An electrostatic model of the BaTiO<Subscript>3</Subscript> cubic phase

Based on an analysis of the optical properties of barium titanate crystals in the paraelectric phase, the range of possible combinations of the values of effective charges and dipole electronic polarizability of Ba, Ti, and O ions at T = 573 K was found. The potential profile in the vicinity of positions of Ti ions is analyzed and shown to be multiminimum under certain conditions. The most likely directions of titanium ion displacements with respect to the central position are the [100], [010], and [001] axes.     

Interrelations between Interionic Separation,Lattice Energy,and Plasma Energy for Alkali Halide Crystals

A simple empirical relationship has been established for the estimation of lattice energies for alkli halide crystals directly from the values of interionic distances. Another new relation has also been proposed between the lattice energy and plasma energy. The calculated plasma energy values are utilized in the estimation of electronic polarizability in alkali halide crystals, in order to test the applicability of the proposed relations. Good agreement is observed between the computed and literature values of electronic polarizability. The merits of the present approach is discussed.     

Relationship between refractive index,optical electronegativities and electronic polarizability in alkali halides,III–V,II–VI group semiconductors

Refractive indices have been evaluated from DUFFY'S optical electronegativities. The validity of the proposed empirical relation has been tested in the case of II–Vi, III–V compound semiconductors and alkali halides by comparing the calculated values of n with those in the literature. The estimated refractive indices are used in Classius-Mossotti relation to evaluate electronic polarizabilities in the above compounds. The nature of the bonding in terms of Δχ and n is discussed. Good agreement is observed between the computed and literature values of electronic polarizability.     

Electrostatic model of the LiТаO<Subscript>3</Subscript> ferroelectric

Possible combinations of the electronic polarizability tensor components for oxygen and tantalum ions have been established based on the analysis of the refraction coefficients of LiТаO₃ crystal in the far-IR region. The local electric field on structurally nonequivalent ions in the LiТаO₃ unit cell was calculated within the modified point-multipole model. A combination of the electronic polarizability tensor components for oxygen and tantalum ions and their effective charges is established, which provides a good correspondence of the calculation results with the experimental data on LiТаO₃ crystals obtained by ⁷Li nuclear magnetic resonance and ¹⁸¹Та nuclear quadrupole resonance and with the known value of the crystal spontaneous polarization.     

Measurements of dc Kerr Constants for a Homologous Series of Nematic Compounds

The dc Kerr constants of seven p,p′-n-alkoxyazoxybenzene homologous compounds have been measured as functions of temperature in the isotropic phase. The observed pretransitional behavior near the isotropic-nematic transition is consistent with the phenomenological model of Landau-de Gennes with the Onsager's loal-field correction included in the dielectric tensor. The dc polarizability anisotropy and the average orientation of the permanent dipole with respect to the long molecular axis are deduced from the experimental results. Their variations with increase of methylene groups in the alkyl chains are discussed.     

Relationship between composition,density and refractive index for germania silica glasses

The density and the refractive index for various compositions of binary SiO₂GeO₂ glass prepared by a flame deposition technique, similar to that used to make low-loss optical waveguides, have been measured by standard Archimedes method and the Becke line method, respectively. The density as a function of composition is calculated considering the effective volume of the ions contained in the glass to be invariant. The refractive index as a function of composition is also calculated, based on the Lorenz-Lorenz equation, by computing the electronic polarizability of fused silica and germania. All calculated results are in good agreement with the observed data.     

Vibrational properties of As2S3 glass

Vibrational densities of states and infrared and Raman spectra have been calculated for a structural model of As₂S₃ glass. The calculations are based on simple semi-empirical forms for interatomic potentials, electric dipole moment and Raman polarizability. The bands of the calculated spectra agree well with those of the observed infrared and Raman spectra of As₂S₃ glass in intensity and position, although a small concentration of the wrong SS bonds remains in the structural model and causes an additional peak in the higher frequency region. The calculated depolarization ratio of the Raman spectra is consistent with the observed one.     

