Dielectric properties and phase p,T –diagram of CuBiP<sub>2</sub>Se<sub>6</sub> layered crystals

Abstract

Purpose: CuBiP 2 Se 6 layered crystals exhibit a temperature-dependent antiferroelectric ordering of the Cu + and Bi 3+ ions in the lattice. The temperature dependence of the static dielectric permittivity reveals the first-order ’’displacive’’ antiferroelectric phase transition at Tc=136 K At thys time no literature data on the effect of hydrostatic pressure on the dielectric properties and antiferroelectric phase crystals CuBiP 2 Se 6 . The aim of this paper is to investigate the p,T-phase diagram CuBiP 2 Se 6 layered crystals via broadband dielectric measurement. Methods: Studied CuBiP 2 Se 6 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 e∗ 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 e∗ of CuBiP 2 Se 6 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 CuBiP 2 Se 6 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 CuBiP 2 Se 6 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.