Anomalous Conductivity Behavior Research Articles

Investigations on anomalous behavior of ionic conductivity in NaPF6 salt loaded hydroxyethyl cellulose biodegradable polymer electrolyte for energy storage applications

AbstractThis article investigates the influence of NaPF6 salt content (0–30 wt.% in a varying interval of 5 wt.%) on the structural, electrical, and biodegradable properties of HEC/NaPF6 solid biopolymer electrolyte (SBE) films. The interaction of salt with the HEC polymer matrix is confirmed by FTIR and SEM studies. The elemental composition and mapping confirm the appearance of NaPF6 moieties in the HEC polymer matrix. XRD deconvolution reveals that HEC samples with 20 wt.% (H4) and 10 wt.% of salt (H2) have a significantly lower crystallinity index than pure HEC polymer. The H2 and H4 samples show the highest room temperature conductivity values (1.62 × 10−5 and 1.13 × 10−5 S cm−1, respectively) among all other prepared samples since carrier concentration influences the ionic conductivity and shares a similar order of conductivity. Thus, the H2 and H4 samples are employed as electrolyte separators in the sodium ion battery, and the results suggest that the H2‐based electrolyte system is more significant. Battery matrices like open circuit voltage (V), current density (μA cm−2), power density (mW kg−1), energy density (Wh kg−1) and discharge capacity (μA h−1) were calculated and found to be 2.48, 5.49, 44.60, 1.69, and 71.05, respectively for H2 electrolyte based cell. Wagner polarization reveals that H2 and H4 constitute the predominant charge carriers (ions) with total ion transference numbers of ⁓0.98 and ⁓0.99, respectively. To evaluate sample degradability, H2 and H4 samples were subjected to 20 and 5‐day biodegradation processes, during which the polymers completely (100%) broke down.

A localized collocation scheme with fundamental solutions for long-time anomalous heat conduction analysis in functionally graded materials

This paper makes the first attempt to develop a novel localized collocation scheme based on fundamental solutions for long-time anomalous heat conduction analysis in functionally graded materials. In the present numerical framework, the Laplace transformation and Fixed Talbot numerical inverse Laplace transformation are employed to deal with the time fractional derivative in anomalous time fractional heat conduction model. The localized collocation scheme based on fundamental solutions is applied to solve Laplace-transformed time-independent partial differential equations (PDEs), and the generalized reciprocity method (GRM) coupled with the derived problem-dependent generalized fundamental solution is proposed to deal with the inhomogeneous term in Laplace-transformed time-independent PDEs. Numerical tests demonstrate that the developed computational strategy can be considered as one of the competitive alternatives in the simulation of anomalous heat conduction behavior of functionally graded materials. Furthermore, the effect of time fractional derivative order on the behavior of anomalous heat conduction is numerically investigated.

Anomalous Behavior of Viscosity and Electrical Conductivity of MgSiO3 Melt at Mantle Conditions

AbstractSilicate melts have served as transport agents in the chemical and thermal evolution of Earth. Molecular dynamics simulations based on a deep neural network potential trained by ab initio data show that the viscosity of MgSiO3 melt decreases with increasing pressure at low pressures (up to ∼6 GPa) before it starts to increase with further compression. The melt electrical conductivity also behaves anomalously; first increasing and then decreasing with pressure. The melt accumulation implied by the viscosity turnover at ∼23 GPa along mantle liquidus offers an explanation for the low‐velocity zone at the 660‐km discontinuity. The increase in electrical conductivity up to ∼50 GPa may contribute to the steep rise of Earth's electrical conductivity profiles derived from magnetotelluric observations. Our results also suggest that small fraction of melts could give rise to detectable bulk conductivity in deeper parts of the mantle.

Effects of sintering temperature on ac conductivity, permittivity, and permeability of manganese doped cobalt ferrite nanoparticles

This paper reports on the effects of magnetic and electric properties of a non-stoichiometric composition of cobalt ferrite nanoparticles doped with manganese content at the weight percent 0.25. Its toroid and disc-shaped samples were sintered at two different temperatures 750 °C and 1050 °C. The studied results show the dependence of the permittivity and permeability on the microstructural features, particularly crystallite/grain size that change with the sintering temperature. The anomalous behavior of ac conductivity is marked outside a hump region with a decreased sintering temperature. A rightward shift of the characteristic frequency in the absorption of electric modulus is observed with the increased sintering temperature. Similarly, a rightward shift of the resonance frequency in the spectra of the imaginary part of the magnetic modulus is marked with the increased sintering temperature. The higher magnitude of the imaginary part of the electric modulus at the characteristic frequency is expected to dissipate as eddy current loss. Similarly, the higher magnitude of the imaginary part of the magnetic modulus at the resonance frequency is assumed to dissipate as a residual loss. Both of them are selectable by the sintering temperature. This behavior may make this material suitable to be used in thermoelectric and thermomagnetic sensors/switches.

