Strongly connected<i>ex situ</i>MgB<sub>2</sub>polycrystalline bulks fabricated by solid-state self-sintering

Tanaka, Hiroya; Yamamoto, Akiyasu; Shimoyama, Jun–ichi; Ogino, Hiroshi; Kishio, K.

doi:10.1088/0953-2048/25/11/115022

Cited by 49 publications

(53 citation statements)

References 39 publications

(57 reference statements)

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“…1, we obtain RRR ≈ 4.9, and using the value of Δρ g suggested by Yamamoto et al, we obtain A F ≈ 0.66. These results, as compared with those deducible from the data reported in the review paper of Rowell [29], as well as with the more recent data for bulk samples [31], [32], show that our material exhibits good grain connectivity. In particular, A F = 0.66 is very high with respect to those reported in the literature for polycrystalline samples; this can be ascribed to the fact that grain boundaries in MgB 2 produced by Mg-RLI are predominantly constituted by metallic Mg.…”

Section: Reactive Liquid Mg Infiltration Technology and Cavity Desupporting

confidence: 87%

Microwave Response of Coaxial Cavities Made of Bulk Magnesium Diboride

Gallitto

Camarda

Vigni

et al. 2014

IEEE Trans. Appl. Supercond.

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Abstract-We report on the microwave properties of coaxial cavities built by using bulk MgB 2 superconductor prepared by reactive liquid Mg infiltration technology. We have assembled a homogeneous cavity by using an outer MgB 2 cylinder and an inner MgB 2 rod and a hybrid cavity by using an outer copper cylinder and the same MgB 2 rod as inner conductor. By the analysis of the resonance curves, in the different resonant modes, we have determined the microwave surface resistance R s of the MgB 2 materials as a function of the temperature and the frequency, in the absence of dc magnetic fields. At T = 4.2 K and f ≈ 2.5 GHz, by an mw pulsed technique, we have determined the quality factor of the homogeneous cavity as a function of the input power up to a maximum level of about 40 dBm (corresponding to a maximum peak magnetic field of about 100 Oe). Contrary to what occurs in many films, R s of the MgB 2 material used does not exhibit visible variations up to an input power level of about 10 dBm and varies less than a factor of 2 on further increasing the input power of 30 dB.

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Section: Reactive Liquid Mg Infiltration Technology and Cavity Desupporting

confidence: 87%

Microwave Response of Coaxial Cavities Made of Bulk Magnesium Diboride

Gallitto

Camarda

Vigni

et al. 2014

IEEE Trans. Appl. Supercond.

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“…At 5K its J c curve lies parallel under the J c curve of MgB 2 derived from 12LB. Especially for the latter sample, it should be noted that the behaviour is not so different from the performances of the pure samples reported in literature by several groups [27][28][29][30][31].…”

Section: Characterization Of Mgb 2 Bulk Samplescontrasting

confidence: 47%

High temperature heat treatment on boron precursor and PIT process optimization to improve theJ_cperformance of MgB₂-based conductors

Vignolo

Bovone

Bernini

et al. 2013

Supercond. Sci. Technol.

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Abstract:Promising results reported in our previous works led us to think that boron's production process plays a crucial role in MgBB 2 synthesis. A new method for boron preparation has been developed in our laboratory. This particular process is based on magnesiothermic reaction (Moissan's process) with the addition of an initial step that gives boron powder with nano-metric grain size. In this paper we report our efforts regarding optimization of PIT method for these nanometric powders and the resolution of problems previously highlighted such as the difficulty in powder packaging and the high friction phenomena occurring during cold working. This increases cracking during the tape and wire manufacturing leading to its failure. Packaging problems are related to the amorphous nature of boron synthesized in our laboratory, so a crystallization treatment was applied to improve boron's crystallinity. To prevent excessive friction phenomena we synthesized non-stoichiometric MgB 2 and using magnesium as lubricant. Our goal is the J c improvement, but a global physical-chemical characterization was also made to analyze the improvement given by our treatments: this characterization includes X-ray diffraction, ρ(T) measurement, SEM image, besides magnetic and transport J c measurements. IntroductionAfter 12 years since the discovery of superconductivity in MgB 2, many efforts have been done in order to improve its performances and make it competitive with traditional superconductors. This is possible due to its relatively high critical temperature (T c ) that permits to use MgB 2 -based conductors at 20 K by using a cryocooler. Also compared to other superconducting materials MgB 2 tapes are easy to manufacture and of low cost. Despite the good results have been achieve so far, huge efforts are necessary especially on J c improvement, which is the main parameter from application point of view. This could be achieved by obtaining a complex balance between connectivity, upper critical field (H c2 ) and pinning force induced by grain boundaries, precipitates Experimental Boron powder preparation and characterization.Details of boron synthesis and purification have been given in [9]. Once boron is purified at the end of the process two amounts of powder were taken from the same batch to effect the heat treatment of crystallization. The first one (12LB) has been set in an iron boat and placed in a tubular furnace at 1200 °C for 120 minutes, under Ar flow. The second sample (17LB) was put in tantalum crucible, sealed in a quartz ampoule, and heat treated at 1700 °C through an inductive furnace, for 30 minutes. X-ray analysis was made on these powders at the end of the treatment, on pristine powder (LB), and on commercial boron (CB), to verify the improvement of crystal quality led by heat treatment. XRD measurements were performed using a PHILIPS (PW 1170/90 Cu Kα) diffractometer at 40 KV and 30 mA. MgB 2 bulk, powder and wire preparation and their characterization.After thermal treatment the powders are used to synthesize...

