High-Temperature Dielectric Relaxation and Electric Conduction Mechanisms in a LaCoO3-Modified Na0.5Bi0.5TiO3 System

This research study examines the high-temperature dielectric relaxation and electric conduction mechanisms in (x)LaCoO₃-(1 - x)Na_0.5Bi_0.5TiO₃ samples, where x is 0.05, 0.10, and 0.15. The findings demonstrate that all the samples exhibit two dielectric transitions: first, a frequency-dispersive shoulder at a lower temperature (T_s) around 425-450 K, which is associated with polar nanoregions (PNRs), and second, from ferroelectric to paraelectric transition at the Curie temperature (T_c) approximately between 580 and 650 K. The impedance analysis reveals the negative temperature coefficient of resistance behavior of the specimens. The broad and asymmetric relaxation peaks obtained from modulus spectroscopy demonstrate a wide range of relaxations, suggesting non-Debye-type behavior. Furthermore, the conductivity studies provide insights into understanding the transport phenomena in the samples. The oxygen vacancies resulting from the addition of LaCoO₃ into the Na_0.5Bi_0.5TiO₃ ceramics are responsible for the relaxation and conduction processes, and the charge carrier is doubly ionized oxygen ion vacancies. All samples except for LCNBT10 at 1 kHz exhibit a negative magnetodielectric response.

DC and AC Tests of Moisture Electrical Pressboard Impregnated with Mineral Oil or Synthetic Ester—Determination of Water Status in Power Transformer Insulation

In this study, the conductivity and permittivity of electrical pressboard—insulating liquid—water composites were investigated, and the electrical properties of the composites and water were analysed comparatively. Mineral oil and synthetic ester were used as insulating liquids. It was found that the presence of water caused an increase in the permeability of the composite in the frequency range below 100 Hz. The value of static permittivity determined by water in the content of 5 wt. % was approximately 15. To obtain this value caused by liquid water, its volume should be approximately five (oil) and four times (ester) higher than its actual content, respectively. The determined values of the activation energy of the DC conductivity of the composites were several times higher than the values of the activation energy of the conductivity of the liquid water. The experimental values of the dielectric relaxation times were many orders of magnitude higher than the dielectric relaxation times of water. This means that the experimental results obtained for the dielectric permittivity, the activation energy of conductivity and the dielectric relaxation times for moisture electrical pressboard impregnated by mineral oil or synthetic ester exclude the possibility of the presence of liquid water in the composites. It was found that the conductivity of the composites increased exponentially with increasing water content. Such dependencies are characteristic of hopping conductivity, caused by the quantum phenomenon of electron tunnelling between nanometre-sized potential wells. As the increase in conductivity is determined by the presence of water in the composites, therefore, the nanometre potential wells were single-water molecules or nanodrops.

Ion trapping model of the ac conductivity in disordered solids

In this paper, we develop an approach based on ions trapping to describe the conductivity spectra in disordered solids. Applying the multiple trapping model and the diffusion equation for ions, we obtained a new expression for the ac conductivity, which allows us to describe the conductivity spectra in wide ranges of frequencies and temperatures. In the high-temperature region, the new expression for the ac conductivity reproduces the Jonscher behavior, and with decreasing temperatures transforms into an expression of the NCL-type. A new expression for the ac conductivity was successfully tested on the conductivity spectra of ion-conducting glasses.

A 'mixed' dielectric response in langasite Ba3NbFe3Si2O14

The temperature dependence of the structural and dielectric properties of polycrystalline Ba3NbFe3Si2O14 has been studied using high temperature X-ray diffraction and impedance spectroscopy. In situ X-ray diffraction with temperature (330-873 K) and subsequent Rietveld refinement shows that Fe-langasite crystallizes in a single phase P321 structure, in the measured temperature range. The dielectric constant ε' exhibits low frequency dispersion and large variation (25-104), with temperature and frequency. The real part of the ac conductivity (σ') also shows a change of seven orders of magnitude (10-6 to 10-13). The conductivity was observed to diverge from the 'universal dielectric response' (UDR), σ(ω,T) = σdc + A1ωn. Three frequency (10 Hz-10 MHz) and temperature (123-573 K) dependent regions were observed: (a) a low frequency, frequency independent region, (b) a mid frequency, dispersive region, and (c) a high frequency, dispersive region. This behaviour can be understood by a double power law: σ(ω,T) = σdc + A1ωn2 + A2ωn1, which is similar to the modified Jonscher's law and holds good for other complex dielectric materials as well. The 'sub-linear' variation with frequency for n2 at all temperatures and for n1 above 323 K is attributed to hopping polarization. Remarkably, a 'super-linear' ac conductivity was observed with n1 ≥ 1 below 323 K. This anomalous behaviour is attributed to hopping between non-uniform potential wells. The dielectric relaxation studies in combination with Seebeck measurements (300-573 K) reveal that the colossal dielectric permittivity and deviation from the UDR are predominantly due to the hopping polarization of positively charged species in a distributed potential. It is suggested that this model may be applicable to understand the conductivity mechanism in a broad range of complex materials.

