Frequency Dependence Research Articles

Biogeoacoustic variability in muddy ocean bottom sediment

Both physical and biological benthic processes can influence seabed heterogeneity and contribute to spatiotemporal variability in geoacoustic properties. In particular, how biological processes affect both sediment acoustic properties and their variability is poorly understood. To address this deficiency, recent measurements investigated spatial variability in the upper few decimeters of sediment near the water-seabed interface within a fine-grained sediment deposit on the New England shelf. At each measurement location, acoustic probes were inserted into the sediment to collect direct in situ measurements of sediment sound speed and attenuation at near-ambient conditions, after which cores were collected from the inter-probe propagation paths for ex situ analysis of sediment physical, biological, and acoustic properties. Relationships among sediment properties, such as bulk density, porosity, grain size distribution, organic matter composition, infaunal community composition, and acoustic measurements spanning several frequency decades (10–1000 kHz) will be explored in this paper. Frequency dependence of sediment acoustic properties will also be discussed in the context of sediment acoustics models for mud based on the viscous grain shearing and extended Biot theories. [Sponsored by ONR.]

The crucial role of granular packing structure in marine sediment acoustics

Motivated by the acoustic properties of marine sediments, we study via discrete-element method simulations the frequency dependence of dispersion and attenuation in model marine sediments. By numerically solving for the motion of each grain in a packing, rather than solving a continuum wave equation, we find that the granular packing structure, which is not explicitly considered in existing sediment-acoustics models, plays a crucial role in determining how attenuation and wave speed vary with frequency. Prior work has typically postulated a wave equation that is motivated by grain- scale forces, including viscous effects from the interstitial fluid, without explicitly considering the disordered packing structure of the grains. However, the packing structure is known to produce complex, nonlinear behavior (e.g., during shear or quasistatic compression), and how it affects dispersion and attenuation is not known. We consider linearized forces between particles (i.e., springs and dashpots), and demonstrate that the disordered packing structure leads to emergent scaling laws that do not agree with PDE-based approaches. Our results demonstrate that the granular packing structure must be explicitly considered when constructing theories for the acoustic properties of marine sediments.

Impedance of electric field sensors in magnetized plasmas: particle-in-cell simulations

To obtain both the intensities and phases of electric fields, it is necessary to calibrate the data observed by the sensor by consulting the sensor characteristics. The frequency profile of the sensor impedance obtained from the simulation is roughly consistent with that obtained from the theory. However, some differences are identified in the frequency profile of the sensor impedance obtained from the simulation compared to the theory. We conducted simulations using the particle-in-cell (PIC) simulation tool to analyze the impedance of electric field sensors immersed in magnetized space plasmas. The simulation model comprised a dipole sensor placed in a three-dimensional simulation box filled with electrons and ions. The dipole sensor was represented by perfect conductor rods. We carefully selected simulation parameters and employed an appropriate feeding technique to accurately evaluate the sensor impedance. We observed significant changes in the frequency dependence of the sensor impedance as cyclotron frequency varied. To understand the simulation results, we introduced the linear dispersion relation. By comparing the real part of the sensor impedance with the ω-k\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\omega-k$$\\end{document} diagram, we found that the impedance peaks corresponded to frequencies at which branches of plasma waves were present, with k=khalf\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$k=k_{\ ext{half}}$$\\end{document}, representing half the wavelength equal to the tip-to-tip sensor length, i.e., the sensor can be assumed as the half-wavelength dipole antenna.Graphical

Sporadic-E studies over Southern Hemisphere geomagnetic mid-latitudes

Sporadic-E (Es) are characterized by denser layers whose formation could be related to wave activity in the lower thermosphere, such as planetary waves, tides, and gravity waves. The first aim of this work was to analyze the Es layer occurrence under different geophysical conditions to establish the importance of these waves. Thus, we used ionosonde observations of four different locations at mid-latitudes that are King George Island (62.2°S, 58.8°W), Argentine Islands (65.3°S; 64.3°W), on the Antarctic Peninsula longitude sector, and Canberra (35.3°S; 149.0°E) and Hobart (42.9°S; 147.3°E), on the Australian sector. The data are divided for winter, equinox, and summer during low (1986–87) and high (1989–90) solar activity levels. Seasonal means of the Es layer frequency and height parameters have been computed. The results show that the diurnal variations of the Es layer occurrence and their frequency parameters are similar for all seasons and solar activity levels over the two longitude sectors. These results do not support the expectations that gravity-wave momentum-fluxes are significant in this case study. The height of the Es layers over Antarctica is about 10 km higher than over Australia. Also, the Es occurrence is higher at night over Antarctica. Computed blanketing Es layer frequency (fbEs) using known formulae are almost identical to those observed for all locations and seasons during low and high solar activity. The Es frequency dependence on solar activity level is also different from what has been shown elsewhere.

