Electron-Phonon Interaction as a Mechanism of Phase Transition in the CuInP2S6 Crystal

D.M. Berchaa, S.A. Berchaa, K.E. Glukhova, M. Sznajderb aInstitute of Physics and Chemistry of Solid State, Uzhgorod National University, 54 Voloshin St., 88000 Uzhgorod, Ukraine b Faculty of Mathematics and Natural Sciences, University of Rzeszów, S. Pigonia 1, 35-959 Rzeszów, Poland

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Studies on the phases of CuInP2S6 crystal exhibiting phase transitions of the order-disorder type are performed. A possibility for the cooperative Jahn-Teller effect to occur in this crystal is analyzed. For this purpose, the procedure of constructing the potential energy matrix is generalized for the case of crystal and it is illustrated by the construction of the adiabatic potentials for Γ5-Γ5 vibronic coupling for the proto- and paraelectric phases of CuInP2S6. The structure of the obtained potentials is analyzed together with the discussion on the appearance of spontaneous polarization in this crystal.

DOI: 10.12693/APhysPolA.126.1143 PACS numbers: 64.60.Cn, 71.15.Mb, 71.70.Ej