Transport phenomena of Cu-S-Te chalcogenide nanocomposites: frequency response and AC conductivity

In this work, the development and electrical characterization of several chalcogenide nanocomposites have been reported. X-ray diffraction (XRD) has been used to reveal their microstructures. Mott's variable range hopping model has been used to interpret the DC conductivity data of the nanocomposites at lower temperatures. The DC conductivity data at higher temperatures has been explained well using Greave's model. To explain the AC conductivity data, the Meyer-Neldel (MN) conduction rule has been employed. The AC conductivity spectra at different temperatures have been analyzed using Almond-West formalism. Different conduction models, namely, correlated barrier hopping (CBH) and modified non-overlapping small polaron tunneling (NSPT), have been used to interpret the conduction mechanism of the nanocomposites. Scaling of the AC conductivity spectra reveals that the electrical relaxation process is independent of temperature, but depends on the nanocomposite composition. The conductivity mechanism is explained using a schematic structural model.

Functional Energy Accumulation, Photo- and Magnetosensitive Hybridity in the GaSe-Based Hierarchical Structures

We report on the complex GaSe-based hierarchical structures GaSe(CS(NH2)2), GaSe(SmCl3) and GaSe(CS(NH2)2(SmCl3)) synthesized by an intercalation method. The conductive properties of synthesized clathrates and their relation to hierarchical structural complexity were explored by an impedance spectroscopy technique. The impedance response, thermostimulated discharge spectra, and photo- and magnetoresistive effects are reported. Based on the obtained results, the impurity energy spectra were calculated. A strong low-frequency inductive response, observable in the GaSe(SmCl3) clathrate, makes this material promising for the development of gyrator-free nanodelay lines potentially applicable in nanoelectronics. Hierarchical GaSe(CS(NH2)2(SmCl3)) clathrate, on the other hand, reveals hysteresis of the current–voltage characteristics, apparently confirming an accumulation of electric energy at interphase boundaries. A relevant spin battery effect, observable experimentally in stationary magnetic fields, demonstrates a principal possibility of the electric energy accumulation at a quantum level.

Unexpected Giant Microwave Conductivity in a Nominally Silent BiFeO3 Domain Wall

Nanoelectronic devices based on ferroelectric domain walls (DWs), such as memories, transistors, and rectifiers, have been demonstrated in recent years. Practical high-speed electronics, on the other hand, usually demand operation frequencies in the gigahertz (GHz) regime, where the effect of dipolar oscillation is important. Herein, an unexpected giant GHz conductivity on the order of 10³ S m^-1 is observed in certain BiFeO₃ DWs, which is about 100 000 times greater than the carrier-induced direct current (dc) conductivity of the same walls. Surprisingly, the nominal configuration of the DWs precludes the alternating current (ac) conduction under an excitation electric field perpendicular to the surface. Theoretical analysis shows that the inclined DWs are stressed asymmetrically near the film surface, whereas the vertical walls in a control sample are not. The resultant imbalanced polarization profile can then couple to the out-of-plane microwave fields and induce power dissipation, which is confirmed by the phase-field modeling. Since the contributions from mobile-carrier conduction and bound-charge oscillation to the ac conductivity are equivalent in a microwave circuit, the research on local structural dynamics may open a new avenue to implement DW nano-devices for radio-frequency applications.

Dielectric and electromagnetic interference shielding properties of high entropy (Zn,Fe,Ni,Mg,Cd)Fe2O4 ferrite

The new (Zn,Mg,Ni,Fe,Cd)Fe2O4 high entropy ferrite with average crystallite size 11.8 nm was synthesized in two stages by annealing of co-precipitated amorphous precursor. The dielectric spectroscopy confirms, that the electrical conductivity and polarization processes are associated with the mobility of electrons in the structure of ferrite. It was concluded, that the both, high frequency complex dielectric permittivity as well as complex magnetic permeability are strongly temperature and frequency dependent. The AC electrical conductivity is associated with quantum mechanical tunneling of electrons and related to the transfer of charge carriers between Fe2+ and Fe3+ ions. Moreover, the microwave absorption properties were determined. The best microwave absorption properties have been confirmed in the frequency range 1.9 to 2.1 GHz for a layer which is 0.8-1 cm thick. For this range, reflection loss (RL) is lower than -25 dB and shielding effectiveness (SE) lower than -50 dB.

