"Nanocomposites and nanomaterials"

Electronic and optical properties of the In4/3P2S6 crystal perspective for ferrielectric heterostructures
T. Babuka1, L.Yu. Kharkhalis1, K.E. Glukhov1, O.O. Gomonnai2
1 Institute for Physics and Chemistry of Solid State, Uzhhorod National University, 54 Voloshin St., 88000 Uzhhorod, Ukraine
E-mail: tanya.babuka@gmail.com
2 Uzhhorod National University, 54 Voloshin St., 88000 Uzhhorod, Ukraine

Nowadays, considerable attention is devoted to the 2D functional materials based on the nonlinear dielectrics that exhibit a rich variety of ferroelectric, pyroelectric, high-κ, and piezoelectric functionalities [1]. In particular, the transition metal thio/selenophosphates (TPS) is a broad class of van der Waals layered solids in which metal cations are embedded into the lattice framework of thiophosphate (P2S6)4-. Using the compositions of M4+[P2X6]4_ and M1+M3+[P2X6]4_type gives a possibility to experimentally construct the excellent heterostructure CuInP2S6/In4/3P2S6 [2]. While the CuInP2S6 crystal is investigated well it is very little information about the In4/3P2S6.  Therefore, it is of interest to study the peculiarities of the chemical bonds and the electron band structure of this crystal. It is known this compound is described by monoclinic (space group P21/c) at room temperature and rhombohedral (Rh3) at high temperatures (above 945 K28) and can be thought of as a parent matrix to CuInP2S6 and AgInP2S6 [1]. The presence of an ordered arrangement of unoccupied octahedral sites is the main peculiarity of the In4/3P2S6 crystalline structure. 
The main aim of the present report is to investigate the electronic and optical properties of the In4/3P2S6 crystal. Using the DFT method we performed the calculations of the spatial distribution of electron density, band structures, and total and partial density of In4/3P2S6 crystals. We obtained the refractive indices and extinction coefficients, real and imaginary parts of the dielectric function, and the absorption coefficient for different polarizations along crystal axes. 
Additionally, the model of the CuInP2S6/In4/3P2S6 heterostructure has been proposed and its parameters were determined. 

1.	Susner M., Belianinov A., Borisevich A., [et al.]. High‑Tc Layered Ferrielectric Crystals by Coherent Spinodal Decomposition// ACS Nano-2015.- 9 ’P.’ 12365–12373 ’ 2015.
2.	Susner M., Chyasnavichyus M., Puretzky A., [et al.]. Cation−Eutectic Transition via Sublattice Melting in CuInP2S6/In4/3P2S6 van der Waals Layered Crystals//ACS Nano.- 2017.-11.- P.7060–7073.