Li<Superscript>+</Superscript> ion conductivity and transport properties of LiYP<Subscript>2</Subscript>O<Subscript>7</Subscript> compound

A lithium yttrium diphosphate LiYP₂O₇ was prepared by a solid-state reaction method. Rietveld refinement of the X-ray diffraction pattern suggests the formation of the single phase desired compound with monoclinic structure at room temperature. The infrared and Raman spectrum of this compound was interpreted on the basis of P₂O₇ ^4? vibrations. The AC conductivity was measured in the frequency range from 100 to 10⁶ Hz and temperatures between 473 and 673 K using impedance spectroscopy technique. The obtained results were analyzed by fitting the experimental data to the equivalent circuit model. The Cole–Cole diagram determined complex impedance for different temperatures. The angular frequency dependence of the AC conductivity is found to obey Jonscher’s relation. The temperature dependence of σ _AC could be described in terms of Arrhenius relation with two activation energies, 0.87 eV in region I and 1.36 eV in region II. The study of temperature variation of the exponent(s) reveals two conduction models: the AC conduction dependence upon temperature is governed by the correlated barrier hopping (CBH) model in region I (T < 540 K) and non-overlapping small polaron tunneling (NSPT) model in region II (T > 540 K). The near value of activation energies obtained from the equivalent circuit and DC conductivity confirms that the transport is through ion hopping mechanism dominated by the motion of the Li⁺ ion in the structure of the investigated material.     

Acoustic study of adsorbed liquid layers

Interference measurements of small variations in the velocity and attenuation of surface acoustic waves (SAWs) are used to investigate water layers up to 15 nm thick adsorbed on the surface of a lithium niobate crystal. The frequency dependence of the relative variation of the SAW velocity with the adsorption of water vapor is measured in the range from 40 to 400 MHz. Acoustic techniques are used to experimentally estimate the frequency dependence of the dielectric constant of adsorbed water and its dipole relaxation frequency along with the dependence of the adsorption layer thickness on the water vapor pressure in the surrounding medium. A simple expression is proposed for calculating the dispersion of the SAW velocity in a solid loaded with a thin liquid layer.     

Electrical conduction and polarization in PbWO<Subscript>4</Subscript> crystals

The regularities of ion-electron processes in an undoped PbWO₄ single crystal upon transition to a quasi-equilibrium state in an external dc electric field with a linear variation in the temperature in the range 290–600 K are investigated using different methods. The total conductivity, thermally stimulated polarization current, and thermally stimulated depolarization current are measured. It is assumed that the temperature dependence of the conductivity can be described within the theory of small-radius polarons. The thermally stimulated polarization (depolarization) currents are interpreted in terms of the space-charge (peaks of the current in the range 400–550 K) and dipole (peaks of the current in the range 290–370 K) mechanisms of generation of a polarization charge in the sample. The inference is drawn that the dominant contribution to the dipole polarization is made by dipolons, namely, doubly charged (cation-anion) vacancy pairs coupled through electrostatic interaction. The basic parameters of relaxation phenomena and charge transfer are calculated.     

The evolution of the molecular relaxation parameters described by the Cole–Cole model at the isotropic-nematic phase transition*

This paper presents the dielectric properties of the isotropic liquid and nematic phase at the phase transition. One strong molecular relaxation is observed in both phases. It is interpreted as related to the relaxation around a short molecular axis, due to the fact that molecules possess a strong longitudinal dipole moment. In the isotropic liquid the relaxation is described by the Debye model, while after entering the nematic phase (at cooling) relaxation becomes described by the Cole–Cole model. The distribution parameter of the Cole–Cole model changes from 0.05 (10 degrees above the temperature of the Iso-N transition) to 0.09 (exactly at the phase transition Iso-N), and finally, it reaches 0.35 (10 degrees below the Iso-N transition). Additionally, we observe that ion contribution to the dielectric response is not influenced by the phase transition. All relaxation parameters are discussed within the context of the phase transition phenomena.     

