Hopping Energy Research Articles

Effect of Fe doping on structural, magnetic, and electrical properties of non-magnetic and magnetic rare earth-based perovskite chromites La0.5Nd0.5Cr1-x Fe x O3 (0 ≤ x ≤ 1)

The structural, magnetic, and electrical properties of new series La0.5Nd0.5Cr1-x Fe x O3 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) have been reported. All the phases crystallize in the orthorhombic symmetry with Pbnm space group. The unit cell volume of La0.5Nd0.5Cr1-x Fe x O3 increases monotonically with increasing Fe doping. Magnetization studies showed that all our investigated phases (except x = 0.8 and 1.0) exhibit a paramagnetic–anti-ferromagnetic transition at low temperature. The variation in Neel temperature (T N) with increasing x can be explained in terms of magnetic interactions due to Fe doping. Irreversibility between the zero-field-cooled (ZFC) and field-cooled (FC) magnetization is clearly seen close to T N. All the phases show that insulating behavior and the transport properties are dominated by the polaron hopping mechanism with increase in polaron hopping energy with Fe content.

Suppression of charge noise using barrier control of a singlet-triplet qubit

It has been recently demonstrated that a singlet-triplet spin qubit in semiconductor double quantum dots can be controlled by changing the height of the potential barrier between the two dots ("barrier control"), which has led to a considerable reduction of charge noises as compared to the traditional tilt control method. In this paper we show, through a molecular-orbital-theoretic calculation of double quantum dots influenced by a charged impurity, that the relative charge noise for a system under the barrier control not only is smaller than that for the tilt control, but actually decreases as a function of an increasing exchange interaction. This is understood as a combined consequence of the greatly suppressed detuning noise when the two dots are symmetrically operated, as well as an enhancement of the inter-dot hopping energy of an electron when the barrier is lowered which in turn reduces the relative charge noise at large exchange interaction values. We have also studied the response of the qubit to charged impurities at different locations, and found that the improvement of barrier control is least for impurities equidistant from the two dots due to the small detuning noise they cause, but is otherwise significant along other directions.

An Evolutionary Mobility Aware Multi-Objective Hybrid Routing Algorithm for Heterogeneous WSNs

Researchers have faced numerous challenges while designing WSNs and protocols in numerous applications. Amongst all sustaining connectivity and capitalizing on the network lifetime is a serious deliberation. To tackle these two problems, the authors have considered Mobile Wireless Sensor Networks (MWSNs). In this paper, the authors put forward an Evolutionary Mobility aware multi-objective hybrid Routing Protocol for heterogeneous wireless sensor networks (EMRP). EMRP selects the optimal path from source node to sink by means of various metrics such as Average Energy consumption, Control Overhead, Reaction Time, LQI, and HOP Count. The Performance of EMRP when equated with Simple Hybrid Routing Protocol (SHRP) and Dynamic Multi-Objective Routing Algorithm (DyMORA) using parameters such as Average Residual Energy (ARE), Delay and Normalized Routing Load. EMRP improves AES by a factor of 4.93% as related to SHRP and 5.15% as related to DyMORA. EMRP has a 6% lesser delay as compared with DyMORA.

Influence of Polyethylene Glycol (PEG) in CMC-NH4BR Based Polymer Electrolytes: Conductivity and Electrical Study

The present work was carried with new type and promising polymer electrolytes system by development of carboxyl methylcellulose (CMC) doped NH4Br and plasticized with polyethylene glycol (PEG). The sample was successfully prepared via solution casting with no separation phase and good mechanical properties. The electrical conductivity and thermal conductivity of CMC-NH4Br-PEG based PEs system have been measured by the electrical impedance spectroscopy method in the temperature range of 303–373 K. The highest ionic conductivity gained is 2.48 x 10-3 Scm-1 at ambient temperature for sample contain with 8 wt. % PEG. It can be concluded that the plasticized is accountable for the conductance and assist to enhancing the ionic conductivity of the CMC-NH4Br-PEG electrolyte system. The addition of PEG to the CMC-based electrolyte can enhance towards the cation mobility which is turn increases ionic conductivity. The conductivity-temperature of plasticized BdPEs system was found obeys the Arrhenius relation where the ionic conductivity increases with temperature and activation energy for the ions hopping of the highest conducting PEs system only required small value to migrate. The electrical studies show a non-Debye behaviour of BdPEs based on the analyzed data using complex permittivity, e* and complex electrical modulus, M* of the sample at different temperature.

