Activation Energy For Hopping Research Articles

Complexes of Li, Na, and Mg with 2D allotropies of second and third period: a theoretical study.

Complexes of Li, Na, and Mg with graphene, silicene, phosphorene nanoflakes (NFs), and their 2D allotropies have been studied at dispersion corrected TPSS/def-TZVP level of theory. The energy partition analysis of the complexes revealed that for most of the complexes exchange and correlation energies represent dominant contributions to the binding with strong charge transfer from the metal atom to a NF. The exceptions are Mg complexes of graphene and phosphorene NFs where binding is due to dispersion and correlation terms. This difference is also reflected in large Mg-NF distances suggesting weak intermolecular interactions in these complexes. The calculated activation energies for metal hopping are easily achievable at room temperatures for carbon and silicon allotropies. However, they are significantly higher for phosphorus allotropies reaching almost 18kcal/mol. Generally, activation energies for hopping increase with binding energies for graphene, silicene, and phosphorene NFs. This trend does not observe however for graphene, silicene, and phosphorene 2D allotropies.

Nitrogen-Doped Lithium Lanthanum Titanate Nanofiber-Polymer Composite Electrolytes for All-Solid-State Lithium Batteries

Currently cation doping is common for improving ionic conductivity of metal oxide-based lithium-ion conductors. In this work, anions (nitrogen ions) have been doped to perovskite Li3xLa2/3 − xTiO3 (LLTO) nanofibers by heat treatment in the ammonia-containing atmosphere, and substituted for oxygen anions partially in the perovskite structure. Density-functional theory (DFT) calculation results reveal that nitrogen doping weakens the bonding of Li ions on the A sites in perovskite ABO3 structure and allows for larger lattice distortion, reducing the activation energy for Li-ion hopping in both the forward and backward jumping directions. Experimental results have also confirmed that nitrogen doping has improved ionic conductivity of LLTO. Nitrogen-doped LLTO nanofibers have been incorporated with a poly (vinylidene fluoride)-co-hexafluoropropylene (PVDF-HFP) polymer to form a solid-state composite electrolyte, which exhibits ionic conductivity of 3.8 × 10−4 S·cm−1 at room temperature and an electrochemical stability window of up to 4.9 V vs Li∣Li+. The all-solid-state Li metal∣composite electrolyte∣LiFePO4 lithium batteries, which employ nitrogen-doped LLTO nanofibers, show better rate capability and cycling stability at room temperature than the counterparts with pristine LLTO nanofibers.

Computational Modelling of Ceria-Based Solid Oxide Fuel Cell Electrolyte Materials