Improved Calculation of the Shear Modulus of Rectangular Prisms from Their Resonant Frequency Overtones

Abstract The shear modulus (G) is an important parameter for characterizing the strength of and wave propagation through a given material. This study improves the empirical model for estimating shear modulus using the impulse excitation technique based on an experimental analysis of 19 soda-lime silica glass bars. Analysis of the frequency equations relating the shear modulus to the torsional resonant frequencies of rectangular prisms has been used to provide improved equations for calculating G for higher orders of vibration. These were tested by measuring the shear modulus of several novaculite rocks of different porosities up to the seventh order of vibration. These were found to be nearly frequency independent. The updated frequency equations provide a distinct improvement over previously available methods when values for higher order vibrations, and thus the frequency dependence of G, are of interest.

The local electronic interaction and strain effects on transverse dynamical spin susceptibility of [formula omitted]-graphyne

We present the behaviors of dynamical transverse spin susceptibilities of undoped β-graphyne monolayer using the Green’s function approach in the context of Hubbard model Hamiltonian. Such dynamical spin susceptibility is proportional to inelastic cross section of neutron beam from the layer. Specially, the effects of magnetic field, on-site coulomb repulsion strength and strain parameter on the spin excitation modes of β-graphyne monolayer are investigated via calculating correlation function of transverse components of spin density operators. Our results show the increase of absolute value of compressive strain parameter leads to move the magnetic excitation modes to higher energies. Also the intensity of peaks in inelastic cross section reduces with absolute value of compressive strain parameter. We also show that applying biaxial tensile strain causes to decrease the intensity of peaks in dynamical transverse spin susceptibility. Finally the effects of magnetic field and on-site coulomb repulsion interaction strength on frequency dependence of dynamical spin structure factor of β-graphyne layer are studied. Moreover the frequency positions of spin excitation mode of β-graphyne monolayer have been investigated due to the effects of biaxial strains, applied magnetic field and Hubbard parameter strength in details.

Method of Selecting Surgical Treatment for Children with Congenital Deformity of the Spine and Thorax

Introduction. Spinal anomalies are considered to be the most severe pathology of the axial skeleton. Intrauterine formation of deformity with its subsequent progression during growth is the reason for the need for surgical intervention. The prevalence of patients with congenital scoliosis in the total structure of spinal deformities is up to 2%. In terms of the malignancy of the course of the disease, children with unsegmented rod and rib synostosis represent one of the most unfavorable groups of patients. Aim. To perform a comparative analysis of the results of surgical treatment of children with congenital scoliosis with unilateral lateral vertebral segmentation disorder and rib synostosis using different techniques. Methods. The work is a monocenter cohort study of “case-control” type (III level of evidence). The design of the work is a monocenter cohort retro and prospective study. The results of surgical treatment of patients between 2010 and 2020 were analyzed. The study included 45 patients aged 3 to 7 years with the diagnosis of congenital scoliosis with unilateral lateral segmentation disorder of vertebral bodies and rib synostosis. The patients were divided into 2 groups depending on the surgical treatment method applied. In the first group (n = 24), patients underwent thoracoplasty with implantation of an individual rib/rib/vertebral distractor; in the second group (n = 21), patients underwent spinal surgery in the scope of vertebrotomy at the apex of the curvature and correction of the deformity with a multifocal spinal system. The data of medical records, as well as MSCT, radiographs, and pulse oscillometry were included in the analysis of the results. Results. Me (median) of scoliosis before treatment in group 1 patients 58.5, IQR = 19.75; after treatment — Me = 40.0, IQR = 20.0. Me of kyphosis before surgery 22, IQR = 4.5; after surgery Me = 26.0, IQR = 4.0. In the second group, Me of scoliosis before treatment 58.0, IQR = 3.0; after treatment, Me = 20.0, IQR = 6.0. Me of kyphosis before surgery 22, IQR = 2.0; after surgery Me 28.0, IQR = 4.0. When comparing MSCT data, group 1 patients showed an increase in lung tissue volume by 21% of the initial lung volume, in group 2 the increase amounted to 27%. The analysis of external respiratory function indices demonstrates improvement of reactive component indices by 21.1%, frequency dependence of resistive component by 46.4%, resistive component by 50% in group 1 patients, in group 2 there is an improvement of reactive component indices by 21.1%, resistive component by 50.9% and frequency dependence of reactive component by 46.7%. Conclusion. Corrective intervention on the spine at an early age makes it possible to achieve effective correction of the deformity; similar changes are observed both in lung volume and functional state of the respiratory system due to the mediated correction of the thorax shape.

