Szigeti Effective Charge Research Articles

Influence of Szigeti effective charge on coherent Raman scattering of laser radiation in magnetized direct gap semiconductors

By considering the hydrodynamic model of semiconductor-plasmas, an analytical investigation is performed to study the influence of Szigeti effective charge (qs) on coherent Raman scattering (CRS) of laser radiation in a transversely magnetized direct gap semiconductor arising from electron density perturbations and molecular vibrations of the medium both produced at the transverse optical phonon frequency. Assuming that the origin of CRS lies in the third-order susceptibility of the medium, an expression is obtained for Raman gain coefficient (gR). Numerical estimates are made for a representative n-type InSb crystal duly shined by pulsed 10.6 μm CO 2 laser. The threshold field (E0 th ) for inciting CRS is identified. The dependence of gR on pump field strength E0, externally applied magnetic field (in terms of electron cyclotron frequency ωc) and doping concentration (in terms of plasma frequency ωp) is reported for both cases viz., qs = 0 and qs ≠ 0. In absence of qs, the results are found to be well in agreement with available literature.

Dependence on geometry of coherent Raman-scattered Stokes mode in weakly polar magnetized semiconductors

Abstract Using electromagnetic treatment, a detailed analytical investigation is made of the coherent Raman scattering (CRS) of the Stokes component of scattered wave in an obliquely magnetized (with respect to the direction of propagation) weakly polar III–V semiconductor. The origin of the CRS process lies in the third-order nonlinear optical susceptibility arising from the induced nonlinear current density (due to finiteness of Szigeti effective charge and differential polarizability) and interaction of pump wave with the density fluctuation generated within the medium. The agreement in magnitude of the third-order Raman susceptibility between our calculated values and experimental as well as other theoretical values is found to be good. Using the coupled mode theory of plasmas the steady-state Raman gain coefficient is determined via the effective susceptibility. The results suggest that magnetic field enhances the CRS gain coefficient by a factor of three when cyclotron frequency is tuned to optical phonon frequency under moderate pump field strengths. For field strengths E0>108 V m−1, the contribution of effective charge is nearly wiped off and the Raman gain spectrum becomes dependent on differential polarizability only. The CRS gain coefficient increases with increasing scattering angle and results in a maximum value for the backscattered mode. The backward Raman gain is found to be nearly 104 times larger than forward gain. The analysis also suggests the possibility of observing optical phase conjugation via CRS in weakly polar III–V semiconductors subjected to an external magnetic field.

Deformation dipole and effective charge in rock-salt structure crystals

The study is done on the deformation dipole model. By the combined use of the self-consistent field treatment of the local density approximation and the spherical solid model, the numerical calculations are carried out for the dipole polarizability and the deformation dipole tensor of the ions in the rock-salt structure lithium halide crystals. The Szigeti effective charge is obtained from the deformation dipole tensor. The calculated results are compared with those in other alkali halide crystals. The ease of the cation migration is discussed in connection with the deformation dipole tensor of the counter anion.

Dipole and Deformation Dipole Polarization of Ions in Rock-Salt Structure Crystals

The comparative study is done on the dipole and deformation dipole polarization. With the local density approximation, the values of the dipole polarizability and the deformation dipole tensor of the ions in the rock-salt structure alkali iodide crystals are calculated. The Szigeti effective charge is obtained from the deformation dipole tensor. The crystalline potential is treated by the spherical solid model. The response to the perturbation is calculated by the self-consistent field potential. The calculated results are compared with those in other alkali halide crystals. The ease of the ionic migration is discussed by using the deformation dipole tensor.

Evidence for Ionic Bonding in YH3delta

The infrared transmission spectra of YH(3-delta) and YD(3-delta) thin films have been measured in the energy range from 300 to 6000 cm(-1), and the optical constants have been calculated by Kramers-Kronig analysis. From a fit of the frequency-dependent conductivity and the dielectric loss functions with one Drude term and five Lorentz oscillators, the longitudinal and transverse optical-phonon frequencies have been determined. The Born and Szigeti effective charges have been calculated and the ionicities of the ions in YH(3-delta) have been derived. We find that hydrogen does not enter as a proton in the compound, but that it is negatively charged, with a Szigeti effective charge of nearly 0.5e.

Evidence for Ionic Bonding in YH(3-delta).

The infrared transmission spectra of YH(3-delta) and YD(3-delta) thin films have been measured in the energy range from 300 to 6000 cm(-1), and the optical constants have been calculated by Kramers-Kronig analysis. From a fit of the frequency-dependent conductivity and the dielectric loss functions with one Drude term and five Lorentz oscillators, the longitudinal and transverse optical-phonon frequencies have been determined. The Born and Szigeti effective charges have been calculated and the ionicities of the ions in YH(3-delta) have been derived. We find that hydrogen does not enter as a proton in the compound, but that it is negatively charged, with a Szigeti effective charge of nearly 0.5e.

