XPS and electronic structure of ferroelectric Sn2P2S6 crystals

Abstract

Electronic properties of uniaxial ferroelectric Sn₂P₂S₆ single crystal are studied by X-ray photoelectron spectroscopy. X-ray photoelectron spectra (XPS) of the valence band (VB) and of the principal core levels (CL) are obtained from different crystallographic planes in both paraelectric and ferroelectric phases. The XPS were measured with monochromatized Al Ka radiation in the energy range 0–1400 eV. The VB consists of five bands with the maxima between 3.3 and 14.5 eV below the Fermi level. Experimental energies of the VB and core levels are compared with results of theoretical ab initio calculations of molecular model of the Sn₂P₂S₆ crystal. Electronic structure of the VB is revealed. Ferroelectric phase transition changes atom’s charge and bonds strength, VB electronic structure, CL lines width, and chemical shifts for the Sn, P, and S states which are crystallographic plane-dependent.
Keywords: Sn₂P₂S₆, ferroelectric, crystals, XPS, electronic structure
PACS: 71.20.-b, 77.84.-s, 78.70.En, 79.60.-i