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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]

Dielectric properties of a ferroelectric liquid crystal 2-methylbutyl 4-decyloxybenzylidene-4'-n-aminocinnamate (DOBAMBC) confined in untreated and treated porous Anopore membrane were investigated depending on the frequency and temperature. The confinement of a ferroelectric liquid crystal in an untreated Anopore membrane leads to the disappearance of the Goldstone mode. Moreover, despite the modification of the pore surface with various surfactants, no the Goldstone mode or other additional relaxation processes were observed. The relaxation rate of the molecular δ-process is slightly shifted for untreated and treated Anopore membrane in comparison to the bulk. Generally, the relaxation rate temperature dependence shows the Arrhenius-type course, while for lecithin-treated Anopore, it is similar to the Vogel–Fulcher–Tammann-type dependence. Dielectric spectra are dominated at low frequencies by conductivity and electrode polarization effects and are modified in geometric constraints. [ABSTRACT FROM AUTHOR]

Bitumen with 50/70 penetration was prepared and modified by doping with the unsaturated polyester resin based on isophthalic acid at 5% by weight (w/w%). The structural, mechanical, and thermal properties of bitumen and bitumen modified with unsaturated polyester resin %5 (UPR) were determined. The dielectric properties of bitumen and modified bitumen were investigated in the frequency and temperature ranges of 0.1-106 Hz and (-)40°C- 40°C, respectively. Polarization mechanisms, glass-transition temperature, and ductility of all samples were determined and compared to each other. The glass transition temperature of the modified bitumen shifts toward low temperatures in comparison to the bitumen. So, it can be suggested that the use of modified bitumen is very attractive in regions where the temperature differences are high. Also, the dielectric analysis method is an innovative alternative to determining modified bitumen's low-temperature performance. It was found that the modification with UPR provide strength and flexibility to asphalt. [ABSTRACT FROM AUTHOR]

Epoxy nano-magnetic composites exhibit remarkable and promising properties by synergistically combining the properties of epoxy resin and magnetic nanofillers. The current study deals with the synthesis of Fe3O4, NiFe2O4, and CoFe2O4 nanoparticles and their respective nanoparticles-doped epoxy composites, as well as the structural, optical, and dielectric characterization of the resultant nano-composites. To investigate the surface morphology of the synthesized nanoparticles, field emission electron microscopy (FESEM) analysis was employed. By measuring electron diffraction spectroscopy (EDS), the presence of various chemicals was verified. X-ray diffraction (XRD) was used to determine the structural details of the synthesized nanoparticles and nanoparticles-doped epoxy composites. The structural chemistry and surface functionality of the nano-epoxy composites were investigated using Fourier transform infrared spectroscopy (FTIR). The magnetic properties of the synthesized nanoparticles and nanoparticles loaded epoxy composites were also studied using a vibrating sample magnetometer (VSM). UV–visible reflection spectroscopy was also carried out to find the optical properties of the synthesized nanoparticles, neat (undoped) epoxy, and nanoparticles-doped epoxy composites. Dielectric spectroscopy measurements of nanoparticles-doped epoxy composites were performed using an Agilent E4980A precision LCR (Inductance Capacitance Resistance) meter with an Agilent 16451B-test fixture LCR and vector network analyzer (VNA) in the frequency span of 10 kHz to 2 MHz and 200 MHz to 20 GHz, respectively. The influence of the synthesized nanoparticles on the neat (undoped) epoxy composites and the results in view of future applications are fully discussed. [ABSTRACT FROM AUTHOR]

Interfacial characteristics of nanocomposites are critical limiting factors in the design of polymer nanocomposites. The nanocomposites have complex structures and play a pivotal role in controlling functional properties. Analysis of interfacial layers in polymer nanocomposites, existing between the polymer matrix and the nanoparticles plays a major role in determining their characteristics. High-frequency analysis of electrical conductivity and dielectric properties of carbon nanofillers which are embedded in an epoxy matrix were analysed using alternating current dielectric spectra. This article provides a correlation between the electrical transport properties and dielectric behaviour of epoxy carbon nanocomposites at different temperatures are investigated with variations in frequency. Electrical transport properties of nanocomposites are primarily dictated by electron tunnelling and matrix, nanofillers conductivity. Dielectric spectroscopy in the frequency range 10 Hz–8 MHz has been performed on epoxy nanocomposites with and without hybrid carbon nanofillers at one weight percentage (2:3 ratio). Dominant dielectric relaxation mode is observed in the base composite at a low-frequency region (≥10 Hz), whereas nanocomposite with hybrid carbon nanofillers is observed to induce two dielectric relaxations in the kHz region. Increase in non-monotonic variations in dielectric spectra makes the nanocomposite suitable for high temperature low sag conductor core, aerospace and cryogenic engineering applications. [ABSTRACT FROM AUTHOR]