The significant advances in materials development for solid oxide fuel cells (SOFCs) and modelling techniques have challenged researchers to develop streamlined methodologies aiming at faster and more reliable fabrication of highly efficient cells. Instead of adopting a trial-and-error technique to discover the optimal composition of fuel cell component materials, alternative tools and techniques should be developed for predicting the likely best compositions in a cost-effective and timely manner. Many formulations have been studied for application as SOFC electrolytes over the years and doubly-doped ceria materials have been of considerable recent interest.Here, a simulation methodology to calculate the lattice parameter and the oxygen ion migration energy of ceria-based electrolyte formulations was developed, and the results were analysed and benchmarked against corresponding results obtained experimentally in order to verify the efficacy of the simulation methodology. To this end, a supercell consisting of 2 x 2 x 2 ceria unit cells doubly-doped with samarium and gadolinium was modelled and simulated using molecular mechanics force field methods using the CP2K computational chemistry suite. Two compositional series were modelled with the general formula Ce32-(x+y)SmxGdyO64-(x+y)/2 where x and y are the number of samarium and gadolinium dopant atoms per supercell respectively. The first compositional series, Series One, had equal amounts of dopants but different total dopant concentration with values of x = y = 1, 2, 8, or 16. Series Two had a fixed total dopant concentration (x + y = 8) but different amounts of each dopant in each structure such that x had integer values from 0 to 8 (x = 0 ... 8) and y = 8 - x. Moreover, two doping strategies were simulated for each compositional series depending on how the dopant atoms and resulting vacancies were distributed throughout the crystal. The first doping strategy places one dopant atom in two or more of the eight minicubes comprising the 2 x 2 x 2 supercell for Series One structures and, for Series Two structures, one dopant atom is placed in each minicube starting with one gadolinium atom in each minicube and then progressively replacing one gadolinium atom with one samarium atom in each of the subsequent structures of this series until there is one samarium atom in each minicube. The second doping strategy places the dopants exclusively in the four minicubes that let the dopants be as far as possible from each other. In all cases, the oxygen vacancies are chosen to be the nearest neighbours, i.e., in the nearest lattice positions, to the dopant atoms.For each structure, the lattice parameter was calculated using a cell optimisation technique utilizing the conjugate gradient method where the soft particle mesh Ewald (SPME) sums method and the DIPole Polarizable Ion Model (DIPPIM) for the long- and short-range potentials respectively. To estimate the activation energies associated with hopping of an oxygen ion from a specific site to a neighbouring site in the structures studied, the following steps were applied: The positions of the dopant atoms in the pure crystal were assigned.The at a distance within 3.0 Å was generated.The climbing image nudged elastic band (CI-NEB) method was applied to determine all the activation barriers of the doped crystal.The average energy barrier was calculated. The results obtained for the lattice parameter were comparable to those observed experimentally and exhibited the same linear trends satisfying Vegard's law, albeit the trend for the fixed dopant concentration series had a slight negative slope. Simulation-derived values of the activation energy showed the same trends as those observed experimentally. The simulations also produced transition state curves showing the saddle point and energy minima for each structure; information that could not be obtained experimentally and that can shed some light on the mechanism of ionic conduction. It was found that the position of oxygen vacancies within the crystal structure play a key role in determining the activation energy of ion hopping, and that the different patterns of doping do not affect the overall trends in lattice parameter and activation energy. They do however produce different patterns in the energy profiles contributing to the energy barriers to ion hopping within the crystal structure.This work demonstrates that computational simulations of SOFC electrolyte materials provide results comparable with those obtained experimentally and could also provide insights into the mechanisms of ionic conduction. The incongruence of the computational and experimental results was attributed to the limitations of the molecular mechanics force field methodology utilised, with the expectation that an ab initio density functional theory (DFT) calculation would yield closer conformance. Figure 1

Complementary study of anisotropic ion conduction in (110)-oriented Ca-doped BiFeO3 films using electrochromism and impedance spectroscopy

Oxygen vacancies are ubiquitous in oxides, and taking advantage of their mobility is the cornerstone for a variety of future applications. The visualization and quantification of collective defect flow based on electrochromism is a powerful approach to explore oxygen kinetics and electrochemical reaction even in cases that electronic conduction is considerably mixed, but whether or not the measured kinetic properties harmonize with those obtained by the conventional impedance spectroscopy remains veiled. Here, we identify complementary relationships between the two methods by investigating the oxygen vacancy transport in Ca 30%-doped bismuth ferrite thin films epitaxially grown on SrTiO3 (110) substrates. We find that the activation energy of ionic hopping is 0.78 (or 0.92 eV) for the application of an electric bias along [001] (or [11¯0]) due to the grain elongation along [001]. We anneal the films in an N2 gas environment at high temperatures to suppress the electronic contribution for access to standard impedance spectroscopy. The oxygen kinetic properties obtained from the two methods are consistent with each other, complementarily revealing the collective phase evolution as well as the ionic impedance of the bulk, grain boundary, and interfacial regions. These comparative works provide useful insights into ionic defect conduction in oxides in an intuitive and quantitative manner.

