Search

The dielectric and ultrasonic properties of a bent-core main-chain liquid-crystalline polymer network have been investigated. Dielectric measurements on this material showed two maxima in the real and imaginary components of the dielectric permittivity at 365 K and 450 K along with a temperature hysteresis showing the first order nature of the two phase transitions. Longitudinal ultrasonic attenuation and ultrasonic velocity measurements at 10 MHz frequency revealed some anomalies at the phase transition temperatures respect to the dielectric results. Above room temperature, a large ultrasonic attenuation was observed which can be related to the glass transition of this sample. Moreover, the piezoelectric sensitivity of this bent-core main-chain liquid-crystalline polymer network has also been studied. [ABSTRACT FROM AUTHOR]

The temperature dependence of ultrasonic velocity and ultrasonic attenuation were measured in polyurea elastomer composites with inorganic nanoparticles. The decrease in the ultrasonic velocity along with an attenuation maximum was observed above the glass transition temperature, Tg. The shape and position of this peak are directly proportional to the amount of embedded nanoparticles. In addition, the sharp anomalies in the ultrasonic velocity and ultrasonic attenuation were observed above the glass transition temperature in semicrystalline polyurea elastomers. These anomalies are related to the corresponding first order phase transition of these crystalline domain-containing networks. The ultrasonic attenuation peak related to glass transition is considerably smaller in these polyurea networks showing a small influence of the soft domains below the melting temperature, Tm. The first order phase transition in the semicrystalline polyurea elastomers shows a large temperature hysteresis of more than 10 K, which was confirmed by dielectric investigations. The addition of small amounts of inorganic nanoparticles resulted in a shift of the first order phase transition temperature in semicrystalline nanocomposites. [ABSTRACT FROM AUTHOR]

Dielectric spectroscopy results of organic polymer Polydimethylsiloxane (PDMS) with different ZnO nanoparticle concentrations are presented in wide temperature range. Dielectric loss was measured as a function of electromagnetic field frequency at various temperatures. Our measurements have shown that the value and position of dielectric loss peak on a temperature scale depends on the concentration of ZnO nanoparticles within PDMS. The temperature behaviour of dielectric losses was compared with temperature dependencies of ultrasonic attenuation in the samples. It is shown that the maximum of dielectric losses in PDMS nanocomposite is described according to the Vogel-Fulcher law and the glass transition increases with ZnO concentration. [ABSTRACT FROM AUTHOR]

The ultrasonic investigations were performed in Sn2P2S6family layered crystals, where tin was substituted by lead. We have shown that in mixed crystals the anomalies of ultrasonic velocity and attenuation appear in the vicinity of the phase transitions. The critical ultrasonic anomalies shifted to lower temperatures when Pb concentration increased from 0.1 to 0.3 in material. The relative change of longitudinal ultrasonic velocity along z-axis at the phase transition temperature gradually decreased from 30% in pure Sn2P2S6to 15% for sample withy= 0.3 content of Pb. Such large velocity change causes the large ultrasonic attenuation anomaly. The ultrasonic velocity and attenuation behaviour in the ferroelectric phase was described using Landau theory implying increase of order parameter relaxation time:τ=τ0/(TC–T) and free energy expansion including sixth order terms. It was shown that prefactorτ0increases with Pb content. [ABSTRACT FROM PUBLISHER]

We have investigated dielectric and acoustic properties of PbFe1/2Nb1/2O3ceramics, obtained by conventional ceramic technology, in 120–450 K temperature interval. Dielectric response showed diffused dielectric permittivity maximum caused by ferroelectric phase transition around 380 K, but no dielectric anomalies associated with magnetic phase transition at low temperatures were observed. Formation of the polar phase was confirmed by ultrasonically detected piezoelectric sensitivity. Ultrasonic investigations using pulse-echo method showed two anomalous regions in temperature dependencies of ultrasonic velocity and attenuation, associated with magnetic and ferroelectric phase transitions. [ABSTRACT FROM AUTHOR]

The ultrasonic and piezoelectric investigations were performed in CuInP2S6 family layered crystals, where Cu, In, S were substituted by Ag, Bi and Se. We have shown that in CuBiP2Se6 crystals the anomalies of piezoelectric sensitivity and ultrasonic velocity appears in the vicinity of two phase transitions at 145 K and 220 K. In AgBiP2S6 layered crystals the only one anomaly of ultrasonic velocity and attenuation was observed at 220 K. In these crystals below room temperature the large ultrasonic attenuation and corresponding velocity dispersion were observed. Such ultrasonic behaviour was supposed to be determined by acoustoionic interaction due to large ionic conductivity of Ag+ cations. [ABSTRACT FROM PUBLISHER]

Ultrasonic method was applied for evaluation of piezoelectricity in layered crystals of CuInP2S6 family and of La(Mg1/2Ti1/2)O3-BaTiO3 (BT-LMT) electroceramics. Amplitude of electric signal appearing on the plate under ultrasonic excitation is proportional to appropriate piezoelectric constant. In CuInP2S6 family piezosensitivity was observed only in low temperature phase. In BT-LMT ceramics piezosensitivity had anomalies at low temperature phase transitions and had long tails in the high temperature paraelectric phase. Field-induced hysteresis loops of such ultrasonically detected piezoelectric signal amplitude in the ferroelectric phase were observed. In the paraelectric phase field-induced piezosensitivity due to electrostriction appeared in layered crystals and BT-LMT ceramics when DC bias electric field was applied. In centrosymetric AgInP2Se6 crystals comparatively large piezoelectric sensitivity was induced due to electrostriction by DC bias electric field applied along c-axis. [ABSTRACT FROM AUTHOR]

In current contribution we present results of elastic and piezoelectric investigations of CuInP2S6 crystals with applied DC electric field along polar c-axis. The behaviour of piezoelectric effect have been controlled by measuring of the signal appearing on CuInP2S6 plate, which works as receiving ultrasonic transducer. It was shown that piezoelectric sensitivity in the polar phase increases with DC field, then saturates, and after reversion of voltage the piezoelectric signal decreases, at field near coercive changes sign, and saturates again at high voltage of opposite polarity. Consequently, the hysterezis loops of piezoelectric signal amplitude were observed. In the vicinity of coercive field peaks of longitudinal ultrasonic attenuation, elastic nonlinearity and ultrasonic velocity minima were observed. The layered CuInP2S6 crystals exhibit extremely large elastic nonlinearity. [ABSTRACT FROM AUTHOR]

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]

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 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]

The investigation results of ultrasonic and piezoelectric properties of Sn 2 P 2 (S,Se) 6 , CuInP 2 S 6 and CuCrP 2 S 6 ferroelectric-semiconductors single crystals are presented. In Sn 2 P 2 S 6 type crystals ultrasonic attenuation caused by acoustoelectric interaction after illumination showed fast and long term relaxations. Anomalies of ultrasonic velocity and attenuation at phase transitions have been established in CuInP 2 S 6 and CuCrP 2 S 6 crystals. The piezoelectric detection of longitudinal ultrasonic signal by thin plate of CuCrP 2 S 6 crystal was observed. In the high temperature phase pretransitional effects in ultrasonic and piezoelectric properties were clearly seen. Such effects can be determined by polar clusters, existing above phase transition temperature. [ABSTRACT FROM AUTHOR]