A new copper(II) complex with 2-amino-6-methylpyrimidin-4-(1H)-one, [Cu(C5H7N3O)4](NO3)2·H2O (Cupyrim), has been synthesized and studied by X-ray diffraction, elemental analysis and FT-IR spectroscopy. The Cu(II) is four-coordinate in a square planar geometry by four nitrogen atoms of the four organic ligands. Hirshfeld Surface Analysis was conducted to understand crystalline packing. Overall, the structure is maintained by metal coordination as well as strong and weak (C,N)–H···O hydrogen bonds and C–H...π interactions. The IR spectrum primary peaks have been assigned to the vibration modes of the ligand functional groups. An investigation of the inhibitory properties of Cupyrim toward "Cyclin-dependent Kinase 2" (CdK2) and "inducible nitric oxide synthase" (iNOS) proteins was aided by molecular docking research. According to molecular docking, Cupyrim exhibits promising inhibitory efficacy against Parkinson's, schizophrenia, and Alzheimer's disorders. The temperature dependence of the real and imaginary part of the dielectric permittivity was analyzed with the Cole-Cole formalism as well as DSC diagrams from 45-147 °C. [ABSTRACT FROM AUTHOR]

High-tilt angle ferroelectric liquid crystal material in surface stabilised geometry (SSFLC) is investigated for the smectic layer reorientation and its molecular dynamics by electro-optical and dielectric spectroscopy techniques. Smectic layer reorientation (5 $^o$ o to 45 $^o$ o ) is obtained by controlled cooling rate and applying electric field in the vicinity of transition temperature from chiral nematic (${N^*}$ N ∗ ) to chiral smectic C ($Sm{C^*}$ Sm C ∗ ) phase. After slow cooling down to room temperature, the stripe domain textures along the rubbing are observed with quasi-bistable states. Dielectric spectroscopy has revealed the unusual increment in the dielectric permittivity. A dielectric relaxation process at lower frequency than Goldstone mode with the increase in DC bias up to 2 $V$ V is observed in the sample cooled without any bias. This increment is found to be originated by the heliconical structure within the stripes which is seen in the optical textures recorded at the time of dielectric scan. However, this increment is not observed in the sample cooled under DC bias. Thus, there exist different phenomena in the high tilt angle SSFLC sample cooled in different conditions of DC bias; stripe domains, smectic layers reorientation, heliconical stricture and twisted structure within stripes which are significant to explore deeply in high-tilt angle ferroelectric liquid crystals. [ABSTRACT FROM AUTHOR]

The PANI-NiO composites were synthesized by employing an in situ chemical polymerization technique, with varying weight percentages of NiO dopant (PANI-5%NiO and PANI-10%NiO). Additionally, AC conductivity, dielectric constant and dielectric loss were investigated within a frequency range from 20 Hz to 1 MHz. XRD confirmed the phase purity and high crystallinity. SEM reveals the granular shape with a porous surface. In addition, the incorporation of NiO with different concentrations influences the composite’s dielectric properties. All samples exhibited frequency-dependent dielectric properties in line with the Maxwell–Wagner model. Notably, the AC conductivity of PANI-10% NiO composite increased as the frequency increased, this behaviour was certified with Jonscher’s power law. The I–V characteristics confirm the ohmic nature of all synthesized samples. Therefore, the potential of PANI and PANI-NiO composites, as efficient dielectric materials, has been explored and can be useful for device applications in diverse fields. [ABSTRACT FROM AUTHOR]

Broadband dielectric spectroscopy in the frequency range from 10−2 Hz to 107 Hz was used to study the effect of hydrophobic aerosil nanoparticles on the dynamics of the Goldstone mode in a ferroelectric liquid crystal near the point of spontaneous polarisation sign reversal. The obtained results show that an important role in the modification of the dynamics of the Goldstone mode and the phenomena at the point of spontaneous polarisation sign reversal is played not only by the presence of the nanoparticles themselves in the ferroelectric liquid crystal structure, but also the state of the surface of these nanoparticles. Similarly to the hydrophilic aerosil, the polarisation sign reversal temperature slightly decreases with the increase of the hydrophobic aerosil concentration. For small concentrations of hydrophobic aerosil, only slight changes in the dynamics of the Goldstone mode over the entire temperature range are detected. The observed deviations are due to the different influence of aerosil nanoparticles on the structure and dielectric properties of the tested composite caused by the specific surface treatment. The presence of the Goldstone mode above and below the point of polarisation sign reversal seems to confirm the model of two conformers with different structure and opposite dipole moments. [ABSTRACT FROM AUTHOR]

We studied the dielectric properties of a polar nematic phase (NF) sandwiched between two gold or ITO electrodes, serving as a cell surface. In bulk, NF is expected to exhibit a Goldstone mode (phason), because polarisation can uniformly rotate with no energy cost. However, because the coupling between the direction of nematic director and polarisation is finite, and the confinement, even in the absence of the aligning surface layer, induces some energy cost for a reorientation of polarisation, the relaxation frequency of the phason mode is measured in a kHz regime. The phason mode is easily quenched by a bias electric field, which enables fluctuations in the magnitude of polarisation to be followed in both the ferroelectric and paraelectric nematic phases. This amplitude (soft) mode is also influenced by boundary conditions. A theory describing the phase and amplitude fluctuations in the NF phase shows that the free energy of the system and, consequently, the dielectric response are dominated by polarisation-related terms with the flexoelectricity being relevant only at a very weak surface anchoring. Contributions due to the nematic elastic terms are always negligible. The model relates the observed low-frequency mode to the director fluctuations weakly coupled to polarisation fluctuations. [ABSTRACT FROM AUTHOR]

