Hopping Frequency Research Articles

Hopping Rate and Migration Entropy as the Origin of Superionic Conduction within Solid-State Electrolytes.

Inorganic solid-state electrolytes (SSEs) have gained significant attention for their potential use in high-energy solid-state batteries. However, there is a lack of understanding of the underlying mechanisms of fast ion conduction in SSEs. Here, we clarify the critical parameters that influence ion conductivity in SSEs through a combined analysis approach that examines several representative SSEs (Li3YCl6, Li3HoCl6, and Li6PS5Cl), which are further verified in the xLiCl-InCl3 system. The scaling analysis on conductivity spectra allowed the decoupled influences of mobile carrier concentration and hopping rate on ionic conductivity. Although the carrier concentration varied with temperature, the change alone cannot lead to the several orders of magnitude difference in conductivity. Instead, the hopping rate and the ionic conductivity present the same trend with the temperature change. Migration entropy, which arises from lattice vibrations of the jumping atoms from the initial sites to the saddle sites, is also proven to play a significant role in fast Li+ migration. The findings suggest that the multiple dependent variables such as the Li+ hopping frequency and migration energy are also responsible for the ionic conduction behavior within SSEs.

Mechanochemical Synthesis and Fluoride Ion Conductivity Studies in SrSnF4 Polymorphs

Investigations on SnF2-based solid electrolytes are gaining significant scientific attention because of their promising applications as solid electrolytes for all-solid-state fluoride ion batteries (FIBs) operating at room temperature. FIBs are potential alternatives for expensive Li-ion batteries with toxic and flammable liquid electrolytes. SrSnF4 belongs to the MSnF4 (M: Pb, Ba, and Sr)-type materials exhibiting a layered structure. Here, we present the structural and transport characteristics of two polymorphs of SrSnF4 using X-ray diffraction and impedance spectroscopy techniques. SrSnF4 crystallizing in a cubic fluorite structure is obtained just by mechanical milling the powder samples of SrF2 and SnF2 taken in a 1:1 ratio for 10 h, whereas annealing the milled powder at 623 K in the N2 atmosphere transforms SrSnF4 from its cubic phase to the stable tetragonal structure. The structural details of both the cubic and tetragonal SrSnF4 have been obtained by performing the Rietveld refinement. The resultant phase change after soft annealing enhances the room-temperature conductivity value from 2.05 × 10–6 S/cm for the cubic phase to 1.16 × 10–5 S/cm for the tetragonal phase. The transport number measurement by the dc polarization technique with the cell of configuration Ag/SrSnF4/Ag reveals that the conductivity is due to the ions. The frequency response of conductivity data is analyzed using the Almond–West formalism to find their hopping frequency and mobile carrier concentration factor at different temperatures. The scaling of the frequency-dependent conductivity spectra shows that the relaxation behavior of the mobile ions is temperature independent.

Mixed ionic-electronic transport in Na2O doped glassy electrolytes: Promising candidate for new generation sodium ion battery electrolytes

In the present communication, newly developed glassy electrolytes, Na2O–ZnO–CdO, have been considered to discuss their electrical transport behavior at ambient temperature. The AC conductivity and relaxation behavior of them have been studied in the light of Almond-West formalism. The electrical conductivity (mixed conduction) is found to be a function of frequency as well as temperature. In the low-frequency range, it shows a flat conductivity owing to the diffusional motion of Na+ ions, whereas at high frequency, the conductivity shows dispersion. The DC conductivity ( σ dc ) and hopping frequency have been computed from the best fitted plots of experimental data. The AC conductivity at different concentrations and a constant temperature has been reported. The variation in the conductivity data with reciprocal temperatures indicates the dynamical behavior of charge carriers via hopping conduction in sodium oxide glassy systems. Mixed conduction in the present system may be dominated by polaron hopping in the samples with a lower Na2O content with a percolation type of motion of the electron/polaron. On the other hand, three-dimensional Na+ motion is the dominating charge carrier for the samples with a higher Na2O content. A negligible small difference in pathways in the I–V characteristics in both the directions should make the present system a promising candidate for the new generation battery electrolyte.