Angular resolved UV photoemission from ordered layers of carbon monoxide on a nickel(100) surface

Angular resolved UPS measurements have been performed on the (√2 × √2)R45° and compressed structures of the adsorption system CO/Ni(100). Due to the operation of dipole selection rules the dependence of normal exit photoemission on angle of photon incidence is found to be a sensitive probe of initial state symmetry. The polar angular dependence of emission from the 4σ orbital follows closely that predicted by Davenport, provided that a correction for refraction and total photoelectron current conservation is applied. Such polar angular dependences show band shifts indicative of dispersion effects, which become more marked at higher CO coverages. An azimuthal angular dependence of emission was not observed despite the presence of ordered adlayers.     

Selective response of DPPV/zeolite composites toward acetone,methanol, and n-heptane vapors

In this work, doped poly(p-phenylene vinylene)/zeolite composites was prepared to detect the three different chemical vapors (acetone, methanol, and n-heptane) and to investigate the effects of zeolite type, chemical vapor type, and vapor concentration based on the electrical conductivity response and selectivity properties of the sensing materials. Before blending with PPV, zeolite Y (Si/Al?=?5.1 and Na⁺), mordenite (Si/Al?=?18 and Na⁺), and 5A (LTA) (Si/Al?=?1.0 and Na⁺) were ion exchanged with Cu²⁺ at 80 % ion exchanged to prepare 80CuNaY, 80CuNaMOR, and 80CuNa5A. 80CuNaY exhibited the highest electrical conductivity response under acetone and methanol exposures while 80CuNaMOR showed the highest response in n-heptane exposure which depended on the adsorption and solubility properties of each porous material. When adding doped poly(p-phenylene vinylene) (dPPV) into the 80CuNaY matrix, the minimum detection vapor concentration decreased in acetone, methanol, and n-heptane vapors. For the selectivity, the composite between 80CuNaY and dPPV responded only in the polar vapors (acetone, methanol) whereas the composite between dPPV and 80CuNaMOR or dPPV_[90]80CuNaMOR responded only in the nonpolar vapor (n-heptane). The interactions between the sensing materials and the chemical vapors were investigated and identified by FTIR and AFM techniques.     

Contact potential measurements on “clean” CdS surfaces

Contact potential difference (cpd) measurements were carried out on {112&#x0304;} surfaces of high conductivity CdS cleaved in ultrahigh vacuum. A modified Kelvin method was employed. A change in cpd upon illumination with white light (surface photovoltage) was observed, indicating the presence of intrinsic surface states in these surfaces. Long exposure (about 24 hr) to water vapor (2 × 10⁻⁸ torr) caused an increase of about 1.0 V in cpd and a reduction in surface photovoltage. This increase in cpd was attributed primarily to a decrease in the electron affinity of the surfaces brought about by the molecular dipole moment of physically adsorbed water molecules. The “clean” surfaces exhibited no appreciable affinitity for spectroscopically pure oxygen, except under white light illumination apparently due to the increase of the density free electrons at the surface.     

Ionic conduction and dielectric relaxation in polycrystalline Na2SO4

In the present paper, the ionic conductivity and the dielectric relaxation properties of Na₂SO₄ have been investigated by means of impedance spectroscopy measurements over wide ranges of frequencies and temperatures. The frequency dependent impedance data has been modeled by appropriate equivalent circuit representing the bulk and grain boundary properties of the sample. Phase transition temperatures and the activation energies of conduction in different phases have been determined from the temperature dependence of the dc conductivity. Dielectric relaxation has been studied using the complex electric modulus and permittivity formalisms. From the electric modulus formalism it is concluded that the relaxation mechanism is independent of temperature. The dielectric permittivity spectra were analyzed by the Cole–Cole formula where different parameters are determined.     

Influence of a polar ambient medium on multiphoton resonances in dipole molecules

The influence of fluctuations of a polar ambient medium on multiphoton resonances in dipole molecules interacting with an external electromagnetic field is studied. It is shown that the electric fields created by the fluctuating dipole moments of the medium strongly influence the fulfillment of the multiphoton resonance conditions. Cases of slow and fast fluctuations of the polar ambient medium are considered separately. It is established that the temperature dependence of the multiphoton resonance probability is non-Arrhenius because of the influence of the fluctuations on the profile of the potential barrier. For fast fluctuations it is predicted that the rate of the multiphoton transition will decrease as the intensity of the fluctuations of the polar ambient medium increases.     

