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The ultrasonic velocity and attenuation anomalies were observed near the elastic phase transitions (PT) in the vicinity of 270 K in Cu6PS5(I,Br) mixed superionic crystals, where I was partially substituted by Br. We have shown that elastic anomalies at phase transition gradually decrease with increasing of iodine concentration in the material. The critical anomalies were described by relaxational Landau theory, which implies the increase of order parameter relaxation time: τ = τo/(Tc - T). The prefactor τo increases with increasing iodine content in crystal. The ultrasonic anomalies near low temperature superionic phase transitions were weak. These transitions were observed using piezoelectric detection of ultrasonic waves by surface barrier. The temperature dependencies of detected by surface barrier signal were measured and it was shown that this method is very sensitive for indication of phase transitions in such superionic crystals. [ABSTRACT FROM AUTHOR]

Results of ultrasonic and piezoelectric properties investigation of mixed CuInP2 (SXSe1 - X)6 layered ferroelectric single crystals are presented. The piezoelectric detection of longitudinal ultrasonic signal by thin plates of CuInP2(SxSe1- x)6 crystals (x = 0.05, 0.1, 0.2 and 0.25) was observed and the temperature dependencies of piezoelectric properties have been studied. The piezoelectric sensitivity decreased upon heating and vanished at higher temperature, where crystals exhibit phase transition (PT) to centrosymmetric phase. At transition temperatures the anomalies of ultrasonic velocity and attenuation have been observed. At room temperature, above PT, the electrostriction-induced piezoelectricity was observed under DC bias electric field applied along c-axis of the CuInP2(SxSe1- x)6 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 ultrasonic velocity and attenuation anomalies were observed near phase transitions (PT) in CuInP 2 (S,Se) 6 semiconductor crystals, where S was partially substituted by Se. It was shown that, crystals became piezoelectric not only in low temperatures below PT in ferroelectric phase but also at room temperature, which is far above the phase transition and under DC bias electric field, the electrostriction induced piezoelectricity appears. The anomalies of ultrasonic velocity, attenuation, second harmonic, and acoustoelectric voltage were also observed near the phase transitions in Cu 6 PS 5 I single crystals. These crystals belong to the polar symmetry group 3m at room temperature and exhibit a ferroelastic phase transition at 270 K. [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]

Investigation results of dielectric and ultrasonic properties of layered CuInP2S6 crystals are presented. At low frequencies, dielectric spectra are highly influenced by the high ionic conductivity with the activation energy of 7357.4 K (0.635 eV). The high-frequency part of the spectra is determined by relaxational soft mode. The critical slowing down and Debye-type dispersion show the order--disorder type of the phase transition. The temperature dependence of the relaxational soft mode and dielectric contribution show a quasi-one-dimensional behaviour. Ultrasonic velocity exhibits critical slowing down which is accompanied by attenuation peaks in the phase transition region. Layered CuInP2S6 crystals have extremely large elastic nonlinearity in the direction perpendicular to layers. The nonlinear elastic parameters substantially increases at the PT temperature. [ABSTRACT FROM AUTHOR]

Abstract: Electric properties of Cu7GeS5I and Cu7SiS5I crystals were studied in a broad temperature (120 – 300 K) and frequency (1 MHz – 3 GHz) range. The ionic conductivity has been distinguished from contact effect. The DC conductivity has been extracted from experimental results. From this DC conductivity the activation energy has been calculated and compared with activation energy obtained from the electrical modulus. [Copyright &y& Elsevier]