Journal of Advanced Dielectrics

In this study, carbon black (CB) powder-loaded polyurethane (PU) composites (CB–PU composites) were prepared by melt mixing method with different volume percentages (45, 50, 55, 58 and 61 vol.%) of CB in the PU matrix. The prepared CB–PU composites had been further studied for surface morphology using the field-emission scanning electron microscopy (FESEM) technique. Dielectric properties in terms of real permittivity ($𝜀\prime )$ and imaginary permittivity ($𝜀\prime \prime )$ of the fabricated composites were computed using an Agilent E8364B vector network analyzer in the frequency range of 8–12 GHz ($X$-band). Dielectric loss factor of the prepared CB–PU composites was computed in terms of the dielectric loss tangent (tan ${\delta }_e$ = $𝜀\prime \prime$/$𝜀\prime )$. Microwave absorbing properties were appraised in terms of the reflection loss (RL) which in turn was calculated for varying thicknesses of the prepared composites from the measured real and imaginary permittivity data. The minimum RL was observed as −20.10 dB for the absorber with a thickness of 2.2 mm and the bandwidth achieved was 1.92 GHz for RL $\le -$10 dB. Based on the above results these CB–PU composites have potential use as effective microwave absorbers in 8–12-GHz ($X$-band) frequency range.

Thin films of polycrystalline (Ba${{}_{1-}}_x$${\text{Sr}}_x)$TiO₃ ($x$ = 0.2 and 0.3) with Perovskite structure were prepared by a dip and dry technique on a platinum-coated silicon substrate. The good quality thin films with uniform microstructure and thickness were successfully produced by dip-coating techniques annealed at 730${}^{\circ }$C for 1 h. The resulting thin film shows a well-developed dense polycrystalline structure with more uniform grain size distribution. The BST thin films were characterized for their structural, Raman spectroscopy, morphological properties, and complex impedance properties. The dielectric constant-frequency curve showed the good dielectric constant and loss dielectric loss with low-frequency dispersion. The BST 0.3 thin film reveals that the dielectric constant and dielectric loss at a frequency of 1 kHz were 578 and 0.02, respectively. The obtained results on dielectric properties can be analyzed in terms of the Maxwell–Wagner model.

Structural and dielectric properties of Ce-doped ${\text{BaTi}}_{0.97}$${\text{Y}}_{0.03}$O₃ powders, with the chemical formulation (Ba${{}_{1-}}_x$${\text{Ce}}_x)$(Ti(${{}_{0.97-}{}_x}_{/4})$- ${\text{Y}}_{0.03})$O₃ such as $x$ = 0%, 1%, 3%, 5%, 7% and 9%, produced by the sol–gel method, have been investigated. X-ray diffraction analysis showed that Ce${}^{3+}$ ions incorporated Ba sites until $x$= 7% indicating that this concentration represents a solubility limit of Ce${}^{3+}$ ions in ${\text{BaTi}}_{0.97}$${\text{Y}}_{0.03}$O₃ matrix. Scanning electron microscopy (SEM) analysis showed a decrease in grain size down to the same concentration of 7%. Raman spectroscopy analysis showed the appearance of ${\text{A}}_{1g}$ mode, which we attributed to the effect of incorporation of Ce${}^{3+}$ and Y${}^{3+}$ in BaTiO₃ matrix. Dielectric measurements revealed that doping with cerium lowers the temperature of permittivity maximum at the ferroelectric-to-paraelectric transition (FPT) of the ${\text{BaTi}}_{0.97}$${\text{Y}}_{0.03}$O₃ sample, and reaches a value that should be below ${40}^{\circ }$C for $x$= 9%. Moreover, the phenomenon of dielectric resonance was observed on all Ce-doped samples, which was not the case with other dopants as reported in the literature.

The coming Big Data Era requires progress in storage and computing technologies. As an emerging memory technology, Resistive RAM (RRAM) has shown its potential in the next generation high-density storage and neuromorphic computing applications, which extremely demand low switching voltage and power consumption. In this work, a 10 nm-thick amorphous GeS₂ thin film was utilized as the functional layer of RRAM in a combination with Ag and Pt electrodes. The structure and memory performance of the GeS₂-based RRAM device was characterized — it presents high on/off ratio, fast switching time, ultralow switching voltage (0.15 V) and power consumption (1.0 pJ and 0.56 pJ for PROGRAM and ERASE operations, respectively). We attribute these competitive memory characteristics to Ag doping phenomena and subsequent formation of Ag nano-islands in the functional layer that occurs due to diffusion of Ag from electrode into the GeS₂ thin film. These properties enable applications of GeS₂ for low energy RRAM device.

