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The combination of PbHfO3 and PbSnO3 in perovskite solid solutions presents valuable opportunities to study the formation mechanisms of incommensurate phases. Crystals of PbHf1-xSnxO3 with 8% Sn were grown and measured using broadband dielectric spectroscopy to investigate the nature of relaxation and the effects of phase transitions. Our findings reveal significant alterations in the dielectric response of the PbHf0.92Sn0.08O3 solid solution, shedding light on the influence of Sn doping on lattice dynamics during the phase transition. [ABSTRACT FROM AUTHOR]

Recently, hybrid double-perovskite structures have attracted attention due to their versatile multifunctional properties originating from the variety of different constituent units in these materials. Here, we report the synthesis and comprehensive multitechnique characterization of a novel hybrid double-perovskite formate-based material [CH3CH2NH3]2NaGa(HCOO)6. The heat capacity measurements indicate that this compound has a structural phase transition at 379 K. In the low-temperature phase, the compound crystallizes in the non-centrosymmetric polar Pn structure, which exhibits a long-range order of ethylammonium (EA+) cations. Surprisingly, the Pn space group is not affected by the transition to the high-temperature disordered phase, which indicates that the transitions are isosymmetric making this compound a unique member of the formate-based double-perovskite family. The presence of the second-harmonic generation response in both phases confirms their non-centrosymmetric nature, while the dielectric spectroscopy experiments reveal that the transitions have a continuous order–disorder character. The observation of the pyroelectric current, but the absence of the electric polarization switching indicate that this compound is not properly ferroelectric. The electron paramagnetic resonance experiments of a compound slightly doped with paramagnetic Fe3+ impurities confirm the continuous character of the transition and allow us to probe the EA+ cation and framework dynamics in this system. The vibrational spectroscopy data confirm that the phase transition is primarily driven by the progressive ordering of EA+ cations and the resulting changes in the hydrogen bond strength. The temperature-dependent luminescence studies show that the [EA]2NaCr0.931Ga0.069(HCOO)6 perovskite is a promising material for noncontact temperature monitoring. [ABSTRACT FROM AUTHOR]

Using DFT-based molecular dynamics simulation of Cu+ cations flipping and In3+ cations displacive dynamics, we clarify the dipole ordering of CuInP2S6 ferrielectrics through the second order Jahn-Teller effect which determines the double-well potential for copper cations as well as three-well potential for indium cations inside the structural layers. The temperature dependence of the spatial distribution of Cu+ and In3+ cations is also described within the quantum anharmonic oscillator model. In3+ cations play a decisive role in the character of the polar ordering: at ambient or for positive pressures, the first order transition occurs; with the rise of negative compression, the ferrielectric transition evolves to the second order. The peculiarities of spontaneous polarization switching are related to the contributions of copper and indium cationic sublattices. [ABSTRACT FROM AUTHOR]

Using DFT-based molecular dynamics simulation of Cu+ cations flipping and In3+ cations displacive dynamics, we clarify the dipole ordering of CuInP2S6 ferrielectrics through the second order Jahn-Teller effect which determines the double-well potential for copper cations as well as three-well potential for indium cations inside the structural layers. The temperature dependence of the spatial distribution of Cu+ and In3+ cations is also described within the quantum anharmonic oscillator model. In3+ cations play a decisive role in the character of the polar ordering: at ambient or for positive pressures, the first order transition occurs; with the rise of negative compression, the ferrielectric transition evolves to the second order. The peculiarities of spontaneous polarization switching are related to the contributions of copper and indium cationic sublattices. [ABSTRACT FROM AUTHOR]

The broadband dielectric properties of high sensitivity piezoelectric 0.36BiScO3-0.64PbTiO3 ceramics with average grain sizes from 1.6 μm down to 26 nm were investigated in the 100–500 K temperature range. The grain size dependence of the dielectric permittivity was analysed within the effective medium approximation. It was found that the generalised core-shell (or brick wall) model correctly explains the size dependence down to the nanoscale. For the first time, the grain bulk and boundary properties were obtained without making any assumptions of values of the parameters or simplifications. Two contributions to dielectric permittivity of the grain bulk are described. The first is the size-independent one, which follows the Curie-Weiss law. The second one is shown to plausibly follow the Kittel's law. This seems to suggest the unexpected persistence of mobile ferroelectric domains at the nanoscale (26 nm grains). Alternative explanations are discussed. [ABSTRACT FROM AUTHOR]

In this paper, the full-wave analysis of the direct scattering problem in the rectangular waveguide is derived. The numerical calculation results of the scattering characteristics are presented. To show the advantage of our proposed model, we compared direct problem results with three-dimensional simulation software Ansys HFSS calculations. An excellent agreement is observed when compared these two approaches. [ABSTRACT FROM AUTHOR]

Dielectric properties of 0.945([Bi.sub.0.5][Na.sub.0.5])Ti[O.sub.3]-0.055BaTi[O.sub.3] (BNBT5.5) ceramics are analyzed. The studies have shown that BNBT5.5 is a relaxor with a characteristic relaxation time that follows Vogel-Fulcher's law and the Vogel-Fulcher parameters of the relaxation time are calculated.

Dielectric properties of barium titanate (BaTi[O.sub.3]) particles, synthesized directly in the pores of MCM-41 materials, are investigated. The results have confirmed successful incorporation of BaTi[O.sub.3] into porous matrix, but no phase transition is observed from paraelectric to ferroelectric phase as the particle size is smaller than the critical size.