Modeling Na2s Based Glassy Electrolytes for High Performance Solid State Sodium Ion Batteries

Limited availability of lithium and safety concerns due to flammability of liquid electrolytes pose significant challenges to commercial lithium-ion batteries. To overcome these limitations, it is essential to explore technologies beyond conventional lithium ion batteries, particularly for electric power grid applications. Sodium ion batteries, particularly those employing solid electrolytes, are being explored as potential candidates. Solid state electrolytes are typically non – toxic and more environmental friendly, which provides them an edge over their liquid counterparts. However, obtaining relatively high ionic conductivity at room temperatures is challenging. In this work, we studied sodium sulfide (Na2S) based glasses as electrolytes for solid state sodium ion batteries. More specifically, sodium sulfide – silicon sulfide [0.5Na2S – 0.5SiS2] glass was explored. These glassy electrolytes were modeled using classical molecular dynamics (MD) approach. The interactions between various ions in the glass were defined using Buckingham type potential. All the glasses were formed using a typical melt – quench technique. Due to amorphous nature of the glass, a large number of initial glass structures were studied to obtain statistically reasonable model. The density of glass obtained through MD was observed to match quite well to the experimentally reported value. Further structural validation of the molecular model was performed by comparing the pair distribution function (PDF) for different pairs of ions for actual glass to those obtained from MD simulations. The ionic conductivity values for these glasses at room temperature have been observed to be in the range of ~ 10-5S/cm, which agreed well with the values obtained from the molecular simulations. Furthermore, the activation energy for ion hopping within the glass was obtained through MD and compared well with experimental data. A KMC site model was developed, based on inputs from MD, to evaluate the ionic conductivity of these glasses at a much larger length scale and the results agreed well with experimental measurements. Interactions at the anode – electrolyte interface play a key role in determining the performance of sodium ion batteries. Ab initio MD simulations of pure sodium metal and glassy electrolyte interface were performed. Structural configuration of the sodium anode – glass interface was estimated by calculating the density distribution and PDF’s for various ion pairs. Additionally, Na+ ion transport near the interface was studied carefully to determine specific metallic sites that accommodate Na+ ions. The distribution of these favorable sites along with their respective site energies were calculated and provided as inputs to KMC site model that simulated actual battery charging – discharging cycles based on the above inputs from ab initio MD.

Metal-insulator transition in a disordered nanotube

According to the Anderson localization theory, the wavefunctions of a sufficiently strong disordered system are localized. We show that shifting hopping energy between nearest neighbors would induce an anomalous localization-delocalization transition in a disordered square lattice nanotube modelled by tight-binding. For this purpose, the consecutive level spacing statistics and the singularity spectrum analyses were performed. The quantum analysis of singularity spectrum reveals distinctive multifractality structures of the wavefunctions associated with localized and delocalized phases. We find that while in finite-size limit the system has a sudden metal-insulator transition, in large-scale limit the system experiences a rapid but continuous crossover. Interestingly, we report a critical value of hopping energy for which the system behavior is fairly close to metallic phase and especially independent of the system size. Passing this critical value, a great difference in the electronic transport properties of the system occurs. It follows that in the large-scale size, the system tends to follow semi-metallic behavior, while in finite size behaves more like to an insulator. The localization-delocalization transition is also reflected in the electrical current. In accordance with the indicators studied, we find that in delocalized regime there is a spreading electrical current throughout the whole system with an azimuthal symmetric characteristic.