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“…[17][18][19][20] Considerable effort is being made to better the J c values of exsitu MgB 2 via excess Mg and various nanoparticles as additives, spark plasma sintering, ball milling, etc. 4,[15][16][17][18][19][20][21][22][23][24][25][26] The improvement in J c has been chiefly attributed to improved connectivity of superconducting grains, 27 pinning and upper critical field, 2,28 and/or change in anisotropy. 29 In our previous work, 23 the superconducting properties of ex-situ MgB 2 samples were found to vary as a function of excess Mg as well as the sintering temperature and the highest J c was observed in samples sintered at 900 C with 5% excess Mg.…”

Section: Introductionmentioning

confidence: 99%

Effect of excess Mg and nano-additives on the superconducting properties of weakly connected bulk MgB2

Bhadauria

Gupta

Kishan

et al. 2013

Journal of Applied Physics

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Articles you may be interested inConnectivity and critical current density of in-situ processed MgB2 superconductors: Effect of excess Mg and non-carbon based additives A new scaling relation for n-AlN doped superconducting MgB2SiC and carbon nanotube distinctive effects on the superconducting properties of bulk Mg B 2Series of ex-situ polycrystalline MgB 2 bulk samples, by adding different additives like more of excess Mg (5 wt. %), nanoparticles of Ag (3 wt. %), and SiC (10 wt. %) to a previously optimized composition MgB 2 þ Mg (5 wt. %), were prepared by solid state synthesis route. Detailed investigations were carried out by XRD, SEM, and thermoelectric power S(T), resistivity q(T), and magnetization M(B) at temperatures T ¼ 4.2-300 K and applied fields B ¼ 0-8 T. All the samples typically show low connectivity (i.e., normal state current carrying cross section $0.9%-3%). The effect of different additives was different on the critical current density (J c ) of the samples. The J c , for instance at T ¼ 4.2 K and B ¼ 1 T, varied between 4.8 Â 10 7 and 2.8 Â 10 8 A/m 2 for various samples. In comparison to the previously optimized values, the J c was enhanced by further addition of 5 wt. % Mg and degraded both by nano-SiC and nano-Ag addition. However, many of the other properties of the samples were not much affected. For instance, the samples did not show any change in the superconducting onsets, S(T) and the parallel upper critical field (B jj c2 (T) $ 11-13 T at 20 K and 20-21 T at 4.2 K). The J c (B) dependence also shows similar behavior in all the samples, where the J c is found to scale as B À1 up to a sample independent crossover field B cr $ 2 T and 1.3 T at T ¼ 4.2 and 20 K, respectively. At higher fields B > B cr , the J c (B) curves branch out and decrease rapidly towards zero at a sample dependent characteristic field. We try to understand these results quantitatively in terms of changes in connectivity, pinning, and anisotropy driven percolation. However, all our results and analysis point out that the intra-particle regions stay unaffected and mainly the inter-particle regions get affected by the additives leading to the J c variation in the weakly connected samples.

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Strongly connectedex situMgB₂polycrystalline bulks fabricated by solid-state self-sintering

Cited by 49 publications

References 39 publications

Microwave Response of Coaxial Cavities Made of Bulk Magnesium Diboride

Microwave Response of Coaxial Cavities Made of Bulk Magnesium Diboride

High temperature heat treatment on boron precursor and PIT process optimization to improve theJ_cperformance of MgB₂-based conductors

Effect of excess Mg and nano-additives on the superconducting properties of weakly connected bulk MgB2

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Strongly connectedex situMgB2polycrystalline bulks fabricated by solid-state self-sintering

Cited by 49 publications

References 39 publications

Microwave Response of Coaxial Cavities Made of Bulk Magnesium Diboride

Microwave Response of Coaxial Cavities Made of Bulk Magnesium Diboride

High temperature heat treatment on boron precursor and PIT process optimization to improve theJcperformance of MgB2-based conductors

Effect of excess Mg and nano-additives on the superconducting properties of weakly connected bulk MgB2

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Product

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Strongly connectedex situMgB₂polycrystalline bulks fabricated by solid-state self-sintering

High temperature heat treatment on boron precursor and PIT process optimization to improve theJ_cperformance of MgB₂-based conductors