Translational Hopping Research Articles

Effect of the film thickness on the impedance behavior of sol–gel Ba 0.6Sr 0.4TiO 3 thin films

Perovskite Ba 0.6Sr 0.4TiO 3 sol–gel thin films with different thicknesses are fabricated as MFM configuration to study the effect of the film thickness on the dielectric relaxation phenomenon and the ionic transport mechanism. The frequency dependent impedance, electric modulus, permittivity and AC conductivity have been investigated in this context. Z⁎ plane for all the tested samples shows two regions, corresponding to the bulk mechanism and the distribution of the grain boundaries–electrodes process. Electric modulus versus frequency plots reveal non-Debye relaxation peaks. The observed decrease in both the impedance and permittivity with the increase in film thickness is attributed to the grain size effect. The frequency dependent conductivity plots show three regions of conduction processes, i.e. low-frequency region due to DC conduction, mid-frequency region due to translational hopping motion and high-frequency region due to localized hopping and/or reorientational motion.

Electrical Properties of the Perovskite Ba(Pr1/2Ta1/2)O3 Ceramic

Lead-free perovskite Ba(Pr1/2Ta1/2)O3 was prepared by conventional ceramic fabrication technique at 1350°C/5hr in air atmosphere. The crystal symmetry, space group and unit cell dimensions were determined from the XRD-data using FullProf software. XRD analysis of the compound indicated the formation of a single-phase orthorhombic structure with the space group Pmmm. EDAX and SEM studies were carried out in order to evaluate the quality and purity of the compound. Permittivity data showed low temperature coefficient of capacitance (TCC = 11%) up to 100°C. The frequency variation of ac conductivity data, were found to obey the double power law. The electrical conduction in the system might be due to the short-range translational type hopping of charge carriers.

Structural and electrical studies on Bi2VO5.5/Bi4Ti3O12 multilayer thin films

The textured multilayer (ML) thin films of bismuth layered ferroelectric (FE) compounds, Bi2VO5.5 (BVO) and Bi4Ti3O12 (BTO) with different individual layer thicknesses were fabricated via pulsed laser deposition technique on Pt(111)/TiO2/SiO2/Si substrates. X-ray diffraction studies confirmed that BVO and BTO retained their respective crystal structures in these multilayer (ML) thin films. The atomic force microscopy and scanning electron microscopy studies showed smooth and dense microstructures. The polarization hysteresis (P–E) studies on a representative (BVBT30) ML thin film at 300 K confirmed the remnant polarization (2Pr) and coercive field (Ec) to be ~20 μC/cm2 and 250 kV/cm, respectively. The value of Pr obtained was greater than that of the single layer thin film of BVO (Pr ~ 5.6 μC/cm2). The room temperature dielectric constant (er′) and the loss (D) for BVBT30 ML measured at 100 kHz were 170 and 0.01, respectively. The frequency and temperature dependent dielectric constant, impedance, modulus and ac conductivity of these ML thin films were studied as a function of frequency (100 Hz–1 MHz) in the 25–300 °C temperature range. Two distinct electrical responses were observed in these films, which were attributed to the grain effects at low temperatures and grain boundary effects at higher temperatures. The frequency dependent electrical conductivity was fitted well with the double power law which evidenced two different types of contributions to the conductivity; the low frequency conductivity being due to the short range translational hopping and the high frequency conductivity was due to the localized or reorientational hopping.

Onset of 3D Collective Surface Diffusion in the Presence of Lateral Interactions:Na/Cu(001)

3He spin-echo measurements are used to follow the picosecond motion of sodium atoms on a copper (001) substrate. 2D correlated motion arising from repulsive adsorbate interactions is observed for coverages as low as 0.04 ML. At coverages greater than 0.05 ML there is a pronounced onset of motion perpendicular to the surface. The perpendicular motion is thermally activated and seems related to the basic translational hopping diffusion process. The correlated motion is modeled successfully using a molecular dynamics simulation and a dipolelike lateral interaction. A simple model which relates the apparent height of the atom with its local coverage is shown to reproduce the experimental observations.

