Muralidhar Miryala | Shibaura Institute of Technology (original) (raw)

Papers by Muralidhar Miryala

Journal of Physics D: Applied Physics

Although the fascinating effect of superconductivity was discovered more than 100 years ago, only... more Although the fascinating effect of superconductivity was discovered more than 100 years ago, only a few low-temperature superconductors, especially Nb3Sn and NbTi, have reached everyday-life use. After the discovery of superconductivity in MgB2 in 2001, a boom appeared in interest in employing MgB2 in commercial applications, facilitated by simple crystallographic structure, high critical temperature, low-cost raw ingredients, simple and fast production, and other advantages for moderate temperature applications. It only lacks high flux pinning and good mechanical performance. In this review, the implications of manufacturing procedures on the superconducting properties, crystal and electronic structure of MgB2 are discussed. The advantages and drawbacks of various manufacturing processes will be presented, as well as the ways how to improve MgB2 superconducting performance. The impact of oxygen reduction, elements doping, the introduction of defects and additives, and the effect of...

Open Archive Toulouse Archive Ouverte (University of Toulouse), May 23, 2018

Journal of Alloys and Compounds

Superconductors are used in a wide range of applications, each requiring specific magnetic field ... more Superconductors are used in a wide range of applications, each requiring specific magnetic field strengths to operate at their best. The optimal magnetic strength is determined by the superconducting properties, such as critical current density (J c). In this study, we propose that by using different compositions of liquid source, the superconducting properties and microstructure of bulk superconductors can be optimized according to their intended application. Ba 3 Cu 5 O 8 , Yb 2 O 3 :BaCuO 2 :CuO (1:10:6) and Er123 + Ba 3 Cu 5 O 8 (1:1) were tested as liquid sources, and ternary single-grain bulks (Gd, Y, Er) Ba 2 Cu 3 O y were produced using the top-seeded infiltration growth process (TSIG) in the air. Microstructural analysis with a scanning electron microscope revealed that using Er123 +Ba 3 Cu 5 O 8 (1:1) as the liquid source resulted in a significant reduction in the 211 secondary phase particle size, with a mean particle size reduction of 43.13% compared to the conventional Ba 3 Cu 5 O 8. Each composition of the liquid source had a significant impact on the superconducting properties, and the Er123 + Ba 3 Cu 5 O 8 liquid source yielded the highest J c of 81.91 kA/cm 2 in selffield and 28.29 kA/cm 2 at 1 T for (Gd, Y, Er)−123 ternary system. These results emphasize the importance of liquid sources in controlling the final microstructure, which ultimately determines the performance of the bulk ternary (Gd, Y, Er)−123 system produced by the IG process.

Coatings

This article reports the effect of a nanoscale addition of TiO2 on the structure and superconduct... more This article reports the effect of a nanoscale addition of TiO2 on the structure and superconducting parameters of the high-temperature superconductor YBa2Cu3O7-δ (Y123). Polycrystalline compounds of Y123 with different percentages of TiO2, x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0, were fabricated using the thermal treatment method. An analysis using X-ray diffraction confirmed the formation of Y123 phases for all composite samples. Field-emission scanning electron microscopy (FESEM) analysis revealed the growth of grain size and decrease in porosity, with a sign of partial melting of grains for the samples with TiO2 addition. The magnetic and electric transport properties were investigated using AC susceptibility measurement and the four-probe method, respectively. It was observed that the superconducting transition temperature, Tc-onset, for a pure sample determined by ACS and 4PP was 95.6 K and 95.4 K, respectively. These values were found to decrease with the addition of TiO2, while...