Anomalous conductivity behavior induced by in situ metastable amorphous phase in BaTiO3/Ni0.5Zn0.5Fe2O4 ceramic composite

The electrical conductivity of ferroelectric-ferromagnetic ceramic composites usually increases monotonously with elevated temperature, which may seriously deteriorate their performance. In this work, we report an anomalous conductivity behavior induced by in situ metastable amorphous phase in a semi-conductive ceramic composite, 0.1BaTiO3(BTO)/0.9Ni0.5Zn0.5Fe2O4(NZFO). The ceramic composites with in situ formed amorphous BTO phase (a-BTO) or crystalline BTO phase (c-BTO) were successfully prepared. The effect of such metastable amorphous phase on the electrical transport properties of the ceramic composite was investigated. A comparative study reveals that a-BTO could act as a buffering phase preventing the electrical conductivity of the composite from monotonous increment above a critical temperature (513 K), whereas such effect does not occur when BTO is pure crystalline. Around 513 K, a change in the activation energy of dc conductivity has been observed for the c-BTO/NZFO sample. Whereas for the a-BTO/NZFO sample, the Arrhenius relation fails to describe its behavior above 513 K owing to decreased conductivity, which is rarely seen in semiconductors. The activation energy of relaxation is identical for both systems, i.e. 0.204 eV, because their dielectric relaxation is dominated by crystalline NZFO phase. The findings of this work are inspiring for the design of novel electronic materials constituted by a crystalline phase and an amorphous phase with adjustable performance.

Anomalous proton conduction behavior across a nanoporous two-dimensional conjugated aromatic polymer membrane.

We investigate aqueous proton penetration behavior across a newly synthesized nanoporous two-dimensional conjugated aromatic polymer (2D-CAP) membrane using extensive ReaxFF reactive molecular dynamics simulations. We found that the proton penetration energy barrier across 2D-CAP is twice as high as that of graphtetrayne, even though 2D-CAP exhibits a larger pore size. Detailed analysis indicates that the anomalous high proton conduction energy barrier of 2D-CAP originates from its unique atomic nanopore structure. The hydrogen atoms at the periphery of the 2D-CAP nanopores can form a stable local hydrogen bond network with water molecules inside or surrounding the nanopores. The mobility of water molecules involved in this local hydrogen bond network will be significantly lowered, and the proton transportation process across the nanopores will thus be impeded. Our results show that the proton penetration behavior across nanoporous 2D materials is influenced not only by the pore size, but also by the decorated atoms or functional groups at the pore edges. Hydrogen atoms at the periphery of nanopores with certain geometry can form a stable local hydrogen bond network with neighboring water molecules, further hampering the proton conductivity.

Anomalous Conductance near Percolative Metal-Insulator Transition in Monolayer MoS2 at Low Voltage Regime.

Conductivity of the insulating phase increases generally at an elevated drain-source voltage due to the field-enhanced hopping or heating effect. Meanwhile, a transport mechanism governed by percolation in a low compensated semiconductor gives rise to the reduced conductivity at a low-field regime. Here, in addition to this behavior, we report the anomalous conductivity behavior to transform from a percolative metallic to an insulating phase at the low voltage regime in monolayer molybdenum disulfide (MoS2). Percolation transport at low source-drain voltage is governed by inhomogeneously distributed potential in strongly interacting monolayer MoS2 with a substrate, distinct from the quantum phase transition in multilayer MoS2. At a high source-drain voltage regime, the insulating phase is transformed further to a metallic phase, exhibiting multiphases of metallic-insulating-metallic transitions in monolayer MoS2. These behaviors highlight MoS2 as a model system to study various classical and quantum transports as well as metal-insulator transition in two-dimensional systems.

