Analysis of the microstructure of bulk MgB₂ using TEM, EBSD and t-EBSD

Area of Science:

• Materials Science
• Condensed Matter Physics
• Superconductivity

Background:

• Bulk superconducting MgB2 is promising for supermagnet applications due to its high transition temperature (38.5 K).
• Nanoscale grain size (100-200 nm) in MgB2 presents challenges for conventional EBSD analysis.
• Flux pinning sites are critical for enhancing the performance of MgB2-based supermagnets.

Purpose of the Study:

• To adapt and apply the transmission EBSD (t-EBSD) technique for analyzing nanoscale MgB2 samples.
• To investigate the crystallographic properties and phase distribution in spark-plasma sintered MgB2.
• To identify and map secondary phases like MgB4 and MgO for their potential role as flux pinning sites.

Main Methods:

• Preparation of Transmission Electron Microscopy (TEM) slices using focused ion beam (FIB) milling.
• Analysis of prepared slices within a Scanning Electron Microscope (SEM) using a custom-built sample holder.
• Identification of Kikuchi patterns for MgB2, MgB4, and MgO phases for multiphase EBSD mapping.

Main Results:

• Successfully applied t-EBSD to analyze MgB2 samples with nanoscale grains.
• Achieved good Kikuchi pattern quality on various MgB2 sample types, overcoming limitations of reflection EBSD.
• Presented the first EBSD mappings of multiphase MgB2, MgB4, and MgO, revealing the spatial distribution of secondary phases.

Conclusions:

• t-EBSD is a viable technique for characterizing nanoscale MgB2 for supermagnet applications.
• The spatial distribution of MgB4 and MgO phases can be visualized, aiding in the assessment of their flux pinning capabilities.
• This study provides crucial microstructural insights for optimizing MgB2 materials for high-performance magnetic applications.