Correlation between chemical shift of SiK alpha lines and the effective charge on the Si atom and its application in the Fe-Si binary system

High-resolution Si Kalpha(1,2) (K-L-3,L-2) x-ray fluorescence spectra of Si, SiB6, SiC, Si3N4, SiO2, and Na2SiF6 were measured on a double-crystal spectrometer. From SiB6 to Na2SiF6, the chemical shifts for the Si Kalpha lines relative to pure Si were 0.05, 0.19, 0.45, 0.62, and 0.96 eV, respectively. The value increased systematically with increased atomic number of the neighbor atoms of Si. Calculation by the discrete variational Hartree-Fock-Slater method showed that the effective charges on Si in SiC and Na2SiF6 were 0.37 and 1.85 electrons, and the values in Si3N4, SiO2 were found in former literature to be 1.24 and 1.40 electrons, which increased in the same sequence as the chemical shift. These facts certified the direct correlation between the effective charges on Si and the chemical shift of Si Kalpha lines. An empirical curve of effective charges on Si versus chemical shifts in Si Kalpha lines was obtained. With this empirical curve, we found that Si held positive charge in the Fe-Si binary system based on the Si Kalpha chemical shift measurement, although the electronegativity of Si (1.90) was greater than that of Fe (1.83), which made it seem reasonable to assume that the charge transfer should be from Fe to Si. We determined the effective charges on Si in FeSi2, FeSi, and Si steel to be 0.50, 0.56, and 0.63 electrons, which increased with the increasing Fe concentration.