Transport phenomena in superionic Na<Subscript><Emphasis Type="Italic">х</Emphasis></Subscript>Cu<Subscript>2 − <Emphasis Type="Italic">х</Emphasis></Subscript>S (<Emphasis Type="Italic">х</Emphasis> = 0.05; 0.1; 0.15; 0.2) compounds

The electronic and ionic conductivity, the electronic and ionic Seebeck coefficients, and the thermal conductivity of Na _x Cu_2 ? x S (x = 0.05, 0.1, 0.15, 0.2) compounds were measured in the temperature range of 20–450 °С. The total cationic conductivity of Na_0.2Cu_1.8S is about 2 S/cm at 400 °С (the activation energy ≈ 0.21 eV). Over the studied compounds, the composition Na_0.2Cu_1.8S has the highest electronic conductivity (500–800 S/cm) in the temperature range from 20 to 300 °С, and the highest electronic Seebeck coefficient (about 0.2 mV/K) in the same temperature range is observed for Na_0.15Cu_1.85S composition; the electronic Seebeck coefficient increases abruptly above 300 °С for all compounds. The thermal conductivity of superionic Na_0.2Cu_1.8S is low, which causes high values of the dimensionless thermoelectric figure of merit ZT from 0.4 to 1 at temperatures from 150 to 340 °С.     

Dielectric characterization of semiconducting ZnPc films sandwiched between Gold or Aluminum electrodes

The dependencies of complex dielectric functions (the dielectric constant, ε ₁, and the dielectric loss, ε ₂), on frequency and temperature of zinc phthalocyanine (ZnPc) thin films sandwiched between either gold or aluminum Ohmic-electrode contacts have been investigated in the temperature range of 93–470 K and frequency range 0.1–20 kHz. It is found that both values of ε ₁ and ε ₂ decrease with increasing frequency and increase with decreasing temperature. The rate of change depends greatly on the temperature and frequency ranges under consideration. Around room temperature, neither ε ₁ nor ε ₂ show any appreciable change through the whole range of frequencies. Thus, the dielectric dispersion is found to include of both dipolar and interfacial polarizations. The dependencies of both dielectric functions on frequency at different temperatures were found to follow a universal power law of the form ω ⁿ , where the index 0<n≤?1. This indicates that the correlated barrier hopping (CBH) model is a suitable mechanism to describe the dielectric behavior in ZnPc films. Furthermore, the results of the dielectric response indicate that polarization in these films could be in the form of non-Debye polarization. However, the Debye polarization can be traced below room temperature. The obtained results of the relaxation-time, τ, dependency on temperature have shown that a thermally-activated process may be dominated in ZnPc thin films conduction at high temperatures. Partial phase transition (from α- to β-phase) has been observed around 400 K in molecular relaxation-time, τ, and optical dielectric constant, ε _∞. Arrhenius behavior has been observed for all the dielectric loss and conductivity relaxation-times above room temperature and their activation energies are explained and reported. The optical dielectric constant ε _∞ was found to increase with temperature.     

The role of zirconium oxide as nano-filler on the conductivity,morphology, and thermal stability of poly(methyl methacrylate)–poly(styrene-co-acrylonitrile)-based plasticized composite solid polymer electrolytes

The plasticized composite solid polymer electrolytes (CSPE) involving polymer blends poly(methyl methacrylate)-poly(styrene-co-acrylonitrile) (PMMA-SAN), plasticizers ethylene carbonate (EC), and propylene carbonate (PC) with lithium triflate (LiCF₃SO₃) as salt and varying concentration of composite nano-filler zirconium oxide (ZrO₂) is prepared by solution casting technique using THF as solvent. The powder X-ray diffraction (XRD) studies reveal amorphous nature of the CSPE samples. Fourier transform infrared (FT-IR) spectroscopy studies reveal interaction of Li⁺ ion with plasticizers, both C=O and OCH₃ group of the PMMA, while nitrile group of SAN is inert. AC impedance and dielectric studies reveal that the ionic conductivity (σ), dielectric constant (ε’), and dielectric loss (ε”) of the prepared CSPE samples increase with increasing content of ZrO₂ nano-filler up to 6 wt% and decrease with further additions. The temperature dependence of ionic conductivity follows Arrhenius relation and indicates ion-hopping mechanism. The sample Z2 (6 wt% ZrO₂) with relaxation time τ of 8.13?×?10^–7 s possess lowest activation energy (E_a?=?0.23 eV) and highest conductivity (2.32?×?10^–4 S cm^?1) at room temperature. Thermogravimetric analysis (TGA) reveals thermal stability of highest conducting sample Z2 up to 321 °C after complete removal of residual solvent, moisture, and its impurities. Differential scanning calorimetric (DSC) studies reveal absence of glass transition temperature (T_g) corresponding to atactic PMMA for the CSPE Z2, while isotactic PMMA component shows T_g around 70 °C, which is due to increased interaction of filler with PMMA leading to change in its tacticity. Scanning electron microscopy (SEM) analysis reveals blending of PMMA/SAN polymers and lithium triflate salt. The incorporation of nano-filler ZrO₂ leads to change in surface topology of polymer matrix. Rough surface of the CSPE Z2 leads to new pathway for ionic conduction leading to maximum ionic conductivity.     