Resonant generation of propagating second-harmonic spin waves in nano-waveguides

Generation of second-harmonic waves is one of the universal nonlinear phenomena that have found numerous technical applications in many modern technologies, in particular, in photonics. This phenomenon also has great potential in the field of magnonics, which considers the use of spin waves in magnetic nanostructures to implement wave-based signal processing and computing. However, due to the strong frequency dependence of the phase velocity of spin waves, resonant phase-matched generation of second-harmonic spin waves has not yet been achieved in practice. Here, we show experimentally that such a process can be realized using a combination of different modes of nano-sized spin-wave waveguides based on low-damping magnetic insulators. We demonstrate that our approach enables efficient spatially-extended energy transfer between interacting waves, which can be controlled by the intensity of the initial wave and the static magnetic field.

Development of method for frequency regulation of output current in high-voltage transformerless resonant chargers of capacitive energy storage devices

The object of research is high-voltage systems of electric discharge installations for various technological purposes. The work reports solving the problem of enabling the rate of charging of a capacitive energy storage, set by the requirements of a certain high-voltage technology. The quantitative characteristics of the deviation of the output current of the resonant inverter from the set stabilized value when changing the switching frequency of inverter switches in the range of output voltage change from 0 to 20 kV were determined. Using the Fourier transform of the rectangular input voltage, the frequency regulation possibility of the output current of the charger for capacitive energy storage devices was analyzed. Estimation dependences of the output current of resonant inverter on the load resistance and frequency deviation from resonant frequency were derived. These dependences could be used to implement frequency control over the switching inverter transistors, with the help of which the given effective value of the output current of the resonant inverter is obtained. A method of frequency regulation of the output current in high-voltage transformerless resonant charging devices of capacitive energy storage devices has been developed. Special feature of this method is that it is based on the frequency dependence of reactive resistances of the inductance and capacitance of the resonant circuit connected in series. Owing to that, it makes it possible to adjust the switching frequency of the inverter’s power switches depending on the relative resistance of the load and the specified growth rate of the capacitive energy storage voltage. The results reported here could be used in the design of benches for testing the electrical strength of high-voltage cables, as well as for the construction of high-voltage transformerless chargers in systems of electric discharge impulse processing of materials

4D printing of betanin/gelatin/nano-chitin complexes-functionalized surimi via disulfide bonds, and its applicability in dysphagia diets

Betanin/gelatin/nano-chitin complexes were fabricated to functionalize surimi for 4D printing based on the pH responsiveness of betanin, and the application of functionalized surimi was investigated in terms of dysphagia diets. Gelatin and nano-chitin in synergy could protect betanin against heat and UV irradiation by forming hydrogen bonds and electrostatic interactions (CIELab, DSC, XRD, FTIR and TEM). The further functionalized surimi with betanin/gelatin/nano-chitin complexes exhibited low heating loss, heat chromatic aberration, superior thermal stability and compact microstructure (TGA, and SEM). Rheological tests indicated that betanin/gelatin/nano-chitin complexes could reduce the strength of interaction and form new interaction with surimi protein and promoted the surimi to have great shearing-thinning performance, excellent strain deformation resistance, low frequency dependence and great thixotropy. The newly formed interactions were found to be disulfide bonds and hydrophobic interactions and they could further enhance suitable water distribution, and result in a fine and dense network (SDS-PAGE, chemical forces, LF-NMR and AFM). 4D printing of the functionalized surimi demonstrated the excellent color changeable merits (conforming first-order kinetic equation) and color reversibility characteristics along time, and could be also classified as potential dysphagia foods (IDDSI). Hence, surimi functionalized with betanin/gelatin/nano-chitin complexes could effectively realize innovative 4D printing, as well as expand interactive and visual experience of surimi products suitable for various specialized requirements like dysphagia diets.