Anomalous behavior of thermal conductivity at high temperatures for molecular crystals composed of flexible molecules

The temperature dependence of thermal conductivity κ(Т) of selected molecular polycrystals consisting of flexible molecules was investigated within 20–260 K. The materials were para-chloronitrobenzene, pentachloronitrobenzene and freons F-112 and F-113. The κ(Т) of these crystals increased with temperature in the interval where processes of phonon–phonon scattering were dominant. The increase was observed both in the orientationally-ordered and -disordered phases and is typical of the thermally activated heat transfer by localized molecular excitations [M. A. Strzhemechny et al., Chem. Phys. Lett. 647 (2016) 55]. In a wide interval of temperatures, irrespective of the glass transition temperature, the κ(Т) could be described by a sum of three components: κ(Т) = А/Т + В + κТА(Т). The term A/T accounts for phonon–phonon scattering processes and B accounts for diffuse phonon scattering. The third contribution is described by the Arrhenius equation, κТА(Т) = κ0 ехр(−Е/kBТ), where E is the activation energy and κ0 is the pre-exponential factor characterizing intensity of the activation process. A comparative analysis of anomalous thermal conductivities of some other molecular crystals was carried out. It was found that κ0 linearly depended on E and a similar relationship was evident for a series of quasicrystals.

Magnetotransport properties and phase separation in iron substituted lanthanum-calcium manganite

Crystal and magnetic structure of iron substituted La0.7Ca0.3Mn0.5Fe0.5O3 manganite was investigated by powder neutron diffraction in the 10–300 К temperature range. It is established that the unit cell parameters at 300 K are a = 5.447(2) Å, b = 7.709(3) Å, c = 5.467(3) Å and they change vs. temperature with rates da/dT ∼ 1.3*10–4 Å*K−1, db/dT ∼ 1.7*10–4 Å*K−1 and dc/dT ∼ 1.6*10–4 Å*K−1, respectively. It was also realized the measurements of magnetization and electrical resistivity in the 5–300 K temperature range including in magnetic fields up to 1 T. Magnetic phase separation was observed. Upon the field increase the glass, Tg, and irreversibility, Tirr, temperatures decrease, while the magnetic ordering temperature, Tmo, increases. Upon the temperature increase both the residual magnetization, Mr, and coercive field, Hc, decrease. A complex frustrated magnetic state in which the long-range G-type antiferromagnetic phase coexists with the short-range ferromagnetic clusters was established. An average size of ferromagnetic clusters is Dav ∼ 20 nm. An anomalous temperature behavior of electrical conductivity for La0.7Ca0.3Mn0.5Fe0.5O3 was found which confirms a transformation of various magnetic states. Different models of conduction mechanism were considered. The origin of the unusual magnetic state, the electrical conduction mechanisms, and the relationship between magnetic and electrotransport properties in this sample were discussed.

Phonon wave interference in graphene and boron nitride superlattice

The thermal transport properties of the graphene and boron nitride superlattice (CBNSL) are investigated via nonequilibrium molecular dynamics simulations. The simulation results show that a minimum lattice thermal conductivity can be achieved by changing the period length of the superlattice. Additionally, it is found that the period length at the minimum shifts to lower values at higher temperatures, and that the depth of the minimum increases with decreasing temperature. In particular, at 200 K, the thermal conductivities of CBNSLs with certain specific period lengths are nearly equal to the corresponding values at 300 K. A detailed analysis of the phonon spectra shows that this anomalous thermal conductivity behavior is a result of strong phonon wave interference. These observations indicate a promising strategy for manipulation of thermal transport in superlattices.

Understanding the anomalous conduction behavior in ‘n’ type tungsten oxide thin film during hydrogen gas sensing: Kinetic analyses of conductance transients

Promising hydrogen sensing characteristics are reported for sol–gel synthesized ‘n’ type WO3 thin films. During hydrogen gas sensing using WO3 films, irrespective of the test gas concentration and thickness of the sensing films, a temperature dependent anomalous change in surface conduction behavior of the sensor is reported. The nature of such gradual change in conduction behavior was further investigated by analyzing the response and recovery conductance transients. It was identified that the observed anomalous characteristics are superposition of several donor and acceptor type adsorption–desorption processes with their characteristic time constants. From the temperature variations of these characteristic time constants we have estimated the activation energies of the processes involved during sensor response and recovery. By correlating the estimated activation energies with the steps of the surface reactions, we have made an attempt to explain the observed gradual change in conduction behavior of WO3 thin films during hydrogen gas sensing.