Journal of Alloys and Compounds, 2023

Superconductors are used in a wide range of applications, each requiring specific magnetic field ... more Superconductors are used in a wide range of applications, each requiring specific magnetic field strengths to operate at their best. The optimal magnetic strength is determined by the superconducting properties, such as critical current density (J c). In this study, we propose that by using different compositions of liquid source, the superconducting properties and microstructure of bulk superconductors can be optimized according to their intended application. Ba 3 Cu 5 O 8 , Yb 2 O 3 :BaCuO 2 :CuO (1:10:6) and Er123 + Ba 3 Cu 5 O 8 (1:1) were tested as liquid sources, and ternary single-grain bulks (Gd, Y, Er) Ba 2 Cu 3 O y were produced using the top-seeded infiltration growth process (TSIG) in the air. Microstructural analysis with a scanning electron microscope revealed that using Er123 +Ba 3 Cu 5 O 8 (1:1) as the liquid source resulted in a significant reduction in the 211 secondary phase particle size, with a mean particle size reduction of 43.13% compared to the conventional Ba 3 Cu 5 O 8. Each composition of the liquid source had a significant impact on the superconducting properties, and the Er123 + Ba 3 Cu 5 O 8 liquid source yielded the highest J c of 81.91 kA/cm 2 in selffield and 28.29 kA/cm 2 at 1 T for (Gd, Y, Er)−123 ternary system. These results emphasize the importance of liquid sources in controlling the final microstructure, which ultimately determines the performance of the bulk ternary (Gd, Y, Er)−123 system produced by the IG process.

Journal of Magnetism and Magnetic Materials, 2013

MnAl is a promising rare-earth free permanent magnet for technological use. We have examined the ... more MnAl is a promising rare-earth free permanent magnet for technological use. We have examined the effects of consolidation by back-pressure, assisted equal channel angular extrusion processing on mechanically-milled, gas-atomized Mn-46% at. Al powder. X-ray diffraction showed both that the extruded rod consisted mostly of metastable τ phase, with some of the equilibrium γ 2 and β phases, and that it largely retained the as-milled nanostructure. Magnetic measurements show a coercivity of ≤4.4 kOe and a magnetization at 10 kOe of ≤40 emu/g. In addition, extrusions exhibit greater than 95% of the theoretical density. This study opens a new window in the area of bulk MnAl magnets with improved magnetic properties for technological use.

Coatings

A revisited study of perovskite-based manganite La0.67Sr0.33MnO3 (LSMO) deposited onto corning-gl... more A revisited study of perovskite-based manganite La0.67Sr0.33MnO3 (LSMO) deposited onto corning-glass (CG) substrates is reported here. The LSMO films were fabricated with RF sputtering with different deposition times, varying from 60 to 180 min, resulting in films with thicknesses of 35.0–109.7 nm. Rietveld refinements of the XRD spectrum showed that the samples exhibited hexagonal structures with a space group of R-3c (167) and remained unmodified structures. Clusters of monolayer growth were observed from the morphologies of the films. Interestingly, the average particle size obtained with an AFM perceived an insignificant variation of 31.7–35.6 nm despite the film thickness increment. Optical, electrical and magnetic properties were studied, as particle-size variation usually has a notable contribution to changes in these properties. It was found that the optical band gap (Eg) was in direct variation with the deposition time due to enhanced thickness and surface roughness. The te...

Scientific Reports, 2020

Ca2Fe2O5 (CFO) is a potentially viable material for alternate energy applications. Incorporation ... more Ca2Fe2O5 (CFO) is a potentially viable material for alternate energy applications. Incorporation of nitrogen in Ca2Fe2O5 (CFO-N) lattice modifies the optical and electronic properties to its advantage. Here, the electronic band structures of CFO and CFO-N were probed using Ultraviolet photoelectron spectroscopy (UPS) and UV-Visible spectroscopy. The optical bandgap of CFO reduces from 2.21 eV to 2.07 eV on post N incorporation along with a clear shift in the valence band of CFO indicating the occupation of N 2p levels over O 2p in the valence band. Similar effect is also observed in the bandgap of CFO, which is tailored upto 1.43 eV by N+ ion implantation. The theoretical bandgaps of CFO and CFO-N were also determined by using the Density functional theory (DFT) calculations. The photoactivity of these CFO and CFO-N was explored by organic effluent degradation under sunlight. The feasibility of utilizing CFO and CFO-N samples for energy storage applications were also investigated th...

Journal of Physics: Conference Series

The large coherence length of MgB2 material allows large defects such as grain boundaries to act ... more The large coherence length of MgB2 material allows large defects such as grain boundaries to act as strong pinning centres. As an alternative to the high-cost commercial nano precursors, we used a novel ultra-sonication technique to refine a cheap rough boron precursor and avoid the use of the expensive commercial nano amorphous boron powder. Recent novel low-cost ultra-sonication technique proved to improve the critical current density, J c, of MgB2. Here, we discuss the consequences of ultra-sonication duration in hexane medium on the boron precursor as well as the superconducting properties of MgB2 bulks. XRD revealed small peaks corresponding to unreacted Mg. First derivative of susceptibility was plotted as a function of temperature to explain the Tc,onset and ΔTc. J c was found to grow if the MgB2 bulk was prepared of boron ultra-sonicated for up to 30 minutes and then reduced with further boron ultra-sonication (60 minutes). SEM micrographs showed that boron powder subjected ...

