Multiple Relaxation Processes Research Articles

Influence of Pr-cations on structural, spectral, elemental, and electrical features of Zr2–R type ferrites

Hexagonal ferrites have gained much attraction due to extensive applications in telecommunication and stealth fields. R-type hexagonal ferrites are rare hexagonal ferrites used in various technological applications. In the current work, the sol-gel auto-combustion method was used to prepare samples of R-type hexagonal ferrites with the chemical formula BaZr2Fe4-xPrxO11 (x = 0.00, 0.03, 0.06, and 0.09) respectively. The impact of substituting Praseodymium (Pr) on its structural, electrical, dielectric, and magnetic properties was investigated. X-ray diffraction (XRD) patterns suggest all samples exhibit a single phase. The lattice parameters and unit cell volume experienced alterations with varying Praseodymium (Pr3+) substitution levels. The atomic dynamics study of the Pr-doped R-type hexagonal ferrites was evaluated using FTIR analysis. Two absorption bands in the infrared spectroscopy were utilized to designate the tetrahedral and octahedral sites. X-ray photoelectron spectroscopy (XPS) findings verified the presence of all metal ions alongside their respective electronic states. Jonscher's power law elucidates the conduction mechanism of charge carriers in the synthesized ferrite samples. Impedance analysis was employed to investigate the influence of relaxation time and grain boundaries on the electrical characteristics of the fabricated nanomaterials. Impedance Cole-Cole plots provide evidence that all samples demonstrate multiple relaxation processes of a non-Debye nature. The minimum reflection loss (RL) of −32.46 dB at 3.27 GHz was achieved for x = 0.09. Pr-doped R-type hexagonal ferrite has potential applications in microwave high-frequency applications.

Energy relaxation in a vacuum capacitor-resistor circuit: measurement of multiple decays with divergent time constants

The decay of the electrical energy in a resistor-vacuum capacitor circuit is shown to involve multiple relaxation processes, with dramatically different time constants. This is measured using a vacuum capacitor to eliminate the effect of a dielectric between the plates (polypropylene capacitors are shown to exhibit similar behavior). A simple phenomenological model accounts for this behavior in spite of the difficulty in applying Maxwell's equations to such a circuit. These results will lead to a revision of our understanding of the physics of circuits, having particular impact on applications that use capacitors as sensors in collecting precision data (such as found in quantum measurements and dielectric spectroscopy).

ZnO nanofiller concentrations modified P(VDF-HFP)/PEO polymer matrix-based nanocomposites of enhanced optical and dielectric properties for emerging optoelectronic and energy storage devices

Wide bandgap metal oxide nanoparticles incorporated polymer blend matrix-based polymer nanocomposites (PNCs) are established as innovative multifunctional and properties tunable materials in the dimensional design and fabrication of promising performance extensive flexible type advanced devices. For further progress in these materials, herein, the detailed structural and promising properties of solution-cast prepared ternary PNC films, composed of poly(vinylidene fluoride-co-hexafluoropropylene) P(VDF-HFP)/ poly(ethylene oxide) PEO (50/50 wt%) host matrix and zinc oxide (ZnO) nanofiller (0, 1, 2, 5, and 10 wt%), are characterized. A sequence of employed experimental techniques, namely SEM, XRD, FTIR, and DSC, confirm that the surface morphology, polymorphic crystallographic character, polymer-polymer interactions, polymer-nanoparticle interfaces, crystalline phase thermal transitions, and degree of crystallinity of these PNCs largely affected with varying nanofiller concentrations. The optical study conducted with a UV–Vis spectrophotometer revealed high photo sensing and UV shielding characteristics with an energy bandgap of about 3.0 eV, demonstrating widespread applications of these semiconducting PNC materials in emerging optoelectronic device technologies. The broadband dielectric spectroscopic (BDS) characterization over the 20 Hz–1 GHz range explained harmonic field frequency and nanofiller concentration tunable dielectric permittivity (about 3 to 13) with low losses and multiple relaxation processes, predominantly ruled by microstructural interfaces and interactions developed in these ternary hybrid complex materials. The meaningful broadband dielectric characteristics of P(VDF-HFP)/PEO/ZnO materials demonstrated that they could be used as innovative nanodielectrics for energy storage purposes in capacitive devices, and flexible dielectric substrate and insulators for the fabrication of frequency-adjustable discrete and integrated microelectronic devices.