Dielectric studies on binary polar mixtures of propanoic acid with esters

It is interesting to see the nature of intermolecular interactions between associative and non-associative polar liquids. Binary polar–polar liquid mixtures of ethyl acetate, ethyl benzoate, ethyl acrylate, ethyl butyrate, n-butyl acetate and benzyl benzoate, each with propanoic acid were subjected to dielectric studies at temperatures 25 °C, 35 °C and 45 °C. Static permittivity (ε_o) and dielectric constant at high frequency (ε_∞) were found through dielectric measurements for different concentrations of each system. The Bruggeman dielectric factor, Kirkwood correlation factor and the excess permittivity were determined. Deviations from the linearity of various models suggest molecular association through hydrogen bonding between the polar–polar constituents of the mixtures. The formation of cyclic and linear α-multimers in the above systems were identified. The results and their temperature dependence were interpreted accordingly.     

Electrical transport characteristics of ZnO–Bi2O3–B2O3 glasses

Optically clear glasses in the ZnO–Bi₂O₃–B₂O₃ (ZBBO) system were fabricated via the conventional melt-quenching technique. Dielectric constant and loss measurements carried out on ZBBO glasses unraveled nearly frequency (1 kHz–10 MHz)-independent dielectric characteristics associated with significantly low loss (D?=?0.004). However, weak temperature response was found with temperature coefficient of dielectric constant 18?±?4 ppm °C^?1 in the 35–250 °C temperature range. The conduction and relaxation phenomena were rationalized using universal AC conductivity power law and modulus formalism respectively. The activation energy for relaxation determined using imaginary parts of modulus peaks was 2.54 eV which was close to that of the DC conduction implying the involvement of similar energy barriers in both the processes. Stretched and power exponents were temperature dependent. The relaxation and conduction in these glasses were attributed to the hoping and migration of Bi³⁺ cations in their own and different local environment.     

Effects of oxygen partial pressure on the ferroelectric properties of pulsed laser deposited Ba0.8Sr0.2TiO3 thin films

The Ba_0.8Sr_0.2TiO₃ thin films were grown on the Pt–Si substrate at 700 °C by using a pulsed laser deposition technique at different oxygen partial pressure (PO₂) in the range of 1–20 Pa and their properties were investigated. It is observed that the PO₂ during the deposition plays an important role on the tetragonal distortion ratio, surface morphology, dielectric permittivity, ferroelectric polarization, switching response, and leakage currents of the films. With an increase in PO₂, the in-plane strain for the BST films changes from tensile to compressive. The films grown at 7.5 Pa show the optimum dielectric and ferroelectric properties and also exhibit the good polarization stability. It is assumed that a reasonable compressive strain, increasing the ionic displacement, and thus promotes the in-plane polarization in the field direction, could improve the dielectric permittivity. The butterfly features of the capacitance–voltage (C–V) characteristics and the bell shape curve in polarization current were attributed to the domain reversal process. The effect of pulse amplitude on the polarization reversal behavior of the BST films grown at PO₂ of 7.5 Pa was studied. The peak value of the polarization current shows exponential dependence on the electric field.     

