TUBITAK (Scientific and Technical Research Council of 
Turkey), with the project number TBAG-2215. 
 
 
References 
 
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  [3]  M. Egilmez, A. Gunel, S. Okur, M. Tanoglu, L. Ozyuzer, Key Engineering Materials 266,         
1197 (2004).  
  [4]  A. Sharoni, O. Millo, G. Leitus, S. Reich, J. Phys. Condens. Matter. 13, L503 (2001).  
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  [6]  D. K. Aswal, S. Sen, A. Singh, T. V. Chandrasekhar, J. C. Vyas, L. C. Gupta, S. K. Gupta, 
        V.C. Sahni, Physica C 363, 149 (2001). 
  [7]  M. Egilmez “Electrical, Microstructural and Mechanical Properties of MgB2/Mg Metal Matrix  
        Composites”, M. S. Thesis, May 2004, Izmir Institute of Technology, Turkey. 
  [8]  Kirk-Othmer Encyclopedia of Chemical Technology, Ed. H. F. Mark, Vol. 3, Interscience  
        Publishers, John Wiley and Sons, Inc, New York, 1967. 
  [9]  R. A. Ribeiro, S. L. Bud’ko, C. Petrovic, P. C. Canfield, Physica C 382, 194–202 (2002).  
[10] Y. Zhao, F. Feng, D. X. T. Machi, C. H. Cheng, K. Y. Nakao, N. Chikumoto, Physica C, 378- 
        381, 122 (2002).  
0
0.2
0.4
0.6
0.8
1
1.2
20 25 30 35 40 45 50
500 oC
2 hours
1GPaρ
 
(Τ
)  
/  
ρ 
(50
 
K)
T (K)


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Fabrication of superconducting MgB2 from boron oxide (B 2O3), and its microstructural and electrical characterization

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