XPS and electronic structure of ferroelectric Sn2P2S6crystals

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 0n1400 eV. The VB consists of ve 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.