Electrical Impedance Spectroscopy: “First Principles” analysis and simulations of electrical response in the classical range of frequencies below 1 THz and the resulting new role of Electrical Impedance Spectroscopy in electrical characterisation within Condensed Matter Physics

In order to investigate the full potential of the Electrical Impedance Spectroscopy (EIS) when used to address various aspects of conductive and dielectric response within the field of Condensed Matter Physics and Electrochemistry, a new analysis of the electrical impedance experiments has been undertaken. Within the framework of quantum mechanical band structure and using the concept of electrochemical potential for each of the relevant energies, the problem of electrical response in condensed phase has been formulated, using augmented Maxwell equations of Classical Electrodynamics, as a boundary value problem of a set of coupled, non-linear parabolic equations in energy, space and time. The result of this numerical analysis is a principal possibility of a complete electrical characterisation of both monocrystals, glassy solids and liquids. The EIS has been put in this way on a new qualitative level and should be considered now as the most general electrical experimental characterisation tool available. In this article, a methodology of numerical simulations of electrical response in condensed matter systems at classical frequencies (from ~1 THz down to dc) is presented and the numerical simulation results are then discussed, using monocrystalline Silicon, chalcogenide glass ion conductor Agx(AsS2)1−x and simple aqueous chloride solution as experimental test cases. Some other unique results of the new EIS analysis will also be discussed. These include the possibility of a clear distinction between the contribution to the electrical response from bound and mobile electrical charges, the possibility of simultaneous and independent determination of the mobile electrical charges mobility and their density in one EIS experiment and incorporation of the interfacial regions of the system under test (SUT) as an essential part of the overall electrical response.

Electrical and gas sensing properties of novel cobalt(II), copper(II), manganese(III) phthalocyanines carrying ethyl 7-oxy-4,8-dimethylcoumarin-3-propanoate moieties

The synthesis of metallophthalocyanines (M [Formula: see text] Co, Cu, Mn) bearing four ethyl 7-oxy-4,8-dimethylcoumarin-3-propanoate moieties was performed. These novel compounds were characterized by elemental analysis, [Formula: see text]H-NMR spectroscopy, FT-IR, UV-vis and mass spectral data. DC and AC electrical properties of the films of metallophthalocyanines were investigated in the temperature range of 295–523 K. AC measurements were performed in the frequency range of 40–10[Formula: see text] Hz. Activation energy values of the films took place between 0.55 eV–0.93 eV. Impedance spectroscopy measurements revealed that bulk resistance decreases with increasing temperature, indicating semiconductor properties. DC conductivity results also supported this result. Their gas sensing properties were also investigated for the vapors of Volatile Organic Compounds (VOCs), [Formula: see text]-butyl acetate (200–3200 ppm) and ammonia (7000–56000 ppm) between temperatures 25–100°C. Sensitivity and response times of the films for the tested vapors were reported. The results were found to be reversible and sensitive to the vapors of [Formula: see text]-butyl acetate and ammonia. It was found that Mn(OAc)Pc showed better sensitivity than CoPc and CuPc for [Formula: see text]-butyl acetate vapors at all measured vapor concentrations and temperatures. Mn(OAc)Pc also showed better sensitivity than CoPc and CuPc for ammonia vapors at 22°C.

Dielectric relaxation and localized electron hopping in colossal dielectric (Nb,In)-doped TiO2 rutile nanoceramics

The large dielectric relaxation and the frequency-dependent a.c. conductance were successfully explained by a modified electron hopping model.