Investigation of conduction mechanisms and permittivity-conductivity correlation in a Gd-based perovskite structure.

Currently, the development of perovskites has required a lot of attention for fundamental investigation and electronic devices. The present study reported the electrical conductivity and the dielectric properties of a GdCa2Cu3Oδ (GdCaCuO) system prepared via the solid-state reaction method. The X-ray diffraction results indicate that GdCaCuO crystallizes in the tetragonal perovskite structure. The studied compound reveals elevated dielectric permittivity and significant electrical phenomena including the influence of multiple conduction and relaxation mechanisms on the transport of charges. From the impedance results, it is observed that the electrical and dielectric properties of the studied compound are governed by the contribution of the grain and the grain boundary regions. The Nyquist results and the blocking factor (αR) were used to confirm the aforementioned properties. From the modulus results, we confirm again the presence of multiple relaxation processes and various types of polarization effects. The semiconductor character of the GdCaCuO ceramic is due to the activation of hopping conduction processes within the DC regime. Consequently, both the variable range hopping and the small polaron hopping models are used at low- and high-temperature ranges, respectively. At various temperatures, the conductivity spectra of the GdCaCuO ceramic conform to the double Jonscher power law. The power law behavior is attributed to the activation of hopping and tunneling conduction mechanisms. The presence of large dielectric dispersion in GdCaCuO is observed at low temperatures and decreases rapidly against increasing temperatures.

Molecular Dynamics and Near-Tg Phenomena of Cyclic Thioethers.

This article presents the synthesis and molecular dynamics investigation of three novel cyclic thioethers: 2,3-(4'-methylbenzo)-1,4,7,10-tetrathiacyclododeca-2-ene (compound 1), 2,3,14,15-bis(4',4″(5″)-methylbenzo)-1,4,7,10,13,16,19,22,25-octathiacyclotetracosa-2,14-diene (compound 2), and 2,3,8,9-bis(4',4″(5″)-methylbenzo)-1,4,7,10-tetrathiacyclododeca-2,8-diene (compound 3). The compounds exhibit relatively high glass transition temperatures (Tg), which range between 254 and 283 K. This characteristic positions them within the so-far limited category of crown-like glass-formers. We demonstrate that cyclic thioethers may span both the realms of ordinary and sizeable molecular glass-formers, each featuring distinct physical properties. Furthermore, we show that the Tg follows a sublinear power law as a function of the molar mass within this class of compounds. We also reveal multiple dielectric relaxation processes of the novel cyclic thioethers. Above the Tg, their dielectric loss spectra are dominated by a structural relaxation, which originates from the cooperative reorientation of entire molecules and exhibits an excess wing on its high-frequency slope. This feature has been attributed to the Johari-Goldstein (JG) process. Each investigated compound exhibits also at least one intramolecular secondary non-JG relaxation stemming from conformational changes. Their activation energies range from approximately 19 kJ/mol to roughly 40 kJ/mol. Finally, we analyze the high-pressure molecular dynamics of compound 1, revealing a pressure-induced increase in its Tg with a dTg/dp coefficient equal to 197 ± 8 K/GPa.

