Translational Hopping Research Articles

A correlation between microstructural and impedance properties of MnFe2-xCoxO4 nanoparticles

A comprehensive study of physical properties and impedance analysis of MnFe2-xCoxO4 (x = 0.00, 0.40, 0.80, 1.20, 1.60, 2.00) nanoparticles prepared by citrate-nitrate method has been carried out. Structural analysis by Rietveld refinement indicated the formation of pure cubic structure with the space group Fd3‾m. The chemical composition and approximate grain size of the samples were determined by energy dispersive X-ray spectroscopy and field-emission scanning electron microscopy, respectively. The presence of Co has a strong influence on space charge modulation and affect the grain-boundary resistance. The results showed that sample x = 1.20 has less mobility, less polarizability, and therefore lower dielectric constant which is preferred for high frequency or power applications to minimize electric power loss. Impedance analysis demonstrate that small polaron hopping are responsible for the short-range translation hopping in conduction process of the samples (except for x = 1.60).

Impedance Spectroscopy Analysis of PbSe Nanostructures Deposited by Aerosol Assisted Chemical Vapor Deposition Approach.

This research endeavor aimed to synthesize the lead (II) diphenyldiselenophosphinate complex and its use to obtain lead selenide nanostructured depositions and further the impedance spectroscopic analysis of these obtained PbSe nanostructures, to determine their roles in the electronics industry. The aerosol-assisted chemical vapor deposition technique was used to provide lead selenide deposition by decomposition of the complex at different temperatures using the glass substrates. The obtained films were revealed to be a pure cubic phase PbSe, as confirmed by X-ray diffraction analysis. SEM and TEM micrographs demonstrated three-dimensionally grown interlocked or aggregated nanocubes of the obtained PbSe. Characteristic dielectric measurements and the impedance spectroscopy analysis at room temperature were executed to evaluate PbSe properties over the frequency range of 100 Hz–5 MHz. The dielectric constant and dielectric loss gave similar trends, along with altering frequency, which was well explained by the Koops theory and Maxwell–Wagner theory. The effective short-range translational carrier hopping gave rise to an overdue remarkable increase in ac conductivity (σac) on the frequency increase. Fitting of a complex impedance plot was carried out with an equivalent circuit model (Rg Cg) (Rgb Qgb Cgb), which proved that grains, as well as grain boundaries, are responsible for the relaxation processes. The asymmetric depressed semicircle with the center lower to the impedance real axis provided a clear explanation of non-Debye dielectric behavior.

Impedance Spectroscopic Study of Nickel Sulfide Nanostructures Deposited by Aerosol Assisted Chemical Vapor Deposition Technique.

This research aims to synthesize the Bis(di-isobutyldithiophosphinato) nickel (II) complex [Ni(iBu2PS2)] to be employed as a substrate for the deposition of nickel sulfide nanostructures, and to investigate its dielectric and impedance characteristics for applications in the electronic industry. Various analytical tools including elemental analysis, mass spectrometry, IR, and TGA were also used to further confirm the successful synthesis of the precursor. NiS nanostructures were grown on the glass substrates by employing an aerosol assisted chemical vapor deposition (AACVD) technique via successful decomposition of the synthesized complex under variable temperature conditions. XRD, SEM, TEM, and EDX methods were well applied to examine resultant nanostructures. Dielectric studies of NiS were carried out at room temperature within the 100 Hz to 5 MHz frequency range. Maxwell-Wagner model gave a complete explanation of the variation of dielectric properties along with frequency. The reason behind high dielectric constant values at low frequency was further endorsed by Koops phenomenological model. The efficient translational hopping and futile reorientation vibration caused the overdue exceptional drift of ac conductivity (σac) along with the rise in frequency. Two relaxation processes caused by grains and grain boundaries were identified from the fitting of a complex impedance plot with an equivalent circuit model (Rg Cg) (Rgb Qgb Cgb). Asymmetry and depression in the semicircle having center present lower than the impedance real axis gave solid justification of dielectric behavior that is non-Debye in nature.