Tidal Migration of Exoplanets around M Dwarfs: Frequency-dependent Tidal Dissipation

The orbital architectures of short-period exoplanet systems are shaped by tidal dissipation in their host stars. For low-mass M dwarfs whose dynamical tidal response comprises a dense spectrum of inertial modes at low frequencies, resolving the frequency dependence of tidal dissipation is crucial to capturing the effect of tides on planetary orbits throughout the evolutionary stages of the host star. We use nonperturbative spectral methods to calculate the normal mode oscillations of a fully convective M dwarf modeled using realistic stellar profiles from MESA. We compute the dissipative tidal response composed of contributions from each mode, as well as nonadiabatic coupling between the modes, which we find to be an essential component of the dissipative calculations. Using our results for dissipation, we then compute the evolution of circular, coplanar planetary orbits under the influence of tides in the host star. We find that orbital migration driven by resonance locking affects the orbits of Earth-mass planets at orbital periods P orb ≲ 1.5 days and of Jupiter-mass planets at P orb ≲ 2.5 days. Due to resonantly driven orbital decay and outward migration, we predict a dearth of small planets closer than P orb ∼ 1 day and similarly sparse numbers of more massive planets out to P orb ∼ 3 days.

Exploration of structural and dielectric properties of orthorhombic Ta2O5 nanoplatelets towards the potential optoelectronic devices

The dielectric characteristics of tantalum pentoxide (Ta2O5) nanostructures, synthesized by hydrothermal process, have been investigated in the temperature range of 80 K to 400 K and frequency range of 20 Hz to 2 MHz. X-ray diffraction (XRD) confirms the formation of highly crystalline and orthorhombic phase of the nanostructures sintered at 950 ºC. The electron microscope images reveal that the synthesized nanostructures change their morphology to nanoplatelets upon increasing the sintering temperature. Further, UV–visible absorbance, FTIR and Raman spectra of the synthesized nanostructures were obtained to investigate their optical properties. The experimentally obtained dielectric results indicate that both the dielectric constant (ε) and dielectric loss (D) values increase with increasing operating temperature. Also, the dielectric constant increases to 20 while the dielectric loss decreases to <0.025 at room temperature on increasing the sintering temperature. At 300 K and 1 kHz, the value of ε becomes almost twice that of as-synthesized nanostructures i.e. from 10 to 20 on increasing the sintering temperature to 950 ºC. The enhancement in dielectric constant can be justified by the thermally activated orientational and interfacial polarization associated with the increase in the grain size of the Ta2O5 nanoplatelets at higher sintering temperatures. Furthermore, the frequency dependence of ε indicates the high effect of the distribution of relaxation time in the Ta2O5 nanoplatelets at lower frequencies. Overall, this study provides a better understanding of the structural and dielectric behaviour of Ta2O5 nanostructures in correlation with varying sintering temperature. The results suggest that the orthorhombic Ta2O5 nanoplatelets have potential applications as alternative dielectric materials in various electronic and optoelectronic devices.

Comparison of Two Clinical Devices for the Measurement of Distortion Product Otoacoustic Emissions in Normal-Hearing Adults.

Otoacoustic emissions (OAEs) are low-intensity sounds generated by the cochlea and associated with the function of the outer hair cells. Since OAE measurements do not require active participation of a listener, OAEs are considered an objective measure of cochlear function. While distortion-product OAEs (DPOAEs) are commonly used in clinical practice, limited information is available on the performance of various clinical devices. This study compared two commercial clinical devices, Titan and Eclipse from Interacoustics, and collected normative data for DPOAEs in people with normal hearing. The data collection and analysis were focused on signal and noise amplitudes as well as signal-to-noise ratios (SNRs). Sixty-three participants with normal hearing (age 23.2±2.0 years) were included in the study. DPOAEs were measured at 31 frequencies ranging from 500 to 10,000 Hz. DPOAE amplitude differed across frequencies. Additionally, a high number of unreliable responses were observed at the edge frequencies (<828 Hz and >6,072 Hz). There were no significant differences between the two devices in terms of DPOAE amplitudes, but the recorded-noise levels (amplitude) differed significantly. SNRs of the recorded OAEs were frequency dependent (higher frequencies showed larger SNRs), and significant differences in terms of SNR were found between the two devices. Despite the above-mentioned differences, the OAEs recorded with both devices met the pass criteria for the SNR (≥6 dB) consistently across frequencies, and thus the differences do not compromise the test outcomes. The frequency dependence of the OAE amplitudes and the corresponding SNRs may be relevant for clinical practice.