Experimental Study and Numerically Supported Approach to Interpretation of Spontaneous Transitions into a State of High Conductivity in Poly(vinyl chloride) Composite Films

The results of experimental studies of conductivity anomalies are analyzed for film samples of specially synthesized PVC and polyacetylene copolymer, in which polyene conjugated bonds are built in PVC macromolecules. In such samples spontaneous and stimulated conductivity jumps by 12 orders of magnitude take place, and the lifetime of each of these states can be very large - minutes, hours and more. The nonlinear model is considered which describes the anomalous behavior of conductivity as a result of percolation transition associated with reversible thermal "shorting" of insulating gaps between conductive regions.

Anomalous conductivity behaviour in copper solutions used for surface finishing

Conductivity measurements have been obtained for copper solutions used in both electrodeposition and electroless process solutions, in particular sulphate, nitrate, acetate and chloride. A discontinuity in the conductivity data with varying temperature was observed which corresponded to a stage-wise ionic dehydration and a critical transition temperature of ∼50°C. Similar behaviour has been noted previously for nickel salts, both by the authors and other workers, and it may be more common than previously supposed.

An explanation for anomalous thermal conductivity behaviour in nanofluids as measured using the hot-wire technique

Several efforts have been made to explain thermal conductivity enhancements in fluids due to the addition of nanoparticles. However, until now, there has been no general consensus on this issue. In this work a simple experiment is described that demonstrates a possible cause of misinterpretation of the experimental data of thermal conductivity obtained when using the hot-wire technique (HWT) in these systems. It has been demonstrated that the thermal conductivity of a two-layer sample of two non-miscible phase systems determined by means of the HWT must be modelled using a series thermal resistance model with consideration of the interfacial layers between different phases. This result sheds light on the thermal conductivity enhancement in nanofluids with respect to the values corresponding to the base fluid, suggesting that this increase can be explained using the above-mentioned model and not by application of empirical formulae for effective media, as done before.

Anomalous electrical transport properties of CdSe quantum dots at and below room temperature

Here we report the dielectric relaxation and anomalous ac conduction behavior of CdSe quantum dots in the temperature (T) range of 77K≤T≤300K and in the frequency (f) range of 100Hz≤f≤1MHz. Interfacial polarization exhibits strong temperature dependence only above 250K and dielectric loss spectrum undergoes a shallow minimum. Superlinear power law behavior of the ac conductivity was observed above certain frequencies, along with the universal dielectric response at comparatively lower frequencies. Extraction of the temperature dependent dc contribution, hopping frequencies, frequency exponents and activation energies values were done by theoretical fitting and was observed that for T=77–200K, classical hopping over barrier (HOB) is the prevailing charge transport mechanism whereas for T=250–300K, the charge transport mechanism is correlated barrier hopping (CBH). Analysis of the Nyquist plotting and non-Debye electric modulus spectra have also been conferred in this context.

Anomalous behavior of proton transport and dimensional stability of sulfonated poly(arylene ether sulfone) nonwoven/silicate composite proton exchange membrane with dual phase co-continuous morphology

Herein, anomalous behavior of proton conductivity and dimensional stability of sulfonated poly(arylene ether sulfone) (SPAES) nanofiber nonwoven fabric/silicate composite membrane (denoted as ‘SN/S membrane’) featuring dual phase co-continuous morphology, which could be potentially applied to proton exchange membrane fuel cells (PEMFCs), is systematically investigated. The SN/S membrane is fabricated via in situ sol–gel synthesis of tetraethoxysilane (TEOS)/3-glycidyloxypropyltrimethoxysilane (GPTMS) mixture directly inside the electrospun SPAES nonwoven. In comparison to a typical SPAES (matrix)/silicate (domain) composite membrane, the SN/S membrane having structural uniqueness provides significant improvement in relative humidity (RH) variation-driven dimensional change, although its proton conductivity is decreased due to the presence of ionically inert continuous silicate phase. A noteworthy finding of this study is that the phase morphology of composite proton exchange membranes plays a crucial role in determining the membrane properties such as proton conductivity and dimensional stability.

Research of Water Response under the Action of the Infrared Human Body Radiation by Water Conductometric Sensors

Non-equilibrium thermal and biothermal radiation generated by heated solid materials and hematothermal living organisms are studied by water conductometric sensors. Engineering aspects and physical features of developed water conductometric sensors are given. Procedure and measuring technique are described. Our experiments show the anomalous behavior of water conductivity and associated differential parameters under water heating by biological objects compared with traditional heating sources. Water response to human action strongly depends on psychophysiological and psychoemotional state of the person. Moreover the responses to the action by left and right human hands are substantially different and as a rule are specific to the gender. The possible physicochemical mechanisms of such anomalous water behavior are studied. It is suggested that the observed effects are associated with resonant excitation of vibration-rotation energy levels of water under the influence of bioradiation generated by human organism consisting of approximately 70% water. The results obtained have good perspectives for future applications in different fields of human activity.

