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Broadband dielectric properties of tungsten disulfide (WS2) nanotubes/polyurethane (PU) composites over a wide temperature range (300 K–450 K) are presented for concentrations up to 2 wt%. Although no electrical percolation was observed in composites, at room temperature the dielectric permittivity of thermosetting composites with 2 wt% inclusions is 2 times higher than the dielectric permittivity of the pure polymer, that indicate that the composites are suitable for antistatic applications. Broadband dielectric properties of the composites are mainly governed by the α relaxation, the dynamics of the "soft" molecular segment of the PU chain. The Vogel temperature decreases with increase in the concentration of the WS2 nanotubes. At higher temperatures (above 380 K) the electrical conductivity dominates in properties of pure PU and composites with the WS2 inclusions as well. The DC conductivity increases with the WS2 concentration in thermosetting composites, while its activation energy is almost independent from the WS2 concentration far from melting point. The DC conductivity has some change in slope close to 420 K. Above room temperature, the large ultrasonic relaxational attenuation maxima and the velocity dispersion were observed. It was found that the attenuation peak in composites shifted to lower temperatures after addition of nanoparticles. The ultrasonic attenuation data of thermosetting composites were fitted to the relaxation equation with the single temperature‐dependent relaxation time. The thermal activation energy of the relaxation process, which was calculated from the ultrasonic data, was found to increase in PU with the concentration of WS2 nanotubes. POLYM. COMPOS., 39:4477–4485, 2018. © 2017 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

In SnPS ferroelectric under compression, the second-order phase transition line is observed down to the tricritical point as the transition temperature decreases to 250 K. A tricriticality at a similar temperature is also revealed in the mixed crystals on SSe substitution. For the mixed crystals with SnPb substitution, ultrasound, hypersound, and low-frequency dielectric studies also show heterophase features appearing on decrease of the ferroelectric transition temperature below a so-called 'waterline temperature' near 250 K. Such behavior agrees with the Blume-Emery-Griffiths (BEG) model appropriate for the ferroelectric system under investigation with a three-well local potential for the order parameter fluctuations. The BEG model modified by the random-field phase diagram in the vicinity of the tricritical point qualitatively explains the influence of the cationic substitution on the (PbSn)PS ferroelectric properties. [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.