Abstract
For the purpose of optimizing the gaseous phase and electrochemical advantages of both the C14 and C15 phases in AB2 metal hydride (MH) alloys, a systematic study was established to predict and understand the factors that affect the C14/C15 phase abundance. The study was constructed based on 6 series of transition metal-based AB2 alloys that were designed with the choices of A-site elements being Ti, Zr, and Hf and the choices of B-site elements being Cr, Co, and Cu. The average electron density (e/a) was proven to be one of the most influential parameters in determining the C14/C15 phase abundance: as e/a increased, C14/C15 became less/more dominant, respectively. However, with different A-site compositions but same overall e/a, a shift in e/a was observed in the C14/C15 phase abundance vs. e/a relationship. The average atomic radius of A atoms was shown to correlate very well with the C14/C15 threshold when the choice of A-site elements is limited to any of Ti + Zr combinations (pure or mixed). The average chemical potential for electronic charge of A atoms had a nearly perfect linear correlation to the C14/C15 threshold even with the addition of Hf in the selection of A-site elements. The combination of e/a and the average chemical potential for electronic charge can be used to predict the C14/C15 phase abundance and assist future AB2 MH alloy development.
Published Version
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