Title: THE EFFECT OF SIZE FACTOR ON THE PHASE TRANSITION IN SN_2P_2S_6 CRYSTALS: EXPERIMENTAL DATA AND SIMULATION IN ANNNI MODEL
Author(s): A.V.Drobnich (Uzhhorod National University, 46 Pidhirna Str., 88000 Uzhhorod, Ukraine), A.A.Molnar (Uzhhorod National University, 46 Pidhirna Str., 88000 Uzhhorod, Ukraine), A.V.Gomonnai (Institute of Electron Physics of the National Academy of Sciences of Ukraine, 21 Universytetska Str., 88000 Uzhhorod, Ukraine), Yu.M.Vysochanskii (Uzhhorod National University, 46 Pidhirna Str., 88000 Uzhhorod, Ukraine), I.P.Prits (Uzhhorod National University, 46 Pidhirna Str., 88000 Uzhhorod, Ukraine)

Size effect on the fundamental properties of Sn$_2$P$_2$S$_6$ ferroelectric is studied. The decrease of Raman peak frequency, accompanied by the band broadening and asymmetry, is observed in the spectra of microcrystalline Sn$_2$P$_2$S$_6$ powder. Theoretical calculations, performed in the ANNNI model for Sn$_2$P$_2$S$_6$ microcrystals of different size, predict the decrease of the ferroelectric phase transition temperature with the decrease of the microcrystal size parameter.

Key words: microcrystals, size effects, Raman scattering, ANNNI model
PACS: 36.40.Ei, 63.22.+m