Solid solutions of (1-x)Pb(Ti0.5Zr0.5)O3–xCdNb2O6 system with x = 0.0125 ÷ 0.0500, Δx = 0.0125 were obtained by two-stage solid phase synthesis followed by sintering using conventional ceramic technology and experimental studies of crystal structure, dielectric, piezoelectric, and ferroelastic properties. At 0.0250 ≤ x the studied samples belonged to the region with a tetragonal unit cell, at 0.0250 < x ≤ 0.0375 they consisted of tetragonal phases with close cell parameters, and at x > 0.0375 a heterogeneous region was formed with clusters of phases with non-tetragonal symmetry. A twofold increase in the piezoelectric parameters was achieved compared to the PZT-Pb(W,Cd)O3 composition. [ABSTRACT FROM AUTHOR]

A new series of hydrogen-bonded liquid crystals was prepared by mixing 4-n-alkoxy-2.3-difluorobenzoic acid and 4-pentyl-4-biphenylcarbonitrile (5CB). Thermal and liquid crystal behaviour was established using differential scanning calorimetry and polarizing optical microscopy. The influence of terminal acid donors on mesogenic behaviour was discussed in detail. It was found that all complexes with a (1:1) molar ratio exhibit the smectic B phase. In addition, the binary phase diagram that has been established revealed that the mixtures with lower concentration exhibit a nematic phase at room temperature with large stability. Dielectric, electro-optic and viscoelastic properties of 5CB/9OBAFF with molar fraction x = 0.1 were discussed. [ABSTRACT FROM AUTHOR]

Hydrogen-bonded liquid crystals (HBLC) formed by mixing 4-alcyloxy-2-fluorobenzoic acid (nOBAF) and the 4-pentyl-4-biphenylcarbonitrile (5CB) at (1:1), (1:3) and (3:1) (mol/mol) ratios have been investigated. Four HBLC series are prepared by changing the carbon chain length from 7 to 10 designated 5CB/nOBAF. The fluorobenzoic acids (nOBAF) are the proton donors while the pyridine unit (5CB) is the proton acceptors. Thermal behaviour and phase diagrams of the individual series have been established using differential scanning Calorimetry (DSC) and polarising optical microscopy (POM). It was found that all complexes exhibit nematic (N) and smectic G (SmG) phases. For the nematic phase, the dielectric anisotropy was increased while the thresholds voltage was decreased. This can be explained by the strong longitudinal dipole moment of the nematic phase compared to the nOBAF compounds. Furthermore, as the alkoxy chain length increases, the birefringence, response time, rotational viscosity, and splay elastic constant all decrease by the way of the reduction of the order parameter for the longer chains. In addition, hydrogen-bonded proton transfer between cyano and carboxylic acid groups have been explored by Fourier transform infrared spectroscopy (FTIR) for the first time. [ABSTRACT FROM AUTHOR]

This paper describes a novel dielectric spectroscopic technique to investigate the milk freshness and adulterated agents using a customized, open-ended, coaxial probe. An inversely proportional relationship was found between temperature and shelf-life and the real part of the complex permittivity (e') of the samples at 0.1-3GHz. At 2GHz, a linear relationship was found in e' and e", storage time, and water content. In addition, total of five adulterants' agents were investigated and a linear relationship was found between both e' and e" parts, and their concentrations (R² > 0.99). This approach could be the potential basis of rapid online milk quality monitoring in milk production facilities. [ABSTRACT FROM AUTHOR]

A dielectric response spectrum formula applicable to a medium with ionic conductivity is presented. An analytical expression for the ionic conductivity spectrum σ(ω) of a material with the vibration-diffusion particle motion is discussed. The residence time τR is introduced into the model to drive a non-zero static conductivity σ(0). A τR change within ∞-0 continuously transforms the vibrational σ(ω)-Lorentzian into the diffusion σ(ω)-Drude response of free independent particles. [ABSTRACT FROM AUTHOR]

This paper presents the results of a study of the dielectric response in single crystals of barium strontium niobate doped with thulium of various concentrations. It is shown that the dielectric permittivity increases with increasing concentration of thulium. For as-grown samples the dispersion of the permittivity is observed in the frequency region of 106 Hz. The dependence is not observed for the samples polarized under DC field. For all the samples studied, the switched polarization increases and the coercive field decreases under action of an AC field. [ABSTRACT FROM AUTHOR]

The paper presents some general patterns of the temperature behavior of thermodepolarization currents, dielectric permittivity and conductivity of dielectric materials containing water molecules or hydrogen bonds – crystallohydrates, polyelectrolytes, and biopolymers. The results indicate that the anomalies of these properties are observed at 4, 20, 35, 46, 65–76°С, which are "threshold points" of water, when its structure changes abruptly. The observed anomalies are probably due to a change in the proton energy at a transition to an excited level in the double-well potential at heating, while the equilibrium of the system is achieved by slow stepwise heating. [ABSTRACT FROM AUTHOR]