Low temperature process of electronic charge transport mechanism in PANi/MWCNT nanocomposites: tubular morphology

In this work, we investigate the tuning of the electrical transport dimensionality of polyaniline-multiwalled carbon nanotube nanocomposites (PANi/MWCNTs) for electronic device applications. The microstructure and its correlations with electrical transport properties, and the conductivity of nanocomposites were studied from 75 to 330 K. The samples have been prepared with a new low-temperature system in which a layer of polymer has been coated on MWCNTs in a whole tubular morphology. The enhancement in conductivity of the nanocomposites is due to the charge transfer effect from the quinoid rings and the π-π interaction of the PANi to the MWCNT. The synthesized nanocomposites are investigated in the framework of existing theoretical models in 1, 2 & 3 dimensions (phonon assisted tunneling within the carbon nanotube and clusters) and systematically studied and compared in terms of transport parameters. Charge localization length and most probable hopping distance were found to decrease with wt% of MWCNT, whereas the charge hopping energy increases in nanocomposites. The distinction between thermally activated processes and the determination of cross-over temperature were achieved by exploring the temperature dependence of the fractional exponent of the dispersive conductivity. The enhanced transport properties of these categories of nanocomposites due to a combination of MWCNTs in conducting polymer matrix can be applied for photodetectors, organic solar cells, supercapacitors, and electronic strategies.

Photophysical behavior of systematically substituted (di-2-pyridylaminomethyl) benzene ligands and its Re(I) complexes: A combined experimental and theoretical approach

Abstract The photophysical behavior of a series of flexible di-2-pyridylaminomethyl substituted ligands systematically substituted on a rigid benzene core and their corresponding mono-metallic Re(I) complexes have been investigated by steady state and time-resolved fluorescence spectroscopy in different composition of DMSO–water binary solvent mixtures. Unusual fluorescence properties in lower DMSO content ( X DMSO = 0.1–0.3) solvent mixtures is consistent with fascinating property of DMSO, which is known to perturb the hydrogen bonding ability of water with the solute. Spin allowed inter-ligand π–π * transition is more apparent in (1, 3) substituted systems. The calculated spectroscopic parameters of the complexes are significantly different from the ligands, mainly due to ligand to metal charge transfer. The experimental observations are in very good agreement with the theoretical results obtained at B3LYP/6-31G(d,p)/LANL2DZ level of density functional theory (DFT) calculation. Natural bond orbital (NBO) analysis and examination of frontier molecular orbitals reveal that the basic architecture of the symmetrically substituted multi-chromophoric ligand can induce excitation energy hopping, similar to an artificial antenna system.

Effect of annealing in an H2 gas atmosphere on the physical properties for 70V2O5·30TeO2 (mol%) glasses

Powdered 70V2O5·30TeO2 (mol%) glasses were annealed in an H2 gas atmosphere at 473K for 1h and 2h, respectively. The difference between their physical properties before and after annealing was investigated. The mass of the powders decreased with an increase in the annealing time. Glass transition temperature (Tg) was 512±0.1–513±0.1K for the annealed powders, indicating that the Tg values became lower than the as-quenched glass powder (Tg=517±0.1K). The fraction of reduced vanadium ion (Cv=V4+/(V4++V5+)) increased with an increase in the annealing time: Cv=0.020±0.003, 0.024±0.003 and 0.0272±0.0033. From IR observation, it was determined that the glass structure in the annealed glasses ultimately incorporated a much larger amount of TeO3 trigonal pyramid units compared with the as-quenched glass powder. It was determined that the DC electrical conductivity (σ) of the pelletized powders, which were n-type semiconducting, depended on the annealing time of the powders. The largest σ was (5.78±0.28)×10−5Scm−1 at 473K for the pellet of the powder annealed for 2h. The activation energy for electron hopping (W) was determined to be 0.380±0.0005–0.420eV±0.0005eV, indicating that W decreased with an increase in the annealing time. The annealing contributed to the release of O from the glasses by changing the unit in the glasses from the TeO4 to TeO3: TeO4+H2→TeO3+H2O↑.