Evaluation of vibration properties of an 18-story mass timber–concrete hybrid building by on-site vibration tests

Timber–concrete hybrid structural systems are a practical option to provide tall mass timber buildings with a lateral load-resisting system. This paper discusses the dynamic behavior of an 18-story timber–concrete hybrid building based on the vibration properties evaluated by on-site vibration tests. First, microtremor measurements and human-powered excitation tests were carried out and the obtained vibration data were analyzed using a stochastic subspace identification method to derive natural frequencies, damping ratios, and mode shapes. Then, a finite-element (FE) model was developed based on detailed structural design information, and its eigenvalues and eigenvectors were compared with the test results. The vibration test results showed various mode shapes, including in-plane deformation of the floor diaphragm composed of cross-laminated timber (CLT) panels. The damping ratios in all the modes were scattered between 1 and 3%, and no frequency dependency was observed. The modal properties of the FE model agreed well with the test results by considering the additional stiffness of non-structural components. In order to simulate the in-plane deformation of the CLT floor diaphragm, detailed modeling of the connection between each CLT floor panel and the connection between CLT floor panels and concrete cores is recommended. The findings provide practitioners with an insight into dynamic properties and FE modeling methods of tall timber–concrete hybrid buildings.

Large magnetocaloric effect and exchange bias properties in Mn-Ni-Co-Sn full Heusler alloy

We have studied the structural, magnetic, magnetocaloric properties and exchange bias (EB) of a Mn-rich Mn-Ni-Co-Sn Heusler alloy, by means of the combined experimental and theoretical investigations. The alloy possesses tetragonal structure at room temperature (RT), and exhibits a first order martensitic transition at around 335 K. It also shows a large magnetocaloric effect in the vicinity of martensitic transition, with a maximum isothermal magnetic entropy change of around 35 J/kg.K, which is significantly larger than that reported for many other Heusler systems. Frequency dependence of spin freezing temperature obeying the dynamical scaling and Vogel-Fulcher law, along with the memory effect confirms the presence of cluster spin glass (CSG) state at low temperatures in the alloy. It shows EB effect at low temperatures, with a maximum EB field of 0.099 Tesla at 2 K, after field cooling in presence of 1 Tesla. Strong exchange coupling among the CSG clusters embedded in a strong ferrimagnetic matrix is found to be responsible for the observed EB. Ab-initio calculations using density functional theory on a representative Mn50Ni35.94Co6.25Sn7.81 alloy (very close to our experimental composition) shows the tetragonal structure with the ferrimagnetic ordering as the ground state, which is in good agreement with the experimental results. Exchange mechanism behind the observed EB in the present alloy has been discussed in the light of varying interatomic distances between different atomic pairs, and hence the magnetic coupling.

Synaptotagmin-7 Counteracts Short-Term Depression during Phasic Dopamine Release.

Dopamine neurons switch from tonic pacemaker activity to high-frequency bursts in response to salient stimuli. These bursts lead to superlinear increases in dopamine release, and the degree of this increase is highly dependent on firing frequency. The superlinearity and frequency dependence of dopamine release implicate short-term plasticity processes. The presynaptic Ca2+-sensor synaptotagmin-7 (SYT7) has suitable properties to mediate such short-term plasticity and has been implicated in regulating dopamine release from somatodendritic compartments. Here, we use a genetically encoded dopamine sensor and whole-cell electrophysiology in Syt7 KO mice to determine how SYT7 contributes to both axonal and somatodendritic dopamine release. We find that SYT7 mediates a hidden component of facilitation of release from dopamine terminals that can be unmasked by lowering initial release probability or by predepressing synapses with low-frequency stimulation. Depletion of SYT7 increased short-term depression and reduced release during stimulations that mimic in vivo firing. Recordings of D2-mediated inhibitory postsynaptic currents in the substantia nigra pars compacta (SNc) confirmed a similar role for SYT7 in somatodendritic release. Our results indicate that SYT7 drives short-term facilitation of dopamine release, which may explain the frequency dependence of dopamine signaling seen in vivo.