Investigations on the electrical conductivity and complex dielectric permittivity of a ferrofluid subjected to the action of a polarizing magnetic field

From complex impedance measurements of a kerosene-based ferrofluid with magnetite particles, in the range 20 Hz - 2 MHz and at different values of a polarizing magnetic field, H in the range 0 - 90 kA/m, electrical conductivity and complex dielectric permittivity were determined. The conductivity mechanism in ferrofluid was explained using both the Mott's VRH model and CBH model, thus allowing us to determine for the first time the effect of H on the hopping distance of charge carriers, on maximum energy barrier height and on the hopping frequency. The dielectric behavior is explained in terms of Schwarz relaxation process, determining that the mechanical mobility of ions on particle surface increases by increasing of H. Also, an original method was proposed to evaluate the effect of H on the dielectric activation energy, EA(H) finding a decrease of it by approximately 30 meV by increasing of H by 86.37 kA/m.

Origin of improved Na+ ionic conductivity in the NASICON-type solid state electrolyte with Sm modification

The NASICON-type (Na1+xZr2SixP3-xO12, 0≤x ≤ 3) sodium-ion solid state electrolyte (SSE) has emerged as an alternative for liquid electrolyte due to its good chemical/electrochemical stability, high thermal stability and high safety. However, the insufficient ionic conductivity and poor understanding of Na+ transport mechanism hinder the further development of sodium-ion SSE. Herein, we report Sm modified Na3+xZr2-xSmxSi2PO12 (0≤x ≤ 0.4) electrolytes with a highest ionic conductivity of 2.25 × 10−3 S cm−1 at 25 °C when x = 0.2. The introduction of Sm element adjusts the Si/P ratio in NASICON phase and densifies the electrolyte pellets by formation of Na3Sm(PO4)2. To get a deep insight into the enhanced mechanism of Na + transport in grains, low-temperature electrochemical impedance spectra (LT-EIS) and Jonscher's power law relationship are employed to analyze the electrical behavior of grains. The results demonstrate that the regulation of Si/P ratio can evoke lower migration energy, more charge carrier concentration and higher hopping frequency, which synergistically improve the ionic conductivity in grains.

Structural behavior and non-Debye dielectric response of copper doped Al:ZnO nanoparticles

In present work we have studied the copper and aluminium doped ZnO Al0.02Zn0.98-xCuxO nanoparticles by varying the concentration of copper from x = 0.00, 0.02, 0.04, 0.06. XRD, TEM, Raman spectroscopy and Rietveld's refinement was used for the study of doping effect on lattice parameters and bond length. Variation in lattice strain was compatible with the variation in lattice parameters. Ac electrical conductivity increases while dielectric constant decreases with the increase in frequency. Electrical conductivity was found to increase with the doping concentration, which was maximum for Al0.02Zn0.94Cu0.04O. Similarly, dielectric constant also increases with doping concentration and gives maximum value for Al0.02Zn0.94Cu0.04O. Almond-West equation fitted curves gives hopping frequency in the range of 1652 Hz–46,446 Hz. Relaxation time obtained from KWW fitting shows increasing trend with doping concentration of copper. It varies from 4.0✕10−5 to 5.6✕10−8 s.

Near‐Room‐Temperature Quasi‐Solid‐State F‐Ion Batteries with High Conversion Reversibility Based on Layered Structured Electrolyte

AbstractSolid‐state fluoride ion batteries (SSFIBs) are anion‐shuttle‐driven and alkali‐metal‐free emerging energy storage systems, and have the advantages of low cost, high safety, and energy density. However, the current major challenges of SSFIBs or quasi‐SSFIBs are the lack of high‐conductivity fluoride electrolytes and the difficulty of mild‐temperature operation of full cells. Here, a 2D fluoride conductor (KSn2F5) synthesized by mechanochemical method is employed as the compatible solid electrolyte with a high F‐ion conductivity of 10−4 S cm−1 at 60 °C. The high concentration and frequent hopping of charge carriers in F‐vacancy‐rich KSn2F5 contribute to the higher ionic conductivity compared to most reported fluoride structures. Integrating this layered electrolyte with high‐voltage CuF2 cathode and Sn/SnF2 anode, a highly reversible cycling of conversion‐type quasi‐SSFIBs with a discharge capacity of 150 mAh g−1 for at least 70 cycles at 60 °C is achieved. The interface engineering aided by tetra‐n‐butylammonium fluoride salt facilitates the F‐ion transfer between cathode and electrolyte and fluorination/defluorination conversion mechanism of CuF2 cathode with optimized multiphase and nanodomain distributions.