Molecular Dynamics of Rare-Event Electrostatic Channeling

Cascade reactions are potential green reactions since all the reaction transformations take place in a single pot without purification steps, but their reaction efficiency is limited by the transport efficiency of intermediates between adjacent steps [1]. Understanding the mechanism of multi-enzyme metabolic pathways is of great importance for the design of practical cascades for chemical conversion. Molecular dynamics simulations of cascades can elucidate and quantify physicochemical effects on intermediate transport, but is challenged by processes whose time scales exceed the typical picosecond to nanosecond range. Here, we show how infrequent metadynamics (InMetaD) [2], umbrella sampling (US) and kinetic Monte Carlo (KMC) can be combined to elucidate rare-event transport processes. We build on a previously studied glucose-6-phosphate (G6P) intermediate within a bridged supramolecular structure comprising the enzymes hexokinase (HK) and glucose-6-dehydrogenase (G6PDH) [3].When the previous polylysine bridge is replaced by polyarginine, electrostatic interactions between negatively-charged G6P and the positively charged bridge are enhanced, but diffusive transport of G6P on the bridge surface, via a hopping mechanism, is slowed to time scales exceeding 10 ns. InMetaD is an advanced sampling technique that boosts a system out of energy minima by biasing the predefined collective variables and estimates unbiased kinetics by reweighting the biased time. We investigated the hopping mechanism of G6P on arginine peptides as a rare event using InMetaD, and computed the hopping time to be 125.5 ± 2.7 ns at 310 K and hopping activation energy to be 25.1 ± 3.7 kJ/mol at the ionic strength of 0 mM.We conducted US simulations to capture the configurational change in the desorption process and calculate the desorption energy. By considering the energy barriers calculated above, the KMC simulations were performed to study the transfer efficiency of G6P. The results show that even at a high ionic strength of 120 mM, arginine peptides are still able to transfer G6P with the lag time 5 seconds, much smaller than lysine peptides with the lag time of 59 seconds reported before [4]. Our work indicates that arginine peptides are a better bridge candidate for electrostatic channeling in terms of decreased lag time compared with lysine peptides. This can help in the future design of efficient artificial cascade reactions by using electrostatic channeling. References ： K. C. Nicolaou, D. J. Edmonds, and P. G. Bulger, Angew. Chemie - Int. Ed., 45, 7134–7186 (2006). doi:10.1002/anie.200601872R. Casasnovas, V. Limongelli, P. Tiwary, P. Carloni, and M. Parrinello, J. Am. Chem. Soc., 139, 4780–4788 (2017). doi:10.1021/jacs.6b12950Y. Liu, I. Matanovic, D. P. Hickey, S. D. Minteer, P. Atanassov, and S. Calabrese Barton, ACS Catal., 8, 7719–7726 (2018). doi:10.1021/acscatal.8b01041Y. Liu, D. P. Hickey, J. Guo, E. Earl, S. Abdellaoui, R. D. Milton, M. S. Sigman, S. D. Minteer, and S. Calabrese Barton, ACS Catal., 7, 2486–2493 (2017). doi:10.1021/acscatal.6b03440 Figure 1

Novel 2D allotropic forms and nanoflakes of silicon, phosphorus, and germanium: a computational study.

The structural variability offered by 2D materials is an essential feature in materials design. Despite its significance, obtaining assemblies with suitable stability remains a challenge. In this work, we theoretically explore novel silicon, phosphorus, and germanium, analogues of haeckelites at hybrid DFT level. Both 2D systems and nanoflakes (NF) have been studied. All materials have been found dynamically stable; Si-, P-, and Ge- analogues of haeckelites were found to be more stable in comparison to the corresponding honeycomb structure than haeckelites in comparison with graphene. All 2D materials showed metallic behavior; however, the difference between inorganic haeckelites and the corresponding honeycomb allotropes is less than that between haeckelites and graphene. Si-, P-, and Ge-, allotropes have much higher electron affinities (EAs) compared to carbon allotropes, while haeckelites have higher EAs than honeycomb structures. Furthermore, Si-, P-, and Ge-structures also exhibit low hopping activation energies for lithium atoms. It makes these materials potentially promising as a component in Li-ion batteries.

Isotope Effect in the Liquid Properties of Water Confined in 100 nm Nanofluidic Channels.

Liquids confined in 10-100 nm spaces show different liquid properties from those in the bulk. Proton transfer plays an essential role in liquid properties. The Grotthuss mechanism, in which charge transfer occurs among neighboring water molecules, is considered to be dominant in bulk water. However, the rotational motion and proton transfer kinetics have not been studied well, which makes further analysis difficult. In this study, an isotope effect was used to study the kinetic effect of rotational motion and proton hopping processes by measurement of the viscosity, proton diffusion coefficient, and the proton hopping activation energy. As a result, a significant isotope effect was observed. These results indicate that the rotational motion is not significant, and the decrease of the proton hopping activation energy enhances the apparent proton diffusion coefficient.

In Situ Diffusion Measurements of a NASICON-Structured All-Solid-State Battery Using Muon Spin Relaxation.

