Abstract
An analysis of the P2S6 cluster electronic structure and its comparison with the crystal valence band in the paraelectric and ferroelectric phases has been done by first-principles calculations for Sn2P2S6 ferroelectrics. The origin of ferroelectricity has been outlined. It was established that the spontaneous polarization follows from the stereochemical activity of the electron lone pair of tin cations, which is determined by hybridization with P2S6 molecular orbitals. The chemical bonds covalence increase and rearrangement are related to the valence band changes at transition from the paraelectric phase to the ferroelectric phase.
Highlights
For such perovskite ferroelectrics as BaTiO3, the main origin of spontaneous polarization is commonly related to the hybridization interaction between the transition-metal and oxygen ions [1].Another mechanism involves cations with “lone pair” electrons which have a formal ns2 valence electron configuration [2]
The second and the third factors represent the nonlinear interaction of Ag Bu2 type; they govern an anisotropy of polar shifting of atoms in the elementary cell and define appearance of the dipole structure motives (−Sn−P2 S6 −), which are related to the polar normal coordinates of Bu symmetry
The appearance of the spontaneous polarization in the Sn2 P2 S6 compound is accompanied by the significant changes of an electronic structure that are observed in all subbands of this crystal valence band (VB)
Summary
For such perovskite ferroelectrics as BaTiO3 , the main origin of spontaneous polarization is commonly related to the hybridization interaction between the transition-metal and oxygen ions [1]. Another mechanism involves cations with “lone pair” electrons which have a formal ns valence electron configuration [2]. The first one describes short range repulsive forces and is related to the rigid ion (with frozen electronic configuration) shifts from original high symmetry positions Such a term is small for the cases of “closed-shell” d0 or p0 cations. The geometrical (or hybrid improper) mechanism, which is related to the rotational modes that trigger instability of polar mode [5,6], could be considered in studying the ferroelectricity nature
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