Summerfield scaling model and electrical conductivity study for understanding transport mechanisms of a Cr3+ substituted ZnAl2O4 ceramic.

Solid-state and sol-gel procedures were used to prepare ZnAl1.95Cr0.05O4 nanocrystal spinels. From the results obtained by X-ray diffraction (XRD) and transmission electron microscopy (TEM), it can be concluded that the samples prepared by sol-gel synthesis are better crystallized than the ones resulting from the solid-state method. Studies by spectroscopy of impedance were done in function of frequency (40-107 Hz) and temperature (540-680 K) in the sample prepared by sol-gel synthesis. The electrical conductivity spectra obey Jonscher's law and two models were observed studying the variation of the exponent 's' as a function of temperature, Correlated Barrier Hopping (CBH) and Non-overlapping Small Polaron Tunnelling (NSPT). The predominant conduction mechanism is bipolaron hopping. The scaling behavior of conductivity spectra was checked by Summerfield scaling laws. The time-temperature superposition principle (TTSP) points to a common transport mechanism working for the low and middle frequency ranges. The scaling mechanism fails in the high-frequency ranges suggesting that conduction dynamics, and the usual hopping distance of mobile species, have changed. The values obtained for the activation energy from the hopping frequency, conductivity σ dc, bulk resistance R gb, and relaxation (f max), in the temperature range of 540-680 K, are very close. A higher and negative temperature coefficient of resistivity (TCR coefficient) equal to -2.7% K-1 is found at 560 K. This result shows that our compound is suitable for uncooled infrared bolometric applications and infrared detectors.

Structural, Dielectric and Electrical Properties of Homovalent Doped SrSn1-xTixO3 (0 ≤ x ≤ 0.08) System

The samples SrSn1-xTixO3 with composition 0≤x≤0.08 have been prepared using sol-gel chemical route by sintering at 1173 K. All the samples are found to be single phase crystallized in orthorhombic structure. The dielectric properties indicate the existence of interfacial and orientation polarization in samples found to be stable up to 300 oC. Thermal dependence of electrical conductivity represents two conduction regions with activation energy (0.77-0.94) eV in region-1 and (0.19-0.27) eV in region-2 respectively. The plot of dc conductivity with hopping frequency results unit slope representing that the charge carriers remain same in both processes. DC conductivity of samples are found to be increased with Ti4+, due to reduction in polaron size. The present materials can be potentially used in thermally stable capacitor and mixed ionic and electronic conductors (MIECs) applications.

Photonics based frequency hopping spread spectrum system for secure terahertz communications.

Terahertz (THz) spectrum (100 GHz-10 THz) is considered the next frontier in the design of high-speed wireless communication systems. While the high-power THz sources have commercially become available, it increases the possibility of developing THz jammers to disrupt the THz communication link. Therefore, the development of novel anti-jamming solutions is the need of the hour. In this work, we present the photonics-based THz communication system and demonstrate the frequency hopping spread spectrum (FHSS) technique which acts against the single/multi-tone jamming attack in the frequency window of 110 GHz-170 GHz. By tuning the output wavelength of the distributed feedback lasers, the THz carrier frequencies are swept back and forth within the scanning window. The frequency tuning range was measured for different scanning rates of the laser which decreases rapidly with the increase in the scanning rate. Next, we demonstrate the THz FHSS technique in a real-time communication system by transmitting a 6 Gbps NRZ signal in both wireless and THz-fiber-based links within the link distance of 1.75 m. We experimentally found that the measured bit error rate in the THz FHSS system is the time average of the measured BER for individual carrier frequencies within the hopping frequency window. By combining with the forward error correction codes and by using the tunable filter in the receiver, we believe that the proposed technique will offer a novel and compact solution against the single/multi-tone jammer for high-bit rate THz communications.