Sn2P2(SexS1-x)6 (x = 0.1, 0.2 and 0.3) crystals were grown by the vapor transport technique and their dielectric, pyroelectric and ferroelectric properties in the vicinity of phase transition were evaluated. The dielectric properties of the investigated crystals show clear anomalies associated with the ferroelectric-paraelectric phase transitions in all the compositions. The spontaneous polarization behavior of Sn2P2(SexS1-x)6 crystals in the vicinity of the ferroelectric-paraelectric phase transition is discussed. The knowledge about the ferroelectric responses of Sn2P2(SexS1-x)6 crystals in a broad temperature range is essential for applications in the energy storage technology. The aim of this work was to investigate the dielectric, pyroelectric and ferroelectric properties of Sn2P2(SexS1-x)6 with different selenium content and compare to the parent compounds Sn2P2S6 and Sn2P2Se6. [ABSTRACT FROM AUTHOR]

Dielectric (impedance) spectroscopy of liquid crystals is a powerful experimental technique. It is especially essential because liquid crystals in many applications are still controlled by the electric field. In this paper, the problems with the high frequency (>1 MHz) measurements in classical (in the shape of the flat capacitor) measuring cells are discussed. The procedure for overcoming measurement difficulties was presented and applied to the dielectric response of antiferroelectric, binary mixture. Additionally, the paper presents the first example of extending the measuring range of dielectric spectroscopy from 1 MHz to ~50 MHz by overcoming the parasitic effect related to resonance in measuring setup. [ABSTRACT FROM AUTHOR]

We investigated the impact of two types of nanoparticles, magnetic (γFe2O3) and nonmagnetic one (CeO2) dispersed in nematic 5CB matrix. Dielectric spectroscopy was used to investigate the dielectric behavior of the nematic 5CB doped by both kinds of nanoparticles. By fitting a suitable equivalent electric circuit model to the experimental data we show the change of electro–physical parameters of the nematic in the bulk and at the nematic–electrode interface. It is found that the impedance modulus decreases with increasing the concentration of nanoparticles. This increase is attributed to an increase of the conductivity, which is related to the mobile charge carriers accumulating near the electrodes. For nonmagnetic nanoparticles, both the diffusion constant D and the mobility μ were increased with increasing concentration. Surprisingly, for magnetic nanoparticles, the increase of D and μ is followed by a considerable decrease at concentration higher than 3%. [ABSTRACT FROM AUTHOR]

Dielectric spectroscopic measurements of five homologous series of orthoconic antiferroelectric liquid crystalline (OAFLC) esters (S)-MHPOBC ((S)-4-(1-methylheptyloxy) carbonyl phenyl 4'-octyloxy-4-biphenylcarboxylate) has been investigated. The investigated compound contains SmC*, SmCA* and SmA phase with SmCA* phase at a broad temperature range. Parameters such as absorption curve, dispersion curve, Cole-Cole plot, relaxation frequency, relaxation time, dielectric strength and electrical conductivity has been discussed. The structure property correlations of these compounds are also highlighted in the light of the dielectric measurements. Compound S1.6 (FF) and S2.6 (FH) has dielectric strength of around 250 in the SmC* phase due to the presence of Goldstone mode. [ABSTRACT FROM AUTHOR]

In this work we present the results of study of the influence of Eu doping on temperature behavior of the dielectric response and conductivity in the frequency range of 10 Hz–1 MHz and the temperature range of 300–750 K, and low temperature (5–400 K) specific heat of the Na1/2Bi1/2TiO3 (NBT) single crystals. It is shown that volume conductivity of NBT is thermally activated with activation energies Ea = 75 meV at T < 320 K and Ea = 700–900 meV at T > 620 K. Eu doping of NBT modifies the behavior of the conductivity with the activation energy being the same at T < 320 K and the deviation of the dependency from Arrhenius law for T > 320 K. Although the comparison of the results of dielectric response experiments for NBT and NBT:Eu3+ reveals significant changes of lattice dynamics induced by Eu doping at T > 320 K, the behavior of the low temperature specific heat remains almost the same. [ABSTRACT FROM AUTHOR]

In this work we present the results of study of the influence of Eu doping on temperature behavior of the dielectric response and conductivity in the frequency range of 10 Hz–1 MHz and the temperature range of 300–750 K, and low temperature (5–400 K) specific heat of the Na1/2Bi1/2TiO3 (NBT) single crystals. It is shown that volume conductivity of NBT is thermally activated with activation energies Ea = 75 meV at T < 320 K and Ea = 700–900 meV at T > 620 K. Eu doping of NBT modifies the behavior of the conductivity with the activation energy being the same at T < 320 K and the deviation of the dependency from Arrhenius law for T > 320 K. Although the comparison of the results of dielectric response experiments for NBT and NBT:Eu3+ reveals significant changes of lattice dynamics induced by Eu doping at T > 320 K, the behavior of the low temperature specific heat remains almost the same. [ABSTRACT FROM AUTHOR]

