Materials Literature
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CONTENTS I. Introduction 298 II. Contrast in the electron microscope, and methods of increasing the contrast 298 III. Structural studies of polymers using contrast intensification methods. Effect of contrast materials 303
Introduction 453 1. The Dynamic Approach to the Problem of Ferroelectricity 454 1.1. Lattice Dynamics and Stability of Non-piezoelectric Crystals 455 a) General Vibration Equations and the Condition of Structural Stability 455 b) Dielectric Properties of Crystals and Their Relation to the Characteristic Frequencies 45…
It is shown how the correct tensors for the description of the rigid-body motion of molecules in crystals can be obtained from a lattice dynamical calculation. This helps in understanding the tensor S introduced in the paper by Schomaker & Trueblood (Acta Cryst. (1968). B24, 63). An expression for the anisotropic temp…
Electron spin resonance (ESR) studies have been made of gamma-irradiated Nb2O5–Na2O–SiO2 glasses. The samples received a gamma-irradiation dose of 2 × 107 R at liquid-nitrogen temperature, and were investigated at that temperature. A broad spectrum which is characterized by an axially symmetric g tensor and hyperfine…
Spin reorientation due to change in sign of the temperature-dependent anisotropy energy has been studied in ${\mathrm{Mn}}_{2\ensuremath{-}x}{\mathrm{Cr}}_{x}\mathrm{Sb}$ ($x=0 \mathrm{and} 0.03$) by nuclear spin echo measurements. The behavior of the dipole and quadrupole hyperfine interactions and ${T}_{2}$ is repor…
Excitation and luminescence emission spectra of NaI(Tl) single crystals with high Tl content (>0.1 mole%) have been analyzed as a function of temperature and concentration. At high Tl concentrations, both single and dual Tl centers influence the optical properties of the crystal. We have found evidence that energy…
An investigation of some of the characteristics of the thallous double center (dimer) in NaI: Tl was carried out over the temperature range 15 to 300\ifmmode^\circ\else\textdegree\fi{}K and for thallium concentrations of 0.08 to 1.01 mole% Tl. A measurement of the lifetime of the dimer excited state resulted in a valu…
Relativistic augmented-plane-wave calculations for Gd, Dy, Er, and Lu are reported. Energy bands, histograms of the density of states, and Fermi-surface cross sections are given. The Fermi surfaces of Dy, Er, and Lu are found to be quite similar to the one given earlier for yttrium. The Fermi surface of Gd is found to…
19 F nuclear magnetic resonance signals of aqueous solutions containing beryllium and fluoride ions have been used to study the equilibrium and kinetic processes occurring. Detailed studies of line widths, intensities, chemical shifts, and coupling constants have been made. This leads to an equilibrium constant determ…
The fluorescence of phosphors NaLn1–xEuxTiO4(Ln = La, Gd, Y, Lu) with ordered Sr2TiO4 structure is reported. The unactivated host lattices show broad-band emission peaking at about 450 nm. The quenching temperature of this fluorescence is below room temperature. The relative intensities of the Eu3 + emission lines dep…
The crystal structure of Sc 2 O 3 (C-type; a 0 = 9.8459 ± 15 Å at 20 ± 2 °C) was refined from X-ray powder diffractometer data. Isotropic individual temperature factors were used in full-matrix F (19 reflections) and F 2 (41 reflections) programs. The positional parameters were determined as u(Sc) = −0.0355 ± 1, x(O)…
Raman scattering from crystalline NaNO3 has been observed in all polarization orientations. Except for small intensity contributions in some orientations which are probably due to depolarization effects in the birefringent crystal, the polarizability activities of both internal and external modes follow the expected s…
X-ray diffraction data at 25 and - 196\ifmmode^\circ\else\textdegree\fi{}C have been used to obtain radial distribution functions for amorphous and hexagonal selenium. The amorphous selenium exhibited strong correlation peaks at 2.34, 3.75, 5.8, 7.2, and 9.3 \AA{}, with minor peaks at 4.3, 4.7, 5.1, 7.7, 10.0, and 10.…
The absorption coefficient, reflectivity, and electroreflectance of SrTi${\mathrm{O}}_{3}$ in the neighborhood of the fundamental absorption edge are reported. The absorption coefficient shows an exponential rise with incident energy (Urbach rule) over five orders of magnitude. Its logarithm has a slope of $\frac{1}{\…
The frequency wave-vector dispersion relation for the normal modes of vibration of ${\mathrm{Li}}^{7}$F at 298\ifmmode^\circ\else\textdegree\fi{}K has been measured by means of slow-neutron inelastic scattering techniques. Triple-axis crystal spectrometers at two reactor facilities at the Oak Ridge National Laboratory…
A theoretical and experimental study was made of the shift in atomic core-electron binding energies caused by the chemical environment. Two models are presented to account for these “chemical shifts.” The first uses an energy cycle to break the core-electron binding energies into a free-ion contribution and a classica…
Abstract Bei Polyäthylen kann die senkrecht zur longitudinalen Lamellenoberfläche gemessene Kristalldimension l und damit der Schmelzpunkt der kristallinen Bereiche durch die Wahl der Kristallisationsbedingungen in weiten Grenzen variiert werden. Aus der nach der T HOMSON ‐Gleichung zu erwartenden und auch gefundenen…
The sharp-line spectrum of exchange-coupled chromium ion pairs has been investigated with the aid of piezospectroscopic techniques. The lines shift and split under stress in characteristic ways which permit positive identification of a principal fluorescent transition with each of the four nearest-neighbor pair types.…
The modified potassium dihydrogen phosphate (KDP) model of a two-dimensional ferroelectric with the inclusion of an arbitrary electric field $\mathcal{E}$ is considered. The nature of the phase transition is unaffected by the inclusion of an external field, whereas the transition temperature depends on $\mathcal{E}$ w…
Polarized Raman spectra of tetragonal BaTi${\mathrm{O}}_{3}$ have been obtained at room temperature with He-Ne laser excitation. Using several different crystallographic directions for the phonon wave vector q, most of the vibrational modes for q\ensuremath{\sim}0 have been classified using Raman data alone. Three pai…