Structural, magnetic, elastic, and dielectric properties of Mn0.3−xCdxCu0.2Zn0.5Fe2O4 nanoparticles

The doping of the spinel ferrites with selective dopants usually improves the properties of the parent ferrite. In this paper, the structural, magnetic, elastic, and dielectric properties of Mn0.3−xCdxCu0.2Zn0.5Fe2O4 (x = 0.00–0.30, in steps of 0.05) via citrate–nitrate method were reported. The samples were structurally characterized using the techniques of X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The Rietveld refinement of XRD patterns showed the formation of the spinel phase of the samples that can be indexed in the cubic symmetry with the Fd-3m space group confirmed by FTIR spectrometry. The nonmonotonic variant of saturation magnetization with an increase of Cd substitution can be explained based on the different cation distribution in the tetrahedral and octahedral sites of spinel structure and Yaffet–Kittel-type noncollinear ordering. According to the dielectric results, the conduction arises for x = 0.05, 0.10, 0.15, 0.25, and 0.30 is due to the short-range translation hopping assisted by small polaron mechanism and for x = 0.00 and 0.20 is ascribed to the localized orientation hopping assisted by large polaron.

Investigation on the structural, magnetic, dielectric and impedance analysis of Mg0.3-xBaxCu0.2Zn0.5Fe2O4 nanoparticles

An exhaustive study of the structural, magnetic, and impedance analysis on Mg0.3-xBaxCu0.2Zn0.5Fe2O4 (x = 0.00–0.30, in steps of 0.05) ferrites were performed. The crystallographic structure was studied by X-ray diffraction experiments and Rietveld refinement revealed that all samples crystallize in a cubic spinel structure with the Fd3‾m space group. The non-monotonic behavior of the saturation magnetization can be explained according to Néel's model and the variation of the lattice parameter. An improvement in dielectric properties has also observed in the Ba-substituted Mg–Cu–Zn ferrite so that sample x = 0.05 has the best structural, magnetic and dielectric properties. The obtained results demonstrate that the conduction in the Ba-substituted Mg–Cu–Zn ferrite is due to the short-range translation hopping assisted by a small polaron hopping mechanism.

Optical and electrical properties and conduction mechanism of [(CH3)2NH2]2CoCl4

Monoclinic crystals of [(CH3)2NH2]2CoCl4 are of the space group P21/n. Unit cell dimensions are as follows: a = 8.5393 Å, b = 11.3905 Å, c = 13.4069 Å and β = 91.02°. This compound undergoes several phase transitions. The optical properties were measured by means of UV–visible absorption spectroscopy in the range 200–800 nm. Analysis of the data revealed the existence of direct allowed optical transition mechanisms with bandgap energy equal to 3.84 eV. The electrical conductivity of [(CH3)2NH2]2CoCl4 was studied in the frequency range 10−1–106 Hz and in the temperature range 411–449 K by means of impedance spectroscopy. Impedance and modulus analyses indicated temperature‐independent distribution of relaxation times and non‐Debye behavior in this material. A super‐linear power law was observed for the AC conductivity, which was analyzed based on the jump relaxation model σac = σdc + A1ωs1 + A2ωs2. Accordingly, the first AC term A1ωs1 corresponds to translational hopping motion and the second term A2ωs2 to well‐localized hopping and/or reorientational motion. Conduction takes place via correlated barrier hopping in phases I and II.

Conduction in Polyaniline-Emeraldine Salt/Bentonite Composites Using Impedance Spectroscopy

In this study, different mass concentrations of Polyaniline-emeraldine salt (PAni-ES) was mixed with bentonite clay. XRD analysis showed the incorporation of PAni-ES in bentonite. The AC conductivity was calculated from Impedance measurements. The conductivities increased with increasing concentration of PAni-ES. The AC conductivities follow a transition from frequency-independent to frequency-dependent at a critical frequency, ωc. Above ωc, the conductivity follows a universal power law behavior as described for disordered materials. Using jump relaxation model, the conductivity is governed by translational ion hopping in the low-frequency region, and well-localized ion hopping in the high-frequency region.

