Searching for Mixed Octahedral-Tetrahedral Interstitial Hydrogen Occupation in Pd-Ti Sublattices: A Computational Study

Abstract

With hydrogen conversion and storage technologies promising a revolution in the energy industry if volumetric energy density is increased, the loading of hydrogen to high concentrations in metal lattices has become of special interest. Here we use Projector Augmented-wave density functional theory methods to search the Pd-Ti-H system for stable instances of mixed tetrahedral-octahedral site occupation. We compute the energies of 42 hydrides constructed from seven metal sublattices: Ni₃Ti-prototype Pd₃Ti, CdI₂-prototype PdTi₂, and FCC four-atom unit cells of Pd, Pd₃Ti, PdTi, PdTi₃, and Ti. Our results suggest that mixed octahedral-tetrahedral occupation is energetically unfavorable in most cases, but a Li₃Bi-prototype hydride may be stable within the Pd₁-ₓTiₓH₃ system.