In situ muon spin relaxation is demonstrated as an emerging technique that can provide a volume-averaged local probe of the ionic diffusion processes occurring within electrochemical energy storage devices as a function of state of charge. Herein, we present work on the conceptually interesting NASICON-type all-solid-state battery LiM2(PO4)3, using M = Ti in the cathode, M = Zr in the electrolyte, and a Li metal anode. The pristine materials are studied individually and found to possess low ionic hopping activation energies of ∼50−60 meV and competitive Li+ self-diffusion coefficients of ∼10–10–10–9 cm2 s–1 at 336 K. Lattice matching of the cathode and electrolyte crystal structures is employed for the all-solid-state battery to enhance Li+ diffusion between the components in an attempt to minimize interfacial resistance. The cell is examined by in situ muon spin relaxation, providing the first example of such ionic diffusion measurements. This technique presents an opportunity to the materials community to observe intrinsic ionic dynamics and electrochemical behavior simultaneously in a nondestructive manner.

Proton Conductivity via Trapped Water in Phosphonate-Based Metal–Organic Frameworks Synthesized in Aqueous Media

Metal-organic frameworks (MOFs) are promising candidates for proton-conducting applications. Herein, we report the aqueous synthesis of two new phosphonate-based MOFs comprising glyphosate linkers, [Mg(dpmp)]·2H2O (Mg-NU-225) and [Fe(dpmp)]·2H2O (Fe-NU-225), (dpmp = N,N'-diphosphonomethyl-2,5-piperazinedione), and explore their proton conductivities. Single crystal X-ray diffraction measurements revealed that both frameworks display a two-dimensional layered structure with a cyclic ring ligand which forms in situ from the condensation of two glyphosate molecules. Under humid conditions and over a wide temperature range, water molecules are trapped between adjacent layers and facilitate rapid proton conduction. Mg-NU-225 and Fe-NU-225 recorded proton conductivities of 1.5 × 10-5 and 1.7 × 10-5 S cm-1, respectively, along the plane direction and 1.6 × 10-3 and 9.1 × 10-5 S cm-1 perpendicular to the plane direction at 55 °C and 95% relative humidity, as confirmed by two-contact probe impedance methods. The mechanism of proton transport was found to be that of the Grotthuss model from the low activation energy for proton hopping.

Investigation on resistive humidity sensing in sulfosuccinic acid doped polyaniline films

In this work, the possibility of humidity sensor based on conducting polymer, polyaniline (PANI) doped with a novel organic dopant, sulfosuccinic acid (SSA) is explored. PANI-SSA based sensors show considerably high humidity sensitivity, limit of detection (LOD) of 8%RH and linearity covering a wide range of relative humidity (RH) from 30% to 80%. Molar ratio of PANI-SSA is varied to get optimum sensing response at around 1:2 ratio. In order to understand the physical phenomena behind the humidity sensing property, various characterizations such as thickness dependent sensing response, thermo gravimetric analysis, scanning electron microscopy, temperature dependent conductivity as a function of RH are performed. The origin of the sensing response is attributed to the adsorption of water molecule at the surface of PANI-SSA films leading to the lowering of activation energy of electron hopping.

Thermal Analysis, Dielectric Response and Electrical Conductivity of Silicon Phthalocyanine Dichloride (SiPcCl2) Thin Films

This research is a detailed examination of the effect of post-annealing on the structure and electrical conductivity of silicon phthalocyanine dichloride (SiPcCl2) thin films. Differential thermal analysis (DTA) is used to determine the temperature limit of thermal stability for a sample of silicon phthalocyanine dichloride (SiPcCl2). The results of differential thermal analysis (DTA) proved that silicon phthalocyanine dichloride (SiPcCl2) is thermally stable up to 415 K. The dielectric behavior and the electrical conductivity of silicon phthalocyanine dichloride (SiPcCl2) thin films were investigated under a temperature effect from 303 K to 383 K and a frequency from 200 Hz to 20 MHz. The frequency and temperature dependence of dielectric loss and dielectric constant values were explained in terms of dielectric polarization theory. The alternative current (AC) conductivity response toward the frequency change obeys Jonscher’s power law. The correlated barrier hopping (CBH) model is utilized and adapted to fit the conduction mechanism in the high- and low-frequency regions. Both the complex electric modulus and the impedance formalisms are used to illustrate the dielectric characteristics of the silicon phthalocyanine dichloride (SiPcCl2). The potential height value of the hopping barrier, Wm, and activation energy value, Eac, for dielectric relaxation were determined.