Experimental Analysis of Rayleigh and Sezawa Modes Resonance Frequencies in SAW Devices Manufactured on Sc0.3Al0.7N/Si†

GHz operating single port SAW resonators have been manufactured on Sc0.3Al0.7N/Si substrate. The thickness of the ScAlN thin layer was 0.8 μm. Advanced nano‐lithographic techniques have been developed for devices manufacturing. Rayleigh and Sezawa modes have been evidenced on Sc0.3Al0.7N/Si structure. The targeted applications are temperature sensors for harsh environmental operations. The sensitivity and temperature coefficient of frequency (TCF) of the manufactured devices have been experimentally determined and analyzed. The mode shapes of the resonances that appear in the devices supported on Sc0.3Al0.7N/Si substrate were evidenced by finite element method (FEM) simulations. A technique that combines FEM with Coupling of Modes (COM) was used for the determination of the resonance frequencies. Simulations performed for the temperature dependence of the resonance frequency led to results close to the experimental ones for the Rayleigh mode as well as for the Sezawa mode for devices supported on Sc0.3Al0.7N/Si substrate. © 2024 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Microfabrication of piezoelectric MEMS based on thick LiNbO3 single-crystal films

Microfabrication procedure of piezoelectric micro electro-mechanical systems based on 5 μm thick LiNbO3 films on SiO2/Si substrate at wafer scale including deep dry etching of thick LiNbO3 films by implementing pulsed mode of Ar/SF6 gas was developed. In particular, two (YXlt)/128°/90°LiNbO3-Si cantilevers with tip mass were fabricated and characterized in terms of resonance frequency (511 and 817 Hz), actuation and acceleration sensing capabilities. The quality factor of 89.5 and the electromechanical coupling of 4.8% were estimated from measured frequency dependency of electrical impedance, fitted by using Butterworth–Van Dyke model. The fabricated piezoelectric micro-electro-mechanical systems have demonstrated highly linear displacement with good sensitivity (5.28 ± 0.02 μm V−1) as a function of applied voltage and high sensitivity to vibrations of 667 mV g−1 indicating a suitability of the structure for actuation purposes and for acceleration or frequency sensing with high precision, respectively.

A hybrid constitutive model of high-damping viscoelastic materials used for vibration control of civil structures

The dynamic mechanical properties of high-damping viscoelastic (VE) materials exhibit significant frequency and temperature dependences in the glass transition zone. However, the current state of VE constitutive models face a challenge in balancing the accuracy, simplicity, and ease of structural dynamic analysis. In this study, a power-law and exponent-law hybrid model is proposed to model the frequency-dependent and temperature-dependent complex modulus of VE materials. The equivalence of hybrid model and existing VE constitutive models is presented. A total of 12 groups of experimental data are collected to validate the accuracy of hybrid model. An efficient numerical method for the hybrid model is proposed and then validated through a viscoelastically damped frame. Results show that the hybrid model is equivalent to two rheological models or fractional derivative models owning to the unshared model coefficients. The hybrid model is superior to the eight-parameter fractional derivative model in predicting the complex modulus over a wide equivalent frequency range. The proposed numerical method performs quite well in calculating seismic responses of proportional and non-proportional damped frames.

Elaboration of La (Sr/Na) Mn (Ti) O3 ceramic, structural, and morphological investigations, and contribution of direct and indirect interactions on transport properties

The charge carrier's dynamics of La0.7(Sr5/6Na1/6)0.3Mn0.7Ti0.3O3 (LSNMTO) ceramic is conducted using the temperature and frequency dependences of the electrical conductivity and their scaling formalisms. The structural study indicates that LSNMTO crystallizes in a rhombohedral R3‾c perovskite structure with no detectible secondary phases. A phase transition from the high-temperature metallic behavior to the low-temperature semiconductor nature is observed from the electrical conductivity curve at TS-M = 415 K. Further, it is observed that the cation-anion-cation and the cation-cation interactions are present in the material, and play important role in governing the electrical behaviors of LSNMTO. From 200 K to 415 K, the Non-adiabatic Small Polaron Hopping is the predominant conduction process, although the Mott-Variable Range Hopping mechanism governs the conductivity at low temperatures. In the intermediate temperature range, the dynamic of the charge carriers is explained using the Shklovskii Efros model. The frequency-activated conductivity obeyed the universal laws (double-Jonscher and Jonscher laws). At high frequencies, the dispersion of the conductivity spectra is attributed to the presence of hopping and tunneling conduction processes. The Time-Temperature Superposition Principle (TTSP) is obeyed over a large temperature range from 160 K to 350 K. Below 160 K, the deviation from the TTSP is attributed to the coexistence of hopping and tunneling conduction mechanisms. Deviations from the Summerfield scaling and shifts of the isotherms to higher values on decreasing the temperature are due to the local structural disorder in LSNMTO. Therefore, the structural particularities of LSNMTO can result in diverse conduction pathways giving an increase to the deviations from the Summerfield scaling. The studied ceramic exhibits a very motivating maximum negative temperature coefficient of resistance NTCR = −13.36% which is significantly elevated as compared to previously investigated compounds.