Sulfonated SBA-15 mesoporous silica-incorporated sulfonated poly(phenylsulfone) composite membranes for low-humidity proton exchange membrane fuel cells: Anomalous behavior of humidity-dependent proton conductivity

Sulfonated SBA-15 mesoporous silica (SM-SiO2)-incorporated sulfonated poly(phenylsulfone) (SPPSU) composite membranes are fabricated for potential application in low-humidity proton exchange membrane fuel cells (PEMFCs). The SM-SiO2 particles are synthesized using tetraethoxy silane (TEOS) as a mechanical framework precursor, Pluronic 123 triblock copolymer as a mesopore-forming template, and mercaptopropyl trimethoxysilane (MPTMS) as a sulfonation agent. A distinctive feature of the SM-SiO2 particles is the long-range ordered 1-D skeleton of hexagonally aligned mesoporous cylindrical channels bearing sulfonic acid groups. Based on a comprehensive characterization of the SM-SiO2 particles, the effect of SM-SiO2 (as a functional filler) addition on the proton conductivity of the SPPSU composite membrane is examined as a function of temperature and relative humidity. An intriguing finding is that the proton conductivity of the SPPSU composite membrane exhibits a strong dependence on the relative humidity of measurement conditions. This anomalous behavior is further discussed with an in-depth consideration of the characteristics and dispersion state of SM-SiO2 particles, which affect the tortuous path for proton movement, water uptake, and state of water. Notably, at low-humidity conditions, the SM-SiO2 particles in the SPPSU composite membrane serve as an effective water reservoir to tightly retain water molecules and also as a supplementary proton conductor, whereas they behave as a barrier to proton transport at fully hydrated conditions.

Anomalous Electrical Conductivity Behavior at Elevated Pressure in the Protic Ionic Liquid Procainamide Hydrochloride

Using broadband dielectric spectroscopy, we investigated the effect of hydrostatic pressure on the conductivity relaxation time τ{σ} of the supercooled protic ionic liquid, procainamide hydrochloride, a common pharmaceutical. The pressure dependence of τ{σ} exhibited anomalous behavior in the vicinity of the glass transition T{g}, manifested by abrupt changes in activation volume. This peculiar behavior, paralleling the change in temperature dependence of τ{σ} near T{g}, is a manifestation of the decoupling between electrical conductivity and structural relaxation. Although the latter effectively ceases in the glassy state, free ions retain their mobility but with a reduced sensitivity to thermodynamic changes. This is the first observation of decoupling of ion migration from structural relaxation in a glassy conductor by isothermal densification.

Effect of different anions of lithium salt and MMT nanofiller on ion conduction in melt-compounded PEO–LiX–MMT electrolytes

Polymer nanocomposite electrolyte (PNCE) films composed of poly(ethylene oxide) (PEO), lithium salt (\( {\text{LiX}};\;{\text{X}} = ClO_4^{ - },\;BF_4^{ - },\;C{F_3}SO_3^{ - } \)) and montmorillonite (MMT) clay as nanofiller were prepared by melt-compounded hot-pressed technique at 70 °C under 3 tons of pressure. The ionic conductivity and relaxation behaviour of the films were investigated by dielectric relaxation spectroscopy in the frequency range of 20 Hz to 1 MHz at ambient temperature. The results revealed that the ionic conductivity of the PNCE films having 20:1 stoichiometric ratio of ethylene oxide monomer units to the lithium cation are governed by the size of different anions and the dissociation constant of salt, and also MMT concentration. It was found that PEO–LiBF4 film has comparative high dc ionic conductivity, whereas both the LiBF4 and LiClO4 containing PNCE films exhibit anomalous conductivity behaviour with varying MMT concentration. The PEO–LiCF3SO3 film has two orders of magnitude low value of dc ionic conductivity as compared to that of the other salts electrolyte films, but its conductivity enhances by one order of magnitude when 2 wt.% MMT is added as filler. A correlation between the values of ionic conductivity, conductivity relaxation time and the real part of permittivity at 1 MHz were found and the same was discussed in relation to the transient ion-dipolar type cross-linked structural behaviour of the polymeric nanocomposite electrolytes.