Bis-Tetrapropylammonium tetrabromozincate was synthesized and characterized by X-ray powder diffraction, as well as vibrational and impedance spectroscopy. Rietveld’s refinement of X-ray diffractogram confirmed the crystallization of the compound through the monoclinic system (space group ${\text{C}}_{2/c})$. A temperature study of Raman scattering revealed two phase transitions at approximately $T_1$ = 340 K and $T_2$ = 393 K. The wavenumber and the line width’s evolution as a function of temperature showed some peculiarities associated with these transitions, which suggests that they are governed by the reorientation of the organic part [N(C₃${\text{H}}_7{)}_4$]${}^{+}$. The complex impedance plotted as a double semicircular arc in the studied temperature range and the centers of these semicircles lie below the real axis, which indicates that the material is an on-Debye type. These semicircular arcs are related to the bulk and the grain boundary effects. Furthermore, the alternating current conductivity of [N(C₃${\text{H}}_7{)}_4$]₂ZnBr₄ obeyed Jonscher’s law: ${\sigma }_{AC}(\omega )$ = ${\sigma }_{dc}+A{\omega }^s$ and the conduction could be attributed to the correlated barrier hopping (CBH) model in both region(I) and (II) and the Non-overlapping Small Polaron Tunneling (NSPT) in region (III).

The article presents the results of research the pre-transitional features of the behavior of solid solutions based on lead zirconate-titanate. The presence of a “special” critical temperature $T_d$ on the temperature dependences of the permittivity $𝜀(T)$ and the remanent polarization $P_r(T)$, preceding the temperature of the paraelectric phase transition at the Curie temperature $T_C$, is noted. In the temperature range $T$ < $T_d$, the $P_r(T)$ dependence obeys a power law. In the temperature range $T_d$<$T$<$T_C$, this law is not fulfilled. The results of X-ray experiments make it possible to associate this behavior with reversible disordering at $T$<$T_d$ of an ordered domain structure formed during the polarization of piezoelectric ceramics and with its irreversible disordering in the temperature range $T_d$<$T$<$T_C$. This is due to the appearance of internal mechanical stresses in a polycrystalline ferroelectric due to irreversible depolarization of the samples at temperatures $T_d$<$T$<$T_C$.

(${\text{Y}}_x$Bi${{}_{1-}}_x{)}_{2/3}$Cu₃Ti₄${\text{O}}_{12}$ ($x=$ 0.00–0.30) ceramics were successfully prepared via the conventional solid-state method. X-ray powder diffraction confirmed the lattice constant gradually decreases with increasing Y${{}^3}^{+}$ content. SEM images displayed Y${{}^3}^{+}$ substitution for Bi${{}^3}^{+}$ gave rise to the large abnormal grains, and the size of abnormal grains became larger with the increase of Y${{}^3}^{+}$ substitution. (${\text{Y}}_x$Bi${{}_{1-}}_x{)}_{2/3}$Cu₃Ti₄${\text{O}}_{12}$ ceramics presented the relatively high dielectric constant of 7400 with the dielectric loss of 0.055 when $x=$ 0.20. The analysis of complex impedance suggested the grains are semiconductive and the grain boundaries are insulating. For pure ${\text{Bi}}_{2/3}$Cu₃Ti₄${\text{O}}_{12}$ ceramics, the appearance of additional low-frequency peaks in electrical modulus indicated the grain boundaries are heterogeneous. The investigation of modulus peaks fitting with Arrhenius formula implied that the low-frequency permittivity for all (${\text{Y}}_x$Bi${{}_{1-}}_x{)}_{2/3}$Cu₃Ti₄${\text{O}}_{12}$ ceramics was ascribed to the Maxwell–Wagner relaxation at grain boundaries. In addition, a set of clear dielectric peaks above ${200}^{\circ }$C associated with Maxwell–Wagner relaxation can be found for all (${\text{Y}}_x$Bi${{}_{1-}}_x{)}_{2/3}$Cu₃Ti₄${\text{O}}_{12}$ ceramics in the temperature dependence of dielectric constant. This set of clear dielectric peaks showed a tendency to shift to higher temperatures with the increase of Y${{}^3}^{+}$ substitution. Meanwhile, a tiny dielectric anomaly at room temperature was found in Y-doped ${\text{Bi}}_{2/3}$Cu₃Ti₄${\text{O}}_{12}$ ceramics.

In order to combine the properties of inorganic ion exchanger and conducting organic polymer, a new class of organic–inorganic composite cation exchanger PANI–Ti(IV) phosphosulphosalicylate (PTPSS) was synthesized by intercalating polyaniline (PANI) into Ti(IV) phosphosulphosalicylate (Ti(IV) PSS) using sol–gel chemical route with enhanced properties. PTPSS has been characterized by using Fourier Transform Infrared Spectroscopy (FT-IR), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Energy dispersive X-ray (EDAX), thermo gravimetric analysis (TGA-DTG), and Transmission Electron Microscopy (TEM). Ac electrical conductivity studies were also performed. This material possessed electrical conductivity of ${10}^{-3}$ – ${10}^{-6}$ ${\text{Scm}}^{-1}$which falls in the semiconducting range. The frequency (2 × 10⁵ – 1 × 10⁶ Hz) dependent Ac conductivity at room temperature suggests the evidence for the transport mechanism for the conductivity in PTPSS. The structure of the composite cation exchanger extremely supports its conducting behavior.