Ionic and electronic conductivity of Yb2+xTi2−xO7−x/2 materials

Bulk and grain boundary conductivities of Yb_2+xTi_2−xO_7−x/2 (x = 0, 0.1, 0.18 and 0.29) materials were studied by impedance spectroscopy in the range 300–900 °C in air. Ionic and electronic conductivities were separated by both ion blocking Hebb–Wagner measurements and total conductivity measurements as a function of oxygen partial pressure in the temperature range 700–1000 °C. The oxygen partial pressure dependence of the total conductivity shows that these materials are nearly pure ionic conductors in air and that the ionic conductivity decreases for Yb-rich compositions. This was interpreted as a predominant effect of a decrease in mobility of ionic charge carriers, opposing the expected increase in concentration of oxygen vacancies with increasing Yb content. The studied materials become mixed conductors under typical fuel conditions, except possibly at temperatures below about 700 °C. Yb-excess slightly suppresses the electronic conductivity.     

The Effect of Supercritical CO2 on the Macromolecules Parallel Conformation and Its Relation to the Electrical Conductivity and Dielectric Behavior of Epichlorohydrin Terpolymer

The effect of supercritical CO₂ on the electrical conductivity of poly(epichlorohydrin–Ethylene oxide–Allyl glycidal ether) terpolymer is investigated using dielectric spectroscopy. Impedance measurements were carried out in the frequency range from 100–10 MHz and the temperature range of ?35–70°C with intervals of 5°C. The experimental results of the dielectric constant and the dielectric loss were fitted with the Cole–Cole equation to obtain the maximum relaxation frequencies of the different relaxation processes. As a result of the CO₂ treatment process, enhancement in the polymer chain mobility without noteworthy change in the glass transition temperature was determined. In addition, the level of the DC conductivity and the dielectric strength were increased. These effects were attributed to improvement in the chain dynamics, which arises from enhancement in the parallel conformation of macromolecules.     

Dielectric anomalous response of water at 60 °C

Recently, the paraelectric response of water was investigated in the range 0–100 °C. It showed an almost perfect Curie–Weiss behaviour up to 60 °C, but a slight change in slope of 1/ε_d versus T at 60 °C was overlooked. In this work, we report optical extinction measurements on metallic (gold and silver) nanoparticles dispersed in water, annealed at various temperatures in the range from 20 to 90 °C. An anomalous response at 60 °C is clearly detectable, which we associate to a subtle structural transformation in the water molecules at that temperature. This water anomaly is also manifested by means of a blue shift in the longitudinal surface plasmon resonance of the metallic nanoparticles for the solutions annealed at temperatures higher than about 60 °C. A reanalysis of 1/ε_d (T) for water in the whole temperature range leads us to conclude that the water molecule undergoes a subtle transformation from a low temperature (0–60 °C) configuration with a dipole moment μ₁ = 2.18 D (close to the molecular dipole moment of ice) to a high temperature (60–100 °C) configuration with μ₂ = 1.87 D (identical to the molecular dipole moment in water vapour).     

Investigation of Relaxation Process of Nylon 1212 Using Dielectric Relaxation Spectroscopy

The relaxation processes of α-form nylon 1212 from 50°C up to 160°C were studied by dielectric relaxation spectroscopy (DRS) in a wide frequency range of 63 Hz to 5 MHz. The α relaxation, the electrode relaxation, and the conductivity relaxation of nylon 1212 were observed and analyzed in detail using permittivity and modulus formalism. Electrode polarization and dc conductivity were the origin of high dielectric permittivity values at low frequencies and high temperatures. The strength of the imaginary part of the electric modulus of conductivity relaxation M″ _max was nearly independent of temperature. The distribution of local conductivity and relaxation time became broader with decreasing temperature.     

Structural and dielectric properties of undoped ZnO pellets prepared by solid state route

Undoped zinc oxide has been prepared at various growth temperatures by a conventional sintering process. The crystal structures of the prepared samples were studied by X-ray diffraction. The frequency-dependent dielectric dispersion of all the sintered ZnO ceramics was investigated in the temperature range from ?100 to 30 °C and in the frequency range from 1 Hz to 10 MHz by broadband dielectric spectroscopy. An analysis of the complex permittivity and electric modulus as a function of frequency has been performed assuming a distribution of relaxation times. The pellet sintered at 900 °C showed the lowest value of the dielectric strength. The temperature dependent of the parameter α is discussed. While the charge transport through the grain and grain boundary regions was examined by impedance spectroscopy. Activation energy values extracted from conduction measurements were found to be in the range of 0.09 and 0.3 eV.     

