Near-Surface Material Phases and Microstructure of Scandate Cathodes

Area of Science:

• Materials Science
• Surface Science
• Electron Microscopy

Background:

• Scandate cathodes are crucial for electron emission applications.
• Fabrication via the liquid-solid process yields high-performance cathodes.
• Understanding the nanoscale structure is key to optimizing performance.

Purpose of the Study:

• To characterize the microstructure of high-performance scandate cathodes.
• To investigate the distribution and chemical state of key components.
• To correlate nanoscale features with cathode performance.

Main Methods:

• State-of-the-art electron microscopy techniques (e.g., TEM, SEM).
• Cross-section sample preparation for surface and edge analysis.
• 3D elemental tomography and nanobeam electron diffraction.
• Chemical analysis for phase verification.

Main Results:

• Sub-micron barium aluminate (BaAl₂O₄) particles observed on tungsten (W) particle surfaces and edges.
• Scandium oxide (Sc₂O₃) nanoparticles found near BaAl₂O₄ particles, with distinct phases confirmed.
• Tungsten grains maintained their body-centered cubic metallic structure.
• Internal Sc/Sc₂O₃ particles showed correlated arrangement within W grains, possibly due to surface roughening during synthesis.

Conclusions:

• The liquid-solid process creates distinct oxide phases on W particles without chemical mixing.
• Nanoscale structural features, including particle arrangement, are influenced by the synthesis process.
• The metallic W structure remains stable, supporting excellent emission properties.