Dielectric spectroscopic measurements have been reported on three synthesized pure liquid crystalline compounds having paraelectric (SmA*), ferroelectric (SmC*) and antiferroelectric (SmCA*) phases in the frequency range of 40 Hz–25 MHz. Several relaxation modes i.e. low-frequency PL Mode and high-frequency PH Mode in the SmCA* phase, Goldstone Mode (GM) in SmC* phase and Soft Mode (SM) in SmA* phase have been observed. These materials with wide antiferroelectric range are found to possess low relaxation times, thus making them promising materials for applications. The Cole–Cole plot shows the modes in the SmCA* phase to be much weaker than in the SmC* phase. Dielectric loss is maximum in SmC* phase due to the Goldstone Mode. Additionally, the AC electrical conductivity is found to be maximum in the SmC* phase and is dependent on the frequency. Maximum DC conductivity of these materials is of the order of 10−5 Ohm−1 m−1. [ABSTRACT FROM AUTHOR]

We have synthesised a series of lactic acid derivatives and studied their mesomorphic properties. Studied compounds consist of a molecular core laterally substituted by a chlorine atom, and we modified both terminal chains. We concentrated on the effect of the terminal alkyl chain length in the chiral part. For selected homologues, both enantiomers were prepared and mixed in racemic mixtures. We studied the mesomorphic behaviour and for one homologue a reentrancy of the SmA phase below the tilted SmC phase was detected, for both chiral enantiomers and for the racemic mixture. For chiral compounds with the SmC* phase, ferroelectric properties were studied by dielectric spectroscopy and switching properties were described. Reentrancy of the SmA phase was experimentally proved by several experimental techniques including x-ray measurements. For racemic mixtures and non-chiral analogues, we reached a good alignment, which allowed us to measure the birefringence and analyse the behaviour at the phase transitions. [ABSTRACT FROM AUTHOR]

The influence of capped gold nanospheres (GNSs) on the direct current (DC) electric conductivity ( σ D C ) of a ferroelectric liquid crystal (FLC) confined in a cell with blocking electrodes was experimentally investigated. In framework of this work, several measurement techniques of σ D C , such as dielectric and conductivity spectroscopies, were utilised. However, it was demonstrated that only the capacitive technique allowed estimating values of σ D C of both pure FLC and FLC/GNSs nanodispersion confined in the cell with blocking electrodes. The experimental results confirm the assumption that the gold nanoparticles adsorb the impurities' ions in FLC which leads to the decrease in the conductivity of the FLC layer. [ABSTRACT FROM AUTHOR]

Two chiral ferroelectric reactive mesogens showing paraelectric SmA* and ferroelectric SmC* phase have been explored by means of electro-optical and dielectric measurements. The variations of spontaneous polarisation, relaxation time, effective torsional bulk viscosity, dispersion and polarisation anchoring coefficients with respect to temperature have been reported in the entire mesomorphic range. Additionally, helical pitch, static permittivity, dielectric anisotropy, complex permittivity (both real and imaginary parts) and ACconductivity have been determined as a function of frequency and temperature. Both the reactive mesogens are found to possess negative dielectric anisotropy. Also, the AC conductivity varies with the input frequencies and it is maximum for high frequency of 100 kHz. The results obtained have been discussed in the light of the applicability of these fast switching and negative dielectric anisotropy materials as chiral dopants in ferroelectric and antiferroelectric liquid crystal mixtures. [ABSTRACT FROM AUTHOR]

There are five stages in acid coagulation of milk and most studies miss out on a stage or two depending on the experiments performed. Dielectric studies of milk and various physico-chemical studies on the formation of yogurt are well studied and established. However, most of the papers deal with either a limited range of frequencies in the dielectric studies and hence are unable to reflect all the mechanisms of coagulation that occur, or are done as stand-alone experiments, with no correlations to other physico-chemical processes. In this paper, we discuss the broadband dielectric spectroscopy of lactic-acid coagulation of milk, identify the various stages, and compare it with pH, zeta potential, particle size and microscopy. We establish the superiority of dielectric spectroscopy in the identification of all stages of coagulation, the indifference of the process to fat content. Further a strong correlation between tan δ and pH is seen, that is an indicator of the five different stages of lactic-acid induced coagulation. Penetration depth is calculated as milk coagulates and it is seen to be decreasing with coagulation. Broadband dielectric spectroscopy is seen to reveal the onset of coagulation much earlier than other experimental techniques discussed here. [ABSTRACT FROM AUTHOR]

Glycolipids prepared from palm kernel oil, PKO, in tropical regions represent an excellent opportunity to develop new surfactant formulations for cosmeceutical and pharmaceutical applications while contributing to sustainable economies. Here we report the synthesis of a new mannoside obtained from palm kernel oil, aManPKO, and we characterise its thermotropic properties by using DSC, POM, SAXS, WAXS, FT-IR and broadband dielectric spectroscopy. aManPKO exhibits a monotropic smectic phase with a partially interdigitated bilayer structure, similar to its major unsaturated component, the oleyl mannoside with a C18:1 monounsaturated alkyl chain. The smectic phase of aManPKO vitrifies below room temperature, which is associated to the C18:1 component, but also to the activation of short-range motions, ~4 Å, by cleavage of strong hydrogen bonding between the polar heads of the mannosides. The stability of the liquid crystal phase, on the other hand, is linked to the presence of weak hydrogen bonding, whose breakage leads to the activation of long rate motions in the range of the layer distances, ~39 Å. [ABSTRACT FROM AUTHOR]