Structural and AC conductivity study of CdTe nanomaterials

Cadmium telluride (CdTe) nanomaterials have been synthesized by soft chemical route using mercapto ethanol as a capping agent. Crystallization temperature of the sample is investigated using differential scanning calorimeter. X-ray diffraction and transmission electron microscope measurements show that the prepared sample belongs to cubic structure with the average particle size of 20 nm. Impedance spectroscopy is applied to investigate the dielectric relaxation of the sample in a temperature range from 313 to 593 K and in a frequency range from 42 Hz to 1.1 MHz. The complex impedance plane plot has been analyzed by an equivalent circuit consisting of two serially connected R-CPE units, each containing a resistance (R) and a constant phase element (CPE). Dielectric relaxation peaks are observed in the imaginary parts of the spectra. The frequency dependence of real and imaginary parts of dielectric permittivity is analyzed using modified Cole–Cole equation. The temperature dependence relaxation time is found to obey the Arrhenius law having activation energy ~0.704 eV. The frequency dependent conductivity spectra are found to follow the power law. The frequency dependence ac conductivity is analyzed by power law.     

Thermal conductivity of refrigerant R-415A in the vapor phase

Thermal conductivity of refrigerant R-415A in the vapor phase has been studied by the steady-state method of coaxial cylinders in the range of temperatures 308–415 K and pressures 0.12–1.68 MPa. The approximation dependence of thermal conductivity on pressure and temperature was determined. Thermal conductivity on the dew line and in the ideal gas state was calculated.     

Time dependence of the dipole moment of the <Emphasis Type="Italic">S</Emphasis><Subscript>1</Subscript> electronic state in molecules with charge transfer

It is shown that the time dependence of the dipole moment μ(t) of molecules with charge transfer can be determined on the basis of the correlation functions found from processing of the instantaneous spontaneous emission spectra of the molecules. The time dependence calculated for a solution of dimethylaminobenzonitrile molecules shows that, during the lifetime of an excited electronic state, the dipole moment changes from 9.3 ± 0.7 to 15.7 ± 0.7 D, with the most significant change occurring in the initial, quick, range of the correlation function.     

Electrical properties of MWCNT-composite (Se80Te20)100−xAgx (0 ≤ x ≤ 4) chalcogenide glasses

This article describes the preparation of multi-walled carbon nanotube (MWCNT) chalcogenide glass composite by the melt-quenching technique. MWCNT composite (Se₈₀Te₂₀)_100?xAg_x (0 ≤ x ≤ 4) bulk samples are characterized by the XRD, SEM and EDX. The electrical measurements were carried out in the temperature range of the 308-388 K. Cole–Cole plot has been used to determine the electrical conductivity at room temperature. It has been observed that MWCNT chalcogenide composite have higher value of electrical conductivity than pure glass. The results have been discussed on the basis of increased ionic conductivity (Ag⁺ ions) in MWCNT doped (Se₈₀Te₂₀)_100?xAg_x (0 ≤ x ≤ 4) bulk samples.     

Effect of reversible adsorption on the magnetic properties of iron garnet films

The reversible change in the domain structure and the magnetic domain width in bismuth-containing iron garnet films with an easy magnetization axis oriented normal to their surface during adsorption caused by hydrogen bonds is studied by a magnetooptical method. The dependence of the domain width on the vapor pressure of methyl alcohol or water in a cell with a sample is determined, and the time dependence of the domain width induced by the adsorption-desorption processes occurring between methyl alcohol molecules or water molecules on the film surface is studied. A model is proposed to explain the detected effects.     

Flexoelectric effect modelling

A statistical theory of dipole flexoelectric (FE) polarization in liquid crystals is used to calculate temperature dependence of order parameters, elastic constants and FE coefficients. Two systems with polar wedge-shaped and banana-shaped molecules are investigated. In both cases, the FE coefficients are proportional to the dipole moment component parallel to the molecule symmetry axis. It results from the symmetries of interactions and of the Mayer function. The origin of the FE effect and microscopic pictures of the distorted phases are discussed.     