Magnetic and electric studies of a new Co(II) perovskite-like material

Structural phase transitions in the perovskite-like material [(CH4)12(NH3)2]CoCl4 have been observed using differential thermal scanning. The material shows an order-disorder transition at T 1 = 396 ± 5 K with entropy, (ΔS 1) = 12.8 J/mole/K. A "chain melting" transition with a major endothermic peak at T 2 = 337 ± 3 K and a minor one at T ′ = 316 ± 2 K, has total entropy ΔS = 28 J/mole/K. At low temperatures, the transitions at T 3 = 288 ± 3 K and at T 4 = 188 ± 3 K, have entropies of ΔS 3 = 14.4 J/mole/K and ΔS 4 = 2.6 J/mole/K respectively. AC magnetic susceptibility in the temperature range 78-290 K, in a magnetic field of 160 A/m and at a frequency of 320 Hz is presented. The results indicate changes in symmetry at 188 K. Dielectric permittivity has been studied as a function of temperature in the range 300-430 K and frequency range (60 Hz-100 kHz), confirming the observed transitions. The dielectric permittivity reflects rotational and conformational transition for the material. The variation of the real part of the conductivity with temperature is thermally activated with different activation energies in the range of ionic hopping. The temperature dependence of the dc conductivity and that of the ions hopping rate have indicated that the concentration of mobile ions is independent of temperature. The dependence of the conductivity on frequency follows the universal power law, <artwork name="GPHT31040ei1"> in the temperature range 340 K<T<390 K. Values 0 <s 1 <1 dominate at low frequency and correspond to translational hopping motion and values 1<s 2<2 dominate at high frequencies and correspond to well localized hopping and/or reorientational motion. For T > 396 K, the AC conductivity was fitted to <artwork name="GPHT31040ei2"> with 0<s<1. Comparison with the corresponding Cu-containing material is discussed.

Mn 2+ -Doping Effects on Commensuration and Incommensuration of Ammonium Zinc Chloride Crystal

Ammonium zinc chloride (AZC) crystals doped with Mn2+ in different concentrations were grown from aqueous solutions at constant temperature. The dielectric constant (ϵ), dielectric loss (tan δ) and the ac conductivity (σ ac ) along the polar axis were measured as functions of temperature and frequency. The temperature range covered the four high-temperature phases and the measuring frequency extended between 1–100 kHz. The measured properties facilitated the discussion of a model describing formation, annihilation and pinning of the discommensuration in crystal lattice and/or by structural imperfections. The effect of AZC decomposition in the normal phase and the possibility of protonic evolution on the ac conductivity were also considered. The presence of Mn2+ in the position of Zn2+ affected considerably the anomalies detected around the phase transition temperatures of ϵ, tan δ and σ ac . Conduction by translation and/or reorientation hopping are possible in two different frequency ranges depending on the crystal phase character. *On leave of absence from Physics Department, Faculty of Science, Assiut University, 71516 Assiut, Egypt.

Correlated orientational and translational motions in supercooled liquids

We have carried out NPT molecular dynamics simulations of isolated ellipsoids in a glass forming binary mixture to gain insight into the nature of orientational relaxation (OR) in a viscous liquid. At high pressures when the liquid is highly viscous, the OR is found to occur mainly via correlated hopping, sometimes involving participation of several neighboring atoms, placed in a ring like tunnel. In the glassy state, hopping is found to be accompanied by larger fluctuations in the total energy and the volume of the system. Both orientational and translational hopping are found to be gated, restricted primarily by the entropic bottlenecks, with the orientational motion becoming increasingly slower than the translation as the pressure is increased. Orientational relaxation is found to occur with a wide distribution of decay times.

Comparing the dynamical heterogeneities in binary glass formers and in a glass former embedded in a zeolite – a 2H NMR study

We characterize the nature of the dynamical heterogeneities of the small component in a binary glass former and of a glass former confined in a zeolite matrix by applying 2D 2H NMR. In both cases the dynamics are described by a distribution of reorientation correlation times G(ln τ) which is significantly broader compared to that of the corresponding neat system. For the binary system, the 2D NMR spectra clearly reveal exchange processes within G(ln τ), i.e. the dynamical heterogeneities are transient. It is assumed that these exchange processes are caused by translational hopping in an essentially rigid matrix. In the case of the glass former in the zeolite no evidence for exchange processes within G(ln τ) is found by NMR spectroscopy.

