Irradiation effects on MgB2 bulk samples and formation of columnar defects in high-Tc superconductor

doi:10.1016/S0921-4534(02)01206-6

Physica C: Superconductivity

Volume 382, Issue 1, 15 October 2002, Pages 104-107

https://doi.org/10.1016/S0921-4534(02)01206-6 Get rights and content

Abstract

Irradiation effects on MgB₂ were studied to investigate the pinning property of this new material. It is pointed out that flux pinning at grain boundaries is important for MgB₂ bulk samples. We confirmed this with electron irradiation. Degradation of inter-grain coupling by electron irradiation resulted in degradation of pinning properties. Heavy ion irradiation was also accomplished on MgB₂. Columnar defects introduced by the irradiation improve pinning in higher field regions. Concerning the formation of columnar defects in high-T_c superconductors, we conducted a systematic analysis of Bi2212 single crystal with different irradiation ions. Applying the time dependent line source model to our results, only a third of the electronic losses contributed to the formation of columnar defects.

Introduction

A new superconducting material MgB₂ has the highest transition temperature of conventional inter-metallic superconductors [1]. The working temperature is almost 40 K, and helium-free applications using refrigerators are expected. Furthermore, this material consists of light atoms and has an advantage for industrial usage. This new material, however, shows a rapid decrease of superconductivity in magnetic fields. Improvements of the pinning properties are necessary for practical applications. In this work, we investigated irradiation effects on this material. Columnar defects are well known as effective pinning centers, but the mechanism of their formation is not clear. We also investigated the formation mechanism of the columnar defects in high-T_c superconductors.

Section snippets

Irradiation on MgB₂

Synthesis of MgB₂ was accomplished by a solid state reaction. High purity powders of Mg and B were used for the synthesis. They were mixed well and ground, then pressed into a small rod (8 mm in diameter and 80 mm in length) for the sintering process. The rod was placed into a stainless tube, and the tube was put into a tube furnace. The sample was sintered at 1193 K for 2 h. Throughout the sintering process, high purity argon gas was flowed in the furnace to avoid unexpected reactions, such as

Formation mechanism of columnar defects in high-T_c superconductors

As mentioned above, columnar defects are effective for improving the pinning properties. When a bombarding high-energy ion passes through the high-T_c sample, it loses its energy, exciting electrons within a narrow cylindrical region along its trajectory. The excited high-energy electrons then transfer their energies to the lattice. If the transferred energies are large enough, the lattice of the target will melt partially along the ion trajectories and columnar defects will be formed. Thus

Conclusion

Irradiations on MgB₂ bulk samples have been accomplished. Electron irradiation affects the inter-grain coupling. Heavy ion irradiation introduces columnar defects in MgB₂ and the irreversibility field is improved. Columnar defect formation in Bi2212 is considered using the TDLS model. The effective energy deposition for columnar defect formation is much smaller than S_e.

Acknowledgements

The authors would like to express their acknowledgement to Dr. Izui for fruitful discussions.

References (10)

J. Nagamatsu
Nature
(2001)
Y. Takano
App. Phys. Lett.
(2001)
Y. Bugoslavsky
Nature
(2001)
J.R. Thompson
App. Phys. Lett.
(1992)
J.F. Ziegler
Handbook of Stopping Cross Section for Energetic Ions in All Elements
(1980)

There are more references available in the full text version of this article.

Cited by (30)

