Relative Thermodynamic Stabilities of Sc-Containing Surface Configurations in Scandate Cathodes

Scandate cathodes have been reported to exhibit superior emission properties to other classes of thermionic cathodes. However, a deeper understanding of their fundamental operating behavior is crucial before widespread technological integration. There remains no consensus as to the role of Sc in improved emission. Extensive characterization of scandate cathodes reveals that all high-performance cathodes contain W nanoparticles of a characteristic shape. Surface configurations containing Sc in variety of arrangements were evaluated by ab initio approaches at finite temperature and relative surface excess free energies compared. It was observed that no surface containing both Ba and Sc exhibited a particularly low surface energy, although several with Sc or O/Sc had very low surface energies. However, none of these high-stability configurations exhibit work functions comparable to those attributed to scandate cathodes.