A neutron diffraction study of the interstitial sites of deuterium in the A-15 compound Ti3Ir

The interstitial D sites in the D-doped A-15 compound Ti3IrDx with x = 0.70 and 3.63 were determined by neutron diffraction (space group Pm(3) over bar n (No. 223)). For x = 0.70, we confirm the D occupation of sixfold d positions (6d positions) already found for other H- and D-doped A-15 compounds. The complete and sole occupation of these positions yields the concentration x = 3. Accordingly, we found for the sample with x = 3.63 the additional occupation of 24k (or nearly 24k) positions. Our study suggests in particular a structural mechanism that successively replaces 6d positions by two adjacent and simultaneously occupied 24k positions in order to allow an increase of the D concentration above x = 3. (C) 1997 Elsevier Science Ltd.