Materials Literature
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New organic compounds of positive dielectric anisotropy giving nematic liquid crystals at room temperature, either as the pure compounds or in admixture, are described. These materials are of improved stability, and function well in electro-optical devices based on the twisted-nematic or cholesteric-nematic phase-chan…
This letter cites previous work carried out on the method contained in Misell's (1973) letter, and points out accomplishments and problems that exist in connection with it.
Voids were produced in nickel by protons and Ni++ ions at 500°C. Methods for an accurate determination and quantitative description of the shape of voids are discussed. The voids thus produced in Ni are prominently cubo-octahedral with 100% truncation, or octahedral with partial {100} truncation, and occasionally cubi…
The lattice thermal conductivity in high-concentration harmonic isotopically disordered mixed crystals is calculated within the coherent-potential approximation from the appropriate Kubo formula using the energy current operators of Hardy. The infrared divergence in harmonic systems is eliminated by restriction to fin…
The Raman spectrum of LiO2 in argon matrices has been observed using 4880 Å excitation. The intraionic (O–O)− mode was observed as a sharp intense band at 1097 cm−1; the symmetric interionic (Li+–O2−) mode was recorded as a weaker broad feature at 694 cm−1. Oxygen-18 and lithium-6 substitution confirmed these vibratio…
$2s$ and $3s$ core-electron exchange splittings have been measured for a number of transition-metal compounds. It is found that the $2s$ splittings agree roughly with values from Hartree-Fock calculations, whereas measured $3s$ splittings are smaller by about a factor of 2. This discrepancy is tentatively linked to co…
A deep-defect level in a semiconductor is simulated by a cluster of host atoms surrounding the defect. The system is then treated as a "large molecule," the energy levels and wave functions for the entire cluster being obtained using molecular-orbital techniques. As examples, the substitutional nitrogen-atom impurity…
The amino acid L-tyrosine (C9H11NO3) and its salt L-tyrosine hydrochloride (C9H11NO3·HCl) crystallize respectively in the space groups P212121, a=6.913(3) Å, b=21.118(10) Å, c=5.832(3) Å, and P21, a=11.083(5) Å, b=9.041(4) Å, c=5.099(3) Å, β=91.82(3) Å. Both structures have been refined by neutron diffraction techniqu…
Dispersion curves for lattice vibrations propagating along the five major symmetry directions in a single crystal of rubidium have been measured using inelastic neutron scattering. Care has been taken to identify spurious peaks in the neutron groups and to correct for effects of instrumental resolution. The results, a…
We have been able to extend the dielectric theory of ionicity to include such $d$-electron systems as the noble-metal halides (e.g., CuCl, AgBr, etc.), $AB$ transition-metal compounds (e.g., ScN, MnS, FeO, NiO, etc.), ${A}_{m}{B}_{n}$ crystals (e.g., Zr${\mathrm{F}}_{4}$, Ti${\mathrm{O}}_{2}$, ${\mathrm{Cr}}_{2}$${\ma…
A simple localized-bond-charge model for the calculation of nonlinear optical susceptibilities is presented. We find that there are three important contributions to the nonlinearity, namely, the bond ionicity, the difference in atomic radii of the bonded atoms, and $d$-electron contributions. By including these effect…
The small signal Raman gain in a single-mode glass waveguide amplifier has been measured directly. The measured gain is in good agreement with that calculated from the Raman cross section. The cross section was determined by a comparison of the spontaneous Raman scattering of fused quartz and benzene.
The isobaric temperature dependence of the low frequency dielectric response of KTaO 3 and SrTiO 3 is reported for the range 2-300 K together with its isothermal pressure dependence for hydrostatic pressures up to 12 kbar in the range 77-300 K. The results are used to show that the paraelectric phase of these material…
The electro-optic properties of a new room-temperature positive-dielectric-anisotropy nematic liquid crystal are described. Devices based on the twisted nematic and phase-change effects are shown to operate at very low voltages.
Abstract A direct electron microscope study has been made of defect clusters produced in alkali halides by ionizing radiation. A technique has been developed for preparing foils of alkali halide crystals less than a few hundred nanometres thick for observation in the microscope, and a liquid helium cooled stage allows…
The infrared spectra of lithium isocyanide and of sodium and potassium cyanides in the solid phase were examined over the range 4000 to 140 cm −1 at room temperature. A study of the effect of cooling the solids to liquid nitrogen temperature has been carried out.
On the basis of polarization arguments, the equality τd=τl is proposed as the critical condition for the threshold point of chalcogenide glass switches, τd being the dielectric relaxation time and τl the carrier lifetime. It is shown that this switching criterion is in good agreement with measurements and that it expl…
Abstract Das Mössbauer‐Spektrum von 119 Sn in Sn 2 O 3 zeigt, daß in dieser Verbindung zwei‐ und vierwertiges Zinn vorliegen. Die verhältnismäßig große Quadrupolaufspaltung des Zinn(II) weist auf eine niedrige Symmetrie der ersten Koordinationssphäre hin, während sich Zinn(IV) in ähnlicher Umgebung wie im SnO 2 befind…
It is shown that the electric-field-induced cholesteric-nematic phase transition of mixed liquid crystal possesses two important properties; (i) a sharp threshold in the scattering- vs. -voltage characteristic and (ii) an electrically controllable relaxation time. The mixed liquid crystal is composed of p- n -butoxybe…
The general problem of which insulator configuration is best for gas-insulated systems is considered. A smooth disc is compared with both a corrugated disc and a cone and the cone is seen to have considerable potential. Impulse and switching surge voltages are more severe than 60 Hz when contamination is present on th…