X-ray diffraction studies on dilute solid solution of NaCl with Ag impurities

Abstract

X-ray investigations of Bragg scattering measurements have been carried out on the dilute solid solutions of Ag _x Na_1?x Cl for x = 0.03 and 0.10. The integrated intensities are measured on spherical single crystals, using a home-built manual X-ray diffractometer. The analysis of experimental data indicates an enhancement of Debye-Waller factor in this system. The size effect distortion factors evaluated are compared with the calculated values on the basis of different theoretical models and the results are discussed. The measured cell constant and density data indicate the existence of vacancies in these crystals.     

Softening of phonon modes in C60 crystals induced by laser irradiation: Thermal effects

Reversible softening of the intramolecular A _g(2) pentagonal pinch (PP) mode of a C₆₀ single crystal in the face centered cubic phase has been studied as a function of laser power density by means of Raman scattering. The average temperature rise in the laser excitation spot has been determined using the Stokes to anti-Stokes integrated peak intensity ratio for the H _g(1) phonon mode. Softening of the PP-mode was found to be due to heating of the sample resulting from laser irradiation, in good quantitative agreement with experimental results obtained for uniformly heated samples. These findings are in excellent agreement with results obtained by numerical calculations of the local temperature distribution and average temperature in the laser spot based on calculated integrated intensities of the Stokes and anti-Stokes bands of the PP-mode. These calculations were based on experimental data for the temperature dependence of phonon frequency and width, absorbance, and thermal conductivity in solid C₆₀. Zh. éksp. Teor. Fiz. 114, 1785–1794 (November 1998) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor     

Nucleon momentum distributions and elastic electron scattering form factors for some 1p-shell nuclei

The nucleon momentum distributions (NMD) and elastic electron scattering form factors of the ground state for 1p-shell nuclei with Z?=?N (such as ⁶Li, ¹⁰B, ¹²C and ¹⁴N nuclei) have been calculated in the framework of the coherent density fluctuation model (CDFM) and expressed in terms of the weight function $\left| {f( x )} \right|^2$ . The weight function has been expressed in terms of nucleon density distribution (NDD) of the nuclei and determined from the theory and the experiment. The feature of the long-tail behaviour at high-momentum region of the NMDs has been obtained by both the theoretical and experimental weight functions. The experimental form factors F(q) of all the considered nuclei are very well reproduced by the present calculations for all values of momentum transfer q. It is found that the contributions of the quadrupole form factors F _C2(q) in ¹⁰B and ¹⁴N nuclei, which are described by the undeformed p-shell model, are essential for obtaining a remarkable agreement between the theoretical and experimental form factors.     

Intensity measurements on Σ-hyperonic and kaonic atoms

σ-hyperonic X-ray lines have been observed in 8 elements and their intensities as well as those of the accompaning kaonic X-ray lines have been determined. The σ-atomic cascade has been found to be similar to those of other exotic atoms. The production of σ^? hyperons per stoppedK ^? has been measured by comparing their X-ray intensities. For the first time the intensity attenuation due to the strong absorptive σN interaction could be measured in four cases, and simple optical model calculations have been performed in order to reproduce the data.     

K±p elastic scattering in the QCD inspired eikonalized model

Based on our previous study of the QCD inspired eikonalized model for describing vector meson photoproduction, pp, and $ \bar p $ \bar p p elastic scattering at high energies, we apply the mode to high energy K ^± p elastic scattering. The total cross section σ _tot(s), differential cross section dσ/dt, the ratio of the real part to imaginary part of the forward scattering amplitude ρ(s), and nuclear slope parameter function β(s) are calculated in the model. Our results show that the theoretical prediction for σ _tot(s) is in a good agreement with the experimental data within error bars of the data. For the other theoretical predictions there are no data to test the predictive power of the model. We need the corresponding experimental data to examinate the validity of our QCD inspired eikonalized model. However, our calculations clearly show that the Odderon exchange in the process makes a significant contribution to the observable of ρ(s) and β(s). Therefore, we may conclude that there is a good opportunity to find the QCD Odderon in the K ^± p elastic scattering at high energies.     

Phenomenological description of the microwave surface impedance and complex conductivity of high-T c single crystals

Measurements of the microwave surface impedance Z _s (T) = R _s (T) + iX _s (T) and the complex conductivity σ_s(T) in the ab-plane of high-quality high-T _c YBCO, BSCCO, TBCCO, and TBCO single crystals are analyzed. Experimental data of Z _s (T) and σ_s(T) are compared with calculations based on a modified two-fluid model that includes a temperature-dependent quasiparticle scattering and a unique temperature variation of the density of superconducting carriers. We describe the agreement and disagreement of our analysis with the salient features of the experimental data. We review the existing microscopic models based on unconventional symmetry types of the order parameter and on novel quasiparticle relaxation mechanisms.     