Optoelectronic Stress Sensor Based on a Quantum Dot-Organic Semiconductor Nanocomposite

We studied the electrical and optical responses of a sensor device based on a nanocomposite comprising CdSe quantum dots (QDs) embedded in an organic matrix to compressive stresses. The sensor converted stresses as low as a few kPa into measurable changes in both current density and electroluminescence (EL) intensity. Two distinct operation regions have been identified: at low stresses below 200 kPa, a moderate increase in current density and a sharp decrease in EL intensity with increasing stress were observed; at high stresses above ∼200 kPa, a large increase in current and slow EL quenching were obtained. These behaviors have been attributed to stress-induced increases in the rates of charge hopping and excitonic energy transfer in the nanocomposite. Similar devices may be built on flexible substrates and used to directly image stress distributions and sense touch on a par with human fingers.

Dynamics of Intramolecular Energy Hopping in Multi-Bodipy Self-Assembled Metallocyclic Species: A Tool for Probing Subtle Structural Distortions in Solution

The intramolecular excitation energy transfer (EET) processes in a series of fluorescent-unquenched, self-assembled metallocycles consisting of spatially fixed-separated and parallel-aligned Bodipy chromophores, are investigated here by steady-state and femtosecond-fluorescence upconversion measurements in the solution phase. These multi-Bodipy macrocycles, namely, the rhomboid (A1), the tetragon (A2) and the hexagon (A3), are formed via temperature-regulated Pt(II)–pyridyl coordination and consist, respectively, of two, four, and six Bodipy subunits, which are locked at the corners and aligned with their long molecular axes perpendicular to the rigid polygonal frame formed by the alternating B···Pt(II) connectivities. Extensive simulations and fits to the experimental fluorescence anisotropy decays r(t) show that EET within the cyclic scaffolds is quite uniform and much faster than the intrinsic decay rate of the Bodipy’s. The equalization of the excitation survival probabilities over time of all chromop...

Spin-Triplet Pairing Induced by Spin-Singlet Interactions in Noncentrosymmetric Superconductors

In noncentrosymmetric superconductors, we examine the effect of the difference between the intraband and interband interactions, which becomes more important when the band splitting increases. We define the difference ΔVμ between their coupling constants, i.e., that between the intraband and interband hopping energies of intraband Cooper pairs. Here, the subscript μ of ΔVμ indicates that the interactions scatter the spin-singlet and spin-triplet pairs when μ = 0 and μ = 1,2,3, respectively. It is shown that the strong antisymmetric spin–orbit interaction reverses the target spin parity of the interaction: it converts the spin-singlet and spin-triplet interactions represented by ΔV0 and ΔVμ>0 into effective spin-triplet and spin-singlet pairing interactions, respectively. Hence, for example, triplet pairing can be induced solely by the singlet interaction ΔV0. We name the pairing symmetry of the system after that of the intraband Cooper pair wave function, but with an odd-parity phase factor excluded. The ...

Probing the Absorption and Emission Transition Dipole Moment of DNA Stabilized Silver Nanoclusters.

Using single molecule polarization measurements, we investigate the excitation and emission polarization characteristics of DNA stabilized silver nanoclusters (C24-AgNCs). Although small changes in the polarization generally accompany changes to the emission spectrum, the emission and excitation transition dipoles tend to be steady over time and aligned in a similar direction, when immobilized in PVA. The emission transition dipole patterns, observed for C24-AgNCs in defocused wide field imaging, match that of a single emitter. The small changes to the polarization and spectral shifting that were observed could be due to changes to the conformation of the AgNC or the DNA scaffold. Although less likely, an alternative explanation could be that several well aligned spectrally similar emitters are present within the DNA scaffold which, due to Förster resonance energy transfer (FRET) processes such as energy hopping, energy transfer, and singlet-singlet annihilation, behave as a single emitter. The reported results can provide more insight in the structural and photophysical properties of DNA-stabilized AgNCs.