The electrical, electro-optical and dielectric properties of liquid crystals (LCs) are routinely manipulated in liquid-crystal display (LCD) devices, but their potential application in the development of biosensors is still in a nascent stage. In this review, utilising the electrical properties, electro-optical effect and dielectric anisotropy in LCs, we provide insights into several possible modes of label-free biodetection and describe how capacitance, electro-optical and dielectric measurements of various LCs assist in quantitative analysis of biomolecules. It is concluded that the electrically induced biosensing techniques proposed here provides new incentives for researchers to study the interaction between LCs and biomolecules and to resolve technical hurdles facing the development of LC-based biosensors. [ABSTRACT FROM AUTHOR]

An amorphous material based on multiferroic BiFeO3 was obtained, using melt quenching method. Its dielectric properties were studied within the temperature range −200 to 600°С. The material is characterized by a high dielectric permittivity ε ≈104 (at 200°С and a frequency of 100 Hz), due to the contribution of migration polarization. Using the DTA method, the glass transition temperature Tg ≈ 400°С and crystallization temperature Tcr ≈ 490°С were determined. It was found that the temperatures Tg and Tcr correspond to anomalies of ε, the superposition of which forms a diffuse maximum of the dielectric permittivity. Staged annealing leads to decrease of these anomalies and their shift along the temperature axis in opposite directions. Substantially below of Tg two thermally activated dielectric relaxation processes were revealed. The relaxation time of one of them is obeyed to the Arrhenius law with an activation energy U ≈ 0.53 eV and preexponential factor τ0 ≈ 4.38 10−12 s. [ABSTRACT FROM AUTHOR]

An amorphous material based on multiferroic BiFeO3 was obtained, using melt quenching method. Its dielectric properties were studied within the temperature range −200 to 600°С. The material is characterized by a high dielectric permittivity ε ≈104 (at 200°С and a frequency of 100 Hz), due to the contribution of migration polarization. Using the DTA method, the glass transition temperature Tg ≈ 400°С and crystallization temperature Tcr ≈ 490°С were determined. It was found that the temperatures Tg and Tcr correspond to anomalies of ε, the superposition of which forms a diffuse maximum of the dielectric permittivity. Staged annealing leads to decrease of these anomalies and their shift along the temperature axis in opposite directions. Substantially below of Tg two thermally activated dielectric relaxation processes were revealed. The relaxation time of one of them is obeyed to the Arrhenius law with an activation energy U ≈ 0.53 eV and preexponential factor τ0 ≈ 4.38 10−12 s. [ABSTRACT FROM AUTHOR]

An intermediate structural phase was found between the cubic and tetragonal phases during investigations of dielectric dispersion of highly perfect BaTiO3 single crystals in temperature range 121 °C → 80 °C. The phase was identified as a metastable phase, typical for the first-order phase transitions. It is suggested that the phase is a common property of BaTiO3 single crystals. The manifestation of the metastable phase is usually excluded by growth defects and defects introduced during preparation and measurements which create nucleation centers of a low-temperature phase. [ABSTRACT FROM AUTHOR]

The results of Broadband Dielectric Spectroscopy and Differential Scanning Calorimetry of the 4-ethyl-4′-octylazoxybenzene (4EOB) liquid crystal are presented. Numerical analysis of the dielectric spectra results points to complex dynamics of the liquid crystal molecules in isotropic liquid, nematic and conformationally disordered crystalline phases. Two well-separated maxima on the imaginary part of electric permittivity were detected and described in liquid-like and crystalline phases. A third relaxation process, hidden in the conductivity region, describing conformational disorder of alkyl chains has been found in some plastic crystal phases. Temperature dependences of mean relaxation times characterising conformational disorder, flip-flop motions and rotation around long axis are of the Arrhenius type in liquid-like phases and conformationally disordered crystalline phases, and of the Vogel–Fulcher–Tammann type in the low-temperature crystalline phases for relaxation processes around short and long axis. [ABSTRACT FROM AUTHOR]

The dielectric behavior of the Ba(Ti0.8Ce0.2)O3 ceramics was studied by broadband dielectric spectroscopy in a temperature interval 140–500 K. The broad dielectric relaxation was analyzed by the Havriliak–Negami relationship and the distribution of relaxation times formalism. It was found that the Havriliak–Negami average relaxation time, longest and most probable relaxation times from the distribution of relaxation times follow the Vogel–Fulcher law. The freezing temperature of the longest relaxation time is substantially higher than the freezing temperature of the most probable relaxation time, indicating the distribution of freezing temperatures. The dielectric dispersion has all features inherent to relaxor ferroelectrics and the relaxation is assigned to the dynamics of polar nanoregions. [ABSTRACT FROM AUTHOR]

Novel chiral three-ring compounds with the –CH2O group close to chirality centre were synthesised and their properties were studied. The phase transitions and phase sequences were observed using a polarising optical microscope. The phase transition temperatures and enthalpies were checked by differential scanning calorimetry. A broad-frequency dielectric spectroscopy was also used to confirm the phase transition temperatures as well as the phase sequence. The helical pitch was measured by the spectrophotometry method. It was found that the compounds differing only in one lateral substituted fluorine atom create two different chiral tilted smectic phases, one a ferroelectric phase (SmC*) and the other an antiferroelectric phase (SmCA*). [ABSTRACT FROM AUTHOR]