Micro-structure and motion of two-dimensional dense short spherocylinder liquids

We numerically investigate the micro-structure and motion of 2D liquids composed of dense short spherocylinders, by reducing the shape aspect ratio from 3. It is found that reducing shape aspect ratio from 3 causes a smooth transition from heterogeneous structures composed of crystalline ordered domains with good tetratic alignment order to those with good hexagonal bond-orientational order at an aspect ratio equaling 1.35. In the intermediate regime, both structural orders are strongly deteriorated, and the translational hopping rate reaches a maximum due to the poor particle interlocking of the disordered structure. Shortening rod length allows easier rotation, induces monotonic increase of rotational hopping rates, and resumes the separation of rotational and translational hopping time scales at the small aspect ratio end, after the crossover of their rates in the intermediate regime. At the large shape aspect ratio end, the poor local tetratic order has the same positive effects on facilitating local rotational and translational hopping. In contrast, at the small shape aspect ratio end, the poor local bond orientational order has the opposite effects on facilitating local rotational and translational hopping.

Dielectric and electrical study along with the evidences of small polaron tunnelling in Gd doped bismuth ferrite lead titanate composites

The phase formation of the polycrystalline samples of 0.6BiGdxFe1−xO3–0.4PbTiO3 (x = 0.05, 0.10, 0.15 and 0.20) was studied by X-ray diffraction technique prepared by using solid state reaction route. From analysing the X-ray diffraction pattern, the appearance of morphotrophic phase boundary between rhombohedral and tetragonal phase was observed in some of these composites at room temperature. The dielectric parameters are measured in a frequency range between (102–106) Hz at different temperatures. The nyquist plot (Z′ vs. Z″) fit confirmed the contribution of bulk and grain boundary effect in the materials. Impedance, ac and dc conductivity showed the negative temperature co-efficient of resistance behavior. The temperature dependence of dc conductivity and relaxation time followed Arrhenius equation. The ac conductivity followed by the power law showed that the dynamics of charge carrier arises due to translational hopping motion for x = 0.10–0.20 and localised one for x = 0.05. The increasing behaviour of frequency exponent (n) with temperature strongly suggests that the small polaron tunnelling is the dominant conduction mechanism for the studied samples except for x = 0.05 composition.

Dielectric relaxation behavior and mechanism of Y2/3Cu3Ti4O12 ceramic

Y2/3Cu3Ti4O12 (YCTO) ceramics were sintered in air (YCTO-air) and pure O2 atmosphere (YCTO-O2), respectively. It was found that the permittivity and dielectric loss of YCTO-O2 were decreased drastically in low frequency. The frequency dependent impedance (Z″) and modulus (M″) spectra of YCTO-air and YCTO-O2 show a thermal activated process. The scaling behavior of both Z″ and M″ spectra further suggest that the distribution of relaxation times is temperature independent. The Cole–Cole plot in impedance formalism shows that electrical response of the samples originates from both grains and grain-boundaries. Conductivity (σ′) spectra follow Universal Dielectric Repose law. The short-range translation hopping assisted by small polaron hopping mechanisms for YCTO-O2. Moreover, the scaling behavior of σ′ spectra further confirms that the distribution of local electrical response time is temperature independent.

Effect of substrate temperature on the structural and electrical properties of La and Mn co-doped BiFeO3 thin films

The effect of substrate temperature on the structural and electrical properties of multiferroic Bi0.90La0.10Fe0.95Mn0.05O3 (BLFMO) thin films deposited on Pt (111)/Ti/SiO2/Si substrate using pulsed laser deposition (PLD) has been investigated. Films with substrate temperature ranging from 450°C to 650°C have been deposited. The grain size and roughness are found to increase with substrate temperature. The film deposited at 575°C exhibits maximum remnant polarization around 39μC/cm2 and a coercive field of 400kV/cm. The cyclic fatigue study of the sample shows only 4% loss after 108cycles. Complex impedance study of the BLFMO thin films demonstrates electrical homogeneity of the sample. AC conductivity data has been fitted using Jonscher single power law, and value of n found to be <1 indicating translational hopping conduction mechanism. The lowest leakage current found is 4.37×10−6A/cm2 at 575°C. The leakage current mechanism is found to be dominated by space charge limited current and Fowler-Nordheim conduction mechanism.