The Permittivity and AC Conductivity of the Layered Perovskite [(CH3)(C6H5)3P]2HgI4

The dielectric permittivity and ac conductivity of bis-(Methyltriphenyl-phosphonium)2 tetraiodomercurate (II), [(CH3)(C6H5)3P]2HgI4, has been measured in at 300-400 K and 0.11-20 kHz. The frequency dependent conductivity is interpreted in terms of the jump relaxation model, where translational and reorientational hopping takes place. The conductivity results were fitted to the law σ = σ0 + A1 (T)ωs + A2 (T) ωr, with s &lt; 1 and r &lt; 2. The temperature dependence of the conductivity was fitted to two relaxation processes. The activation energies ΔE1 and ΔE2 are frequency dependent and lie in the ranges of 0.8 eV and 0.2 eV. ΔE1 is associated with translational long range hopping while, DE2 is associated with localized and/or reorientational hopping. PACS Nos. 76, 77.

Nonsense-mediated decay mutants do not affect programmed -1 frameshifting.

Sequences in certain mRNAs program the ribosome to undergo a noncanonical translation event, translational frameshifting, translational hopping, or termination readthrough. These sequences are termed recoding sites, because they cause the ribosome to change temporarily its coding rules. Cis and trans-acting factors sensitively modulate the efficiency of recoding events. In an attempt to quantitate the effect of these factors we have developed a dual-reporter vector using the lacZ and luc genes to directly measure recoding efficiency. We were able to confirm the effect of several factors that modulate frameshift or readthrough efficiency at a variety of sites. Surprisingly, we were not able to confirm that the complex of factors termed the surveillance complex regulates translational frameshifting. This complex regulates degradation of nonsense codon-containing mRNAs and we confirm that it also affects the efficiency of nonsense suppression. Our data suggest that the surveillance complex is not a general regulator of translational accuracy, but that its role is closely tied to the translational termination and initiation processes.

Proton mobility in H-ZSM5 studied by impedance spectroscopy

The electrical properties of dehydrated zeolite H-ZSM5 with different SiO 2/Al 2O 3 ratios (30, 50, 80, 150, 280, and 1000) were examined by complex impedance spectroscopy. We determined the activation energy for proton relaxation, which depends on the spatial distance of the aluminum sites. Classical hopping theory as well as Debye–Hückel theory are in agreement with the experimental data implying that the relaxation originates from translational proton hopping instead of local reorientational motion, as assumed from 1H-MAS-NMR as well as from quantum-chemical calculations.

Global analysis of genomic texts: the distribution of AGCT tetranucleotides in the Escherichia coli and Bacillus subtilis genomes predicts translational frameshifting and ribosomal hopping in several genes.

Present availability of the genomic text of bacteria allows assignment of biological known functions to many genes (typically, half of the genome's gene content). It is now time to try and predict new unexpected functions, using inductive procedures that allow correlating the content of the genomic text to possible biological functions. We show here that analysis of the genomes of Escherichia coli and Bacillus subtilis for the distribution of AGCT motifs predicts that genes exist for which the mRNA molecule can be translated as several different proteins synthesized after ribosomal frameshifting or hopping. Among these genes we found that several coded for the same function in E. coli and B. subtilis. We analyzed in depth the situation of the infB gene (experimentally known to specify synthesis of several proteins differing in their translation starts), the aceF/pdhC gene, the eno gene, and the rplI gene. In addition, genes specific to E. coli were also studied: ompA, ompFand tolA (predicting epigenetic variation that could help escape infection by phages or colicins).