Very Low Frequency Far-Infrared Spectra of Mixtures of Dioxan with the Halogens and Related Molecules

Abstract

There has been considerable interest recently in the study of the submillimetre (or very far-infrared) absorption shown by both polar^1–4 and non-polar molecules.^2,5–8 Such absorption, in the ～5–100 cm^?1 region, for non-polar molecules is thought^2,6 to be caused by fluctuating dipoles associated with classical quadrupole-induced dipole interactions (in general multipole-induced dipole interactions). These effects are said to be “collision-induced” and can be thought of as being due to “collision” complexes in the liquid phase. For polar molecules the absorption is now thought^1–4 to be due to libration of the dipole in a “cage” of surrounding molecules (either molecules of the same species or of solvent). This so-called Poley-Hill model^9,10 is not inconsistent with the idea^1,2 of a residual rotation of the molecular dipole in the liquid phase. This similarity is underlined by the fact that some simple polar molecules^11,12 have a liquid phase Poley-Hill absorption the general shape and position of which follow quite closely that of the pressure broadened, gas phase spectrum. Our interest in the far-infrared region stems from our studies on halogen complexes with various n and bπ donors.^13,14 The pyridine-I₂ system (in cyclohexane) for example shows two bands in the far in frared not present in either component. The band at -183 cm is thought to be the stretching mode of the iodine, perturbed in the complex. The band at ～96 cm to the v(1-I) band, has so far been interpreted molecular″ stretching modebetween donor and acceptor, v(D-A).     

Structure and dielectric properties of polar fluids with extended dipoles: results from numerical simulations

The strengths and shortcomings of the point dipole model for polar fluids of spherical molecules are illustrated by considering the physically more relevant case of extended dipoles formed by two opposite charges ±?q separated by a distance d (dipole moment μ=qd). Extensive molecular dynamics simulations on a high-density dipolar fluid are used to analyse the dependence of the pair structure, dielectric constant ε and dynamics as a function of the ratio d/σ (σ is the molecular diameter), for a fixed dipole moment μ. The point dipole model is found to agree well with the extended dipole model up to d/σ ? 0.3. Beyond that ratio, ε shows a non-trivial variation with d/σ. When d/σ > 0.6, a transition is observed towards a hexagonal columnar phase; the corresponding value of the dipole moment is found to be substantially lower than the value of the point dipole required to drive a similar transition.     

The kaolinite (0 0 1) polar basal plane

Kaolinite is thought to be an efficient ice nucleating agent because kaolinite crystals expose perfect unreconstructed (0 0 1) basal surfaces which provide a suitable template for ice growth. However, we show here with the aid of density functional theory calculations that the unreconstructed basal surface is polar. Various mechanisms to eliminate the macroscopic dipole and in so-doing stabilize the basal surface are considered. The most promising option identified so far involves the adsorption of foreign atoms (for example, Na and Cl atoms) on the perfect basal surface, since this yields a non-metallic surface with a cleavage energy lower than the unreconstructed polar basal surface. A quantitative experimental structure determination of the kaolinite basal surface is called for.     

Optimisation of the dipole-Coulomb approximation for high-l Rydberg states of polar molecules

ABSTRACT

The present work deals with the question of the origin choice to get the maximal accuracy of the dipole-Coulomb approximation in the theory of molecular Rydberg states with high orbital momentum l. Concerning birefringence in polar molecules, the question of adequate origin choice has first been raised in the classical work by Buckingham & Longuet-Higgins in 1968, where it has been taken into account that the dipole moment of a polar molecular core (cation) depends on the origin choice. This dependence also leads to inseparability of dipole and quadrupole corrections to the Rydberg electron spectra in polar molecules. In the present work a new option for the problem is proposed as applied to the dipole-Coulomb approximation. Considering a simplified model of a molecular core as a system of N effective fixed point charges, we show both analytically and numerically that the optimal choice of origin, at least for a linear core, is the geometric centre of the core. On the other hand, results of the present work as well as previous publications show that the problem raised by Buckingham and Longuet-Higgins does not have a universal solution.

Abbreviations: RS: Rydberg state; RSs: Rydberg states; ZEKE: zero electron kinetic energy; MATI: mass-analysed threshold ionisation; QDT: quantum defect theory; DCA: dipole-Couloumb approximation; CD: centre of dipole; CC: centre of charge; GC: geometric centre; DCAGC: dipole-Couloumb approximation with origin in the geometric centre; DCACD: dipole-Couloumb approximation with origin in the centre of dipole