The effective bond charge in alkali halides — another manifestation of the crystals ionicity

The effective bond charge q eff, as determined from experimental values of the third-order optical susceptibility in alkali halides, is analyzed. The correlations of q eff with the ratio of the cation to anion radius, lattice constant and Szigeti effective charge are taken into account. The relationships between q eff and other parameters describing the ionicity show that the magnitude of q eff can be considered as one more parameter related to the ionicity of the crystals.

Relationship between bond charge and the Szigeti effective charge in alkali halides

The effective bond charge q eff , as related to experimental values of the third-order nonlinear optical susceptibility, is determined for some alkali halides within the bond polarizability interpretation of the Phillips-Van Vechten theory. It is shown that the charge decreases strongly for the more ionic alkali halides. Also, monotonic dependencies of q eff on other parameters which correlate with the crystal ionicity, like the Szigeti effective charge and the Sanderson partial charge, are found. The results obtained suggest that for alkali halides with the same cation, q eff is a linear function of the Phillips-Van Vechten ionicity.

Correlation among the transition and melting temperatures and dielectric parameters in some fast ionic conductors

Abstract Three correlationships are established among the optical dielectric constant e∞, Szigeti effective charge e∗s, transition temperature Tc, melting temperature Tm, and optical phonon frequency for many cubic fast ionic conductors. These relations suggest an intense influence of electronic energy state near the band gap to the origin of fast ionic conduction, dominant contribution of short-range or long-range forces to the mobile ion below Tc or to the cage ion above Tc. A curious temperature dependence for e∞ and e∗s values is also interpreted by considering anharmonic dynamical effective charge.

Correlation between Szigeti Effective Charge and Sanderson Partial Charge Values in Ionic Crystals

physica status solidi (b)Volume 168, Issue 2 p. K81-K83 Short Note Correlation between Szigeti Effective Charge and Sanderson Partial Charge Values in Ionic Crystals L. Bosi, L. Bosi Istituto di Fisica del Politecnico di Milano Search for more papers by this author L. Bosi, L. Bosi Istituto di Fisica del Politecnico di Milano Search for more papers by this author First published: 1 December 1991 https://doi.org/10.1002/pssb.2221680234Citations: 4 Piazza Leonardo da Vinci 32, I-20133 Milano, Italy. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume168, Issue21 December 1991Pages K81-K83 RelatedInformation

Dielectric Properties of Mixed Alkali and Silver Halide Crystals

AbstractThe static and optical dielectric constants are calculated for the entire range of composition in twelve systems of mixed crystals of alkali halides and silver halides with NaCl‐type structure, by adopting the method developed by Kamiyoshi and Nigara (KN). Transverse and longitudinal optical mode frequencies are also evaluated using the Lyddane‐Sachs‐Teller relation. Calculated values of static dielectric constants are found to exhibit a sharp non‐linear dependence on composition near the equi‐molar region in KClKBr, KClRbCl, KBrRbBr, KIRbI, RbClRbBr, and AgClAgBr mixed crystals and a slight non‐linear dependence on composition near the NaBr end in NaCl‐NaBr mixed crystals, which is in agreement with experimental data. The usefulness of dielectric constants and optical mode frequencies is demonstrated by investigating the composition dependence of the Szigeti effective charge parameter.

Pressure dependence of effective ionic charges in alkali halides

An estimation of the pressure dependence of the Szigeti effective ionic charge in alkali halides is presented. In the method the empirical connection between electronic and lattice ionicity proposed by Lawaetz is taken into account. The connection links e s ∗ with the ratio of Phillips' electronegativity difference and the plasma energy of a free-valence-electron gas. Changes in the dielectric electronegavity parameter are related to the photoelastic effect.

Effect of magnetic ordering on phonon parameters for infrared active modes in ferromagnetic spinel CdCr2S4

Infrared reflectivity spectra of sintered crystal CdCr2S4 have been measured in the temperature range of 15–300 K. The frequencies of transverse and longitudinal phonon modes were determined from the spectra with the Kramers–Kronig relation. The temperature dependencies of those showed anomalously large shifts near the Curie temperature. The shifts for two modes on the higher-energy side increase and those for other two modes decrease with temperature. These shifts are described well by the terms of spin-correlation function and concluded to be originated from the spin-dependent force constant. The mode dependence of shifts is explained qualitatively from the relation between the linkage of super-exchange interaction and the direction of vibration of the ion. The effects of magnetic ordering were also observed on Szigeti effective charge, optical and static dielectric constants, and phonon damping constants. These are discussed from the viewpoint of the red shift of the absorption edge.

Interaction Between Two Surface Excitations in Degenerate Polar Semiconductors

AbstractA systematic study of the interaction of surface plasmons with surface optical phonons is made for III–V group polar semiconductors to find the factors which can influence the coupling between the two modes of vibrations. It is found that the extent of coupling depends upon the Szigeti effective charge or the ionicity of the compound.