End-of-Waste SiC-Based Flexible Substrates with Tunable Electrical Properties for Electronic Applications

We demonstrated the suitability of polymer composites filled with silicon carbide (SiC) powders derived from a recycling process for applications in electronic devices manufacturing. SiC powders have been synthesized from the process byproducts and used as fillers in the formulation of polystyrene (PS)/SiC composites, which have been used in the preparation of substrates using the solution-casting technique. Different substrates have been prepared by changing the concentration of SiC in the composite in the range from 6.7 to 67 wt % and used in simple electronic devices by performing gold contacts in both planar and stacked configurations. The electrical behaviors of both stacked and planar devices were investigated in direct current (DC) and alternate current (AC) regimes. The experimental results showed that charge percolation could be considered an explanation for the abrupt change in the differential conductivity observed around 30 wt %. Fowler-Nordheim tunneling at high fields has been found to be compatible with static characteristics and with high-frequency AC measurements and, therefore, charge tunneling between SiC islands has been proposed as the physical mechanism provoking the changes in charge transport in the substrates investigated. From this first experimental analysis, it appears that SiC/PS composites could suit their use in tunneling-gate dielectrics (i.e., in transistors suitable for their applications in nonvolatile random-access memory) for low concentrations or as a continuous semiconducting media when SiC is dispersed in high-concentration composites.

Free charge localization and effective dielectric permittivity in oxides

This review will deal with several types of free charge localization in oxides and their consequences on the effective dielectric spectra of such materials. The first one is the polaronic localization at the unit cell scale on residual impurities in ferroelectric networks. The second one is the collective localization of free charge at macroscopic interfaces like surfaces, electrodes and grain boundaries in ceramics. Polarons have been observed in many oxide perovskites mostly when cations having several stable electronic configurations are present. In manganites, the density of such polarons is so high as to drive a net lattice of interacting polarons. On the other hand, in ferroelectric materials like BaTiO3 and LiNbO3, the density of polarons is usually very small but they can influence strongly the macroscopic conductivity. The contribution of such polarons to the dielectric spectra of ferroelectric materials is described. Even residual impurities as for example Iron can induce well-defined anomalies at very low temperatures. This is mostly resulting from the interaction between localized polarons and the highly polarizable ferroelectric network in which they are embedded. The case of such residual polarons in SrTiO3 will be described in more detail, emphasizing the quantum polaron state at liquid helium temperatures. Recently, several nonferroelectric oxides have been shown to display giant effective dielectric permittivity. It is first shown that the frequency/temperature behavior of such parameters is very similar in very different compounds (donor-doped BaTiO3, CaCu3Ti4O12, LuFe2O4, Li-doped NiO, etc.). This similarity calls for a common origin of the giant dielectric permittivity in these compounds. A space charge localization at macroscopic interfaces can be the key for such extremely high dielectric permittivity.

Microwave a.c. conductivity of domain walls in ferroelectric thin films

Ferroelectric domain walls are of great interest as elementary building blocks for future electronic devices due to their intrinsic few-nanometre width, multifunctional properties and field-controlled topology. To realize the electronic functions, domain walls are required to be electrically conducting and addressable non-destructively. However, these properties have been elusive because conducting walls have to be electrically charged, which makes them unstable and uncommon in ferroelectric materials. Here we reveal that spontaneous and recorded domain walls in thin films of lead zirconate and bismuth ferrite exhibit large conductance at microwave frequencies despite being insulating at d.c. We explain this effect by morphological roughening of the walls and local charges induced by disorder with the overall charge neutrality. a.c. conduction is immune to large contact resistance enabling completely non-destructive walls read-out. This demonstrates a technological potential for harnessing a.c. conduction for oxide electronics and other materials with poor d.c. conduction, particularly at the nanoscale.

Field Effect and Strongly Localized Carriers in the Metal-Insulator Transition Material VO(2)

The intrinsic field effect, the change in surface conductance with an applied transverse electric field, of prototypal strongly correlated VO(2) has remained elusive. Here we report its measurement enabled by epitaxial VO(2) and atomic layer deposited high-κ dielectrics. Oxygen migration, joule heating, and the linked field-induced phase transition are precluded. The field effect can be understood in terms of field-induced carriers with densities up to ∼5×10(13)  cm(-2) which are trongly localized, as shown by their low, thermally activated mobility (∼1×10(-3)  cm(2)/V s at 300 K). These carriers show behavior consistent with that of Holstein polarons and strongly impact the (opto)electronics of VO(2).

Ionic charge transport between blockages: Sodium cation conduction in freshly excised bulk brain tissue

We analyze the transient-dc and frequency-dependent electrical conductivities between blocking electrodes. We extend this analysis to measurements of ions' transport in freshly excised bulk samples of human brain tissue whose complex cellular structure produces blockages. The associated ionic charge-carrier density and diffusivity are consistent with local values for sodium cations determined non-invasively in brain tissue by MRI (NMR) and diffusion-MRI (spin-echo NMR). The characteristic separation between blockages, about 450 microns, is very much shorter than that found for sodium-doped gel proxies for brain tissue, >1 cm.

