GeO 2 -added MgB 2 superconductor obtained by Spark Plasma Sintering

Seven MgB2 bulk superconductors with good superconductivity and crystallinity were prepared under the pressure of 50 MPa at 950 °C and different sintering durations (15 ∼ 240 min) by spark plasma sintering (SPS), with the onset critical temperature (T c,onset) around 37.5 K. The superconducting properties and microstructure measured from the facets perpendicular (PeF) and parallel (PaF) to the compression direction of the SPSed MgB2 bulk samples were also analyzed to investigate the effect of the sintering duration on the MgB2 bulks and the discrepancy between the PeF and the PaF. The optimum performance was obtained from the sample prepared for 45 min for both facets, and the critical current density (J c) measured from the PeF and the PaF are 364 kA cm−2 and 344 kA cm−2 in self field at 20 K, respectively. The PeF exhibits better Jc performance than the PaF at low fields and the PaF exhibits better J c performance than the PeF at high fields. It can be concluded that the sintering duration affects the properties of the PeF mainly by changing their crystallite size. While for the PaF, the sintering duration mainly affects the microstructural defects, such as cracks, pores and secondary phase particles, thus further affecting their J c performances. In terms of the flux pinning mechanism of the SPSed MgB2 bulk samples, the PaF is less susceptible to sintering duration than the PeF, and the better J c performance of the PaF at high fields is due to the stronger grain boundary pinning. It can be also found that the point pinning being stronger at higher temperature is the result of the decreasing anisotropy of MgB2 bulk samples with the temperature.

Section: Resultssupporting

confidence: 89%

The discrepancies in different facets of MgB₂ bulk superconductors prepared under various sintering durations by spark plasma sintering

Zhang

Lou

et al. 2021

“…Approximately, a similar behavior of the pinning-force-related parameters was observed in the SPSed samples (heating rate ∼100-150 °C min −1 ) of MgB 2 added with GeO 2 , TeO 2 or Bi 2 O 3 which form secondary Mg-M (M=Ge, Te, Bi) layer phases along the grain boundaries. These samples also exhibit enhanced J c [24,29]. Our results suggest that the size, shape and location of secondary phases are important for pinning efficiency.…”

Section: Resultsmentioning

confidence: 59%

Reactive spark plasma sintering of MgB₂in nitrogen atmosphere for the enhancement of the high-field critical current density

Badica

Burdusel

Popa

et al. 2016

High density bulks (97%–99%) of MgB2 were prepared by spark plasma sintering (SPS) in nitrogen (N2) atmosphere for different heating rates (10, 20 and 100 °C min−1) and compared with reference samples processed in vacuum and Ar. N2 reacts with MgB2 and forms MgB9N along the MgB2 grain boundaries. The high-field critical current density is enhanced for the sample processed in N2 with a heating rate of 100 °C min−1. At 2–35 K, this sample shows the strongest contribution of the grain boundary pinning (GBP). All samples are in the point pinning (PP) limit and by increasing temperature the GBP contribution decreases.

“…Processing conditions and effect of different additions on the superconducting properties of MgB 2 bulk specimens. The effect on J c at high and low field is represented by either an increase () or decrease () in J c relative to unmodified MgB 2 , processed under the same conditions [5][6][7][8][9][10][11].…”

Section: Methodsmentioning

confidence: 99%

“…Carbon doping has led to significant improvements in J c at high field but also causes a severe reduction in T c [3,4]. Simple oxide additions in both in situ and ex situ processed materials can improve J c values at high field, but decrease J c at low field without having a significant effect on T c [5][6][7][8][9]. Others have reported a decrease in J c at both high and low fields [10,11].…”

Section: Introductionmentioning

confidence: 99%

Design and characterisation of ex situ bulk MgB₂ superconductors containing a nanoscale dispersion of artificial pinning centres

Matthews

Liu

Grovenor

et al. 2020

MgB2 pellets containing a nanoscale dispersion of artificial pinning centres have been successfully manufactured through a powder metallurgy route based on the oxide dispersion strengthened (ODS) concept more usually used for steels and superalloys. Commercial MgB2 powder and Y2O3 nano-powder were mechanically alloyed in a high energy planetary ball mill and consolidated using the field assisted sintering technique. The composite powders were ball milled for different times up to 12 h and characterised by means of particle size analysis, x-ray diffraction (XRD) and scanning transmission electron microscopy (STEM). The microstructure and superconducting properties were characterised by density, XRD, STEM and magnetic property measurements. The powder microstructure comprised Y2O3 particles dissolved into the MgB2 matrix. After consolidation there was a near-uniform dispersion of precipitated YB4 and MgO particles. A bulk 0.5 wt% Y2O3-MgB2 composite showed the best superconducting performance with a significant improvement in J c at high field compared with unmodified MgB2, and only a small reduction in T c . The results suggest that the ODS concept is promising to improve the superconducting properties of MgB2.