To the explanation of the “white” line in the X-ray K-absorption spectrum of sulfur in NaBiS2

Abstract

The maximum in the K-absorption spectra of sulfur in LiBiS2, NaBiS2, and KBiS2, which is located more than 12 eV above the absorption edge and is especially strong for NaBiS2, cannot be explained within single-electron calculations. Apparently, it is not related to any ordering in the arrangement of alkali metal and bismuth atoms in the cation sublattice. A scheme is considered in which a Na2S-Bi2S3 solid solution is formed with subsequent oxidation of Na2S with the formation of sulfate Na2SO4 with sulfur in the valence state +6, as a result of which the absorption edge shifts by approximately 13 eV. Thus, the initial experimental spectrum is treated as a weighted sum of the K-absorption spectra of sulfur in NaBiS2, Na2S, Bi2S3, and Na2SO4.