A New Class of Superionic Solid-State Lithium-Ion Conductors: Lithium-Phosphido Silicates, Germanates, and Aluminates

Superionic conductors as a solid-state electrolyte materials are essential for use for all-solid-state lithium ion batteries. Whereas intensive research on oxide and sulfide based lithium ion conductors resulted in optimized materials which reach ionic conductivities up to 25 mScm-1 other compound classes are disregarded. A design principle for fabricating new superionic conductors follows the ideas of increasing the carrier densities, changing the diffusion pathways of the mobile species, creating vacancies or increasing structural defects, and including anions that are more polarizable. For example to increase the carrier density, an effective way is especially the aliovalent substitution of cations: for example, in Li3PS4 making a formal substitution from “P5+” to “Ge4+” arises in Li3.25Ge0.25P0.75S4 with a four times higher ionic conductivity.We propose here phosphide-based materials as ionic conductors that result in principle from the aliovalent substitution of [TtS4]4- tetrahedra, which are an important key building block in sulfide-based electrolytes, by [TtP4]8- leading to the analogous complex anions based on phosphorus (Tt = tetrel element = Group-14 element). The resulting higher charge of the [TtP4]8- tetrahedra allows for twice the number of lithium ions per formula unit for charge compensation if compared to [TtS4]4- and in addition, the more negatively charged P3- is more polarizable than S2-. In this context we discovered for example Li8SiP4,[1] β-Li8GeP4,[2] and Li14SiP6 [3] with conductivities up to 1.1 mScm-1 . In addition we recently succeded to synthesize the lithium richest representative, obtained by formal aliovalent substitution of “Tt 4+” by “Al3+” and formation of in Li9AlP4.[4] The insertion of Al3+ leads to formally nine-fold negatively charged [AlP4]9- tetrahedra, resulting in an even higher lithium density per formula unit and a change in spatial extent of the diffusion pathways. This first representative of a novel compound class of lithium phosphidoaluminates has as an undoped material a remarkable fast ionic conductivity of ~ 3 mS cm-1 and a low activation energy of ~ 29 kJ mol−1 as determined by impedance spectroscopy. Temperature-dependent 7Li NMR spectroscopy supports the fast lithium motion. In addition, Li9AlP4 combines a very high lithium content with a very low theoretical density of 1.703 g·cm-3.In this paper we give an overview on the recent development in this material class. All crystalline materials are readily obtained as single phase materials by ball mill synthesis from the elements followed by moderate thermal treatment of the mixtures. In all cases the atomic structures are characterized by X-ray diffraction methods. The lithium-ion mobility was investigated by temperature-dependent nuclear magnetic resonance and electrochemical impedance spectroscopy revealing low activation energies for lithium hopping. In some cases lithium diffusion pathways via both, tetrahedral and octahedral voids are analyzed by temperature-dependent powder neutron diffraction measurements in combination with maximum entropy method (MEM) and DFT calculations. The role of lithium ion occupation in the various tetrahedral and octahedral sites that occur in those compounds is highlighted.

Immittance Studies of Bi6Fe2Ti3O18 Ceramics.

Results of studies focusing on the electric behavior of Bi6Fe2Ti3O18 (BFTO) ceramics are reported. BFTO ceramics were fabricated by solid state reaction methods. The simple oxides Bi2O3, TiO2, and Fe2O3 were used as starting materials. Immittance spectroscopy was chosen as a method to characterize electric and dielectric properties of polycrystalline ceramics. The experimental data were measured in the frequency range Δν = (10−1–107) Hz and the temperature range ΔT = (−120–200) °C. Analysis of immittance data was performed in terms of complex impedance, electric modulus function, and conductivity. The activation energy corresponding to a non-Debye type of relaxation was found to be EA = 0.573 eV, whereas the activation energy of conductivity relaxation frequency was found to be EA = 0.570 eV. An assumption of a hopping conductivity mechanism for BFTO ceramics was studied by ‘universal’ Jonscher’s law. A value of the exponents was found to be within the “Jonscher’s range” (0.54 ≤ n ≤ 0.72). The dc-conductivity was extracted from the measurements. Activation energy for dc-conductivity was calculated to be EDC = 0.78 eV, whereas the dc hopping activation energy was found to be EH = 0.63 eV. The obtained results were discussed in terms of the jump relaxation model.