Coatings, 2022

The development of high-temperature superconductor (HTS) YBa2Cu3O7~δ (Y123) bulks in industrial a... more The development of high-temperature superconductor (HTS) YBa2Cu3O7~δ (Y123) bulks in industrial applications were established years ago. It is one of the developments that currently attracts great attention especially in transportation, superconductor cables and wires. This study is focused on the preparation of the Y123 bulk superconductors by the thermal treatment method due to the promising ways to develop high-quality Y123 superconductors with its simplicity, low cost, and relatively low reaction temperature used during the process. Y123 were added with graphene nanoparticles (x = (0.0–1.0) wt.%). Samples were then characterized by X-ray diffraction (XRD) analysis, field-emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), and alternating current susceptibility (ACS). It was found that Y123 confirmed that the majority of phases in all the XRD patterns was the orthorhombic crystal structure and the Pmmm space group with secondary phases belon...

Superconductor Science and Technology, 2020

Critical current density, J c, in superconductors is strongly connected with size of defects in t... more Critical current density, J c, in superconductors is strongly connected with size of defects in the material. Frequently, the smaller defects, the higher J c. In this work, we tried to reduce the size of cheap commercial boron precursor powder using high energy ultra-sonication in ethanol media. The resulting powder was then utilized in synthesizing bulk MgB2 via sintering at 775 °C. Effect of boron powder ultra-sonication on superconducting properties of the bulk MgB2 was studied and discussed. SEM of ultra-sonicated boron showed fine particles with sharp edges (high-energy surfaces), irregular shapes and clustering of fine particles occurred for longer ultra-sonication durations. XRD proved a high quality of MgB2 with only small traces of MgO. Around 36% improvement in Jc at 20 K and Tc close to 39 K were observed in MgB2 bulk prepared with boron ultra-sonicated for 15 min. Microstructure studies showed numerous nanometre sized MgB2 grains in the bulk. Other bulks (made of boron u...

IEEE Transactions on Applied Superconductivity, 2020

IEEE Transactions on Applied Superconductivity, 2019

We compare the temperature and field dependence of the critical current densities of high-Tc supe... more We compare the temperature and field dependence of the critical current densities of high-Tc superconductor materials intended for various bulk applications like trapped-field magnets. This comprises bulk samples of YBa2Cu3Ox (YBCO), MgB2 and iron-based materials, including also various versions of the YBCO compound like melt-textured ones, infiltration-growth processed ones, and YBCO foams. Critical current densities and flux pinning forces were obtained from magnetization loops measured using Quantum Design SQUID and PPMS systems with applied magnetic fields of up to ±9 T. The obtained data are compared to each other with respect of the optimal cooling temperature possible using modern cryocoolers. Furthermore, we plot the temperature dependencies of the critical current densities versus the normalized temperature t = T /Tc. This enables a direct judgement of the performance of the material in the trapped field applications.

Nanomaterials

In situ MgB2 superconducting samples were prepared by using the spark plasma sintering method. Th... more In situ MgB2 superconducting samples were prepared by using the spark plasma sintering method. The density of the obtained bulks was up to 95% of the theoretical value predicted for the material. The structural and microstructural characterizations of the samples were investigated using X-ray diffraction and SEM and correlated to their superconducting properties, in particular their critical current densities, Jc, which was measured at 20 K. Extremely high critical current densities of up to 6.75 × 105 A/cm2 in the self-field and above 104 A/cm2 at 4 T were measured at 20 K, indicating that vortex pinning is very strong. This property is mainly attributed to the sample density and MgB2 nanograins in connection to the presence of MgO precipitates and areas rich in boron.