The dielectric properties of nanograin ferroelectric lead titanate crystals are examined. The results have shown that the distribution of nanoparticle sizes in the sample taken into account with the Monte Carlo method describes the dielectric properties of PbTi[O.sub.3] nanocrystals quite well.

Broad-band dielectric and phonon response of Nb-doped (1-x)Pb(Zr1-yTiy)O3-xCoFe2O4 composites with x=10%–30% was investigated between 0.1 MHz and 100 THz. At room temperature, a broad distribution of relaxation times causes a constant dielectric loss below 1 GHz. Above room temperature, a strong Maxwell-Wagner relaxation process dominates below 1 GHz due to the conductivity of CoFe2O4 (CF). Two additional relaxation processes are seen between 1 GHz and 1 THz. The lower-frequency one, coming from domain wall motion, disappears above TC≈650 K. The higher-frequency component slows down on heating towards TC, because it is the central mode, which drives the ferroelectric phase transition. Time-domain THz transmission and infrared reflectivity spectra reveal a mixture of polar phonons from both ferroelectric Nb-doped Pb(Zr,Ti)O3 (PZTN) and magnetic CoFe2O4 (CF) components, while the micro-Raman scattering spectra allow to study phonons from both components separately. Similar temperature behavior of phonons as in the pure PZTN and CF was observed. While in CoFe2O4 the Raman-active phonons gradually reduce their intensities on heating due to increasing conductivity and related reduced Raman-scattering volume, some phonons in PZTN disappear above TC due to change of selection rules in the paraelectric phase. Like in the pure Pb(Zr,Ti)O3, the soft phonon and central modes were also observed. [ABSTRACT FROM AUTHOR]

Noise and electrical transport properties of composites based on epoxy resin filled with various carbon inclusions (single-walled carbon nanotubes, high surface area carbon black, and exfoliated graphite) were investigated in depth. The temperature dependence of resistivity shows that Mott's hopping and tunneling between conductive carbon particles dominate the charge carrier transport at low temperature, whereas a positive temperature coefficient effect occurs at higher temperature. Low-frequency noise spectra of the investigated materials comprise 1/fα type components. The noise level is the highest for composites close to the percolation threshold. The percolation threshold value of the system also strongly impacts both the temperature dependence of the noise level and the resistivity. Close to the percolation threshold, the noise level increases due to the carrier tunneling throughout the polymer matrix and decreases due to the rapid expansion of the polymer matrix. In contrast, the latter has almost no influence on the noise level far above the percolation threshold, and the small kink in the temperature dependence of the noise level indicates a crossover between tunneling and thermally activated electron transport mechanisms. [ABSTRACT FROM AUTHOR]

It is well known that disordered relaxor ferroelectrics exhibit local polar correlations. The origin of localized fields that disrupt long‐range polar order for different substitution types, however, is unclear. Currently, it is known that substituents of the same valence as Ti4+ at the B‐site of barium titanate lattice produce random disruption of TiOTi chains that induces relaxor behavior. On the other hand, investigating lattice disruption and relaxor behavior resulting from substituents of different valence at the B‐site is more complex due to the simultaneous occurrence of charge imbalances and displacements of the substituent cation. The existence of an effective charge mediated mechanism for relaxor behavior appearing at low (<10%) substituent contents in heterovalent modified barium titanate ceramics is presented in this work. These results will add credits to the current understanding of relaxor behavior in chemically modified ferroelectric materials and also acknowledge the critical role of defects (such as cation vacancies) in lattice disruption, paving the way for chemistry‐based materials design in the field of dielectric and energy storage applications. [ABSTRACT FROM AUTHOR]

Highlights The electromagnetic properties of epoxy‐based composites filled with carbon‐coated copper (Cu@C) nanoparticles and multi‐walled carbon nanotubes (MWCNTs), along with hybrid MWCNT/Cu@C/Epoxy systems containing varying concentrations of nanoinclusions, were systematically investigated across multiple frequency and temperature ranges. Measurements were conducted in the low‐frequency range (20 Hz–1 MHz) and over a temperature span of 40–500 K, as well as in the microwave frequency range (26–37 GHz) at room temperature. The percolation threshold was identified at approximately 2.5 vol% for composites containing only Cu@C nanoparticles and at 0.3 vol% for composites with MWCNTs. Notably, the hybrid MWCNT/Cu@C/Epoxy composites exhibited significantly enhanced electromagnetic properties compared to those of the single‐filled systems. At room temperature, an epoxy composite containing 5 vol% Cu@C and 1 vol% MWCNT exhibits a conductivity of approximately 4 × 10−2 S/m, which increases by nearly two orders of magnitude following a thermal cycle up to 500 K. The total electromagnetic interference (EMI) shielding effectiveness in the 26–37 GHz range was measured between 4 and 9 dB, indicating the material's promising potential for attenuating microwave noise. Dynamic mechanical analysis (DMA) results revealed that increasing the MWCNT content improved the storage modulus of the composites but led to a reduction in the glass transition temperature (Tg), which was observed to range between 40 and 50°C. The incorporation of MWCNTs and Cu@C nanoparticles into epoxy matrices offers a promising approach for the development of lightweight multifunctional composites with superior electrical, mechanical, and EMI shielding properties. The percolation threshold in MWCNT/Epoxy composites is 0.3%. The percolation threshold in Cu@C/Epoxy composites is 2%. The conductivity value of MWCNT/Cu@C/Epoxy composites is around 4 × 10−2 S/m. The total shielding effectiveness in the Ka‐band range between 4 and 9 dB. Glass transition temperature of MWCNT/Cu@C/Epoxy is between 40 and 50°C. [ABSTRACT FROM AUTHOR]