Magnetic levitation force performance of benzil added bulk MgTi<inf>0,06</inf>B<inf>2</inf> superconductors
2021, Cryogenics
MgB₂ superconductors can be proposed as a good candidate for Maglev systems due to their superior structural and superconducting properties. Besides, magnetic levitation and guidance force properties of these superconductors should be increased for commercial applications of Maglev systems. Therefore, the critical current density and magnetic levitation and guidance force properties of MgTi_0.06B₂ superconducting samples were investigated in this study, at measurement temperatures of 20 K and 25 K, depending on benzil (C₁₄H₁₀O₂) addition in different adding amounts of 0, 1.5, 3, 4.5, 6 and 9 wt%. In addition to benzil, nanometer-sized silver particles were added to the samples in a constant ratio of 2 wt% to enhance the structural properties. The maximum critical current density values increased from 67 kA/cm² for pure sample to 92 kA/cm² with benzil adding amount of 3 wt% at T = 20 K, indicating an increment of 37%. In addition, the levitation force in ZFC (zero field cooling) regime and the guidance force in FC (field cooling) regime at 20 K increased at an amount of 46% and 57%, respectively, with 3% benzil addition. It can be said that the suitable amount of benzil addition as a carbon source produces additional pinning centres inside the MgTi_0.06B₂ and thus structural properties, critical current density and therefore, magnetic levitation properties of the samples are increased.
Investigation on superconducting and magnetic levitation force behaviour of excess Mg doped-bulk MgB<inf>2</inf> superconductors
2019, Cryogenics
A series bulk samples of MgB₂ + x wt% of Mg (x = 0, 5, 10, 15, 20 and 30) were fabricated by solid state reaction method. The structural and electromagnetic properties of MgB₂ samples were studied using X-ray diffraction (XRD), scanning electronic microscope (SEM), electrical resistivity (R-T), magnetic hysteresis (M-H), magnetic levitation (F_z) force and lateral force (F_x) measurements. The maximum repulsive and attractive force values of 15 wt% of excess magnesium MgB₂ sample compared to the other samples imply that the intergranular connection between grains enhanced while pore and microcrack density decreased which brings an increase in the values of the radius of a shielding current loop (r) and the critical current density (J_c). It was determined that to obtain the enhancement of the micro and macro structure properties, causing to the higher critical current density, and the maximum levitation and lateral force values, the optimum excess magnesium content was 15 wt% into sample. It is thought that an addition of 10–15% excess magnesium can be tried for spark plasma or other methods –as a further research– and the results showed a potential to guide the researchers to study on the material-fabrication and the magnetic bearing system.
Superconductivity in MgB<inf>2</inf> irradiated with energetic protons
2016, Physica C: Superconductivity and its Applications
Citation Excerpt :
Current transport in superconductors is related to the formation of efficient pinning centers that should prevent the motion of flux lines. In the race for creation of artificial pinning centers, particle irradiation was successfully used, mainly in high temperature superconductors, MgB2 included [1–14]. Particle irradiation creates vacancies and interstitials (Frenkel pairs-FP) in excess of equilibrium concentration both in the magnesium and boron sublattices.
A series of MgB₂ samples were irradiated with protons of 11.3 and 13.2 MeV. Magnetization data shows an insignificant reduction of the critical temperatures but a continuous decrease of the Meissner fraction with increasing fluence or energy. All samples show a consistent improvement of the critical current density compared to the virgin sample and an increase of the pinning energy at high fields as resulted from relaxation data.
Effect of field cooling heights on the levitation force of pure and starch/polystyrene/MWCNT added bulk MgB<inf>2</inf> superconductors
2014, Physica C: Superconductivity and its Applications
A series of MgB₂ pellets with and without addition of carbon from different sources (viz. starch, polystyrene and carbon nanotubes) have been synthesized by solid state reaction under argon atmosphere. XRD analysis indicates a decrease in lattice parameters of MgB₂ with addition of starch, polystyrene (PS) and MWCNT and confirms substitution of carbon in boron sites. The presence of nanosized carbon inclusions between the grain boundaries in the present set of samples is evident in TEM photographs. Resistivity data confirms a decrease in superconducting transition temperature (T_c0) for MgB₂ doped with starch/PS/MWCNT. The effect of different field cooling heights (H_IFC) at 20 K on maximum levitation force (F_MLF) and maximum attractive force (F_MAF) of pure MgB₂ and MgB₂ doped with starch/PS/MWCNT have been investigated. Except for MWCNT, doping of starch and PS in MgB₂ is found to improve F_MLF and F_MAF and the best result is obtained for MgB₂ doped with 1 wt.% PS. Levitation force measured as a function of decreasing initial field cooling height indicates exponential dependence of both maximum levitation force (F_MLF) and maximum attractive force (F_MAF). However, the gap distance between PM and the sample (H_0AF and H_MAF) corresponding to maximum attractive force (F_MAF) and zero attractive force (F_0AF) varies linearly and their difference remains constant. This constancy in (H_MAF − H_0AF) is understood in terms of constant reduction rate of magnetic flux density between H_0AF and H_MAF.