FTGAF-HEX: fuzzy logic based two-level geographic routing protocol in wireless sensor networks

Minimization of energy consumption has become a major challenge in wireless sensor networks (WSNs) as it directly corresponds to the network lifetime. In WSNs, geographic adaptive fidelity (GAF) is one of the most energy efficient location based protocol which extends the network lifetime by identifying equivalence between sensors using geographic location information and then keeping unnecessary sensors in sleep state, while maintaining application fidelity. Still traditional GAF cannot reach to the optimum energy usage since it needs more hop count to transmit data packets to the base station called sink. As a result, it leads to higher energy usage and packet delay due to participation of more sensors. In this paper, a fuzzy logic based topology management protocol named FTGAF-HEX, which bases on GAF is proposed to achieve minimum packet delay with higher energy conservation. Furthermore, we propose to use a generalized version of GAF based on honeycomb virtual grid architecture called Hexagonal GAF (GAF-HEX) to replace the square grid with hexagonal one. Analysis and simulation results show significant improvement of the proposed work compared to traditional GAF in the aspect of various performance metrics i.e., total hop count, energy consumption and distance covered by the data packet before reaching the sink. As a result, compared to traditional GAF-HEX, it needs 37–44% less hop count and consumes 17–24% less energy to prolong the network lifetime.

Structural, magnetic and electrical properties of Fe-doped perovskite manganites La0.8Ca0.15Na0.05Mn1−xFexO3 (x = 0, 0.05, 0.10 and 0.15)

Here, we report the structural, magnetic and electrical properties of new series of Fe-doped perovskite manganites La0.8Ca0.15Na0.05Mn1-xFexO3. Rietveld analysis of powder X-ray diffraction data revealed that all the compounds crystallize in the orthorhombic symmetry with Pnma space group. The lattice parameters and the unit cell volume increases slightly with Fe-doping. Temperature dependent magnetization studies showed that all our investigated compounds exhibit a paramagnetic–ferromagnetic transition with Curie temperature (TC) decreases with increasing x from 253 K to 130 K. All the phases show metal-insulator transition and the values of metal-insulator transition temperature (TMI) are nearly approachable to TC, reflecting strong correlations between the magnetic and electrical properties in our samples. The transport properties are dominated by the Polaron hopping mechanism in temperature range above TMI with increase in polaron hopping energy with Fe content.

Improving lifetime and network connections of 3D wireless sensor networks based on fuzzy clustering and particle swarm optimization

3D wireless sensor network (3D-WSN) has attracted significant interests in recent years due to its applications in various disciplinary fields such as target detection, object tracking, and security surveillance. An important problem in 3D WSN is the sensor energy optimization which determines a topology of sensors to prolong the network lifetime and energy expenditure. The existing methods for dealing with this matter namely low energy adaptive clustering hierarchy, LEACH-centralized, K-Means, single hop clustering and energy efficient protocol, hybrid-LEACH and fuzzy C-means organize the networks into clusters where non-cluster head nodes mainly carry out sensing tasks and send the information to the cluster head, while cluster head collect data from other nodes and send to the base station (BS). Although these algorithms reduce the total energy consumption of the network, they also create a large number of network disconnect which refers to the number of sensors that cannot connect to its cluster head and the number of cluster heads that cannot connect to the BS. In this paper, we propose a method based on fuzzy clustering and particle swarm optimization to handle this problem. Experimental validation on real 3D datasets indicates that the proposed method is better than the existing methods.