CHARACTERIZATION OF DROP CASTED CuTsPc FILMS ON ITO SUBSTRATES

This study evaluated the possibility of utilizing a drop-cast process for CuTsPc -based organic solar cells. CuTsPc thin films were deposited by drop-cast method on ITO substrate. The absorption spectra of these films show two well-defined absorption bands of phthalocyanine molecule, namely, the soret (B) and Q-band. The band gaps calculated from the absorption spectra is found to lie in the range of 1.55–4.04 eV. X-ray diffractogram of the films indicate their polycrystalline nature. Atomic force microscope (AFM) investigations of the films show granular grain like morphology. The data for mobility, dielectric constant, extinction coefficient and refractive index are also presented in this communication.

Synthesis, characterization and electrical properties of peripherally tetra-aldazine substituted novel metal free phthalocyanine and its zinc(II) and nickel(II) complexes

The novel phthalonitrile containing azine segment and its corresponding tetra aldazine substituted metal free- and metallo-phthalocyanines (Zn(II) and Ni(II)) were synthesized and characterized by IR, (1)H NMR, Mass, UV-Vis spectroscopy and elemental analysis and addition to these techniques for substituted phthalonitrile (13)C NMR have been used. In addition, dc and ac electrical properties of the films of these novel phthalocyanines were investigated as a function of temperature (295-523 K) and frequency (40-10(5)Hz). Activation energy values of the films of the phthalocyanines were calculated from straight portions of the Arrhenius plot (lnσ(dc)-1/T curves) as 0.70 eV, 0.93 eV and 0.91 eV for the films of metal free, nickel- and zinc-phthalocyanines, respectively. From impedance spectroscopy measurements, it is observed that bulk resistance decreases with increasing temperature indicating semiconductor property.

Synthesis, characterization, and electrochemical and electrical properties of novel mono and ball-type metallophthalocyanines with four 9,9-bis(4-hydroxyphenyl)fluorene

The new mono-nuclear 4-5 and ball-type homo-dinuclear 6 phthalocyanines have been synthesized from the corresponding phthalodinitrile derivative 3. The synthesized compounds have been characterized by elemental analysis, UV-vis, IR,(1)H-NMR and MALDI-TOF-mass spectroscopies. The redox behaviours of the complexes were identified by cyclic voltammetry and square wave voltammetry. The temperature dependence of the electronic properties of compounds and adsorption of SO(2) on thin film of 6 were investigated by conductivity measurements using an interdigital transducer structure on glass substrate. Dc conductivity, measured between 300-475 K, is thermally activated with the activation energy ranging between 0.67 and 0.90 eV. The ac conductivity is found to vary with frequency, ω, as ω(s) in which the frequency exponent s decreases with temperature suggesting a hopping conduction mechanism for all compounds. The SO(2) sensing result showed that the spin coated film of 6 exhibits very good SO(2) sensing properties, fast response and recovery rate, high sensitivity and good repeatability.

AC Conductivity of Crystalline Materials and Glasses Ascribed to ADWPs

The behavior of the frequency dependence of the conductivity, σ(ω), of numerous crystalline materials and glasses is close to an ω1.0 dependence in the limit of low temperatures and/or high frequencies (referred to as the “nearly constant loss”, or NCL, regime). Detailed analysis of this behavior, including the frequency dependence of both ε′ and ε″, shows that it can be described phenomenologically as produced by a broad distribution of asymmetric double-well potentials (ADWPs) with low activation energies. In order to obtain an understanding of the atomic origins of such potentials, we investigate the composition dependence of this behavior in such materials as crystalline CeO2:1%Y3+ ceramics with variable [Y3+] and alkali germanate glasses with variable alkali concentration. The appearance of a discrete loss peak in CeO2: 1%Y3+ helps us understand the ADWPs as due to “off-symmetry” configurations that undergo wiggling motion between adjacent minimum-energy positions.

Hopping conduction observed in thermal admittance spectroscopy

We observe variable-range hopping conduction in thermal admittance spectroscopy and develop a method to evaluate the signal under this condition. As a relevant example of demonstration we employ Cu(In,Ga)(Se,S)2 thin-film solar cells and show that the fundamental N1 signal, which has been discussed for more than a decade in terms of minority carrier traps, does not display trap parameters, but is generated by the freezing-out of carrier mobility with decreasing temperature when hopping conduction prevails. This effect offers a new approach to carrier hopping and to semiconductors suffering from small mobility.