3D porous NiCo2(CO3)3/reduced graphene oxide aerogel with heterogeneous interfaces for high-efficiency microwave absorption

Advanced electromagnetic absorbing materials (EAMs) with strong absorption and a wide effective absorption bandwidth (EAB), using innovative microstructural design and suitable multicomponents remain a persistent challenge. Here, we report the production of a material by the hydrothermal reduction of a mixture of graphene oxide (GO), Ni(NO3)2·6H2O, and Co(NO3)2·6H2O, resulting in reduced GO (RGO) with a self-assembled 3D mesh structure filled with NiCo2(CO3)3. The unique microstructure of this assembly not only solves the problem of NiCo2(CO3)3 particles agglomerating but also changes the electromagnetic parameters, thereby improving the impedance matching and attenuation ability. High electromagnetic wave absorption (EMA) was achieved by combining the 3D interconnected mesh structure and the various interfaces between NiCo2(CO3)3 and RGO. The minimal reflection loss (RLmin) was −58.5 dB at 2.3 mm, and the EAB was 6.5 GHz. The excellent EMA performance of the aerogel can be attributed to the multiple reflection, scattering, and relaxation process of the porous 3D structure as well as the strong polarization of the interfacial matrix.

Polymer architecture dictates multiple relaxation processes in soft networks with two orthogonal dynamic bonds

Materials with tunable modulus, viscosity, and complex viscoelastic spectra are crucial in applications such as self-healing, additive manufacturing, and energy damping. It is still challenging to predictively design polymer networks with hierarchical relaxation processes, as many competing factors affect dynamics. Here, networks with both pendant and telechelic architecture are synthesized with mixed orthogonal dynamic bonds to understand how the network connectivity and bond exchange mechanisms govern the overall relaxation spectrum. A hydrogen-bonding group and a vitrimeric dynamic crosslinker are combined into the same network, and multimodal relaxation is observed in both pendant and telechelic networks. This is in stark contrast to similar networks where two dynamic bonds share the same exchange mechanism. With the incorporation of orthogonal dynamic bonds, the mixed network also demonstrates excellent damping and improved mechanical properties. In addition, two relaxation processes arise when only hydrogen-bond exchange is present, and both modes are retained in the mixed dynamic networks. This work provides molecular insights for the predictive design of hierarchical dynamics in soft materials.

Highly Recyclable and Tough Elastic Vitrimers from a Defined Polydimethylsiloxane Network

AbstractDespite intensive research on sustainable elastomers, achieving elastic vitrimers with significantly improved mechanical properties and recyclability remains a scientific challenge. Herein, inspired by the classical elasticity theory, we present a design principle for ultra‐tough and highly recyclable elastic vitrimers with a defined network constructed by chemically crosslinking the pre‐synthesized disulfide‐containing polydimethylsiloxane (PDMS) chains with tetra‐arm polyethylene glycol (PEG). The defined network is achieved by the reduced dangling short chains and the relatively uniform molecular weight of network strands. Such elastic vitrimers with the defined network, i.e., PDMS‐disulfide‐D, exhibit significantly improved mechanical performance than random analogous, previously reported PDMS vitrimers, and even commercial silicone‐based thermosets. Moreover, unlike the vitrimers with random network that show obvious loss in mechanical properties after recycling, those with the defined network enable excellent thermal recyclability. The PDMS‐disulfide‐D also deliver comparable electrochemical signals if utilized as substrates for electromyography sensors after the recycling. The multiple relaxation processes are revealed via a unique physical approach. Multiple techniques are also applied to unravel the microscopic mechanism of the excellent mechanical performance and recyclability of such defined network.

Highly Recyclable and Tough Elastic Vitrimers from a Defined Polydimethylsiloxane Network.

Despite intensive research on sustainable elastomers, achieving elastic vitrimers with significantly improved mechanical properties and recyclability remains a scientific challenge. Herein, inspired by the classical elasticity theory, we present a design principle for ultra-tough and highly recyclable elastic vitrimers with a defined network constructed by chemically crosslinking the pre-synthesized disulfide-containing polydimethylsiloxane (PDMS) chains with tetra-arm polyethylene glycol (PEG). The defined network is achieved by the reduced dangling short chains and the relatively uniform molecular weight of network strands. Such elastic vitrimers with the defined network, i.e., PDMS-disulfide-D, exhibit significantly improved mechanical performance than random analogous, previously reported PDMS vitrimers, and even commercial silicone-based thermosets. Moreover, unlike the vitrimers with random network that show obvious loss in mechanical properties after recycling, those with the defined network enable excellent thermal recyclability. The PDMS-disulfide-D also deliver comparable electrochemical signals if utilized as substrates for electromyography sensors after the recycling. The multiple relaxation processes are revealed via a unique physical approach. Multiple techniques are also applied to unravel the microscopic mechanism of the excellent mechanical performance and recyclability of such defined network.