Parameter estimation of multiple frequency-hopping signals based on space-time-frequency analysis by atomic norm soft thresholding with missing observations

In this paper, we address the problem of multiple frequency-hopping (FH) signal parameters estimation in the presence of random missing observations. A space-time matrix with random missing observations is acquired by a uniform linear array (ULA). We exploit the inherent incomplete data processing capability of atomic norm soft thresholding (AST) to analyze the space-time matrix and complete the accurate estimation of the hopping time and frequency of the received FH signals. The hopping time is obtained by the sudden changes of the spatial information, which is implemented as the boundary to divide the time domain signal so that each segment of the signal is a superposition of time-invariant multiple components. Then, the frequency of multiple signal components can be estimated precisely by AST within each segment. After obtaining the above two parameters of the hopping time and the frequency of signals, the direction of arrival (DOA) can be directly calculated by them, and the network sorting can be realized. Results of simulation show that the proposed method is superior to the existing technology. Even when a large portion of data observations is missing, as the number of array elements increases, the proposed method still achieves acceptable accuracy of multi-FH signal parameters estimation.

Enhanced Li+ Ionic Conduction and Relaxation Properties of Li5+2xLa3Ta2-xGaxO12 Garnets

In the current work, we studied the effect of Ga+3 substitutions on the Ta+5 sites in Li5+2xLa3Ta2-xGaxO12 (LLT-Ga) lithium conducting garnets (with x = 0.1–0.5) in order to enhance the ionic conductivity of these materials. The current materials are prepared by solid state reaction and their electrical properties are studied by impedance spectroscopy measurements. XRD data showed that cubic garnet phases are obtained for LLT-Ga garnets. The ionic conductivity increased by one order of magnitude for x = 0.3 composition with a value of ~4 × 10−5 S/cm compared to that of Li5La3Ta2O12 material. Moreover, the hopping frequency and the concentration of mobile Li+ ions were estimated from analysis of the conductivity spectra, and it was found that both the concentration and mobility of Li+ ions increased with increasing Ga+3 content in the materials. The dielectric and relaxation properties were studied in the dielectric permittivity and electric modulus formalisms. The current materials exhibited giant values of the dielectric constant of ε′ ~ 6500, originating from internal effects in the materials.

Unified GRF-based control for adjusting hopping frequency with various robot configurations

The highly dynamic hybrid nature of legged locomotion makes it a very challenging task to control. A proper control strategy, besides the ability to generate stable motions, should also possess generalization capabilities and adjustability to different conditions. In this regard, this work takes a step forward in promoting the concept of Force Modulated Compliance (FMC) control as a bioinspired reflex-based control approach and assesses its potential in generating various hopping motions. The FMC is an easy-to-tune and simplified representation of the neuromuscular control, which functions as an adjustable spring modulated by the ground reaction force. We implemented the FMC controller on EPA-Hopper-II which is an extension of our previous electric-pneumatic actuation (EPA) designs. By optimizing control parameters for hopping frequencies of and different PAM configurations in the robot structure, we show that FMC can generate stable hopping motions and adapt to different configurations. The optimization results also show that leg stiffness has a high correlation with normalized energy consumption. Increases in leg stiffness decrease the normalized energy consumption and vice versa. The outcomes of this study, particularly the highlighted generalization of the FMC control, open new doors for efficient control of legged robots and assistive devices.

A 78.8-84 GHz Phase Locked Loop Synthesizer for a W-Band Frequency-Hopping FMCW Radar Transceiver in 65 nm CMOS.

A W-band integer-N phase-locked loop (PLL) for a frequency hopping frequency modulation continuous wave (FMCW) radar is implemented in 65-nm CMOS technology. The cross-coupled voltage-controlled oscillator (VCO) was designed based on a systematic analysis of the VCO combined with its push-pull buffer to achieve high efficiency and high output power. To provide a frequency hopping functionality without any overhead in the implementation, the center frequency of the VCO is steeply controlled by the gate voltage of the buffer, which effectively modifies the susceptance of the VCO load. A stand-alone VCO with the proposed architecture is fabricated, and it achieves an output power of 13.5 dBm, a peak power efficiency of 9.6%, and a tuning range of 3.5%. The phase noise performance of the VCO is −92.6 dBc/Hz at 1-MHz and −106.1 dBc/Hz at 10 MHz offset. Consisting of a third-order loop filter and a divider chain with a total modulus of 48, the locking range of the implemented PLL with the cross-coupled VCO is recorded from 78.84 GHz to 84 GHz, and its phase noise is −85.2 dBc/Hz at 1-MHz offset.