Sr-doping effects on conductivity, charge transport, and ferroelectricity of Ba0.7La0.3TiO3 epitaxial thin films* *Project supported by the National Natural Science Foundation of China (Grant No. 51872099), the Science and Technology Program of Guangzhou, China (Grant No. 2019050001), the Fund from the Guangdong Provincial Key Laboratory of Optical Information Materials and Technology, China (Grant No. 2017B030301007), and the 111 Project, China.

Sr-doped Ba0.7La0.3TiO3 (BSLTO) thin films are deposited by pulsed laser deposition, and their microstructure, conductivity, carrier transport mechanism, and ferroelectricity are systematically investigated. The x-ray diffraction measurements demonstrate that Sr-doping reduces the lattice constant of BSLTO thin films, resulting in the enhanced phonon energy in the films as evidenced by the Raman measurements. Resistivity-temperature and Hall effect measurements demonstrate that Sr can gradually reduce electrical resistivity while the electron concentration remains almost unchanged at high temperatures. For the films with semiconducting behavior, the charge transport model transforms from variable range hopping to small polaron hopping as the measurement temperature increases. The metalic conductive behaviors in the films with Sr = 0.30, 0.40 conform to thermal phonon scattering mode. The difference in charge transport behavior dependent on the A-site cation doping, is clarified. It is revealed that the increasing of phonon energy by Sr doping is responsible for lower activation energy of small polaron hopping, higher carrier mobility, and lower electrical resistivity. Interestingly, the piezoelectric force microscopy (PFM) results demonstrate that all the BSLTO films can exhibit ferroelectricity, especially for the room temperature metallic conduction film with Sr = 0.40. These results imply that Sr-doping could be a potential way to explore ferroelectric metal materials for other perovskite oxides.

Impedance Spectroscopic Studies of B2O3-Substituted CeO2-Gd2O3 Systems

In this paper, the change in the conduction mechanism due to B2O3 addition in a ceria-based nanoceramic system is understood by studying the nature of conductivity and the variation of electric modulus function with frequency at different temperatures. The studies revealed that oxide ion conduction in the prepared system is prominent only after 500°C. The activation energy for electrical conduction and oxide ion hopping in the system is found to be 0.26 eV and 0.85 eV, respectively. The discrepancy in the values of the activation energies itself is evidence of a different mechanism other than oxide ion hopping occurring in the present sample. The electric modulus function shows two relaxation peaks at lower temperatures corresponding to short-range and long-range relaxation for the charge carriers. Relaxation energies for the processes are found to be 0.27 eV and 0.95 eV. This is evidence of the occurrence of Maxwell–Wagner relaxation phenomena in the ceramic system. Explicitly, thermally activated oxide ion migration, along with the relaxation of electrons at the site of the bound pair (B–Vo)· is observed in the prepared nanocrystalline system.

Relationship among the local structure, chemical state of Fe ions in Fe-O polyhedra, and electrical conductivity of cubic perovskite Ba1−xSrxFe0.9In0.1O3−δ with varying number of oxide ion vacancies

Cubic perovskite oxide Ba1−xSrxFe0.9In0.1O3−δ (BSFI) with varying number of oxide ion vacancies was prepared by heating in N2 and O2 to elucidate the relationship among the local structure of Fe-O polyhedra, the chemical state of Fe ions, and their electrical conductivities. Mössbauer spectroscopy for the N2-heated specimens (BSFI-N2) showed that the volume of microdomains in which the Fe–O–Fe super-exchange interaction worked well increased as the Sr content increased, resulting in reduced activation energy of the small-polaron hopping. It was found that as the Sr content increased, the increase in the mobility of small polarons enhanced the electrical conductivity in BSFI-N2. Further, it was found that the increase in the number of the charge carriers and the small-polaron mobility enhanced the electrical conductivity of the O2-heated specimens (BSFI-O2) with increasing x.