Adding a low frequency limit to fractional wave propagation models

Power-law attenuation in elastic wave propagation of both compressional and shear waves can be described with multiple relaxation processes. It may be less physical to describe it with fractional calculus medium models, but this approach is useful for simulation and for parameterization where the underlying relaxation structure is very complex. It is easy to enforce a low-frequency limit on a relaxation distribution and this gives frequency squared characteristics for low frequencies which seems to fit some media in practice. Here the goal is to change the low-frequency behavior of fractional models also. This is done by tempering the relaxation moduli of the fractional Kelvin-Voigt and diffusion models with an exponential function and the effect is that the low-frequency attenuation will increase with frequency squared and the square root of frequency respectively. The time-space wave equations for the tempered models have also been found, and for this purpose the concept of the fractional pseudo-differential operator borrowed from the field of Cole-Davidson dielectrics is useful. The tempering does not remove the singularity in the relaxation moduli of the models, but this has only a minor effect on the solutions.

Hierarchical core-shell FeCo@SiO2@NiFe2O4 nanocomposite for efficient microwave absorption

Narrow absorption band width is a common problem faced by current electromagnetic wave absorbing materials. It is urgent but challenging to explore new design solutions to solve this problem. Herein, a core-shell FeCo@SiO2 @NiFe2O4 composite was prepared by chemical co-precipitation method. The effects of calcination temperature on the structure of the cladding layer, magnetic properties and wave absorption properties of the composite powder were investigated. Results showed that the particles of NiFe2O4 @SiO2 cladding layer uniformly covered on the surface of FeCo powder gradually gathered and grew with the increase of calcination temperature from 500 to 800 ℃, resulting in the destruction of the local structure of the coating layer. The composite powder calcined at 700 ℃ has a uniform and dense coating layer structure, and has high saturation magnetization, high coercivity and excellent electromagnetic wave absorption performance. Consequently, the composite powder calcined at 700 °C has a maximum reflection loss of −52.38 dB with a frequency of 9.5 GHz when the matching thickness is 2.65 mm, and the EAB is up to 8.5 GHz with a matching thickness of 2.24 mm. The electromagnetic wave loss mechanism of the powder originates from the excellent impedance matching characteristics, high electromagnetic wave attenuation constant, multiple dielectric relaxation processes, multiple interface polarizations and high magnetic loss as well as high dielectric loss capability.

Slow Magnetic Relaxation of Linear Trinuclear M(II)–Gd(III)–M(II) Complexes with D3 Point Group Symmetry (M(II) = Zn(II) and Mg(II))

Trinuclear M(II)-Gd(III)-M(II) complexes 1 (M = Zn), 2 (M = Mg), and the magnetically dilute sample 1′ were synthesized and the slow magnetization relaxation originating from Gd(III) ions was investigated in detail. These complexes are crystallographically isostructural and belong to D3 point group symmetry, with M-Gd-M arrayed on the crystallographic 3-fold axis. From the angular-resolved magnetization of a single crystal of 1, an easy-axis-type magnetic anisotropy of Gd(III) with an anisotropy parameter D of −0.21(3) K were revealed. All the complexes underwent slow relaxation under the application of an external magnetic field. The temperature dependence of the relaxation rate τ–1 differed considerably between 1′ and 1, 2 such that: for 1′,τ–1∝ T1.1 over the entire temperature range, whereas for 1 and 2, τ–1 ∝ T1.56 and τ–1 ∝ T1.49 above 3 K, respectively. The discrepancy can be attributed to the presence of competing multiple relaxation processes, such as direct and Raman processes, and at dilution, the direct process becomes faster, leading to its predominance in 1′. For 1 and 2, the larger power number (∼1.5) was attributed to the significantly greater contribution from the Raman process, which may be originated from intramolecular atomic vibrations.