The dielectric behavior of the Ba(Ti0.8Ce0.2)O3 ceramics was studied by broadband dielectric spectroscopy in a temperature interval 140–500 K. The broad dielectric relaxation was analyzed by the Havriliak–Negami relationship and the distribution of relaxation times formalism. It was found that the Havriliak–Negami average relaxation time, longest and most probable relaxation times from the distribution of relaxation times follow the Vogel–Fulcher law. The freezing temperature of the longest relaxation time is substantially higher than the freezing temperature of the most probable relaxation time, indicating the distribution of freezing temperatures. The dielectric dispersion has all features inherent to relaxor ferroelectrics and the relaxation is assigned to the dynamics of polar nanoregions. [ABSTRACT FROM AUTHOR]

Dual-frequency liquid crystal materials are used in fast response electrooptic modulators in different devices for digital information displaying and processing. In an NLC mixture 2f-3333 (ROLIC, Switzerland) there are components with lateral dipole moment. Their molecular relaxation is investigated by a method of dielectric spectroscopy. Values of relaxation time and its activation energy, molecular friction coefficient, rotational diffusion are obtained. They are compared with data obtained by other methods like LC viscosimetry. [ABSTRACT FROM AUTHOR]

A cholesteric liquid crystal (CLC) – cholesteryl tridecylate (X-20) was doped with nanoparticles of shungite carbon (Sh) to effectively improve some physicochemical properties of the CLC matrix for the further use in electronic devices. The influence of Sh (concentration of 0.005 and 0.02 wt. %) on phase transition temperatures of X-20 was studied. Addition of 0.005 wt. % of Sh shifts phase transition temperatures upward, while the concentration increase to 0.02 wt. % leads to the opposite effect. These data were taken into account during the study of dielectric properties in different phase states. The dielectric properties were studied in the frequency range from 20 Hz to 10 MHz. Only for the system X-20/Sh (0.02 wt. %), dispersion of the dielectric permittivity was observed. The dispersion was caused by the appearance of additional relaxation processes and it was substantially more extended than the classical Debye theory suggests. The results of the research show that the 'CLC – Sh nanoparticles' composites can be used as promising materials to increase the efficiency of radio electronics devices. [ABSTRACT FROM AUTHOR]

In this work, we studied and analysed a particular variety of liquid crystals, the so-called dual-frequency nematic liquid crystals (DFNLCs). The interest was to perform dielectric spectroscopy and optical characterisation with two pure and doped mixtures of DFNLCs. By means the dielectric spectroscopy we observed a low value of crossover frequency at room temperature for one dye doped mixture. Additionally, in the spectra studies, a scattering of light at cross-frequency, and a stable and unstable focal conical state was observed, respectively, for the investigated mixtures. [ABSTRACT FROM AUTHOR]

The dielectric, pyroelectric and ferroelectric properties of (PbySn1−y)2P2S6 (y = 0.1, 0.2 and 0.3) single crystals were analysed in the vicinity of phase transition. The measurements were done covering a wide range of frequency (20 Hz to 1 MHz) and temperature (30350 K) range. Structural phase transition temperature decreases with increased lead concentration and evokes the broadening of the dielectric anomaly. The features of this phase transition are discussed and related to stereoactivity of Sn2+ ions and fluctuations of the concentration of Pb2+ ions. Pyroelectric measurements were performed from 190 K to 325 K during the heating cycle. These investigations showed that an increase of lead concentration does not affect the maximum value of pyroelectric coefficient, and the maximum values of pyroelectric coefficients γmax which (in the vicinity of the phase transition temperature) are nearly equal to 250 nC cm−2 K−1 for all the compositions. The temperature evolution of polarization hysteresis loops proved crystals being ferroelectrics. [ABSTRACT FROM AUTHOR]

This paper presents the dielectric properties of the isotropic liquid and nematic phase at the phase transition. One strong molecular relaxation is observed in both phases. It is interpreted as related to the relaxation around a short molecular axis, due to the fact that molecules possess a strong longitudinal dipole moment. In the isotropic liquid the relaxation is described by the Debye model, while after entering the nematic phase (at cooling) relaxation becomes described by the Cole-Cole model. The distribution parameter of the Cole-Cole model changes from 0.05 (10 degrees above the temperature of the Iso-N transition) to 0.09 (exactly at the phase transition Iso-N), and finally, it reaches 0.35 (10 degrees below the Iso-N transition). Additionally, we observe that ion contribution to the dielectric response is not influenced by the phase transition. All relaxation parameters are discussed within the context of the phase transition phenomena. [ABSTRACT FROM AUTHOR]

This paper presents the dielectric properties of the isotropic liquid and nematic phase at the phase transition. One strong molecular relaxation is observed in both phases. It is interpreted as related to the relaxation around a short molecular axis, due to the fact that molecules possess a strong longitudinal dipole moment. In the isotropic liquid the relaxation is described by the Debye model, while after entering the nematic phase (at cooling) relaxation becomes described by the Cole-Cole model. The distribution parameter of the Cole-Cole model changes from 0.05 (10 degrees above the temperature of the Iso-N transition) to 0.09 (exactly at the phase transition Iso-N), and finally, it reaches 0.35 (10 degrees below the Iso-N transition). Additionally, we observe that ion contribution to the dielectric response is not influenced by the phase transition. All relaxation parameters are discussed within the context of the phase transition phenomena. [ABSTRACT FROM AUTHOR]

