Phase ρ, T-diagram of layered  CuCr0.9In0.1P2Scrystals


Purpose. Recently interest of CuCrP2S6 crystals studies has grown significantly. This is due to the promising use of them as multiferous materials for the next generation of magnetoelectric non-volatile storage devices. According to data from calorimetric and ultrasound studies, two phase transitions were identified in CuCrP2S6 crystals at Tc1 ≈ 190 K and Tc2 ≈ 150 which divide three phases: the nonpolar paraelectric (T>Tc1), the antipollar anti-ferroelectric (T<Tc2) and the intermediate quasi-antipollar in the temperature range Tc2<T<Tc1. Dielectric studies and studies of the fundamental absorption edge have made it possible to establish that the intermediate phase is incommensurable. This was evidenced by the brakes on the temperature dependence of the dielectric constant at the second kind phase transition from the paraelectric to the intermediate phase and the parallel shift of the energy position of the edge of the fundamental absorption. The isomorphic substitution of Cr atoms by 10 mol% of In atoms in crystals of CuCrP2S6 does not significantly change the temperature behavior of dielectric properties. The temperature of the phase transition to the anti-ferroelectric phase is slightly reduced, the step on the temperature dependence of ε 'in CuCr0.9In0.1P2S6 crystals becomes blurrier. The main objective of this study is to determine the phase r, T-diagram and analyze its features by studying the temperature dependences of the dielectric properties of CuCr0.9In0.1P2S6 crystals under the influence of high hydrostatic pressures.
Methods. Studied CuCr0.9In0.1P2S6 crystals were grown by the gas transport reaction method. For the dielectric measurement polished plate like 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. Scanning electron microscopy (SEM) studies combined with energy dispersive X-ray spectroscopy (EDX) were performed using a SEM JEOL 7000F microscope.
Results. Studies of a complex dielectric permittivity ε* of CuCr0.9In0.1P2S6 crystals with different values of hydrostatic pressure were performed in a wide temperature range 77 K<T<300K and a pressure of 0 MPa <ρ<600 MPa. An increase in hydrostatic pressure results in an increase in the value of the real of the dielectric constant throughout the studied temperature range. With increasing pressure, the jump-like anomaly in the region of the first kind Phase transition Tc2 is blurred and shifted to a lower temperature region with a coefficient dTc2/dp=-0,045 K/МPа. At the same time, the temperature interval of the intermediate phase decreases. The blurred break at Tc1 also shifts towards low temperatures with a coefficient dTc1/dp=-0,022 K/МПа.
Conclusions. The influence of hydrostatic pressure on the temperature behavior of dielectric properties of CuCrP2S6 layered crystals is studied in the vicinity of the phase transition of crystals. It was observed that under the influence of the hydrostatic pressure the intermediate (incommensurate) phase existence temperature interval was reduced. Coefficients of the baric variation of the temperatures of the first kind phase transition Tc2 and of the second kind phase transition Tc1 were determined. On the phase ρ,T diagram of CuCr0.9In0.1P2S6 crystals an implementation of a polycrytical triple point that separates phase transitions into comparative and incommensurate phases is possible


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