Evolution of dielectric relaxation under elevated electric field of polypropylene-based films

Extensive research has been performed on polypropylene (PP) based films focusing on the improvement of energy storage performance for power capacitor application. The increase of energy storage density was often accompanied with the rising of dielectric losses, especially under high electric field. The gap of electric field between the laboratorial level (0.006 ∼ 0.02 kV mm−1) and practical working condition of capacitor (more than 50 kV mm−1) could be thousands of times, which was often neglected in most research. In the present paper, the systematical study of the dielectric relaxation processes on elevated electric field was carried out on neat PP and three typical kinds of PP-based films, i.e. PP/ZrO2 nanocomposite, PP/maleic anhydride grafted polypropylene (PP-g-MAH) blends, and PP/PP-g-MAH/ZrO2 ternary nanocomposite with the energy storage density 17.3% higher than neat PP. The frequency dependence of dielectric losses under elevated field showed that even under 20 kV mm−1, the loss of ternary PP increased little, while the losses of the binary sample increased much more. The space charge test as well as the DC conductivity test revealed the origin of increased dielectric loss, which was the consequence of extrinsic ion hopping stimulated by the elevated field. Meanwhile, in the ternary PP/PP-g-MAH/ZrO2 nanocomposite, the activation energy of ion hopping was greatly improved due to the enhanced interaction between molecules, so the dielectric loss under high field, the space charge accumulation and the DC conductivity of the ternary sample all showed an extremely low level. This study has directive significance for the application of nanocompositse.

Defects in Pervoskite Ceramics for Enhanced Ionic Conductivity and Chemical Interaction

Oxygen vacancies have been created in pervoskite Li3x La2/3 − x TiO3 (LLTO) materials. The presence of oxygen vacancies decrease the activation energy for lithium ion hopping in the crystalline structure and increase the ionic conductivity of the LLTO material. Strong chemical interaction occurs between the nanofibers and the polymer matrix in the composite solid-state electrolytes based on three-dimensional (3D) hydrogen treated LLTO. The composite electrolyte exhibited a high ionic conductivity at room temperature, and large electrochemical stability window of up to 5.0 V vs. Li/Li. Full cells assembled with the composite electrolyte exhibited good rate capacity and cycling performance.

A2B2O7 (A= La, Pr, Nd, Sm, Gd and B Ti, Zr, Sn) ceramics for mild-temperature NO2 sensing and reduction

Abstract The present work demonstrates the design and synthesis of A2B2O7 (A = La, Pr, Nd, Sm, Gd and B = Ti, Zr, Sn) ceramics to fabricate NO2 sensors for efficient NO2 sensing and reduction at mild temperature. To clarify the sensing mechanism of NO2 sensor, the electron layer mechanism of rare-earth cations at A site and different ionic radius of B-site cations are investigated to discuss the difference from the NO2 sensing and reduction. The unique electronic structure of Pr3+([Xe]4f2) endows the different band structure and the variable valence in nature with +3 and + 4 oxidation states, which would induce different electronic transport, resulting in enhanced NO2 sensing performances and reduction reaction. According to A2B2O7 structure, the activation energy of oxygen hopping is clarified through comparing different ionic radius of B cations, and the surface oxygen species providing a transfer station for oxygen hopping of solid electrolyte are analyzed by various characterization techniques. The results show that high sensitivity obtained over pure Pr2Sn2O7 without any doping at A or B site is as high as 124 nA/ppm towards 25–100 ppm NO2 at 500 °C, which is significantly better than commercial YSZ sensor. This work makes a significant progress in solid electrolytes and gas sensor.

Tailored 2D/3D Halide Perovskite Heterointerface for Substantially Enhanced Endurance in Conducting Bridge Resistive Switching Memory.

Hybrid organic-inorganic halide perovskites (HPs) have garnered significant attention for use in resistive switching (RS) memory devices due to their low cost, low operation voltage, high on/off ratio, and excellent mechanical properties. However, the HP-based RS memory devices continue to face several challenges owing to the short endurance and stability of the HP film. Herein, two-dimensional/three-dimensional (2D/3D) perovskite heterojunction films were prepared via a low-temperature all-solution process and their RS behavior was investigated for the first time. The 2D/3D perovskite RS devices exhibited excellent performance with an endurance of 2700 cycles, a high on/off ratio of 106, and an operation speed of 640 μs. The calculated thermally assisted ion hopping activation energy and the results of the time-of-flight secondary ion mass spectroscopy demonstrated that the 2D perovskite layer could efficiently prevent the Ag ion migration into the 3D perovskite film. Moreover, we found that owing to its high thermal conductivity, the 2D perovskite can control the rupture of the Ag conductive filament. Thus, the 2D perovskite layer enhances endurance by controlling both Ag migration and filament rupture. Hence, this study provides an alternate strategy for improving endurance of HP-based RS memory devices.