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High-density MgB2 (HD-MgB2) superconducting samples ( D ⩾ 2.2 g/cm3), using different sources of magnesium powder as raw material, were synthesized in ambient pressure in a rich Mg environment. The magnesium powders used in the fabrication process include nanometer-sized magnesium particles, powders from Alfa Aesar, ordinary off-the-shelf powder, and magnesium chip. The fabrication procedure involved a double-sintering process in a rich-Mg environment. A transition temperature T c of 39 K was observed. Samples with the equally high density and matching superconducting properties were obtained as well by a triple sintering process of the MgB2 powder directly from Alfa Aesar. [ABSTRACT FROM AUTHOR]

Superconducting MgB2 thick film has been prepared via hybrid physical-chemical vapor deposition method on Al2O3 (0001) substrate by using B2H6 and magnesium ingot as raw materials reacted from 730 to 830°C for 40 min under 20 to 30 kPa. Its thickness is about 40 µm. The MgB2 thick film shows Tc (onset) = 39.0 K and Tc (0) = 37.2 K. X-ray diffraction pattern shows that the film grown along (101) direction has small amount of impurities of Mg and MgO. Scanning electron microscopy and energy dispersive X-ray spectroscopy indicated that these impurities existed indeed and were Mg rich. The MgO film was formed on the surface of the MgB2 thick film to further protect the sample from oxidation. We presented a new mechanism for the formation of the thick film. [ABSTRACT FROM AUTHOR]

Careful investigations on a series of the MgB2 phases quenched at different sintering temperatures during fabrication process have been carried out, and important information is obtained, by the X-ray diffraction (XRD), the scanning electron microscopy (SEM) images, and the temperature dependent magnetization (M–T) measurements. The particle sizes of the raw magnesium and boron powders are on the order of 0.1 mm and 1 μm, respectively. Three stages in the formation of the polycrystalline MgB2 phase are identified in different sintering temperature ranges according to the corresponding superconducting properties and the crystallization conditions. The MgB2 phase first appears in a microscopic scale at about 530 °C according to the M–T measurement. Then, the MgB2 phase forms macroscopically within a narrow temperature range from 653 to 660 °C, while the residual raw materials of the magnesium and boron components persist to the temperature of 700 °C. The optimum sintering temperature range for the MgB2 phase to form is determined from 750 to 900 °C. [Copyright &y& Elsevier]