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In SnPS ferroelectric under compression, the second-order phase transition line is observed down to the tricritical point as the transition temperature decreases to 250 K. A tricriticality at a similar temperature is also revealed in the mixed crystals on SSe substitution. For the mixed crystals with SnPb substitution, ultrasound, hypersound, and low-frequency dielectric studies also show heterophase features appearing on decrease of the ferroelectric transition temperature below a so-called 'waterline temperature' near 250 K. Such behavior agrees with the Blume-Emery-Griffiths (BEG) model appropriate for the ferroelectric system under investigation with a three-well local potential for the order parameter fluctuations. The BEG model modified by the random-field phase diagram in the vicinity of the tricritical point qualitatively explains the influence of the cationic substitution on the (PbSn)PS ferroelectric properties. [ABSTRACT FROM AUTHOR]

Investigation results of ultrasonic and piezoelectric properties of mixed CuIn1 - xCrxP2S6 layered ferroelectric single crystals are presented. The piezoelectric detection of longitudinal ultrasonic signal by thin plates of CuIn1 - xCrxP2S6 crystals (x = 0.2, 0.3) was observed and the temperature dependencies of piezoelectric properties have been studied. They changed upon heating, cooled down at T1 and vanished at higher temperature T2, where crystals exhibit phase transition to centrosymetric phase. At equivalent temperatures the critical anomalies of ultrasonic velocity and attenuation have been observed. At room temperature, above PT, the electrostriction induced piezoelectricity occurred under DC bias electric field applied along c-axis of the CuIn1 - xCrxP2S6 crystals. [ABSTRACT FROM AUTHOR]

Dielectric properties of CuInP2(S0.25Se0.75)6 crystals were investigated in the temperature range 80 < T < 300 K and frequency range 20 Hz < ν < 1.25 GHz. Very broad dielectric relaxation was analyzed in terms of distribution of relaxation times, using Tichonov regularization method. It revealed slowing down of the longest and most probable relaxation times obeying Vogel-Fulcher and Arrhenius laws respectively. The distribution of relaxation times splits into two components near Tm at 1 kHz, and origin of both components are discussed. [ABSTRACT FROM AUTHOR]

The dielectric spectrum of mixed CuInP2(S0.7Se0.3)6 crystals was investigated. The calculated distribution of relaxation times confirms glassy behaviour and the maxima of the distribution of the relaxation times follow Vogel-Fulcher law with parameters: activation energy EA = 9.4 · 10-2 eV, dipole freezing temperature T0 = 21.9 K and attempt frequency υ0 = 1/(2π τ0) = 0.149 THz. From all presented results we see, that CuInP2(S0.7Se0.3)6 crystal shows typical dipolar glass dielectric dispersion and we may conclude that this crystal belongs to new family of materials that exhibits a dipolar glass behavior. [ABSTRACT FROM AUTHOR]

The macroscopic response of 0.83PbMg 1/3 Nb 2/3 O 3 -0.17PbTiO 3 (PMN-17PT) single crystals has been investigated in order to resolve existing controversy about the structural phase transition in the rhombohedral side of (1-x)PbMg 1/3 Nb 2/3 O 3 -xPbTiO 3 phase diagram. The combination of nonlinear dielectric spectroscopy, temperature dependant polarization and strain hysteresis loop measurements and ultrasonic spectroscopy revealed that ferroelectric phase occurs spontaneously in PMN-17PT single crystals. The experimental techniques applied in this work probe the bulk of the sample and can unambigously determine the existence of a spontaneous ferroelectric phase. The experiments showed that zero-field cooled sample has a normal ferroelectric hysteresis loop at room temperature. The electric-field dependence of induced polarization revealed that at a certain electric field the sample undergoes transformation from polydomain to monodomain-like states. The 1 s t order phase transition at 330 K was evidenced by the third order nonlinear dielectric susceptibility for monodomain sample. The nonlinear dielectric response of an unpoled sample does not show such abrupt jump and is more similar to the response of canonical relaxor PbMg 1/3 Nb 2/3 O 3 . Zero-field heating and zero-field cooling experiments also revealed very slow domain formation processes appearing at 300–320 K temperature. They are affected by the experimental conditions. There are evidences that on cooling the domains tend to grow in the sample. [ABSTRACT FROM AUTHOR]