Abstract

Purpose. CuBiP₂Se₆ layered crystals exhibit a temperature-dependent antiferroelectric ordering of the Cu⁺ and Bi³⁺ ions in the lattice. The temperature dependence of the static dielectric permittivity reveals the first-order ’’displacive’’ antiferroelectric phase transition at T_c=136 K. At thys time no literature data on the effect of hydrostatic pressure on the dielectric properties and antiferroelectric phase crystals CuBiP₂Se₆. The aim of this paper is to investigate the p,T-phase diagram CuBiP₂Se₆ layered crystals via broadband dielectric measurement.
Methods. Studied CuBiP₂Se₆ crystals were grown by the gas transport reaction method. For the dielectric measuremen polished platelike crystals were used. All measurements were performed in a direction perpendicular to the layers. The complex dielectric permittivity ε^∗ was measured using an HP4262A capacitance bridge at the frequency 1 MHz. All measurements have been performed on cooling and heating mode with a temperature rate 0.5 K/min. Silver paste has been used for contacting. Hydrostatic pressure was applied a high-pressure chamber, its value being controlled within ±1MPa.
Results. Studies of complex dielectric permittivity ε^∗ of CuBiP²Se⁶ crystals with different values hydrostatic pressure in a wide temperature range 77 K <T <400K and pressure of 0 MPa <p <600 MPa were performed. In the temperature range 120K <T <200K for CuBiP₂Se₆ crystals the law of Curie-Weiss.In the paraelectric phase and antiferroelectric phase Curie-Weiss constant and Curie-Weiss temperature respectively are: , та , . Тhe coefficient , та , for the paraelectric phase and antiferroelectric phase respectively. The transition temperature linearly decreases with increasing pressure with the ratio of -0,049 K/MPa.
Conclusions. Based on the studies of temperature dependences of dielectric permittivity of CuBiP₂Se₆ layered crystals at high hydrostatic pressure, a p,T phase diagram was built, and pressure coefficients for the phase transition temperature shift were determined. Hydrostatic pressure shifts beginning superionic temperature ion transport in the low temperatures region

Keywords: antiferroelectrics, phase transitions, dielectric properties, hydrostatic pressure, phase diagram

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