Journal of Superconductivity and Novel Magnetism, 2021

We successfully refined a cheap commercial boron powder by means of high-energy ultra-sonication ... more We successfully refined a cheap commercial boron powder by means of high-energy ultra-sonication and utilized it in synthesis of bulk MgB2. Rietveld phase analysis of X-ray diffraction pattern revealed completely formed MgB2 with a low amount of MgO. MgB2 bulk prepared of boron ultra-sonicated in ethanol for 15 min showed self-field Jc of around 300 kA/cm2 at 20 K without any compromise in Tc (~39 K). Pinning analysis based on Dew-Hughes expression showed major pinning contribution from grain-boundary pinning (~95.5%), along with a slight contribution from point pinning (4.5%). The microstructure study detected a system of large MgB2 grains (hundreds nm large) and 10–20 nm sized particles, possibly Mg-B-O, formed at MgB2 grain boundaries.

Journal of Superconductivity and Novel Magnetism, 2021

The original version of this article contained a mistake. Captions and art works of Figs. 2, 3 an... more The original version of this article contained a mistake. Captions and art works of Figs. 2, 3 and 4 were mixed up. Thus, this erratum is presented to fix this error. The original article has been corrected. Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Coatings, 2021

The infiltration growth (IG) process is well-known as the most established technique consisting o... more The infiltration growth (IG) process is well-known as the most established technique consisting of Y2BaCuO5 (Y211) precursor powders and liquid phases toward the fabrication of bulk YBa2Cu3Oy (Y123) superconductor for high field industrial applications. We have reported the fabrication of Y123 bulks using this technique at various ratios of liquid phase source. In this study, the use of liquid phase source toward the infiltration growth of bulk Y123 superconductors at different ratios of Y123 and ErBa2Cu3Oy (Er123) mixed with Ba3Cu5O8 (Y035) was investigated to control the Y211 secondary phase content in bulk Y123 samples. The liquid phase content was optimized by varying the mass. The sample fabricated using Y123 liquid phase (Y1Er0) showed the onset of critical temperature Tc-onset = 91.85 K. Tc-onset slightly decreased with the addition of Er123. Microstructure analysis revealed a uniform distribution of Y211 secondary phase particles in the Y123 matrix. The Y1Er0 sample had the ...

Quarterly Report of RTRI, 2012

Resin-impregnated bulk melt-processed high-T c materials have already been used for several pract... more Resin-impregnated bulk melt-processed high-T c materials have already been used for several practical applications to improve the mechanical performance. A large electromagnetic force acts on the superconductors when they trap large magnetic fields, which occasionally leads to device failure. Epoxy resin can penetrate into the bulk superconductors in certain conditions. Taking advantage of the new technology, a compact, lightweight, and mobile permanent high-T c superconducting magnet system was designed and built using melt-processed GdBa 2 Cu 3 O y rings. The maximum trapped field inside the annular magnet reached 0.75 T to 2.59 T, for one to ten rings, respectively. The results clearly demonstrated that one can construct a permanent magnet system using the melt processed LREBa 2 Cu 3 O y compounds. The use of simple superconducting permanent magnet for magnetizing bulk melt-processed materials can open new technological windows in various industrial areas, particular in medicine, railways, space, or naval transport systems.

Physica C: Superconductivity, 2014

In this contribution we will report on the current status, recent developments in GdBa 2 Cu 3 O y... more In this contribution we will report on the current status, recent developments in GdBa 2 Cu 3 O y "Gd-123" and MgB 2 material processing, characterization, and applications at the Railway Technical Research Institute (RTRI). Batch-processing of Gd-123 bulk material grown in air was performed using novel thin film Nd-123 seeds grown on MgO crystals. In this way, we are able to fabricate materials with good quality, and uniform performance. We examined the technology of the uniform performance of the large 45 mm diameter, single grain Gd-123 bulks for use in application of NMR. For this purpose, four 5 mm thick pieces are cut vertically from a single grain Gd-123 material and the magnetic field distribution is measured using a scanning hall sensor. We found that all four pieces are single domain and exhibit a quite uniform field distribution. Furthermore, the batch-processed bulk materials are used for the construction of a chilled maglev vehicle. On the other hand, to optimize the trapped field performance of bulk MgB 2 material, several samples were prepared by solid state reaction at different temperatures ranging from 750 to 950 o C in pure argon atmosphere. X-ray diffraction results indicated that single phase and homogenous MgB 2 bulks are produced when sintering them around 775 o C. Further, atomic force microscopy (AFM) and scanning electron microscopy (SEM) indicated that an uniform grain size results by controlling the processing temperature. So, higher trapped fields can be achieved in sintered MgB 2 material.

