Ferroelectric and Semiconducting Properties of Sn2P2S6Crystals with Intrinsic Vacancies

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Abstract
Thermoelectric properties of Sn2P2S6 (SPS) ferroelectric-semiconductor crystals confirm their hole-type conductivity at room temperature which inverses to the electron-type conductivity at heating to 500 K. Their dielectric susceptibility temperature anomaly near second order phase transition at 337 K and dielectric losses in paraelectric phase both strongly depend on the deviation from the stoichiometric content. Calculated in LDA approach donor energy level of the sulfur vacancies and acceptor level of the tin vacancies are placed near the top of valence band. Such position in the energy gap of donor states mostly determines the semiconductive properties of SPS crystals, and they is related to strong hybridization between sp2 hybrid orbitals of phosphorus atoms and p orbitals of sulfur atoms inside anions (P2S5)4− that contain sulfur vacancy.

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