Single and Multiple Continuous-Wave Interference Suppression Using Adaptive IIR Notch Filters Based on Direct-Form Structure in a QPSK Communication System

The removal filter coefficients in this technique are dependent on the jammer’s power and its Instantaneous Frequency (IF) information, which can both be obtained in the time–frequency domain (adaptive filtering techniques). The dependence of the removing/reducing filter characteristics on the interference power is critical, as it allows an optimal trade-off between removal interference and the amount of self-noise generated by the filter. This trade-off is bounded by the two extreme cases of no notch filter (no self-noise) and full suppression (k1 = 1) for both low- and high-power jammer values. In this paper, a cascade second-order adaptive direct Infinite Impulse Response (IIR) Notch Filter (NF) with a gradient-based algorithm to suppress the Continuous-Wave (CW and MCW) interference is proposed for maximizing the receiver Signal-to-Noise Ratio (SNR) in a Quadrature Phase-Shift Keying (QPSK)-modulated signal. The suppression approach consists of two Adaptive IIR NFs (ANFs) based on a direct-form structure: the Hd1(z) and Hd1(z). The proposal in this work presents a low-complexity Time-Domain (TD) algorithm for controlling the update filter coefficient and notch depth. Simulation results demonstrate that the proposed approach represents an effective method for removing/reducing the impacts of CWI/MCWI, resulting in improved system performance for low- and high-power jammer values when compared with the case of full suppression (k1 = 1); furthermore, it also improves the notch filter’s output SNR for a given Jamming-to-Signal Ratio (JSR) value and Bit Error Ratio (BER) performance. For example, the SNR output of the proposed IIR NF was enhanced by 7 dB versus the case without a filter when Eb/No = 15 dB and JSR = −5 dB. The proposed method can detect and mitigate weak and strong jamming with JSR values ranging from −30 to 40 dB, and can track the hopping frequency interference. Moreover, an improved BER performance is seen as compared to the case without an IIR NF.

Effect of Lithium Iodide on transport phenomenon in Lithium Borophosphate glass Electrolyte

Ion transport study for the lithium iodide doped Lithium Borophosphate (LBP) glass electrolyte x(LiI):[(100−x).(60Li2O:8B2O3:32P2O5)] has been carried out over a range of composition (x=0 to 25 wt.%). The electrical conductivity has been measured by complex impedance spectroscopy from 303 K to 423 K temperature. The physical parameter and conductivity study indicate to obey the Arrhenius relationship and the frequency dependent conductivity is in consonance with Jonscher's universal power law. The Correlated Barrier Hopping (CBH) model for ion transport is observed to follow in the present glass system. Further investigation of the conductivity has also been carried out to calculate the hopping frequency (ωp), relaxation time (τ), power-law exponent (n) and decoupling index (Rτ). The enthalpy for migration and free energy have been estimated using the frequency-dependent power-law exponent (n) behaviour. Charge dynamics between local states due to the activated hopping process has been discussed according to Anderson- Drago and Elliot's model. To reinforce the Lithium ion transport study, several physical parameters such as density (ρ), molar volume (VO), oxygen packing density (OPD), cation concentration (NLi), the mean distance between cations (R′LiI) and the total number of energy states per unit volume at Fermi level N(Ef) have been calculated using various empirical formulae to discuss the present LBP ionic glass system.

Microplastics can affect the trophic cascade strength and stability of plankton ecosystems via behavior-mediated indirect interactions