Journal of Physics D: Applied Physics

Although the fascinating effect of superconductivity was discovered more than 100 years ago, only... more Although the fascinating effect of superconductivity was discovered more than 100 years ago, only a few low-temperature superconductors, especially Nb3Sn and NbTi, have reached everyday-life use. After the discovery of superconductivity in MgB2 in 2001, a boom appeared in interest in employing MgB2 in commercial applications, facilitated by simple crystallographic structure, high critical temperature, low-cost raw ingredients, simple and fast production, and other advantages for moderate temperature applications. It only lacks high flux pinning and good mechanical performance. In this review, the implications of manufacturing procedures on the superconducting properties, crystal and electronic structure of MgB2 are discussed. The advantages and drawbacks of various manufacturing processes will be presented, as well as the ways how to improve MgB2 superconducting performance. The impact of oxygen reduction, elements doping, the introduction of defects and additives, and the effect of...

Open Archive Toulouse Archive Ouverte (University of Toulouse), May 23, 2018

Journal of Alloys and Compounds

Superconductors are used in a wide range of applications, each requiring specific magnetic field ... more Superconductors are used in a wide range of applications, each requiring specific magnetic field strengths to operate at their best. The optimal magnetic strength is determined by the superconducting properties, such as critical current density (J c). In this study, we propose that by using different compositions of liquid source, the superconducting properties and microstructure of bulk superconductors can be optimized according to their intended application. Ba 3 Cu 5 O 8 , Yb 2 O 3 :BaCuO 2 :CuO (1:10:6) and Er123 + Ba 3 Cu 5 O 8 (1:1) were tested as liquid sources, and ternary single-grain bulks (Gd, Y, Er) Ba 2 Cu 3 O y were produced using the top-seeded infiltration growth process (TSIG) in the air. Microstructural analysis with a scanning electron microscope revealed that using Er123 +Ba 3 Cu 5 O 8 (1:1) as the liquid source resulted in a significant reduction in the 211 secondary phase particle size, with a mean particle size reduction of 43.13% compared to the conventional Ba 3 Cu 5 O 8. Each composition of the liquid source had a significant impact on the superconducting properties, and the Er123 + Ba 3 Cu 5 O 8 liquid source yielded the highest J c of 81.91 kA/cm 2 in selffield and 28.29 kA/cm 2 at 1 T for (Gd, Y, Er)−123 ternary system. These results emphasize the importance of liquid sources in controlling the final microstructure, which ultimately determines the performance of the bulk ternary (Gd, Y, Er)−123 system produced by the IG process.

Coatings

This article reports the effect of a nanoscale addition of TiO2 on the structure and superconduct... more This article reports the effect of a nanoscale addition of TiO2 on the structure and superconducting parameters of the high-temperature superconductor YBa2Cu3O7-δ (Y123). Polycrystalline compounds of Y123 with different percentages of TiO2, x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0, were fabricated using the thermal treatment method. An analysis using X-ray diffraction confirmed the formation of Y123 phases for all composite samples. Field-emission scanning electron microscopy (FESEM) analysis revealed the growth of grain size and decrease in porosity, with a sign of partial melting of grains for the samples with TiO2 addition. The magnetic and electric transport properties were investigated using AC susceptibility measurement and the four-probe method, respectively. It was observed that the superconducting transition temperature, Tc-onset, for a pure sample determined by ACS and 4PP was 95.6 K and 95.4 K, respectively. These values were found to decrease with the addition of TiO2, while...