Concentration-driven structural stability and dielectric dispersion in lead free (Ba1−xSc2x/3)Zr0.3Ti0.7O3 ceramics

Lead free scandium doped barium zirconate titanate (Ba1−xSc2x/3)(Zr0.3Ti0.7)O3 abbreviated as (BScZT) (x = 0.02, 0.04, 0.06, 0.08, 0.10) ceramics were prepared by the conventional solid state reaction route and their structural, microstructural and electrical properties were investigated experimentally. X-ray diffraction and Rietveld refinement analysis are indexed by considering cubic symmetry having space group Pm-3 m. Scandium ion (Sc3+) substitution induced A-site vacancies and distortion in three dimensional cation-oxygen networks leads to disorder in the local symmetry as identified in Raman spectra. The microstructural image shows formation of smaller grains of irregular shape and sizes along with aggregative characteristic with successive increase in Sc concentration. Lorentz type quadratic behavior in dielectric dispersion follows modified Curie–Weiss law and indicates a relaxor behavior with diffuse type of phase transition. A non-Debye type of relaxation behavior is observed in these materials. Variation of relaxation strength and diffuse parameters obey the Vogel–Fulcher relation. The ac conductivity highlights the hopping of bound charge carriers between the localized environment at lower temperature and translation hopping at higher temperature is modeled through universal dielectric response.

Microwave sintered Bi0.90La0.10Fe0.95Mn0.05O3 nanocrystalline ceramics: Impedance and modulus spectroscopy

Multiferroic Bi0.90La0.10Fe0.95Mn0.05O3 (BLFMO) nanoceramics were synthesized by PVA sol-gel method, followed by microwave sintering. The structural, microstructural and electrical properties of BLFMO were investigated. The crystal symmetry and unit cell dimensions were determined from the experimental data using Rietveld analysis. BLFMO revealed only one electroactive region as verified from impedance and modulus spectroscopy. Overlapping large polaron tunneling transport mechanism was observed from AC conductivity analysis. Conduction below 250°C (−30°C≤T≤250°C) was attributed to translational hopping while above 250°C (250°C≤T≤350°C) corresponds to electron hopping between charge defects. The relative permittivity varies from 66 to 203 at 1kHz over the measured temperature range (−150°C≤T≤350°C). The electrical conductivity of the microwave sintered BLFMO has been discussed based on defect reaction with Mn doping. The measured DC conductivity in the range of 10−13S/cm at −130°C to 10−4S/cm at 350°C revealed the insulating behavior of the sample. At room temperature, the DC resistivity of the sample was over ~50MΩcm. The stretching constant (β) obtained from KWW (Kohlrausch-Williams-Watts) equation indicates that the sample inclined towards ideal Debye behavior as the temperature increases.

Mechanical detection of ultraslow, Debye‐like Li‐ion motions in LiAlO single crystals

Single crystalline LiAlO is known as a very poor ion conductor. Thus, in its crystalline form it unequivocally disqualifies itself from being a powerful solid electrolyte in modern energy storage systems. On the other hand, its interesting crystal structure proves beneficial to sharpen our understanding of Li ion dynamics in solids which in return might influence application‐oriented research. LiAlO allows us to apply and test techniques that are sensitive to extremely slow Li ion dynamics. This helps us clarifying their diffusion behaviour from a fundamental point of view. Here, we combined two techniques to follow Li ion translational hopping in LiAlO that can be described by the same physical formalism: dynamic mechanical relaxation and electrical relaxation, i.e., ionic conductivity measurements. Via both methods we were able to track the same transport mechanism in LiAlO. Moreover, this enabled us to directly probe extremely slow Li exchange rates at temperatures slightly above 430 K. The results were compared with recent insights from nuclear magnetic resonance spectroscopy. Altogether, an Arrhenius‐type Li diffusion process with an activation energy of ca. 1.12 eV was revealed over a large dynamic range covering 10 orders of magnitude, i.e., spanning a dynamic range from the nano‐second time scale down to the second time scale. image

