Fig. 3.

Results of ab initio silicide phase refinements plotted using VESTA V3.4⁴³. Fe, Cr and Ni atomic sites are interchangeable and shown in magenta. Si atomic sites are shown in turquoise. Residual Coulomb potential maps (ΔV) of the RR2450 π-ferrosilicide phase and carbon-deficient π-ferrosilicide phase solved in the P2₁3 space group setting using the output of the refinements from JANA2006²² are shown. Transparent light-blue residuals are plotted using a 2σ(ΔV) threshold (σ is the standard deviation of map values) and opaque dark-blue residuals are plotted using a 3σ(ΔV) threshold. Maps shown are of: a π-ferrosilicide after kinematical refinement, σ(ΔV) = 1.09 e/Å. Regions initially believed to correspond to a 25% carbon occupancy are circled; b π-ferrosilicide after dynamical refinement, σ(ΔV) = 0.093 e/Å; c carbon-deficient π-ferrosilicide after kinematical refinement, σ(ΔV) = 1.41 e/Å, and; d carbon-deficient π-ferrosilicide after dynamical refinement, σ(ΔV) = 0.054 e/Å. Note that the noise levels in the dynamical difference potential maps, quantified by the values of σ(ΔV), are more than ten times lower than in the kinematical difference potential maps