| About this Abstract |
| Meeting |
MS&T22: Materials Science & Technology
|
| Symposium
|
Integration between Modeling and Experiments for Crystalline Metals: From Atomistic to Macroscopic Scales IV
|
| Presentation Title |
Leveraging Electron Microscopy to Inform Ab Initio Calculation: Deducing Surface Chemistry and Annealing Conditions from Equilibrium Tungsten Nanoparticle Shapes in Scandate Cathodes |
| Author(s) |
Mujan N. Seif, Xiaotao Liu, John Balk, Matthew J. Beck |
| On-Site Speaker (Planned) |
Mujan N. Seif |
| Abstract Scope |
Scandate cathodes (“scandates”) are a high-performing subset of thermionic cathodes composed of a porous Sc-doped W nanocrystalline pellet impregnated with BaO, Al2O3, and CaO. Extensive characterization of scandate cathode microstructure motivates a hypothesis that all high-performance scandates contain W nanoparticles of a characteristic Wulff shape. Here, we evaluate the relationship between Sc and this shape. We utilize density functional [perturbation] theory to compute the finite-temperature excess free energies of several Sc-containing and Sc-omitted surface configurations. With these results, we quantify the relative stability of the configurations as a function of temperature and O2 availability. We then search this T, O2 phase space to find a window wherein the relative surface excess free energies yield the characteristic W nanoparticle shape present in high-performing scandate cathodes. We find that the presence of Sc in certain surface arrangements further stabilizes W configurations and creates multiple regions where the characteristic Wulff shape appears. |