Raman scattering and nonlinear refractive index measurements of optical glasses

The absolute Stokes-Raman scattering cross section is measured for optical glasses of varying composition, from which the nuclear contribution to the nonlinear polarizability is determined. The nonlinearities increase progressively from fluoroberyllate compositions to fluorophosphate to phosphate to silicate and finally to heavy-metal oxide glasses. Although values of the total nonlinear polarizability vary by nearly two orders-of-magnitude it is determined that the ratio of the nuclear to the electronic contribution is nearly constant and is independent of the glass composition. The electrostrictive contribution to the nonlinear polarizability is also calculated using previously measured elasto-optic constants. Correlations in the atomic structure were determined by measuring the position of the lowest-frequency Raman scattering peak and it is found that the correlation length for pure one-component glasses is larger than multi-component glasses. Examination of the low-frequency scattering region shows that there is an 0xcess light-scattering below 30 cm^?1 in all glasses tested. This excess scattering in LaSF-7 was fitted between 2 to 20 cm^?1 to a Lorentzian centered at zero frequency with a halfwidth of 2.5 ± 1 cm^?1, while the fit in pure silica between 5 and 30 cm^?1 yields a halfwidth of 8 ± 3 cm^?1.     

Refractometry of TGS crystals doped with L-threonine impurity under uniaxial pressure

The temperature and spectral dependences of the refractive indices of triglycine sulphate (TGS) crystals doped with L-threonine impurity have been investigated. It is established that the introduction of an impurity weakens the temperature dependence of refractive indices. The electronic polarizability, refractions, and parameters of UV oscillators of mechanically deformed impurity crystals are calculated. The temperature coefficients of the phase transition shift are determined.     

Carbon nanocones: A variety of non-crystalline graphite

Previously known graphitic structures of conical shape – whiskers and helical cones – consist of a single wrapped graphene sheet, which gives a rather amorphous tip structure. Carbon nanocones, on the other hand, are nearly perfect sheets, curved by 1–5 pentagonal rings in the otherwise hexagonal network of carbon atoms. However, the resulting loss of periodicity implies electronic properties quite different from those of graphite and nanotubes. Experimental results have so far been limited by restricted access to sample material, but the cones have shown a unique capability of storing hydrogen gas reversibly at normal temperatures. The cones are characterized by large electrostatic dipole moments which will influence future experiments and technological applications. In this paper we study the interplay between topology, geometry and electronic properties, and investigate the magnitude of the dipole moments as a function of size and apex angle of the cones.     

Temperature coefficient of electronic polarizability in optical glasses

The temperature coefficient of refractive index dn/dT and that of volume expansion β have been measured by an interferometric procedure designed to determine the coefficients simultaneously, with one sample. The temperature coefficient of electronic polarizability φ have been calculated from dn/dT and β. φ is expressed as the sum of the contributions of each glass component, φ_i·φ_i is expressed as follows: φ_i = ß_iγ_i, where ß_i is the thermal change in cation-oxygen distance and γ_i is the change in electronic polarizability due to the inter-ionic distance change. φ_i decreases as the ionic field strength z/a² of the cation increases, which is the same tendency as that of ß_i. γ_i, calculated from φ_i and ß_i, gradually increases as z/a² increases. This means that φ_i is mainly determined by the elongation of the inter-ionic distance, and it also suggests that the deformation of the electron cloud of oxygen ion due to the inter-ionic distance change, γ_i becomes larger, as the electronic polarizing power of the cation increases.     

An Insight on the Polyacetylene Properties Through Resonant Raman Scattering Spectra Analysis

Resonant Raman Scattering spectra of trans polyace-tylene (CH)_X and (CD)_X are interpreted in terms of a model based on a bimodal distribution of conjugation length segments. Such a theory takes into account the electronic and lattice dynamics properties of different conjugation length segments, together with the electronic dipole moments from the transitions and the electron vibration interactions in the excited electronic states. This model accounts also for the Resonant Raman Scattering spectra taken during the isomerization process and from cis rich samples.     

Linear optical properties of BaNaB9O15, BaLiB9O15 and SrLiB9O15 glasses

Transparent BaNaB₉O₁₅ (BNBO), BaLiB₉O₁₅ (BLBO) and SrLiB₉O₁₅ (SLBO) glasses were fabricated via the conventional melt-quenching technique. X-ray diffraction (XRD) and Differential thermal analysis (DTA) studies carried out on the as-quenched glasses confirmed their amorphous and glassy nature, respectively. The optical properties for these as-quenched glasses were investigated. The refractive index, optical band gap, Urbach energy and Fermi energy were determined. The average electronic polarizability calculated from the refractive index expression.     

