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Samulionis V.,Vilnius University | Banys J.,Vilnius University | Vysochanskii Y.,Institute of Solid State Physics and Chemistry of Uzhgorod University
Materials Science Forum | Year: 2010

The paper reviews recent results of ultrasonic and piezoelectric investigation in CuInP2S6 family ferroelectric layered crystals and their solid solutions in the temperature range 100-360 K. It was shown that, Cu substitution by Ag lowers the phase transition temperature. In investigated AgxCu1-xInP2(S,Se)6 crystals above the phase transition (PT) temperature the piezoelectric response was absent and appeared only below the transition. At low temperatures T < 220 K the layered AgxCu1-xInP2Se6 crystals are ferroelectric. Piezoelectric sensitivity in the ferroelectric phase increases with DC field applied along the c-axis, 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 In the paraelectric phase under external DC electric field, applied along c-axis normal to layers, thin AgxCu1-xInP2Se6 plates can effectively excite and detect ultrasonic waves, due to electrostriction. The same behaviour was observed and in AgxCu 1-xInP2S6 crystals. The critical ultrasonic velocity anomalies were observed in the vicinity of PT. In CuInP 2S6 crystals with addition of In i.e. indium rich materials the phase transition temperature could be raised to T > 330 K what is important for applications in medical diagnostics ultrasonic transducers. In all these materials the poling conditions were investigated and it was shown that after long time exposing in DC field the piezoelectric sensitivity sufficiently increases and electromechanical coupling constants as high as > 50 % could be obtained. © (2010) Trans Tech Publications. Source


Dziaugys A.,Vilnius University | Banys J.,Vilnius University | Vysochanskii Y.,Institute of Solid State Physics and Chemistry of Uzhgorod University
Ferroelectrics | Year: 2013

The dielectric properties of Mn2P2S6 and Cu0.52Mn1.74P2S6 crystals were investigated in broad frequency (20 Hz - 1 MHz) and temperature range (100 K - 470 K). No anomaly in temperature dependence of complex dielectric permittivity indicating the polar phase transition can be detected in measured temperature range. The dielectric properties of presented crystals are mainly caused by high conductivity. The frequency spectra of conductivity obey the Almond-West power law. The activation energy of conductivity was found to be EA/k = 0.845 eV (Mn2P2S6) and EA/k = 0.81 eV (Cu0.52Mn1.74P2S6). A suggestion is given that the electric conductivity in these crystals can be interpreted by electronic mechanism. © 2013 Copyright Taylor and Francis Group, LLC. Source


Dziaugys A.,Vilnius University | Banys J.,Vilnius University | MacUtkevic J.,Lithuanian Academy of Sciences | Vysochanskii Y.,Institute of Solid State Physics and Chemistry of Uzhgorod University | And 2 more authors.
Phase Transitions | Year: 2011

Investigation results of dielectric (20 Hz-1 MHz) properties of layered CuBiP2Se6 crystals are presented. The temperature dependence of the static dielectric permittivity reveals the first-order "displacive" antiferroelectric phase transition at Tc = 136 K. In the paraelectric phase, at low frequencies, dielectric spectra are highly influenced by the high ionic conductivity with the activation energy of 2473 K (0.21 eV). In the antiferroelectric phase the electrical conductivity and its activation energy (531.1 K (0.045 eV)) are considerably smaller. At low temperatures, the temperature behaviour of the distribution of relaxation times reveals complex freezing phenomena. A part of long relaxation time distribution is strongly affected by external direct current (DC) electric field and it is obviously caused by antiferroelectric domain dynamics. © 2011 Taylor &Francis. Source

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