Fatigue free relaxor ferroelectric and electrocatalytic hydrogen evolution of yttrium substituted BaBi2Nb2O9 layered structured nanoceramics for energy storage application

Lead-free bismuth layered structured ferroelectric ceramics are highly important in superior energy storage applications. The slim hysteresis curve with high energy storage density and efficiency is expected for wide application. In this regard, the suitable electrocatalyst for the generation of hydrogen gas through water-splitting show high importance as an alternative energy source. The current article aims to investigate the above goals by incorporating 5% yttrium at the place of bismuth for BaBi 2 Nb 2 O 9 relaxor ferroelectrics. The solid-state synthesized method successfully prepared the single-phase material and is confirmed through spectroscopic and morphological analysis. The dielectric characteristics follow diffused phase transition with broad temperature dependence that indicated the space charge polarization in the material owing to the presence of Y 3+ at different domains. The higher degree of diffuseness and low dielectric loss implies the significant role of charge carriers during frequency and temperature variation in the dielectric study. Impedance spectroscopy analysis indicates the non-Debye type relaxation and NTCR behavior of the material that is correlated to the multiple relaxation processes. The slim P-E hysteresis curve and fatigue-free properties of the materials up to 10 6 cycles reflect its usefulness in the potential device as NVRAM applications. The materials are also used for hydrogen evolution reaction (HER) under an electrochemical condition. A lower overpotential value of 180 mV is obtained at 10 mA cm −2 current density. The lower Tafel slope and charge transfer resistance value support its superior HER activity. The above results demonstrated the potential application of the studied material (BaBi 1 · 9 Y 0 · 1 Nb 2 O 9 ) in the energy storage application and as an electrocatalyst for alternative energy source.

Microstructure, electrical, optical and electrochemical characteristics of silver phosphate glasses cathode for magnesium battery applications

The realization of a practical magnesium battery is combined with the development of a high kinetic cathode and compatible electrolyte to facilitate the redox process. For this reason, silver phosphate glasses in the binary system (Fe2O3–AgPO3) are prepared using the conventional quenching method. The glasses were defined in the form [Fe2O3] x [AgPO3](100−x) and the composition with 0 ⩽ x ⩽ 40 wt. %. The molar volumes and densities were measured. These glass systems were characterized using x-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, UV–Vis–NIR spectrophotometer, electrochemical procedures and impedance spectroscopy. X-ray diffraction revealed that pristine AgPO3 sample was formed in a glassy state, whereas two crystalline phases (AgFeP2O7 and Fe2O3) were formed after the incorporation of Fe2O3 by different concentrations. Bond assignments associated with different functional groups were investigated by an FT-IR spectroscopy. The values of the band gap were decreased with the increase of Fe2O3 content. The effect of grains and grain boundaries in a heterostructure made up of Fe2O3 and AgFeP2O7 crystallites grown in silver phosphate glasses was studied using impedance spectroscopy. The complex impedance, electrical conductivity, and complex electric modulus were measured in terms of frequency and temperature dependency in [Fe2O3] x –[AgPO3](1−x). In the studied glass systems, non-Debye relaxation was observed. Under a variable regime, σ ac conductivity follows a modified Jonscher’s law Arrhenius fitting of multiple relaxation processes in the material yielded activation energy of (0.12 eV–0.271 eV) which support a Maxwell–Wagner relaxation model in the heterostructure glasses at high temperatures and low frequencies. The dc conductivity decreases with iron rate and follows the Arrhenius law with very low activation energy (0.12–0.27 eV. Mg//electrolyte//Glass coin cells are assembled and show an initial discharge capacity of up to ∼564 mAh g−1. These materials are attractive for application in modernistic electrochemical devices because of their great compositional and preparation variety which enables tuning the types and techniques of electrical conduction in the material.

