Діелектричні властивості та фазова р,Т-діаграма шаруватих кристалів CuBiP2Se6

Abstract

Наведено результати досліджень температурних залежностей діелектричної проникності шаруватих кристалів CuBiP2Se6 при дії зовнішнього гідростатичного тиску. Встановлено, що дія гідростатичного тиску приводить до зменшення температури антисегнетоелектричного фазового переходу з коефіцієнтом dTc / dp = –0,049 K / MPa.

Приведены результаты исследований температурных зависимостей диэлектрической проницаемости слоистых кристаллов при действии внешнего гидростатического давления. Установлено, что действие гидростатического давления приводит к уменьшению температуры антисегнетоэлектрические фазового перехода с коэффициентом dTc / dp = –0,049 K / MPa.

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 Tc=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.