X-Ray Spectroscopic Studies of some Compounds with the same Chemical Formula and Different Crystal Structure

Abstract
With the x-ray spectroscopy method two groups of semiconducting compounds are investigated. The first group consists of: CdIn₂S₄ (spinel type structure; F d 3 m – O_k⁷), CdGa2S4 and HgGaA ( the "defective" chalcopyrite; I 4^- – S₄²). To the second group belong: Tl₃TaS₄ (that is made of coordinative tetrahedra [TaS₄] and of structure units [TlS₈]; I 4^- 3 m – T₄³ ) and isostructural compounds Tl₃TaS₄ and TI₃AsS₄ (the structural type K₃PS₄; [formula: see text])- flnorescent K-emission bands and absorption K-spectra (XANES) of sulphur in compounds investigated are received with the resolution about 0.2 eV. The primary L_2,3-emission bands of S have been studied using RSM-500 with resolution 0.4 eV. The electron energy structure of the valence bands are similar in isoelectronic compounds CdIn₂S₄, CdGa₂S₄ and HgGa₂S₄ that follows from the likeness of the forms of the x-ray emission bands in these compounds. At the same time the absorption SK-spectra (XANES) are alike only for CdGa₂S₄ and HgGa₂S₄ and differ significantly with SK-spectrum of CdIn₂S₄, that is due to the difference of S-atom sorroundings in these compounds. The similarity of the forms of all x-ray spectra in isostructural and isoelectronic compounds Tl₃PS₄ and Tl₃AsS₄ proves the likeness of the electron-energy structure in these compounds and of the environment of S-atom in these compounds. The emission and absorption spectra of S in Tl₃TaS₄ differ from ones of Tl₃PS₄ and Tl₃AsS₄, that is due to the fact, that Ta-atom is not isoelectronic to atoms of P and As, that results in the difference of S-atom surroundings and the electron-energy structure.