Phase formation of polycrystalline MgB2 at low temperature using nanometer Mg powder

The MgB2 superconductor synthesized in a flowing argon atmosphere using nanometer magnesium powder as the raw materials, denoted as Nano-MgB2, has been studied by the technique of in situ high temperature resistance measurement (HT-RT measurement). The MgB2 phase is identified to form within the temperature range of 430-490 degreesC, which is much lower than that with the MgB2 sample fabricated in the same gas environment Using the micron size magnesium powder, denoted as with a crystal porosity structure Micro-MgB2 and reported previously. The sample density of the Nano-MgB2 reaches 1.7 g/cm(3) less than a mum, as determined by the scanning electron microscope (SEM) images, while the Micro-MgB2 has a much more porous structure with corresponding density of 1.0 g/cm(3). This indicates that the Mg raw particle size, beside the sintering temperature, is a crucial factor for the formation of high density MgB2 sample, even at the temperature much lower than that of the Mg melting, similar to650 degreesC. The X-ray diffraction (XRD) pattern shows a good MgB2 phase with small amount of MgO and Mg and the transition temperature, T-C, of the Nano-MgB2 was determined to be 39 K by temperature dependent magnetization measurements (M-T), indicating good superconducting properties. (C) 2004 Elsevier Ltd. All rights reserved.