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Composition and morphology investigation of MgB2 superconductor doped with NiCoB nanoparticles

Materials composed of fine magnetic particles exhibit unique properties which are strongly affected by morphology (i.e. size and shape) and composition of incorporated nanoparticles. Such materials offer a wide range of versatile applications (i.e. medicine diagnostic and drug delivery, chemical catalysts, memory storage, solar cells etc.). Our research was based on the idea of enhancement of electro-magnetic properties of MgB2 superconductor (T ≈ 39 K) by doping it with ternary transition metal-boron alloy magnetic nanoparticles. We used NiCoB nanoparticles with mean diameter d = 19 ± 4 nm, which were amorphous according to previously XRD measurements. Magnetic measurement of these particles showed the superparamagnetic behaviour. MgB2 wires doped with NiCoB particles were prepared by the in-situ powder in tube method (PIT). The resulting microstructures were characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray analysis (EDS). The SEM-EDS elemental mapping was used for determination of distribution of constituent elements. The analysis of FE-SEM micrographs of doped MgB2/NiCoB sample revealed nearly uniaxial nanoparticles (d = 20 ± 1 nm) along with hexagonal shaped forms (d = 290 ± 20 nm). The X-ray diffraction showed the existence of MgB2 and MgO phases and Si. We suppose that MgO is the result of oxidation of the sample and Si is from the sample holder. The existence of Mg, B and O elements was also confirmed by EDS results. The hexagonal shaped forms were mainly composed of these elements. Small quantities of Ni and Co elements were also detected, obviously due to the using of 1.25 wt. % of NiCoB powder for doping. The quantitative EDS analysis showed that the ratio of detected Mg and B elements was very close to 1:2 and ratio of Mg and O elements was ≈ 1:1. The mean crystallite size of MgB2 phase calculated from MgB2/NiCoB X-ray diffraction pattern was ≈ 30 - 40 nm. These results along with earlier obtained from FE-SEM micrographs indicate that hexagonal forms are in fact MgB2 polycrystals. According to EDS results nearly uniaxial particles seem to be NiCoB particles. Also, the electrical transport measurements performed on doped MgB2/NiCoB superconductor showed an improvement of electro-magnetic properties in respect to pure MgB2 superconductor.

superconductor; nanoparticles; EDS

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