Tailoring electromagnetic response of three-dimensional waffle-like metacomposite based on arrangement angle of ferromagnetic microwires

Three-dimensional waffle-like metacomposite (3DWM) composed of ferromagnetic microwires is proposed with the aim of integrating structure and microwave absorption performance. The metamaterial units were formed by weaving the ferromagnetic microwires into certain pattern along with the quartz fiber substrate, making it a layer-by-layer integral structure without delamination. Based on the significance of angle arrangement of ferromagnetic microwires on the electromagnetic response during the rotation of metacomposite in practical application, this study conducted experiment and simulation considering different angle arrangements ranging from 90° to 165° to reveal their electromagnetic response characteristics and microwave absorption mechanism within X and Ku bands. It has been found that the arrangement angle of ferromagnetic microwire can adjust the complex permittivity. The dielectric loss of 3DWM was mainly originated from multiple Debye relaxation process and the primary magnetic loss came from eddy current loss and exchange resonance. The threshold angle was found to be 135°, within which the improvement of impedance matching led to the enhancement of microwave absorption. In addition, the angle arrangement of ferromagnetic microwire affected the direction of electric and magnetic fields, which determines the dielectric loss and magnetic loss mechanisms. The 3DWM proposed in this study is promising in adjusting electromagnetic response of microwaves as a radar absorbing material in engineering applications.

Electrical transport properties of nanocrystalline and bulk nickel ferrite using complex impedance spectroscopy: a comparative study

In this work, the comparative study on the electrical transport properties of nanocrystalline nickel ferrite (NiFe2O4) and its bulk counterpart has been carried out in detail by using complex impedance spectroscopy in a wide range of frequencies (100 Hz–1 MHz) and temperatures (40 °C–320 °C). The dispersive nature of the dielectric constant and loss factor is explained by the Maxwell-Wagner model and Koop’s phenomenological theory. The value of the dielectric constant for nanocrystalline nickel ferrite is found to be more as compared to its bulk counterpart. The frequency variation dielectric permittivity is well fitted with the modified Debye formula, which suggests the presence of multiple relaxation processes. The temperature dependent ac conductivity follows Jonscher’s universal power law and reveals the presence of multiple transport mechanisms from small polaron hopping (SPH) to correlated barrier hopping (CBH) mechanism near 200 °C. The estimated values of Mott parameters are found to be satisfactory. Thermally activated relaxation phenomena have been confirmed by scaling curves of imaginary impedance () and modulus (). The comparison between the and spectra indicates that both long-range and short-range movement of charge carriers contribute to dielectric relaxation with short-range charge carriers predominating at low temperatures while long-range charge carriers are dominating at high temperatures. Analysis of the semicircular arcs of Nyquist plot indicates the presence of grain boundary contribution to the electrical conduction process for the nanocrystalline sample at high temperatures. The non-Debye type of relaxation has been examined by stretching exponential factor (β) which has been estimated by fitting the modified KWW (Kohlrausch-Williams-Watts) equation to the imaginary electric modulus curve. The value of β is found to be strongly temperature dependent and its value for the nanocrystalline sample is less than that of the bulk system which is explained on the basis of dipole-dipole interaction.

Reduced graphene oxide(rGO)-Ferrite composite inks and their printed meta-structures as an adaptable EMI shielding material

ABSTRACT Electromagnetic interference (EMI) shielding inks are generally conducting inks and therefore, are mostly reflection based. EMI shielding based on reflection are sometimes not suitable for certain applications apart from the fact that they themselves act as secondary source of EM waves. Here, we develop reduced graphene oxide (rGO)- zinc nickel ferrite (ZNF) and rGO-manganese (Mn)-doped zinc nickel ferrite inks for EM absorption in X-band, which have been tested in liquid state, coatings, and as printed meta-structures demonstrating versatile use of the inks. As a coating, the average EMI shielding of more than 30 dB is achieved in the 8 to 12 GHz range. The absorption properties of the rGO based ink can be increased from 50% to more than 80% by addition of a ferrite composite and can further be tuned by Mn doping. The dielectric measurement studies reveal that addition of Mn creates sites for interfacial polarization. The interfaces between polymer matrix, rGO, ZNF, and Mn contribute to conductivity, dipole and interfacial polarization losses, thereby augmenting absorption dominated EMI shielding. Cole-cole plot for the inks also indicates multiple relaxation processes confirming the role interfaces in absorption properties of the composite ink.