Multiple scattering investigation of the 1T-TaS2 surface termination

Multiple scattering theory based on a cluster model is used to simulate full hemispherical X-ray photoelectron diffraction measurements on a 1T-TaS₂(0001) surface. Key points to determine the surface termination are discussed. As the commonly applied single scattering simulations do not give satisfying results, a multiple scattering approach has to be used to accurately simulate the full hemispherical photoelectron diffraction patterns. Differences and similarities between calculations of Ta and S terminated surfaces are presented along with experimental results at room temperature using both, the single and the multiple scattering approaches. We find that the surface is S terminated and that the quantitative difference between the calculations for both terminations permits to show the limits of the single scattering approach for solving surface termination problems. Moreover, by generalizing the results obtained using the multiple scattering approach, we discuss the application of this method to other similar systems.     

Raman scattering studies of sodalite for crystal structure and coloration mechanism

Summary Group-theoretical study of the vibrational modes of chlorosodalite [Na₄Al₃(SiO₄)₃]₂ has been carried out for theT _d ¹ space group. The Raman-active modes are evaluated and comparison is made with the experimental results on sodalite. It is shown that the experimental Raman spectrum does not support the structure of sodalite to beT _d ¹ but confirms it to beT _d ¹ . Raman scattering studies were performed on X-ray irradiated As-grown single crystal of chloro-sodalite to identify the coloration mechanism. Enhancement of oxygen twisting and stretching mode intensities on X-ray irradiation indicates the formation of neutral sodium colloidal aggregate during the coloration process. The authors of this paper have agreed to not receive the proofs for correction.     

Finite dimensional representations of the quantum Lorentz group

All finite dimensional irreducible representations of the quantum Lorentz group SL _q (2,) are described explicitly and it is proved all finite dimensional representations of SL _q (2,) are completely reducible. The conjecture of Podle and Woronowicz will be answered affirmatively.     

Microscopic collective dynamics of atoms in the amorphous metallic alloy Ni33Zr67

The structural properties and microscopic collective dynamics of atoms in the amorphous metallic alloy Ni₃₃Zr₆₇ are studied using molecular dynamics simulations with a pair-additive model potential. The calculated equilibrium structural and dynamic characteristics are compared with experimental data on neutron diffraction and inelastic X-ray scattering. Theoretical analysis of the structural relaxation of microscopic density fluctuations for amorphous metallic alloys is performed within the Lee’s recurrent relation approach. The results of theoretical calculations for the intensity of scattering I(k, ω) for the amorphous metallic alloy Ni₃₃Zr₆₇ are in good agreement with the results of computer simulation and experimental inelastic X-ray scattering data. The low-frequency excitations observed in the longitudinal current spectra are related to the vibrational motions of individual atom clusters, which include Ni and Zr atoms.     

Saturation of Coulomb sum rules in the <Superscript>6</Superscript>Li case

The Coulomb sums S _L(q) of the ⁶Li nucleus have been obtained from electron scattering measurements at 3-momentum transfers q = 1.125–1.625 fm⁻¹. It is found that at q > 1.35 fm⁻¹ the Coulomb sum of the nucleus becomes saturated: S _L(q) = 1 .     

Anisotropy of electron-phonon interactions in alkali metals

Electron-phonon scattering in the solid alkalis is distinguished from that in most other metals by a combination of three circumstances: The phonon spectra and structure factors are very anisotropic, the Fermi surface in the reduced zone is simply connected and virtually spherical and important large momentum transfers (0.7<(q/2k _F)<1.0) fall within the first large peaks of the phonon structure factors. Anisotropy of microscopic contributions to the macroscopic coefficients is controlled by and is quite sensitive to values of electron-ion matrix elements at large momentum transfer, and can be explored by a realistic yet relatively simple theoretical calculation. A brief summary is presented of such calculations, for the all alkalies, of mean free paths, thermoelectric powers, and electron-phonon mass enhancements. The results show marked anisotropy only for lithium, are consonant with experimental low field Hall coefficients and in addition indicate strong anisotropy in the mass enhancement for lithium.     

Electron ionization rate in III–V ternary semiconductors

Theoretical calculations are presented for the ionization rate of electrons in III–V ternary semiconductor compounds considering alloy scattering and carrier-carrier interaction, in addition to optical phonon scattering and ionization scattering. However, alloy scattering is found to be a weak interaction. Fairly good agreement is obtained for Ga_1–x In _x As withx=0.14 and 0.53 with the experimental results and for Ga_0.5 Al_0.5 As with the existing theoretical result which used an indirect method. The alloy scattering potential has been taken in the form of energy band-gap difference. The calculations can be used for any ternary semi-conductor.     

