(a) Four consecutive scans at 165 K showing the quality of the Fe K-Edge XAFS data. (b) Fourier transform of the averaged XAFS data. The dashed thin lines are fits to the data. The first and second shell Fe–As and Fe–Fe peaks are labeled. Peaks are shifted to lower R-values from real distances by atomic phase shifts.
Extracted for the Fe–As bond for the and 0.11 samples as the upper and lower curves. Note that the Einstein temperatures are the same for both samples.
Extracted for the Fe–Fe bonds for the and 0.11 samples as the upper and lower curves. Note that the Einstein temperature for this correlation is higher for the doped sample indicating enhanced Fe–Fe coupling with F doping.
Bond distances for (blue circles) and (black squares) for the first shell Fe–As distance (upper curves) and second shell Fe–Fe distance (lower curves).
In panels (a) and (b) the change density in the planes for and 0.5 are given showing the charge distribution in the As and Fe layers, respectively. The planes at and are shown in (c) and (d). All plots have the same z scale [as in (a)] in units of electrons/Bohr radius cubed.
(a) Slice of the total charge density of 12.5% doped model system based on double unit cell revealing the a plane contain the Fe and O ions. Note the similarity in terms of the delocalized charge in the Fe layer with Fig. 4(c). The intensity scale is the same as in Fig. 5. (b)The difference between the total charge density of the F doped and undoped system for the same plane as in (a) showing that the Fe layer is modified by F doping. The yellow background of the figure denotes zero charge density while green and red are negative and positive charge density, respectively.
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