Correlations Between Superconducting Characteristics and Structure of MgB2-Based Materials, ab-Initio Modeling

The influence of technological parameters (composition of precursor powders, type of additions, temperature, and pressure) on the superconducting characteristics (transition temperature, critical current density, and critical magnetic fields) of MgB₂-based materials (bulk, wires, and thin films) and the correlation with their microstructure were studied. Microstructural observations are in good agreement with ab-initio modeling. The X-ray, Auger spectroscopy, and SEM EDX study show that impurity oxygen and carbon (possibly as dopant) are present in the magnesium diboride structure. The elements are distributed inhomogeneously, thus creating the nanostructure (which can be purposefully changed by manufacturing conditions) responsible for flux pinning and other SC characteristics.

I. Introduction

Magnesium diboride is promising for many commercial applications such as magnetic resonance imaging, fault current limiters, transformers, motors, generators, adiabatic demagnetization refrigerators, magnetic separation, magnetic levitation and bearings, superconducting magnetic energy storage, and magnets for high-energy physics [1]–[6]. Thin films can be used for manufacturing superconducting bandpass filters for ultra-high frequency electromagnetic radiation [7]–[9], etc. The devices based on magnesium diboride can work at liquid hydrogen and neon (20–27 K) temperature and the nowadays highly developed cryo-coolers make the application of magnesium diboride easier and cheaper compared to conventional superconductors. Many process parameters and the underlying technologies can influence the structure (superconducting phase content, material density, connectivity between superconducting grains, homogeneity of the structure) and consequently the functional properties of magnesium diboride based materials. Here, the superconducting properties and microstructure of 1)

bulk materials synthesized by different methods at different pressures (from ambient up to 2 GPa) without and with different additions,

2)

wires produced by Hyper Tech, and

3)

thin films obtained by magnetron sputtering will be described in order to show how their properties can be influenced by the manufacturing method and process parameters (precursor powders and initial composition, pressure, and temperature).