Structure and dielectric behavior of TlSbS2

A comparison of structure and dielectric properties of TlSbS₂ thin films, deposited in different thicknesses (400–4100 Å) by thermal evaporation of TlSbS₂ crystals that were grown by the Stockbarger–Bridgman technique and the bulk material properties of TlSbS₂ are presented. Dielectric constant ε ₁ and dielectric loss ε ₂ have been calculated by measuring capacitance and dielectric loss factor in the frequency range 20 Hz–10 KHz and in the temperature range 273–433 K. It is observed that at 1 kHz frequency and 293 K temperature the dielectric constant of TlSbS₂ thin films is ε ₁=1.8–6 and the dielectric loss of TlSbS₂ thin films is ε ₂=0.5–3 depending on film thickness. In the given intervals, both of dielectric constant and dielectric loss decrease with frequency, but increase with temperature. The maximum barrier height W _m is calculated from the dielectric measurements. The values of W _m for TlSbS₂ films and bulk are obtained as 0.56 eV and 0.62 eV at room temperature, respectively. The obtained values agree with those proposed by the theory of hopping over the potential barrier. The temperature variation of ac conductivity can be reasonably interpreted in terms of the correlated barrier hopping model since it obeys the ω ^s law with a temperature dependent s (s<1) and going down as the temperature is increased. The temperature coefficient of capacitance (TCC) and permittivity (TCP) are evaluated for both thin films and bulk material of TlSbS₂.     

The DC bias function of electrical characterization of PVA inducted nickel chloride composite film

The synthesis of nickel chloride (NiCl₂)-mixed with polyvinyl alcohol films of 15–20 μm in thickness has been carried by solution blending technique. The dielectric properties of the films have been measured in the frequency range of 20 Hz to 1 MHz under a positive bias potential in the range from 0 to 40 V. Improved electric characterization was demonstrated due to ionic incorporation of NiCl₂. The low-frequency polarization was based on the Maxwell–Wagner interfacial model. Hence, this composite film may suggest as suitable electronic polar medium for versatile low-frequency applications.     

Effect of ethylene carbonate plasticizer on agar-agar: NH<Subscript>4</Subscript>Br-based solid polymer electrolytes

Proton-conducting polymer electrolytes based on biopolymer, agar-agar as the polymer host, ammonium bromide (NH₄Br) as the salt and ethylene carbonate (EC) as the plasticizer have been prepared by solution casting technique with dimethylformamide as solvent. Addition of NH₄Br and EC with the biopolymer resulted in an increase in the ionic conductivity of polymer electrolyte. EC was added to increase the degree of salt dissociation and also ionic mobility. The highest ionic conductivity achieved at room temperature was for 50 wt% agar/50 wt% NH₄Br/0.3% EC with the conductivity 3.73?×?10^?4 S cm^?1. The conductivity of the polymer electrolyte increases with the increase in amount of plasticizer. The frequency-dependent conductivity, dielectric permittivity (ε′) and modulus (M′) studies were carried out.     

Dielectric relaxation investigations of 100 MeV Ag-ion-irradiated polyetherimide using thermally stimulated discharge current techniques

The thermally stimulated discharge current technique (TSDC) has been used to elucidate various dielectric relaxation processes in 100 MeV Ag-ion-irradiated polyetherimide (PEI). The irradiated PEI samples (85 μm thickness, area 0.12 cm²) were polarized at different temperatures ranging from 50–200 °C under various biasing fields (50–300 kV/cm). TSDC spectra, in general, consist of four current maxima namely γ, β, α and ρ in ascending order of temperature, appearing around 40, 110, 200 and 230 °C, respectively. The origin of γ - and β -peaks has been attributed to the dipolar nature of ether linkages and carbonyl groups, respectively, whereas α- and ρ-maxima have been attributed to the space charge polarization process. The absence of γ-peak in irradiated samples is attributed to the significant loss in ether linkages due to irradiation. The free radical formation, demerization of carbonyl groups and cross-linking of imide groups due to ion irradiation in PEI have been held to be responsible for the behavior of these relaxation processes. In the vicinity of the β-relaxation, a new relaxation process, termed δ-relaxation, is also observed.     