Pressure and temperature dependence of the static dielectric constants and elastic anomalies of ZnF2

The static dielectric constants εa and εc of ZnF2 have been studied in the range 4–296 °K at zero pressure and in the pressure range 0–5 kbar at 296, 195, and 78 °K. εa and εc exhibit normal temperature behavior. εc decreases with pressure as is normally the case. εa, on the other hand, exhibits an anomalous increase with pressure at room temperature. This anomalous increase is reduced with decreasing temperature and by 78 °K has completely disappeared. The pressure and temperature results are combined with thermal expansion and compressibility data to evaluate the pure volume and the pure temperature dependence of the dielectric constants. The dielectric constants are described by a Clausius–Mossotti relation. The Szigeti effective charge ratios have been determined for the transverse optical (TA) modes along the [100] and c axes. These ratios are found to be rather small, being 0.44 and 0.54 for the two axes, respectively, suggesting that the bonding is partially covalent. The principal components for the Gruneisen tensor have also been determined. Below 80 °K, they are negative. This is due to the negative mode-Gruneisen parameters of the transverse acoustic (TA) modes associated with the C44 and Cs elastic constants. The possible correlation between the pressure anomaly of εa and temperature anomaly of C44 is discussed and attributed to the instability of the chains of F− octahedra.

Hydrostatic pressure effects on TO–LO splitting and softening of infrared active phonons in α-quartz

Infrared spectra of crystalline α-quartz have been measured as a function of pressure up to 50.3 kbar. Pressure induced large frequency shifts, increase in TO–LO splittings and ‘‘softening’’ in various phonon bands have been observed. The pressure dependences of the mode Grüneisen parameters for selected phonons have been calculated. The results are discussed in terms of the pressure induced changes in crystal structure and Szigeti effective charge.

Effective charge of divalent lead: Application to the assignment of infrared modes in ferroelectric Pb5Ge3O11

A correlation between Szigeti effective charge and the electronic polarizability is found for the eight compounds containing divalent lead where experimental data are available. Results in Pb5Ge3O11 contribute to remove some ambiguity about the assignment of polar vibrational modes as external or internal to GeO4 and Ge2O7 entities in ferroelectric lead germanate. Complete TO-LO splittings are also deduced from infrared reflection spectra obtained at room temperature. Results are compared with previous controversial Raman measurements of the polar character of the modes including the soft mode.

Ratio of c/a of Wurtzite Type Crystals: Comparison of Keffer and Portis' Theory with Experiments

The ratio of c / a of five wurtzite type crystals are compared with the theory of Keffer and Portis under the hypothesis that the effective ionic charge equals the Szigeti effective charge. It is shown that the theory can explain reasonably the observation.

Empirical relationship between effective ionic charges and optical dielectric constants in binary and ternary cubic compounds

The effective ionic charge ${Z}^{*}e$ of each ion is determined within a narrow variable range for cubic and near-cubic ternary compounds. The Szigeti effective charge ${e}_{s}^{*}[=\frac{{3\sqrt{\ensuremath{\epsilon}}}_{\ensuremath{\propto}}{Z}^{*}e}{({\ensuremath{\epsilon}}_{\ensuremath{\propto}}+2)}]$ is also evaluated for the anion from the value ${Z}^{*}e$ by using the observed optical dielectric constant ${\ensuremath{\epsilon}}_{\ensuremath{\infty}}$. The correlation between ${e}_{s}^{*}$ and the dielectric constant ${\ensuremath{\epsilon}}_{\ensuremath{\infty}}$ is empirically found for many kinds of binary and ternary compounds as ${\ensuremath{\epsilon}}_{\ensuremath{\infty}}\ensuremath{-}1=\frac{2.0}{[(\frac{{e}_{s}^{*}}{{Z}_{\mathrm{eff}}e})+{(\frac{{e}_{s}^{*}}{{Z}_{\mathrm{eff}}e})}^{2}]}$. The value ${Z}_{\mathrm{eff}}$ indicates the effective chemical valency. In the correlation, the relatively large scatter for some compounds is explained by the $d$- or $f$-electron effect on the dielectric constant ${\ensuremath{\epsilon}}_{\ensuremath{\infty}}$, and by the screening and the anisotropic effects on the effective charge. From these results, the applicable ranges of the equation used and of the localized effective charge are discussed.

Analysis of the Dielectric Behaviour of Alkali Halide Crystals

AbstractAn analysis of the dielectric data at low temperature (2 K) and at room temperature (290 K) is performed for the entire family of NaCl and CsCl structure alkali halide crystals. The recent data on dielectric constants and their pressure and temperature derivatives are used to study the nature of some important physical quantities like the energy gap between bonding and anti‐bonding states, the Phillips‐van Vechten electronegativity parameter and the Szigeti effective charge parameter. Some interesting results are obtained using the Penn model for the electronic dielectric constant and the Lawaetz relation between electronegativity and effective charge parameters.