Journal of Alloys and Compounds, 2023

Superconductors are used in a wide range of applications, each requiring specific magnetic field ... more Superconductors are used in a wide range of applications, each requiring specific magnetic field strengths to operate at their best. The optimal magnetic strength is determined by the superconducting properties, such as critical current density (J c). In this study, we propose that by using different compositions of liquid source, the superconducting properties and microstructure of bulk superconductors can be optimized according to their intended application. Ba 3 Cu 5 O 8 , Yb 2 O 3 :BaCuO 2 :CuO (1:10:6) and Er123 + Ba 3 Cu 5 O 8 (1:1) were tested as liquid sources, and ternary single-grain bulks (Gd, Y, Er) Ba 2 Cu 3 O y were produced using the top-seeded infiltration growth process (TSIG) in the air. Microstructural analysis with a scanning electron microscope revealed that using Er123 +Ba 3 Cu 5 O 8 (1:1) as the liquid source resulted in a significant reduction in the 211 secondary phase particle size, with a mean particle size reduction of 43.13% compared to the conventional Ba 3 Cu 5 O 8. Each composition of the liquid source had a significant impact on the superconducting properties, and the Er123 + Ba 3 Cu 5 O 8 liquid source yielded the highest J c of 81.91 kA/cm 2 in selffield and 28.29 kA/cm 2 at 1 T for (Gd, Y, Er)−123 ternary system. These results emphasize the importance of liquid sources in controlling the final microstructure, which ultimately determines the performance of the bulk ternary (Gd, Y, Er)−123 system produced by the IG process.

Journal of Magnetism and Magnetic Materials, 2013

MnAl is a promising rare-earth free permanent magnet for technological use. We have examined the ... more MnAl is a promising rare-earth free permanent magnet for technological use. We have examined the effects of consolidation by back-pressure, assisted equal channel angular extrusion processing on mechanically-milled, gas-atomized Mn-46% at. Al powder. X-ray diffraction showed both that the extruded rod consisted mostly of metastable τ phase, with some of the equilibrium γ 2 and β phases, and that it largely retained the as-milled nanostructure. Magnetic measurements show a coercivity of ≤4.4 kOe and a magnetization at 10 kOe of ≤40 emu/g. In addition, extrusions exhibit greater than 95% of the theoretical density. This study opens a new window in the area of bulk MnAl magnets with improved magnetic properties for technological use.

Coatings

A revisited study of perovskite-based manganite La0.67Sr0.33MnO3 (LSMO) deposited onto corning-gl... more A revisited study of perovskite-based manganite La0.67Sr0.33MnO3 (LSMO) deposited onto corning-glass (CG) substrates is reported here. The LSMO films were fabricated with RF sputtering with different deposition times, varying from 60 to 180 min, resulting in films with thicknesses of 35.0–109.7 nm. Rietveld refinements of the XRD spectrum showed that the samples exhibited hexagonal structures with a space group of R-3c (167) and remained unmodified structures. Clusters of monolayer growth were observed from the morphologies of the films. Interestingly, the average particle size obtained with an AFM perceived an insignificant variation of 31.7–35.6 nm despite the film thickness increment. Optical, electrical and magnetic properties were studied, as particle-size variation usually has a notable contribution to changes in these properties. It was found that the optical band gap (Eg) was in direct variation with the deposition time due to enhanced thickness and surface roughness. The te...

Scientific Reports, 2020

Ca2Fe2O5 (CFO) is a potentially viable material for alternate energy applications. Incorporation ... more Ca2Fe2O5 (CFO) is a potentially viable material for alternate energy applications. Incorporation of nitrogen in Ca2Fe2O5 (CFO-N) lattice modifies the optical and electronic properties to its advantage. Here, the electronic band structures of CFO and CFO-N were probed using Ultraviolet photoelectron spectroscopy (UPS) and UV-Visible spectroscopy. The optical bandgap of CFO reduces from 2.21 eV to 2.07 eV on post N incorporation along with a clear shift in the valence band of CFO indicating the occupation of N 2p levels over O 2p in the valence band. Similar effect is also observed in the bandgap of CFO, which is tailored upto 1.43 eV by N+ ion implantation. The theoretical bandgaps of CFO and CFO-N were also determined by using the Density functional theory (DFT) calculations. The photoactivity of these CFO and CFO-N was explored by organic effluent degradation under sunlight. The feasibility of utilizing CFO and CFO-N samples for energy storage applications were also investigated th...

Journal of Physics: Conference Series

The large coherence length of MgB2 material allows large defects such as grain boundaries to act ... more The large coherence length of MgB2 material allows large defects such as grain boundaries to act as strong pinning centres. As an alternative to the high-cost commercial nano precursors, we used a novel ultra-sonication technique to refine a cheap rough boron precursor and avoid the use of the expensive commercial nano amorphous boron powder. Recent novel low-cost ultra-sonication technique proved to improve the critical current density, J c, of MgB2. Here, we discuss the consequences of ultra-sonication duration in hexane medium on the boron precursor as well as the superconducting properties of MgB2 bulks. XRD revealed small peaks corresponding to unreacted Mg. First derivative of susceptibility was plotted as a function of temperature to explain the Tc,onset and ΔTc. J c was found to grow if the MgB2 bulk was prepared of boron ultra-sonicated for up to 30 minutes and then reduced with further boron ultra-sonication (60 minutes). SEM micrographs showed that boron powder subjected ...