This work discusses the investigation of filler-matrix interfacial interactions in epoxy matrices filled with different loadings of graphene based fillers - graphene oxide (GO) and n-butylamine functionalized graphene oxide (GO-ButA). To probe whether the matrix cure reactivity has any influence on these interactions, two different curing agents have been used - a polyetheramine based and an aliphatic amine based to process the nano-composites. Interfacial interactions have been extensively investigated using rheology, DMA and fractographic analysis. As a complementary technique for a better understanding of these interactions, the use of dielectric spectroscopy has been explored. Rheology and dielectric spectroscopy confirm the fillers’ participation in the cure reaction. DMA and fractography show strong interfacial interaction signatures in the slow curing polyetheramine epoxies. The fast curing aliphatic amine epoxies are found to be less amenable in promoting these interactions. However, the filler dispersion quality is observed to be fairly impervious to the curing agent used. Besides surface functionalities of the fillers, the interfacial interactions are seen to be influenced by factors like cure reactivity of epoxy matrices too. Interestingly the thermal stability of the nano-composites is found to be influenced cumulatively by the interfacial interactions and the thermal stability of the fillers. [ABSTRACT FROM AUTHOR]

Electrical conductivity behaviour of x(Na0.5Bi0.5)TiO3-(1-x)La(Mg0.5Ti0.5)O3 ceramics with x ranging from 0.95 to 0.8 was analysed in the temperature range from 300 K to 800 K at microwaves (1 MHz – 1GHz frequency region). Analysis of calculated DC conductivity parameters has shown that the activation energy changes at about 690 K which could be associated with the phase change in these materials. The logarithm of preexponential factor of DC conductivity changes linearly according to the activation energy, i.e. it follows Meyer-Neldel rule both below and above the phase transition point. [ABSTRACT FROM AUTHOR]

Dielectric properties of four recently formulated room temperature multi-component liquid crystalline mixtures with paraelectric (SmA*), ferroelectric (SmC*) and antiferroelectric (SmC*A) phases have been studied as a function of temperature and frequency. Under planer anchoring condition, dielectric spectroscopy revealed all the characteristic modes: low frequency PL and high frequency PH mode in SmC*A phase, Goldstone mode (GM) in SmC* phase and soft mode (SM) in SmA* phase. Dielectric behaviour has also been studied under the application of DC bias electric field. With bias electric field, we have been able to study the soft mode dielectric behaviour in the SmC* phase. An unknown high frequency mode (X-mode) with and without bias is also observed in SmC* phase. Dielectric results are explained in the light of generalised Landau theory. The mixtures show very high soft mode electroclinic coefficient in the SmA* phase in addition to fast switching in SmC*A and SmC* phases [30]. [ABSTRACT FROM AUTHOR]

The volume filling fraction dependence of the effective permittivity of the nematic liquid crystal 4-n-pentyl-4'-cyanobiphenyl embedded in different porous membranes and dispersed with aerosil nanoparticles was determined using broadband dielectric spectroscopy in the frequency range from 106 to 109 Hz. The experimental data were analyzed and compared with some existing theories based on the effective medium approximation and their modifications. The obtained effective permittivities as a function of the volume filling fraction lie between the lower limits of the Wiener and Hashin-Shtrikman bounds. The observed shift of the experimental points reflects the changes in the structure of the investigated composites. [ABSTRACT FROM AUTHOR]

Searching for giant dipolar defects, suggested as the explanation of the colossal permittivity (CP) in (Nb + In) co-doped rutile, we have recently published (J. Appl. Phys. 119, 154105 (2016) and Phys. Rev. Mat., in press) temperature-dependent dielectric spectra from sub-Hz to THz range (including 4-point DC conductivity) of several (Nb + In) co-doped rutile ceramics. Using the model of two leaky capacitor in series below ∼1 MHz, we estimated the depletion layer thickness and conductivity. The spectra below ∼10 GHz were fitted with two Cole-Cole relaxations obeying the Arrhenius law, assigned to the effect of depletion layers and grain boundaries. In this paper, using effective medium models, we have for the first time modelled the spectra as a composite of semiconducting grains and substantially less-conducting grain boundaries and near-electrode depletion layers. The CP effect has been fully explained by the combination of surface and internal barrier-layer capacitor effects, without any measurable contribution from the dipolar defects. [ABSTRACT FROM AUTHOR]

Broadband dielectric spectra of dielectric-conductor nanocomposites of poly(ethylene terephthalate) with multiwalled carbon nanotubes (PET-xCNT) were used for calculation of their free-space shielding and absorbing parameters in the frequency range from 1 MHz to 1 THz. Revealed correlation of the composition and frequency dependent microwave dielectric and shielding/absorbing parameters allows determination of the CNT concentration range optimized for the shielding (x ≥ 0.4 vol%) and absorption (0.12 < x < 0.6 vol%) applications. Broadband (two frequency decades) 40 dB shielding, narrowband 30÷40 dB absorption and high attenuation constant up to 104 neper/m were demonstrated. [ABSTRACT FROM AUTHOR]