Sammendrag
Transmission electron microscopy has been used to study ball milled and H cycled NaAlH4 with 10 mol% TiCl3. Isolated from the main phases in this hydrogen storage system, nanocrystalline aggregates of fcc TiH (x) (0a parts per thousand currency signx < 0.67) were found. The value of x was determined based on the assumption of a linear increase of the TiH (x) lattice parameter by increasing H content. The size of the TiH (x) crystallites was in the range 10 to 20 nm, and the lattice parameter decreased from 4.22 A... in TiH0.67 to 4.10 A... in pure fcc Ti. Non-equilibrium ball milling and subsequent H cycling in combination with a small crystallite size are believed to make the TiH (x) phase stable. The present results are the first observations of fcc TiH (x) with low hydrogen content, and the measured fcc lattice parameter of Ti matches first-principles calculations.