In the work it was shown that the In 4 Se 3 crystal is similar by its dynamical properties to the InSe modulated crystal. The transformation of the D group of In 4 Se 3 structure has been investigated. In spite of structure corrugation of In 4 Se 3 layer, it is shown that the region of the weak bond in this crystal by the dynamical characteristics is similar to the weak bond region in InSe crystal.
The electron behavior in incommensurate phase in Sn 2 P 2 Se 6 has been considered as the motion in the Mathieu potential. A simple model of effective potential change under a transition incommensurate -domain-like structure has been proposed. A behavior of the obtained localized levels system versus the model parameters has been investigated.
The energy spectra of charge carriers in several models of the ordered solid solutions and virtual crystal model based on the ferroelectrics of Sn 2 P 2 S 6 type are calculated by the semiempirical pseudopotential method. It is shown that the band gap depends on the employed model of the solid solution.Key words: pseudopotential method, ordered solution, energy states, simulation, virtual crystal, ferroelectrics-semiconductors. 71, 07.05.Tp, 71.15.Hx, 71.20.Nr The physical property investigations of the ferroelectrics of the (Pb y Sn 1−y ) 2 P 2 (S x Se 1−x ) 6 system [1,2] are relevant since one can look after the change of the crystal structure anisotropy and the effect of the anion and cation replacement on both the property anomalies in the critical region and the energy and phonon spectra. It was established [2,3] that the replacement of Sn by Pb in (Pb y Sn 1−y ) 2 P 2 S 6 leads to the decrease of the temperature of the ferroelectric phase transition and this transition does not change its character. The replacement of the S atom by Se in the system Sn 2 P 2 (S x Se 1−x ) 6 leads to the splitting of the phase transition line [4]. The evolution of the phase transition peculiarities for the considered systems has been analyzed based on the investigations of temperature dependency of the heat conduction and the dielectric function [5]. The absorption edge studies of the ferroelectric solid solutions (Pb y Sn 1−y ) 2 P 2 (S x Se 1−x ) 6 helped to establish the main conformities in the variation of the optical parameters (see table 1 from [2]). In particular, the change of the band gap with the concentration of the replacement atoms and the thermal and baric coefficients of the band gap changes were determined. Further, these important experimental characteristics can be used to compare * PACS:
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