Microstructure and dielectric properties of PMN–PT ceramics prepared by the molten salts method

The sintering characteristic and dielectric properties of 0.67PMN–0.33PT ceramics prepared by the molten salt synthesis (MSS) method were investigated. PMN–PT particles synthesized by MSS with smaller grain size and good dispersion could lower the sintering temperature of ceramics; PMN–PT ceramics with relative density above 96% could be obtained in the range 1150–1180 °C. The molten salts species could significantly affect the microstructure and properties of MPN-PT ceramics. In the range 1100–1200 °C, PMN–PT ceramics from the sulfate flux MSS powders showed intergranular fracture, but that from the chloride flux MSS powder showed transgranular fracture. At the same sintering condition, the properties of PMN–PT ceramics from the powders prepared in the chloride flux are better than that from the powders prepared in the sulfate flux, their maximum dielectric constant ε_max≈29,385 and piezoelectric constant d₃₃≈660 pC/N. The above results demonstrated that PMN–PT ceramics prepared by the molten salts method possessed excellent piezoelectric and dielectric properties.     

Temperature and frequency dependent electrical properties of 50 MeV Li3+ ion irradiated polymeric blends

The polymeric blends of polyvinyl chloride (PVC) and polyethylene terephthalate (PET) with equal composition by weight have been irradiated with 50 MeV Li³⁺ ions at different fluences. The AC electrical properties of polymeric blends were measured in the frequency range 0.05–100 kHz, and at temperature range 40–150 ^°C using LCR meter. There is an exponential increase in conductivity with log of frequency and effect is significant at higher fluences. The value of tan δ and dielectric constant are observed to change appreciably due to irradiation. The loss factor (tan δ) versus frequency plot suggests that the capacitors of polymeric blend of PVC and PET may be useful below 10 kHz. No change in dielectric constant was observed over a wide temperature range up to 150 ^°C. Thermal stability was studied by thermogravimetric analysis. Thermal analysis revealed that chain scission is the dominant phenomena in the polymeric blends resulting in the reduction of its thermal stability. It appears from differential scanning calorimetry studies that the melting temperature decreases as fluence increases. FTIR spectra measurements also revealed that the material suffered severe degradation through bond breaking beyond the fluence of 2.3×10¹³ ions/cm².     

Dielectric relaxation in NH4HSO4 above room temperature

The dispersion curves of the dielectric response of NH₄HSO₄ show that the corrected imaginary part of permittivity, εʺ, and its real part ε′ versus frequency reveal a dielectric relaxation around 9.1 × 10⁵ Hz at 31 °C, which shifts to higher frequencies (∼ 10⁶ Hz) as the temperatures increases. The relaxation frequency shows an activated relaxation process over the temperature range 31–83 °C with activation energy E_a = 0.14 eV, which is close to that derived from the dc conductivity. We suggest that the observed dielectric relaxation could be produced by the H⁺ jump and SO₄⁻ reorientation that cause distortion and change the local lattice polarizability inducing dipoles like HSO₄⁻.     

Electric Modulus Spectroscopic Studies of the Dielectric Properties of Carbon Nanotubes/Epoxy Polymer Composite Materials

The electrical properties of epoxy polymer/carbon nanotubes composites were characterized using impedance spectroscopy in the frequency range between 1 Hz and 10 MHz and temperature range between 25°C and 105°C. We report the analysis of the experimental data using the electric modulus formalisms to understand the dielectric relaxation mechanisms. The variation of the real and imaginary parts of the electric modulus versus frequency and temperature were suggestive of two relaxation processes, associated with dipolar relaxation and CNT-polymer interfaces. The Havriliak-Negami model of dielectric relaxation was used for modelling the relaxation processes, extracting the relaxation parameters.     

Effect of H<Subscript>3</Subscript>PO<Subscript>2</Subscript> on the mechanical,thermal, and electrical properties of polymers based on poly (vinyl alcohol) (PVA) and chitosan (CS)

A polymer based on poly (vinyl alcohol) (PVA) and chitosan (CS) with a weight ratio of 80:20 was prepared by solvent casting processes, and the effect of H₃PO₂ was investigated. Thermal analysis shows miscibility of the two polymer amorphous phases since a single T_g was located between those of the individual components and the melting point of the crystalline phase was depressed to 189 °C. It was found that the acid acts as a plasticizer for the PVA-CS blends and its T_g is depressed significantly to 23 °C as the acid concentration increases to 50%. Strain-stress tests also corroborate this effect. The DC conductivity of the blends follows an Arrhenius-type thermal activation behavior with activation energy of 0.1 eV in the 30–90 °C temperature range. Moreover, the conductivity increases with increasing acid content up to a maximum value of approximately 1.4 × 10^?2 S/cm for the blend with an acid concentration of 50%.