V. Samulionis

Dielectric and ultrasonic investigation of phase transition in cuinp2s6 crystals

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.

Ultrasonic dispersion in the phase transition region of ferroelectric materials

Abstract Measurements of longitudinal ultrasonic velocity and attenuation have been performed in several ferroelectric materials. Interesting behaviour of the ultrasonic velocity was observed in Ca 2 Sr(C 2 D 5 CO 2 ) 6 (DDSP) single crystals. The temperature dependence of τ in the DDSP crystal was estimated to be 3.5 × 10 −9 /( T − T c ) s.

Investigation of Ultrasonic and Acoustoelectric Properties of Ferroelectric-Semiconductor Crystals

The ultrasonic velocity and attenuation anomalies were observed near phase transitions (PT) in CuInP2(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.

Elastic and electromechanical properties of new ferroelectric-semiconductor materials of Sn2P2S6 family

Abstract The crystals of ferroelectric-semiconductor Sn2P2S6 exhibit a strong piezoelectric effect. We present measurements of ultrasonic and piezoelectric properties of other crystals of the Sn2P2S6 family: i.e., Sn2P2Se6 and CuInP2S6. The acoustoelectric method was applied to measure electromechanical coupling parameters in the ferroelectric phase of Sn2P2Se6 single crystals. The electromechanical coupling coefficients in lamellar CuInP2S6 crystalline plates were measured by the resonance method. The CuInP2S6 plate was employed as a piezoelectric transducer. The signal detected by this transducer was measured as a function of temperature and it was shown that the piezoelectric coupling disappears in the paraelectric phase. Anomalies at the phase transition have been observed at ultrasonic investigations of CuInP2S6 crystals.

Ultrasonic and Piezoelectric Investigation of Sn2P2S6 Type Photosensitive Ferroelectric-Semiconductor Crystals

The investigation results of ultrasonic and piezoelectric properties of Sn2P2(S,Se)6, CuInP2S6 and CuCrP2S6 ferroelectric-semiconductors single crystals are presented. In Sn2P2S6 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 CuInP2S6 and CuCrP2S6 crystals. The piezoelectric detection of longitudinal ultrasonic signal by thin plate of CuCrP2S6 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.

The Characterization of Two Dimensional Electrostrictive CuInP2S6 Materials for Transducers

The electromechanical properties of layered, two-dimensional materials of CuInP2S6 family have been investigated. It was shown that, at room temperature, which is above phase transition and under DC bias electric field, these materials behave as a piezoelectric because of electrostriction. In this case, the piezoelectric and electromechanical coupling coefficients are odd functions of the bias field and have a linear dependence on the bias field. The relative changes of ultrasonic velocity are found to have a quadratic dependence on the bias DC field. In bias fields of about 20 kV/m, the values of square of electromechanical coupling coefficient could be high enough (>20%) for longitudinal vibrations in thin plates of investigated CuInP2(S,Se)6 materials in the paraelectric phase. In the ferroelectric phase, the external DC electric field acts as polarizing field and electromechanical coupling coefficients sufficiently increase. At the transitions, the piezoelectric anomalies have been observed.

Orientational dependence of ultrasonic velocity near the phase transition in Sn2P2S6 single crystals

Abstract The results of ultrasonic velocity and attenuation measurements in Sn2P2S6 semiconductor crystals near the ferroelectric phase transition are presented for X, Y, Z crystalografic directions. It is shown that in ferroelectric phase for Y and Z directions the temperature dependencies can be well described by Landau theory and dispersion does not occur in the frequency range 10 MHz — 17 GHz. The strong frequency dispersion of ultrasonic velocity have been observed only in the direction of ferroelectric X axis.

Sound behavior near the Lifshitz point in proper ferroelectrics

The interaction between soft optic and acoustic phonons was investigated for

The Critical Behaviour of Ultrasonic Velocity at a Second‐Order Phase Transition in Sn2P2S6 Single Crystals

{\text{Sn}}_{2}{\text{P}}_{2}{({\text{Se}}_{0.28}{\text{S}}_{0.72})}_{6}

Dipolar Glass Behaviour in Mixed CuInP2(S0.7Se0.3)6 Crystals

proper uniaxial ferroelectrics by Brillouin-scattering and ultrasonic pulse-echo techniques. The elastic softening of hypersound velocity of transverse-acoustic phonons and for both longitudinal and transverse ultrasound waves which propagate near direction of the modulation wave vector (in the incommensurate phase at