Cooling the two-dimensional short spherocylinder liquid to the tetratic phase: Heterogeneous dynamics with one-way coupling between rotational and translational hopping.

We numerically demonstrate the transition from the isotropic liquid to the tetratic phase with quasilong-range tetratic alignment order (i.e., with nearly parallel or perpendicular aligned rods), for the cold two-dimensional (2D) short spherocylinder system before crystallization and investigate the thermal assisted heterogeneous rotational and translational micromotions. Comparing with the 2D liquid of isotropic particles, spherocylinders introduce extra rotational degrees of freedom and destroy packing isotropy and the equivalence between rotational and translational motions. It is found that cooling leads to the stronger dynamical heterogeneity with more cooperative hopping and the stronger retardations of rotational hopping than translational hopping. Under topological constraints from nearly parallel and perpendicular rods of the tetratic phase, longitudinal and transverse translational hopping can occur without rotational hopping, but not the reverse. The empty space trailing a neighboring translational hopping patch is needed for triggering the patch rotational hopping with its translational motion into the empty space. It is the origin for the observed increasing separation of hopping time scales and the one-way coupling between rotational and translational hopping. Strips of longitudinally or transversely aligned rods can be ruptured and reconnected with neighboring strips through buckling, kink formation, and patch rotation, under the unbalanced torques or forces from their neighboring rods and thermal kicks.

Nanojacketing and Dejacketing of ds-DNA: A Nondestructive Characterization of a Nanojacketed Sample by Impedance Spectroscopy

A facile approach of nanojacketing DNA in intact conformation is evolved by the in situ polymerization of o-methoxyaniline (OMA) at 30 °C using HAuCl4 as an oxidant and DNA as a soft template. It concomitantly produces poly(o-methoxyaniline) (POMA) and a Au nanojacket encapsulating the double stranded DNA (ds-DNA). The POMA chains remain adhered to the Au nanojacket, facilitating the dissolution of nanojacketed DNA (DNA-Au-POMA) in organic solvent without affecting its conformation. Digestion of the nanojacketed system with saturated iodine solution dejackets the ds-DNA with retention of its conformation, leaving the POMA nanotube. The nanojacketing and dejacketing phenomena are established by transmission electron microscopy (TEM), UV-vis spectroscopy, and CD spectroscopy, and the nanostructure is further characterized by FTIR, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The impedance study of the DNA-Au-POMA sample suggests the Cole-Cole plots at both the impedance and modulus planes and the values of capacitance and electron-transfer resistance of the material (R(et)) are calculated to be 13.74 pF and 388 kΩ, respectively. The presence of a single Debye peak in both the impedance and modulus vs frequency plots suggests an isotropic nature of the system, and the frequency dependent ac-conductivity suggests the presence of short-range translational and reorientational (localized) hopping of charge carriers at lower and higher frequency region.

Dielectric properties and electrical conduction of high-k LaGdO3 ceramics

The temperature and frequency dependent dielectric properties and leakage conduction mechanism in LaGdO3 (LGO) ceramics have been studied, and this material has been identified as a potential high-k candidate for the future complementary metal-oxide-semiconductor (CMOS) and dynamic random access memory (DRAM) technology nodes. The dielectric constant and the loss tangent at 100 kHz were ∼21.5 and ∼0.003, respectively, at ambient conditions without any significant temperature and voltage dependence. The ac conductivity shows the typical features of universal dynamic response (UDR) and obey the double power law σac=σdc+Aωn1+Bωn2 with three types of temperature dependent conduction processes involved; (i) a dc plateau (&amp;lt; 3 kHz) due to long range translational hopping, (ii) a mid frequency region due to the short range hopping (3–100 kHz), and (iii) a high frequency region due to localized or reorientational hopping (100–1000 kHz). The temperature dependent dc conductivity follows the Arrhenius relation with activation energies of 0.05 eV in the 200–400 K range and 0.92 eV in the 400–600 K range. The leakage current behavior reveals bulk limited Poole-Frenkel (PF) conduction mechanism and the estimated optical dielectric constant (ɛ∞) is 3.6.