Coatings, 2022

The development of high-temperature superconductor (HTS) YBa2Cu3O7~δ (Y123) bulks in industrial a... more The development of high-temperature superconductor (HTS) YBa2Cu3O7~δ (Y123) bulks in industrial applications were established years ago. It is one of the developments that currently attracts great attention especially in transportation, superconductor cables and wires. This study is focused on the preparation of the Y123 bulk superconductors by the thermal treatment method due to the promising ways to develop high-quality Y123 superconductors with its simplicity, low cost, and relatively low reaction temperature used during the process. Y123 were added with graphene nanoparticles (x = (0.0–1.0) wt.%). Samples were then characterized by X-ray diffraction (XRD) analysis, field-emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), and alternating current susceptibility (ACS). It was found that Y123 confirmed that the majority of phases in all the XRD patterns was the orthorhombic crystal structure and the Pmmm space group with secondary phases belon...

Superconductor Science and Technology, 2020

Critical current density, J c, in superconductors is strongly connected with size of defects in t... more Critical current density, J c, in superconductors is strongly connected with size of defects in the material. Frequently, the smaller defects, the higher J c. In this work, we tried to reduce the size of cheap commercial boron precursor powder using high energy ultra-sonication in ethanol media. The resulting powder was then utilized in synthesizing bulk MgB2 via sintering at 775 °C. Effect of boron powder ultra-sonication on superconducting properties of the bulk MgB2 was studied and discussed. SEM of ultra-sonicated boron showed fine particles with sharp edges (high-energy surfaces), irregular shapes and clustering of fine particles occurred for longer ultra-sonication durations. XRD proved a high quality of MgB2 with only small traces of MgO. Around 36% improvement in Jc at 20 K and Tc close to 39 K were observed in MgB2 bulk prepared with boron ultra-sonicated for 15 min. Microstructure studies showed numerous nanometre sized MgB2 grains in the bulk. Other bulks (made of boron u...

IEEE Transactions on Applied Superconductivity, 2020

IEEE Transactions on Applied Superconductivity, 2019

We compare the temperature and field dependence of the critical current densities of high-Tc supe... more We compare the temperature and field dependence of the critical current densities of high-Tc superconductor materials intended for various bulk applications like trapped-field magnets. This comprises bulk samples of YBa2Cu3Ox (YBCO), MgB2 and iron-based materials, including also various versions of the YBCO compound like melt-textured ones, infiltration-growth processed ones, and YBCO foams. Critical current densities and flux pinning forces were obtained from magnetization loops measured using Quantum Design SQUID and PPMS systems with applied magnetic fields of up to ±9 T. The obtained data are compared to each other with respect of the optimal cooling temperature possible using modern cryocoolers. Furthermore, we plot the temperature dependencies of the critical current densities versus the normalized temperature t = T /Tc. This enables a direct judgement of the performance of the material in the trapped field applications.

Nanomaterials

In situ MgB2 superconducting samples were prepared by using the spark plasma sintering method. Th... more In situ MgB2 superconducting samples were prepared by using the spark plasma sintering method. The density of the obtained bulks was up to 95% of the theoretical value predicted for the material. The structural and microstructural characterizations of the samples were investigated using X-ray diffraction and SEM and correlated to their superconducting properties, in particular their critical current densities, Jc, which was measured at 20 K. Extremely high critical current densities of up to 6.75 × 105 A/cm2 in the self-field and above 104 A/cm2 at 4 T were measured at 20 K, indicating that vortex pinning is very strong. This property is mainly attributed to the sample density and MgB2 nanograins in connection to the presence of MgO precipitates and areas rich in boron.

