Figure 2. Experimental and calculated diffraction profiles of fcc FeD_x at 988 K and 6.3 GPa.

Refined profiles calculated using the fit parameters optimized for (a) model 1 and (b) model 2. The crystal symmetry is cubic (, Z=4). The atomic sites are Fe 4a(0,0,0), D(O) 4b(1/2,1/2,1/2) and D(T) 8c(1/4,1/4,1/4). The refined structure parameters are given in the main text. Reliable values for the parameters R_wp and χ² are given in the panels. The enlarged 220 reflection peak profiles are displayed in c,d, in which the experimental errors, which are from counting statistics, are given as vertical bars. A best fit is obtained for model 2 with D atoms at the O sites (dark-blue sphere) and T sites (light-blue sphere), as illustrated in the inset of b, where the O sites surrounding the occupied T site are vacant to avoid the violation of the 2-Å rule (ref. 28).