Ionic conduction in silver phosphate glasses doped with silver sulphide

Abstract The dielectric properties of (Ag2S) x ( AgPO3)1‐x and AgPO3 ionic glasses have been investigated at low frequencies (10 Hz‐10 MHz) by complex impedance measurements in the temperature range between 20 and 330 K and at microwave frequencies (8.2–18 GHz) using a waveguide transmission line and also a cavity resonator at 9 GHz from 77 to 300 K. Analysis on the basis of the jump relaxation model has shown that translational and reorientational hopping motions of mobile Ag+ ions are responsible for the observed frequency‐dependent ac conductivity. The temperature dependence of the ac conductivity at fixed frequencies can be fitted using three relaxation processes with characteristic activation energies which differ from each other by an order of magnitude and are closely similar to those obtained from previous ultrasonic attenuation studies on the same glasses. The highest energy (about 0–4 eV) has been associated with the translational hopping motion, responsible for the long‐range ionic diffusion through the glasses in the low‐frequency limit. The smallest activation energy (about 10 meV) has been ascribed to the topological disorder characteristic of glassy materials and probably corresponds to ion hopping between nearly energetically equivalent available sites. The intermediate energy values (0.05–0.1 eV), which depend on the concentration of the modifier, are likely to characterize different reorientational motion and/or different jump lengths.

High-Frequency Conductivity Plateau and Ionic Hopping Processes in a Ternary Lithium Borate Glass

Complete conductivity spectra of a lithium ion conducting glass of composition B2O3-0.56Li2O - 0.45 LiBr have been taken at twelve temperatures from 173 K to 573 K, covering the frequency range from a few Hertz up to about 50 THz. For the first time, a separation of the hopping and vibrational contributions to the spectra has been performed. The resulting frequency dependent hopping conductivity displays a high-frequency plateau similar to those known to exist in crystalline solid electrolytes like RbAg4I5 and Na-β-alumina. In the dispersive regime of the conductivity, there is an increase of the apparent power-law exponent from p = 0.6 to q = 1.3. The spectra are evaluated by combined application of the jump relaxation model and the dynamic structure model. Besides the translational hopping of the lithium ions via the preferred Ā sites, more localized kinds of motion are also detected, viz., hops into the less favoured C̄ sites (and mostly back again) as well as smaller displacements of the ions within their local environment.

Dielectric response of some solid electrolytes at low and high frequencies

Abstract Dielectric properties of (Ag2SO4) x (AgPO3)1−x glasses have been investigated by impedance measurements at low frequencies (1 Hz to 106Hz) and at high frequencies (8·2 GHz to 18 GHz) by waveguide measurements. The frequency dependence of the a.c. conductivity has been interpreted in terms of translational and reorientational ionic hopping motions. The activation energy values extracted from the temperature dependence of fixed frequency a.c. conductivity values agree with the values of the acoustic attenuation.

Ion dynamics in glass-forming systems: I. Conductivity spectra below the glass transformation temperature

Abstract Complete conductivity spectra of a lithium ion-conducting glass of composition B2O3-0·56Li2O-0·45LiBr have been taken at twelve temperatures, covering the frequency range from a few hertz to about 50THz. For the first time, a separation of the hopping and vibrational contributions to the spectra has been performed. The resulting frequency-dependent hopping conductivity displays a high-frequency plateau similar to those known to exist in crystalline solid electrolytes such as RbAg4I5 and Na-β-alumina. In its dispersive regime, the hopping conductivity is empirically decomposed into Jonscher and non-Jonscher contributions of different activation energies. Apart from the ‘new universality’ component, which is still unexplained, the other constituents are interpreted in terms of translational and localized hopping processes.

Frequency Dependent Electrical Properties of Ferroelectric Ba0.8Sr0.2TiO3 Thin Film

The frequency dependent electrical parameters, such as impedance, electric modulus, dielectric constant and AC conductivity for ferroelectric Ba0.8Sr0.2TiO3 thin film have been investigated within the range of 1 Hz and 106 Hz at room temperature. Z* plane shows two regions corresponding to the bulk mechanism and the distribution of the grain boundaries-electrodes process. M" versus frequency plot reveals a relaxation peak, which is not observed in the ε″ plot and it has been found that this peak is a non-Debye-type. The frequency dependent conductivity plot shows three regions of conduction processes, i. e., a low-frequency region due to DC conduction, a mid-frequency region due to translational hopping motions and a high-frequency region due to localized hopping and/or reorientational motion.http://dx.doi.org/10.5755/j01.ms.17.2.490