Diamagnetic and photoabsorption characterisation of gel‐grown cadmium oxalate single crystals

Perfect single crystals of cadmium oxalate trihydrate have been grown using the slow and controlled reaction between Cd⁺² and (C₂O₄)^‐2 ions in agar‐agar gel, resulting in the formation of insoluble product Cd(COO)₂.3H₂O. The optimum growth parameters have been determined. The variation of magnetic moment of the grown crystals under an applied static magnetic field is studied and the material is found to be diamagnetic. The polarizability is found sensitive to optical band gap. An empirical relation between magnetic susceptibility and electronic polarizability has been established. Optical absorption spectra of the sample recorded in the range 200‐2500 nm reveal transitions involving absorption and emission of phonons. The detailed study supports the existence of allowed direct and indirect allowed gaps in the material. The direct allowed transition prevails in the region of relatively higher photon energy. Some feeble disorder in the crystal is conceived to be present. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Temporal structure of X-ray pulses

The propagation of wave packets in media with polarizability frequency dispersion is analyzed based on asymptotic expansions.     

Molybdenum doping of semiconducting vanadium phosphate glasses

The DC conductivity and dielectric properties of glasses of composition (70 ? x) V₂O₅ : x MoO₃ : 30 P₂O₅ have been measured as a function of temperature and frequency for O × 5 mol %. An increase in conductivity by two orders of magnitude is observed for 1 mol % MoO₃ and this is correlated with changes in activation energy and dielectric constant. The results can be explained in terms of small polaron theory, with the main interaction being through the local electronic polarizability at any site. The results indicate that percolation considerations have to be taken into account in describing the electrical properties of transition metal glasses.     

Molecular Polarizabilities,Polarizability Anisotropies and Order Parameters of Nematic Liquid Crystals

Mean Molecular polarizabilities, polarizability anisotropies and order parameters are evaluated in members of three homologous series, using two theoretical models. The variation of polarizabilities and their anisotropies with number of carbon atoms in the alkyl chain is studied. The temperature dependence of order parameter is also presented. The results are compared with the reported values and the merits of the different models are discussed.     

Electronic redistribution around oxygen atoms in silicate melts by ab initio molecular dynamics simulation

The structure around oxygen atoms of four silicate liquids (silica, rhyolite, a model basalt and enstatite) is evaluated by ab initio molecular dynamics simulation. Thanks to the use of maximally localized Wannier orbitals to represent the electronic ground state of the simulated system, one is able to quantify the redistribution of electronic density around oxygen atoms as a function of the cationic environment and melt composition. It is shown that the structure of the melt in the immediate vicinity of the oxygen atoms modulates the distribution of the Wannier orbitals associated with oxygen atoms. In particular the evaluation of the distances between the oxygen-core and the orbital Wannier centers and their evolution with the nature of the cation indicates that the Al―O bond in silicate melts is certainly less covalent than the Si―O bond while for the series Mg―O, Ca―O, Na―O and K―O the covalent character of the M―O bond diminishes rapidly to the benefit of the ionic character. Furthermore it is found that the distribution of the oxygen dipole moment coming from the electronic polarization is only weakly dependent on the melt composition, a finding which could explain why some empirical force fields can exhibit a high degree of transferability with melt composition.     

Synthesis and characterization of cadmium tartrate single crystals

Efforts have been successful to crystallize the electroceramic compound of cadmium tartrate through silica hydrogel. Analysis of thermograms reveals decomposition of the crystals to take place within the temperature range 65 to 442°C in air atmosphere. Some important characteristic data, i.e., valance electron plasma energy, Penn gap, Fermi energy, interionic distance, electronic polarizability have been obtained. The DC conductivity of the crystal typically lies between the conductivities of metal and insulator and we derived several pertinent parameters such as hopping energy, hopping distance, coulomb gap, etc. The micromechanical indentation of the crystal shows nonlinear variation of the impact microhardness as a function of the applied load. The estimation of fracture toughness, fragility coefficient and yield strength has too been made for the synthesized crystal. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thermo-optical characterization of tellurite glasses by thermal lens,thermal relaxation calorimetry and interferometric methods

In this work the thermal lens, thermal relaxation calorimetry and interferometric methods are applied to investigate the thermo-optical properties of tellurite glasses (in mol%: 80TeO₂–20 Li₂O(TeLi), 80TeO₂–15Li₂O–5TiO₂ (TeLiTi-5) and 80TeO₂–10Li₂O–10TiO₂ (TeLiTi-10)). Thermal diffusivity, thermal conductivity, specific heat and the temperature coefficients of refractive index, optical path length, thermal expansion and electronic polarizability were determined. The use of three independent methods was useful for a complete characterization of the studied tellurite glasses. In addition, our results showed that the thermal expansion coefficient and the temperature coefficient of the optical path length (dS/dT) were significantly modified with the introduction of titanium, which may be relevant for the application of these glasses in the photonic area.