Synthesis of carbon-coated cobalt ferrite core–shell structure composite: A method for enhancing electromagnetic wave absorption properties by adjusting impedance matching

Cobalt ferrite has problems such as poor impedance matching and high density, which results in unsatisfactory electromagnetic wave (EMW) absorption performance. In this study, the CoFe 2 O 4 @C core–shell structure composite was synthesized by a two-step hydrothermal method. X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and vector network analysis et al . were used to test the structure and EMW absorption properties of CoFe 2 O 4 @C composite. The results show that the reflection loss (RL) of the CoFe 2 O 4 @C composite reaches the maximum value of −25.66 dB at 13.92 GHz, and the effective absorbing band (EAB) is 4.59 GHz (11.20–15.79 GHz) when the carbon mass content is 6.01%. The RL and EAB of CoFe 2 O 4 @C composite are increased by 219.55% and 4.59 GHz respectively, and the density is decreased by 20.78% compared with the cobalt ferrite. Such enhanced EMW absorption properties of CoFe 2 O 4 @C composite are attributed to the attenuation caused by the strong natural resonance of the cobalt ferrite, moreover, the carbon coating layer adjusts the impedance matching of the composite, and the introduced dipole polarization and interface polarization can cause multiple Debye relaxation processes.

Reservoir computing with dielectric relaxation at an electrode\u2013ionic liquid interface

A physical reservoir device with tunable transient dynamics is strongly required to process time-series data with various timescales generated in the edge region. In this study, we proposed using the dielectric relaxation at an electrode–ionic liquid (IL) interface as the physical reservoir by making the most of designable physicochemical properties of ILs. The transient dynamics of a Au/IL/Au reservoir device were characterized as a function of the alkyl chain length of cations in the IL (1-alkyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide). By considering a weighted sum of exponentials expressing a superposition of Debye-type relaxations, the transient dynamics were well reconstructed. Although such complex dynamics governed by multiple relaxation processes were observed, each extracted relaxation time scales with a power law as a function of IL’s viscosity determined by the alkyl chain length of cations. This indicates that the relaxation processes are characterized by bulk properties of the ILs that obey the widely received Vogel-Fulcher-Tammann law. We demonstrated that the 4-bit time-series signals were transformed into the 16 classifiable data, and the data transformation, which enables to achieve higher accuracy in an image classification task, can be easily optimized according to the features of the input signals by controlling the IL’s viscosity.

In situ constructed honeycomb-like NiFe2O4@Ni@C composites as efficient electromagnetic wave absorber

Rational excogitation of microstructure and chemical constituents is a superior means of constructing electromagnetic wave (EMW) absorption materials with high performance. In this study, a kind of honeycomb-like NiFe2O4@Ni@C composite is prepared via an uncomplicated polymerization, pyrolysis and etching. Porous structure and internal cavity of NiFe2O4@Ni@C contribute to the numerous reflection and scattering of EMW. The strong ferromagnetic resonance of NiFe2O4 core and the multiple relaxation processes of porous carbon shell strongly promote the EMW loss. Additionally, the synergistic effect can improve impedance matching. The results demonstrate that the minimum reflection loss (RL) of honeycomb-like NiFe2O4@Ni@C composites is −65.33 dB at 13.63 GHz. The effective absorption bandwidth (EAB) is 3.68 GHz when the matching thickness is 4.95 mm. The mechanism of EMW dissipation of the honeycomb-like NiFe2O4@Ni@C composites is attributed to multiple reflections and scattering, conductive loss, interfacial polarization and ferromagnetism resonance. This work provides a tactic for the excogitation and synthesis of a low cost, light weight and efficient EMW absorber.