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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]

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]

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]

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]

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]

A series of highly flexible and environmentally friendly composites based on polydimethylsiloxane (PDMS) filled with 200 nm size ferroelectric BaTiO 3 (BTO) particles at different concentrations (from 7 to 23 vol %) have been fabricated by a simple dispersion method. The dielectric, piezoelectric, and ultrasonic properties have been studied. The ferroelectric state of BTO was confirmed by differential scanning calorimetry and ultrasonic spectroscopy. The addition of BTO into PDMS strongly affects the dielectric properties of the composites. At low temperatures close to 160 K, the PDMS matrix exhibits a dielectric anomaly related to a dynamic glass transition, which shifts to higher temperatures as the BTO content increases due to the strong interaction between polymer chains and nanoparticles. Ultrasonic measurements demonstrate the appearance of a piezoelectric voltage signal on a thin plate of the composite with the highest available filler concentration (23 vol %) under longitudinal stress applied by a 10 MHz ultrasonic wave. As a result, at room temperature, the detected signal is characterized by output voltage and specific stored energy values of 10 mV and 367.3 MeV/m 2 , respectively, followed by a further increase with cooling to 35 mV at 150 K. The proposed BTO/PDMS composite system is thus a potential candidate for nanogenerators, namely, a simple, flexible, and lead-free device converting high-frequency (10 MHz) mechanical vibrations into electrical voltage., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

Cation engineering provides a route to control the structure and properties of hybrid halide perovskites, which has resulted in the highest performance solar cells based on mixtures of Cs, methylammonium, and formamidinium. Here, we present a multi-technique experimental and theoretical study of structural phase transitions, structural phases and dipolar dynamics in the mixed methylammonium/dimethylammonium MA 1-x DMA x PbBr 3 hybrid perovskites (0 ≤ x ≤ 1). Our results demonstrate a significant suppression of the structural phase transitions, enhanced disorder and stabilization of the cubic phase even for a small amount of dimethylammonium cations. As the dimethylammonium concentration approaches the solubility limit in MAPbBr 3 , we observe the disappearance of the structural phase transitions and indications of a glassy dipolar phase. We also reveal a significant tunability of the dielectric permittivity upon mixing of the molecular cations that arises from frustrated electric dipoles.

We have investigated the dielectric response of Ba(2)Pr(x)Nd(1-x)FeNb(4)O(15) ceramics (x = 0, 0.2, 0.5, 0.6, 0.8, 1) in the frequency range from 20 Hz to 1 GHz. The obtained results confirmed the continuous transformation from the ferroelectric behavior of Ba2NdFeNb4O15 to the pure relaxor response of Ba(2)PrFeNb(4)O(15) with increasing x. For intermediate x values, coexisting ferroelectric transition and relaxor dielectric signatures were observed, corresponding to two different phenomena in the framework of these materials. Increasing the amount of Pr decreases the ferroelectric phase transition temperatures in these ceramics; a large cooling¿heating hysteresis exceeding 50K was also observed.