Ti K-edge x-ray absorption spectroscopy was used to explore the local titanium environment and valence in 2-4 mol% Ti-doped sodium alanate. An estimate of the oxidation state of the dopant, based upon known standards, revealed a zero-valent titanium atom. An analysis of the near-edge and extended fine structures indicates that the Ti does not enter substitutional or interstitial sites in the NaAlH 4 lattice. Rather, the Ti is located on/near the surface and is coordinated by 10.2±1 aluminum atoms with an interatomic distance of 2.82±0.01 Å, similar to that of TiAl 3. The Fourier transformed EXAFS spectra reveal a lack of long-range order around the Ti dopant indicating that the Ti forms nano-clusters of TiAl 3. The similarity of the spectra in the hydrided and dehydrided samples suggests that the local Ti environment is nearly invariant during hydrogen cycling.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Condensed Matter Physics
- Mechanics of Materials
- Mechanical Engineering