The concentration dependence of the proton chemical shift and the deuterium quadrupole coupling parameter for binary solutions of ethanol

Concentration dependent experimental measurements of the ethanol hydroxyl proton chemical shift σ_H for binary solutions were carried out. The solvents used were carbon tetrachloride (CCl₄), benzene, chloroform, acetonitrile, acetone and dimethylsulphoxide (DMSO). The chemical shift values range from 0.69 ppm (relative to TMS) for dilute ethanol (extrapolated to infinite dilution) in CCl₄ to 5.34 ppm for neat liquid ethanol. Ab initio calculations of the ethanol-solvent hydrogen bond energies show a correlation with the values for the chemical shift. The hydrogen bond energies for ethanol-solvent dimers range from 0.63 kcal mol^?1 for ethanol-CCl₄ to 9.34 kcal mol^?1 for ethanol-DMSO. Theoretical calculations show a linear correlation between the deuterium quadrupole coupling parameter XD ^ar d the isotropic proton chemical shift σ_H: X_D(kHz) = 291.48 ? 14.96 σ_H, where σ_H is the proton chemical shift in ppm relative to TMS (R ² = 0.99). Using the concentration dependent chemical shift data and this equation, X_D ia observed to range from 280 kHz for very dilute concentrations in CCl₄, where the primary species is ethanol monomer, to 210 kHz for the neat liquid that is comprised primarily of cyclic pentamers.     

Nucleon form factors of the isovector axial-vector current

The theoretical and experimental status of the isovector axial-vector current form factors G _A(q ²) and G _P(q ²) of the nucleon is reviewed. We also describe a new calculation of these form factors in manifestly Lorentz-invariant chiral perturbation theory (ChPT) with the inclusion of axial-vector mesons as explicit degrees of freedom.     

Three-dimensional nuclear dynamics in the quantized ATDHF approach

The quantized adiabatic time-dependent Hartree-Fock theory is numerically applied to the low energy large amplitude collective dynamics of heavy ion systems ranging from α + α to ¹⁶O + ¹⁶O. The problem is reduced to three successive steps. First, for the lowest mode the optimal, i.e., maximally decoupled, collective path {φ_q} is evaluated by solving a coupled set of nonlinear differential equations for the single-particle wave functions _q^(a)(r) of φ_q, depending on the collective coordinate q and three spatial coordinates. A density-dependent interaction with a direct finite range Yukawa-term is employed and three-dimensional coordinate- and momentum-grid techniques are used, including fast Fourier methods. In a second step the quantized collective Hamiltonian H_c(q, d/dq) is extracted from {φ_q} by means of generator coordinate techniques involving, besides q, a conjugate variable p. Starting from {φ} this procedure includes the numerical evaluation of the classical potential, (q), of the intertia parameter, (q), of the quantum corrections with regard to rotation, translation and collective q-motion, (q), and of the centrifugal potential. The third step consists of actually calculating the subbarrier fusion cross section by means of WKB methods applied to the collective Hamiltonian H_c(q, d/dq). The theoretical numbers are compared with results from Hartree-Fock calculations with quadrupole constraint, and with experimental data. The microscopic aspects of the dynamics, the relation to other theories, and the practical and conceptual problems arising from the quantized ATDHF theory are discussed in detail.     

Experimental and theoretical Raman results in trans polyacetylene

We present here the experimental and theoretical calculations of Resonant Raman scattering from trans (CH)_x. The new experimental data obtained with U.V. exciting wavelengths are interpreted in terms of the theoretical model based on the bimodal statistical distribution of long and short chains which constitute a given trans (CH)_x sample.     

Comparisons of vector analyzing-power data and calculations for neutron-deuteron elastic scattering from 10 to 14 MeV

High-accuracy analyzing-powerA _y() data forn-d elastic scattering at 12 MeV have been measured using the polarized-neutron facilities at the Triangle Universities Nuclear Laboratory (TUNL). The present data have been combined with our previousn-d measurements at 10, 12, and 14.1 MeV to form the highest-accuracyA _y() data set forn-d elastic scattering below 20 MeV. These data are compared to recent Faddeev-based neutron-deuteron (n-d) calculations which use the Paris and Bonn equivalent separable potentials PEST and BEST, as well as Doleschall's representation of theP- andD-wave nucleon-nucleon interactions. None of these models adequately describe the data in the angular region around the maximum ofA _y(). Possible reasons for the discrepancies are discussed. The sensitivity of the present Faddeev-based calculations to various angular momentum components of the nucleon-nucleon interaction are examined.