The negative effects of microplastics on the normal growth of aquatic organisms have been well studied, but relatively little is known about their potential adverse effects on the function and stability of aquatic ecosystems. We investigated here the effects of polyethylene (PE) microplastics on several aspects of plankton ecosystems, including Daphnia magna behavior, the grazing rate of D. magna on Chlorella vulgaris cells, trophic-cascade effects in the C. vulgaris-D. magna-larval damselfly food chain, the life-history of D. magna, and the stability and persistence of the D. magna-larval damselfly system. PE microplastics decreased the D. magna grazing rate as a result of reductions in their heart rate and hopping frequency. In the trophic-cascade experiment, PE microplastics increased the foraging success of larval damselflies on grazers due to hopping inhibition in grazers, which ultimately strengthened the trophic-cascade effect on algal growth. Long-term exposure to PE microplastics reduced the stability and persistence of the grazer population via increased predation risk and reduced reproductive capacity for grazer species. This study provides evidence that microplastics can affect the trophic cascade strength and stability of plankton ecosystems via behavior-mediated indirect interactions, suggesting that microplastics have more extensive impacts on aquatic ecosystems than presently recognized. Enviromental implicationThe massive production and environmental releasing of microplastics have become ubiquitous in the global environment. The negative effects of microplastics on the normal growth of aquatic organisms have been well studied, but little is known about potential adverse effects on the function and stability of aquatic ecosystems. Here, we found that microplastics increased the positive impacts of larval damselflies on algal growth, and reduced the stability and persistence of plankton ecosystems via a behavior-mediated indirect interaction. To our knowledge, this is the first systematic study assessing the effects of microplastics on the community-level characteristics of a freshwater ecosystem. SynopsisPE microplastics affect trophic cascade strength and reduce the stability and persistence of plankton ecosystems via behavior-mediated indirect interactions.

Conduction process in some promising lithium-ion doped glassy ceramics

A novel glassy ceramic, 0.3Li2O-(0.7)(0.5MoO3-0.4V2O5-0.1ZnO) has been developed using the melt quenching technique. The temperature and frequency dependency of ionic conductivity has been established, following Almond-West formalism and Jonscher's universal power law respectively. The thermally activated nature of the sample can be exposed by its DC conductivity (σdc) study. The effect of composition on hopping frequency and corresponding activation energy has been calculated. The plateau (conductivity dependent on frequency) region in the lower frequency zone is pronounced by the sub diffusive movements of conducting Li+ ions. Whereas, in the dispersive high-frequency zone, Li+ ion migration in a pseudo-three-dimensional space is the main reason for conductivity in percolating networks.

A Synchronization Acquisition Method for the Dual-Sequence-Frequency-Hopping Communication System Based on Software Defined Radio at Low SNR

The Dual-Sequence-Frequency-Hopping (DSFH) communication system based on software defined radio (SDR) system belongs to the field of information and communication security of software engineering. At very low signal-to-noise ratio (SNR), which is lower than -10dB, the DSFH fails to synchronize. Synchronization acquisition method via a combined multi-signal detection (SAMCMD) is proposed. The feature of a short sequence of frequency hopping (FH) frequency point is utilized to express the information of the time of date (TOD), and the time accumulation of several FH signals is used to extend the detection time. This method can not only be appropriate for DSFH but also greatly improve the synchronization performance at low SNR. Explain the principle and structure of the SAMCMD. And obtain the performance of this method of the SDR synchronization acquisition. The conclusions are as below: 1) the longer detection time is, the better the anti-jamming performance of SAMCMD is; 2) SAMCMD can gain about 22.5dB-24dB when the SNR is -20dB and the acquisition probability requirement is 96.31% due to the extension of the detection time, compared with the traditional FH synchronization acquisition method.

Influence of La doping on structure, AC conductivity and impedance spectroscopy of Ba2SnO4 Ruddlesden Popper oxide

A few compositions of (Ba1-xLax)2SnO4 with 0≤x≤0.10 have prepared via solid-state ceramic route followed by calcination at 1000 °C for 8 h. The preliminary phase of samples has analyzed using XRD and found to be crystallized into tetragonal structure up to 4 atoms %. The solubility limit of La at Ba-site has reconfirmed using FTIR and Raman analysis. The AC conductivity spectra of single-phase samples follow universal Jonscher's power law σac=σdc(1+(ffh)n). Further, the thermal dependence of dc conductivity (σdc) and hopping frequency (fh), indicating the presence of Arrhenius type charge transport in the samples. Ghosh scaling applied to σac of all temperatures found to superimpose on a single master curve, indicates the invariance of conduction mechanism. The impedance spectroscopy studies reflect the major contribution of grain in the conduction and relaxation process of all sample. Based on present study, the present material can be potentially used in semiconductor devices, UV-detector, and mixed ionic and electronic conductor (MIECs) by utilizing absorption states and thermo-curves as metastable state.