The role of starch doping on the superconducting properties of MgB <inf>2</inf>
2014, Cryogenics
Citation Excerpt :
Thus in order to make MgB2 suitable for useful applications, enhancement of both critical current density (Jc) and upper critical field (Hc2) is essential. Chemical doping [2–5], irradiation [6] and thermo-mechanical processing [7] are some of the processes, which are found to be effective for enhancing the upper critical field (Hc2) and critical current density (Jc) of MgB2 pellets. Several reports on doped MgB2 system [2–5,8–12] confirm that pure carbon, as well as, carbon available from different sources (viz. B4C [9], SiC [9], graphene [10], CNT [11], polymer [12], carbohydrates [2] etc.) are reported to be very effective additive for enhancing Jc and Hc2 of MgB2.
The effect of different amount of starch addition on structural and superconducting properties of superconducting MgB₂ has been discussed. The samples are synthesized by conventional solid reaction method. XRD analysis confirms that carbon, which is produced during synthesis due to decomposition of starch, is substituted in the B sites. High resolution transmission electron microscope (HRTEM) picture infers the presence of large number of nanosized precipitates (size ∼10–20 nm) in starch doped MgB₂ pellets. Superconducting transition temperature (T_c₀) of MgB₂ (∼38 K) decreases due to the addition of starch. The critical current density (J_c) of starch added MgB₂ samples, however, shows significant improvement in whole field range, especially at high magnetic fields. MgB₂ added with 2 wt.% of starch gives the best performance amongst the investigated samples and at 20 K displays ∼42 times enhancement in J_c under 4 T field compared to that for pure MgB₂. The field dependence of the critical current density (J_c) of starch added MgB₂ is explained fairly well in terms of collective pinning theory. An excellent scaling of the reduced critical current density, Jn(=J_c/J_c(0)) and the reduced field h_n (=H/H₀) is observed for both pure and starch added MgB₂ polycrystalline pellets at different temperatures, where J_c(0) and H₀ are the fitting parameters obtained from collective pinning model. However, the normalized pinning force density (F_P/F_p_(max)) of starch added samples does not display any scaling, but shows an excellent correspondence with modified Dew–Hughes expression. The presence of anisotropy and grain orientation is thought to be responsible for the absence of scaling of normalized pinning force density in starch added MgB₂ pellets.
Critical current density of MgB<inf>2</inf> superconductor with (Bi,Pb)-2223 addition
2014, Journal of Alloys and Compounds
Polycrystalline MgB₂ pellets with and without addition of superconducting Bi_1.8Pb_0.26Sr₂Ca₂Cu₃O₁₀₊_x powder has been synthesized by solid reaction. The effect of (Bi,Pb)-2223 addition on structural and critical current density of MgB₂ superconductor has been investigated. XRD data reveals no substitution for Mg or B. The superconducting transition temperature (T_c₀) of MgB₂ (∼37.97 K) remains almost invariant with 2223 addition. Temperature dependence of the normal state electrical resistivity of 2223 added MgB₂ is well explained by modified Rowell’s model and it suggests that 2223 addition in MgB₂ marginally influences the percentage connectivity and intragrain residual resistivity. Critical current density (J_c) has been estimated at 4, 10, 20 and 30 K from M–H curves using Bean’s model. MgB₂ sample with 1 wt.% of 2223 addition gives the best performance and display nearly two times enhancement in J_c compared to that of pure MgB₂ in the field range between 0 and ±6 T. Our analysis confirms that the observed magnetic field dependence of J_c of the present system is explained well in terms of the collective pinning model. Using the best fitted parameters (J_c (0) and H₀) of collective pinning model, an excellent scaling is established between the reduced critical current density, J_n (=J_c/J_c (0)) and the reduced field h_n (=H/H₀) at different temperatures for both pure and 2223 added MgB₂ polycrystalline pellets. It is also confirmed that δT_c type pinning dominates in pure MgB₂ and for 2223 added MgB₂ major contribution originates from δl type pinning at lower temperatures.

View all citing articles on Scopus

View full text

Irradiation effects on MgB2 bulk samples and formation of columnar defects in high-Tc superconductor

Abstract

Introduction

Section snippets

Irradiation on MgB2

Formation mechanism of columnar defects in high-Tc superconductors

Conclusion

Acknowledgements

Nature

App. Phys. Lett.

Nature

App. Phys. Lett.

Handbook of Stopping Cross Section for Energetic Ions in All Elements

Irradiation effects on MgB₂ bulk samples and formation of columnar defects in high-T_c superconductor

Irradiation on MgB₂

Formation mechanism of columnar defects in high-T_c superconductors