Electronic transport properties and first-principles study of graphene/h-BN and h-BN bilayers

We use a tight binding approach to study of electron transport properties of bilayers of zig-zag graphene/h-BN nanoribbon (GBNNR) and h-BN nanoribbon (BNNR) embedded between two bilayer of zig-zag graphene nanoribbons (GNR), which are considered as electrodes. In this study, the parameters of tight biding hopping and on-site energies are obtained by comparing the tight binding band structure graphene/h-BN and h-BN bilayers with density functional theory (DFT) calculations. We numerically compute the transport properties in terms of transmission and current–voltage characteristic. Our calculations show that the electron transport can open a conduction gap in the GNR/BNNR/GNR structure.

Epitaxial growth and transport property of La0.9Sr0.1MnO3 thin films deposited on MgO, LaAlO3 and SrTiO3 substrates

La0.9Sr0.1MnO3 (LSMO) thin films were grown on (100)-oriented MgO, LaAlO3 and SrTiO3 substrates by pulsed laser deposition, so as to investigate the effect of substrate-induced lattice mismatch on epitaxial growth, electrical resistivity and transport behavior of the films. The X-ray diffraction patterns and pole figures indicated that the LSMO thin films were epitaxially grown on the three kinds of substrate, and the orientation relationship was found to be LSMO (100) [010]//substrate (100) [010]. The measurement of electrical resistivity showed that the LSMO thin films were characteristic of semiconductor, and the transport mechanism was dominated by the small polaron hopping (SPH) model. Compared with MgO and LaAlO3 substrates, the LSMO thin films grown on SrTiO3 substrate exhibited lower resistivity and smaller conductivity hopping energy, due to the less lattice mismatch at film/substrate interface which tended to reduce the Jahn-Teller distortion and thus the localization of charge carriers was decreased.

Balanced and Efficient Energy Multi-hop Routing Algorithm in Heterogenous Wireless Sensor Networks

Background: Wireless Sensor Network (WSN) consists of a set of nodes that collect information from a given area, then cooperate with each other to send it to the Base Station (BS). Since the power resources of the nodes are restricted, a special treatment for their available power is mightily required. In MH routing algorithms, finding the optimal path to route data from a source to destination is one of the most interesting issues. This paper presents BEERAD, a new algorithm for multi-hop (MH) communication between nodes to conserve the energy consumption and extend the network lifetime of the nodes. Methods: Since the sensing, processing, transmitting and receiving tasks consume a valuable part of node energy over time, they must be considered during the path selection process. BEERAD is a Dijkstra-based algorithm which not only accepts the total power consumption at both nodes as the weight of the path but also considers the nodes' residual energy. Results: Several metrics are used to evaluate the available paths in order to select the optimal path, such as; Energy consumption, hop counts, and battery power. These metrics can be considered separately or in combination. BEERAD is tested with various scenarios of WSN. The Simulation results show that it has better performance in comparison with other existing ones from the previous metrics point of view. Conclusion: In the light of BEERAD, this proposal was incorporated as Multi-hop routing protocol being evaluated through simulation. The proposed protocol balances the energy of nodes all over the network over the network lifetime, avoiding the hot spot problem; hence the stability period of the network is enhanced. It also increases the total throughput of the network. Keywords: Wireless sensor network, Routing, path cost, hop counts, Dijkstra Algorithm, Stability period.

Effect of A cation size on structural, magnetic and electrical properties of K2NiF4-type oxide LaSrFeO4

K2NiF4-type oxides La0.8R0.2SrFeO4 (R=La, Nd, Gd, Dy) have been synthesized by Pechini method and their structures were established by Rietveld refinements of the XRD data in the space group I4/mmm. Analysis of cell parameters shows that the decrease in the c from La to Dy compound is much larger than that in a. All the samples show antiferromagnetic behavior with increase in value of Θ with decreasing average <La/R/Sr> site radius. For all compounds, semiconducting behavior persists in the whole temperature range and can be expressed by two conduction mechanisms – Arrhenius model and polaron hopping model. The results suggests that the transport properties are dominated by the adiabatic small polaron hopping mechanism. Both activation energy (Ea) and polaron hopping energy (Ep) decrease with decreasing average ionic radius of rare earth ion at A-site.