Influence of the Grain Size on the Conduction Mechanism of Barium Strontium Titanate Thin Films

Sol-gel barium strontium titanate ( Ba0.6Sr0.4TiO3) thin films with different grain sizes have been successfully fabricated as metal-insulator-metal (MIM) capacitors. The perovskite structure of the material has been confirmed via X-ray diffraction (XRD). In order to correlate the effect of the grain size to the conduction mechanisms of these films, atomic force microscopy (AFM) results are presented. The grain size shows an important effect on the conduction mechanism for the films. The results show that as the grain size increases, both the impedance and the permittivity of the films decrease, whereas the conductivity shows an inverse variation. The Z* plane for all films shows two regions, corresponding to the bulk mechanism and the distribution of the grain boundaries-electrodes conduction process.M´´ versus frequency plots reveal non-Debye relaxation peaks, which are not able to be observed in the e´´ plots. Alternating current (AC) conductivity versus frequency plots show three regions of conduction processes, i.e. a low-frequency region due to direct current (DC) conduction, a mid-frequency region due to translational hopping motion, and a high-frequency region due to localized hopping and/or reorientational motion.

SYNTHESIS, PIEZOELECTRIC, DIELECTRIC AND CONDUCTIVITY STUDIES ON Dy2O3 SUBSTITUTED (Bi0.94Na0.94)0.5Ba0.06TiO3 CERAMICS

Polycrystalline ( Bi 0.94-x Dy x Na 0.94)0.5 Ba 0.06 TiO 3 ceramics (x = 0, 0.04, and 0.08, designated as BNBT6, BNBT6: 4Dy and BNBT6: 8Dy, respectively) were prepared by conventional high temperature sintering method. The X-ray diffraction patterns show pure perovskite structure with no secondary phases. Lattice parameters and unit cell volumes have decreased due to Dy2O3 substitution. SEM micrographs revealed denser samples (ρrel &gt; 97%) with uniformly distributed grain sizes. The room temperature piezoelectric properties of Dy2O3 substituted sample at x = 0.04 were relatively higher: d33 = 147 pC/N, k p = 28% and Q m = 128. The samples exhibited infinitesimal change in thickness (≈ 15 nm) to an applied voltage of 100 V, which could be utilized in actuator applications. Relaxor behavior and broad dielectric maxima with diffuse phase transition were observed. The value of RT dielectric constant has increased while dielectric loss was decreased due to Dy2O3 substitution. Conductivity in the materials obeys Jonscher's universal power law. The conductivity in the low frequency region is associated with short range translational hopping while it is associated with the reorientational hopping in the high frequency region. The charge carrier concentration term remained constant over the entire temperature range of (30–500°C).

Rotation and Translational Motion prior to Self-Assembly: Dynamics of Ethanethiolate on Cu(111)

We investigate the dynamics of low-coverage ethanethiolate on Cu(111) using helium spin-echo spectroscopy. Above 210 K, the measurements are dominated by translational hopping with an activation energy of only 86 ± 5 meV. At lower temperatures (150-210 K) a further process becomes apparent which has the signature of confined motion. We demonstrate the experimental results are consistent with scattering from an anchored rotor, enabling identification of sixfold jump rotation of the ethyl tail group around a static sulfur adsorption site, with a rotational activation energy of 18 ± 8 meV. Our approach represents a new form of rotational spectroscopy which can be used to study rotational surface diffusion.