Study on the formation of MgB2 phase

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 mum, 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 degreesC according to the M-T measurement. Then, the MgB2 phase forms macroscopically within a narrow temperature range from 653 to 660 degreesC, while the residual raw materials of the magnesium and boron components persist to the temperature of 700 degreesC. The optimum sintering temperature range for the MgB2 phase to form is determined from 750 to 900 degreesC. (C) 2004 Elsevier B.V. All rights reserved.