X-ray absorption spectroscopic study of a hot pressed MgB2

Hsieh, Chun-Ming; Chang, Cheng-Hsun-Tony; Chang, Chao‐Wan; Sou, Un Cheong; Sheu, Hwo Shuenn; Hsu, Han Lin; Yang, Hong-Chang

doi:10.1016/j.ssc.2005.09.038

Cited by 14 publications

(7 citation statements)

References 16 publications

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“…The peak position of feature b was related to the π* states of the B 2 O 3 , suggesting that some of the boron combined with oxygen. This change agreed with the results of the O K-edge XANES presented in Figure 4, with peaks at 536.1 eV [ 39 , 42 , 43 ]. The decline in feature c, assigned to the σ* states of the B–C bonds, indicated that some B–C chains were breaking in the film [ 38 , 39 ].…”

Section: Resultssupporting

confidence: 90%

“…Figure 4 displays the O K-edge X-ray absorption near-edge structure spectra of the different films placed in the dry oxygen-rich environment. The spectra had two significant features: one small bump due to the π* state of the O 2 molecule at 529.5 eV [ 42 , 43 , 44 , 45 ], labeled f, and another broad feature attributed to the σ* state of the B–O bonds at 536.1 eV [ 43 , 44 , 45 ], labeled g. There was a significant increase in the σ* states of the B–O bonds in the spectrum of the B 4 C/Pd layers compared with the spectrum of the B 4 C film, which indicated that some of the oxygen was excited and combined with boron under palladium catalysis. The same O 2 peak occurred in the spectra because the samples were placed in a dry oxygen-rich environment.…”

Section: Resultsmentioning

confidence: 99%

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Chemical Modification of B4C Films and B4C/Pd Layers Stored in Different Environments

Feng

Jiang

et al. 2021

Materials

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B4C/Pd multilayers with small d-spacing can easily degrade in the air, and the exact degradation process is not clear. In this work, we studied the chemical modification of B4C films and B4C/Pd double layers stored in four different environments: a dry nitrogen environment, the atmosphere, a dry oxygen-rich environment, and a wet nitrogen environment. The XANES spectra of the B4C/Pd layers placed in a dry oxygen-rich environment showed the most significant decrease in the σ* states of the B–C bonds and an increase in the π* states of the B–O bonds compared with the other samples. X-ray photoelectron spectroscopy (XPS) measurements of the samples placed in a dry oxygen-rich environment showed more intensive B-O binding signals in the B4C/Pd layers than in the single B4C film. The results of the Fourier-transform infrared spectroscopy (FTIR) showed a similar decrease in the B–C bonds and an increase in the B–O bonds in the B4C/Pd layers in contrast to the single B4C film placed in a dry oxygen-rich environment. We concluded that the combination of palladium catalysis and the high content of oxygen in the environment promoted the oxidization of boron, deteriorated the B4C composition.

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Section: Resultssupporting

confidence: 90%

Section: Resultsmentioning

confidence: 99%

Chemical Modification of B4C Films and B4C/Pd Layers Stored in Different Environments

Feng

Jiang

et al. 2021

Materials

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“…A positive correlation between sample density and onset transition temperature T c,0 has been established by Grinenko et al who studied MgB 2 bulks with densities between 16 and 70% of the maximum density [7]. MgB 2 bulks with significantly higher density have been produced by pressure-assisted heat-treatments such as hot isostatic pressing (HIPing) [8][9][10][11][12][13], hot pressing [14][15][16], and spark plasma sintering (SPS) [17][18][19]. However there has been limited exploration of the effect of varying key processing parameters during these procedures on the subsequent density, connectivity and superconducting properties of the material.…”

Section: Introductionmentioning

confidence: 89%

Fabrication and properties of denseex situmagnesium diboride bulk material synthesized using spark plasma sintering

Dancer

Prabhakaran

Başoğlu

et al. 2009

Supercond. Sci. Technol.

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High density ex situ magnesium diboride bulks were synthesized from commercial MgB 2 powder using spark plasma sintering under a range of applied uniaxial pressures between 16 and 80 MPa. The microstructure was characterized using x-ray diffraction, scanning electron microscopy, polarized optical microscopy, Vickers hardness measurements, and density measurements using the Archimedes method. By combining these data with those for other bulk samples we have developed a correlation curve for the hardness and density for magnesium diboride for relative densities of 60-100%. The superconducting properties were determined using magnetization measurements. Comparison to samples of significantly higher porosity indicates a positive correlation between magnetization critical current density and bulk density for magnesium diboride bulks up to around 90% density. Above this level other microstructural processes such as grain growth begin to influence the critical current density, suggesting that full elimination of porosity is not necessary to obtain high critical current density. We conclude that the best superconducting properties are likely to be obtained with a combination of small grain size and minimal porosity.

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“…Following on from earlier work by Giunchi et al [3,15], Perini [16] has reported more recently a trapped field of 1 T in a bulk MgB 2 sample fabricated by an Mg infiltration growth technique. Hsieh et al [17] further reported local J c values in zero field of up to 8x10 8 A/m 2 in samples fabricated by uniaxial hot pressing. Even more recently, Naito et al [1] have reported fields of up to 1.5 T in MgB 2 bulk samples produced by a novel hot pressing technique where the pressure is generated by the expansion of the pellet itself with increasing temperature.…”

Section: Introductionmentioning

confidence: 96%

A trapped field of >3 T in bulk MgB₂fabricated by uniaxial hot pressing

Durrell¹,

Dancer²,

Dennis³

et al. 2012

Supercond. Sci. Technol.

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A trapped field of over 3 T has been measured at 17.5 K in a magnetised stack of two discshaped bulk MgB 2 superconductors of diameter 25 mm and thickness 5.4 mm. The bulk MgB 2 samples were fabricated by uniaxial hot pressing, which is a readily scalable, industrial technique, to 91% of their maximum theoretical density. The macroscopic critical current density derived from the trapped field data using the Biot-Savart law is consistent with the measured local critical current density. From this we conclude that critical current density, and therefore trapped field performance, is limited by the flux pinning available in MgB 2 , rather than by lack of connectivity. This suggests strongly that both increasing sample size and enhancing pinning through doping will allow further increases in trapped field performance of bulk MgB 2 .

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X-ray absorption spectroscopic study of a hot pressed MgB2

Cited by 14 publications

References 16 publications

Chemical Modification of B4C Films and B4C/Pd Layers Stored in Different Environments

Chemical Modification of B4C Films and B4C/Pd Layers Stored in Different Environments

Fabrication and properties of denseex situmagnesium diboride bulk material synthesized using spark plasma sintering

A trapped field of >3 T in bulk MgB₂fabricated by uniaxial hot pressing

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X-ray absorption spectroscopic study of a hot pressed MgB2

Cited by 14 publications

References 16 publications

Chemical Modification of B4C Films and B4C/Pd Layers Stored in Different Environments

Chemical Modification of B4C Films and B4C/Pd Layers Stored in Different Environments

Fabrication and properties of denseex situmagnesium diboride bulk material synthesized using spark plasma sintering

A trapped field of >3 T in bulk MgB2fabricated by uniaxial hot pressing

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A trapped field of >3 T in bulk MgB₂fabricated by uniaxial hot pressing