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

TL;DR

This study demonstrates that using nanometer magnesium powder enables the formation of high-density MgB2 superconductor at significantly lower temperatures than traditional methods, with improved microstructure and superconducting properties.

Contribution

It introduces a low-temperature synthesis method for MgB2 using nanometer Mg powder, resulting in higher density and better superconducting characteristics compared to micron-sized powder methods.

Findings

MgB2 forms between 430-490°C with nanometer Mg powder.

Nano-MgB2 has higher density (1.7 g/cm3) than Micro-MgB2 (1.0 g/cm3).

Transition temperature (Tc) of Nano-MgB2 is 39 K.

Abstract

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 to 490 C, which is much lower than that with the MgB2 sample fabricated in the same gas environment using the micron-sized magnesium powder, denoted as Micro-MgB2, reported previously. The sample density of the Nano-MgB2 reaches 1.7 g/cm3 with a crystal porosity structure less than a micrometer, 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/cm3. This indicates that the Mg raw particle size, besides 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, 650 C. The X-ray diffraction (XRD) pattern shows a good MgB2 phase with small amount of MgO and Mg and the transition temperature, TC, of the Nano-MgB2 was determined as 39 K by the temperature dependent magnetization measurement (M-T), indicating the existence of a good superconducting property.