Journal of Superconductivity and Novel Magnetism, 2021

We successfully refined a cheap commercial boron powder by means of high-energy ultra-sonication ... more We successfully refined a cheap commercial boron powder by means of high-energy ultra-sonication and utilized it in synthesis of bulk MgB2. Rietveld phase analysis of X-ray diffraction pattern revealed completely formed MgB2 with a low amount of MgO. MgB2 bulk prepared of boron ultra-sonicated in ethanol for 15 min showed self-field Jc of around 300 kA/cm2 at 20 K without any compromise in Tc (~39 K). Pinning analysis based on Dew-Hughes expression showed major pinning contribution from grain-boundary pinning (~95.5%), along with a slight contribution from point pinning (4.5%). The microstructure study detected a system of large MgB2 grains (hundreds nm large) and 10–20 nm sized particles, possibly Mg-B-O, formed at MgB2 grain boundaries.

Journal of Superconductivity and Novel Magnetism, 2021

The original version of this article contained a mistake. Captions and art works of Figs. 2, 3 an... more The original version of this article contained a mistake. Captions and art works of Figs. 2, 3 and 4 were mixed up. Thus, this erratum is presented to fix this error. The original article has been corrected. Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Coatings, 2021

The infiltration growth (IG) process is well-known as the most established technique consisting o... more The infiltration growth (IG) process is well-known as the most established technique consisting of Y2BaCuO5 (Y211) precursor powders and liquid phases toward the fabrication of bulk YBa2Cu3Oy (Y123) superconductor for high field industrial applications. We have reported the fabrication of Y123 bulks using this technique at various ratios of liquid phase source. In this study, the use of liquid phase source toward the infiltration growth of bulk Y123 superconductors at different ratios of Y123 and ErBa2Cu3Oy (Er123) mixed with Ba3Cu5O8 (Y035) was investigated to control the Y211 secondary phase content in bulk Y123 samples. The liquid phase content was optimized by varying the mass. The sample fabricated using Y123 liquid phase (Y1Er0) showed the onset of critical temperature Tc-onset = 91.85 K. Tc-onset slightly decreased with the addition of Er123. Microstructure analysis revealed a uniform distribution of Y211 secondary phase particles in the Y123 matrix. The Y1Er0 sample had the ...

Quarterly Report of RTRI, 2012

Resin-impregnated bulk melt-processed high-T c materials have already been used for several pract... more Resin-impregnated bulk melt-processed high-T c materials have already been used for several practical applications to improve the mechanical performance. A large electromagnetic force acts on the superconductors when they trap large magnetic fields, which occasionally leads to device failure. Epoxy resin can penetrate into the bulk superconductors in certain conditions. Taking advantage of the new technology, a compact, lightweight, and mobile permanent high-T c superconducting magnet system was designed and built using melt-processed GdBa 2 Cu 3 O y rings. The maximum trapped field inside the annular magnet reached 0.75 T to 2.59 T, for one to ten rings, respectively. The results clearly demonstrated that one can construct a permanent magnet system using the melt processed LREBa 2 Cu 3 O y compounds. The use of simple superconducting permanent magnet for magnetizing bulk melt-processed materials can open new technological windows in various industrial areas, particular in medicine, railways, space, or naval transport systems.

Physica C: Superconductivity, 2014

In this contribution we will report on the current status, recent developments in GdBa 2 Cu 3 O y... more In this contribution we will report on the current status, recent developments in GdBa 2 Cu 3 O y "Gd-123" and MgB 2 material processing, characterization, and applications at the Railway Technical Research Institute (RTRI). Batch-processing of Gd-123 bulk material grown in air was performed using novel thin film Nd-123 seeds grown on MgO crystals. In this way, we are able to fabricate materials with good quality, and uniform performance. We examined the technology of the uniform performance of the large 45 mm diameter, single grain Gd-123 bulks for use in application of NMR. For this purpose, four 5 mm thick pieces are cut vertically from a single grain Gd-123 material and the magnetic field distribution is measured using a scanning hall sensor. We found that all four pieces are single domain and exhibit a quite uniform field distribution. Furthermore, the batch-processed bulk materials are used for the construction of a chilled maglev vehicle. On the other hand, to optimize the trapped field performance of bulk MgB 2 material, several samples were prepared by solid state reaction at different temperatures ranging from 750 to 950 o C in pure argon atmosphere. X-ray diffraction results indicated that single phase and homogenous MgB 2 bulks are produced when sintering them around 775 o C. Further, atomic force microscopy (AFM) and scanning electron microscopy (SEM) indicated that an uniform grain size results by controlling the processing temperature. So, higher trapped fields can be achieved in sintered MgB 2 material.