Materials Literature
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This review discusses the physical properties of nematic, cholesteric, and smectic liquid crystals. Molecular theories of the liquid crystal phases are discussed and the molecular field theories of the phase transitions between the various liquid crystal phases are presented. The elastic theory and hydrodynamics of li…
We show core-electron energy spectra determined by means of (soft) x-ray photoelectron spectroscopy and appearance potential spectroscopy to be closely related for $2p$ electrons in iron and nickel. An earlier comparison for the first transition-series elements had indicated a systematic difference between appearance-…
In a new technique for studying electron collisions, the electrons are confined by electromagnetic fields and exposed to a known low density of atoms or molecules. Collisions rates are measured by electron diffusion in the trap. The use of spin-oriented atoms allows triplet and singlet contributions to be separated. R…
The dislocation velocity, , on prismatic planes of monocrystalline MgZn2 has been determined by etching as a function of applied stress, τ, chemical composition within the homogeneity range, and temperature, T, between 340 und 456°C. The results are interpreted in terms of a double kink mechanism, where
Doping processes of silicon carbide crystals with scandium are investigated. It is shown that the scandium solubility in SiC is limited within the 1800 to 2600°C temperature range and amounts to (2 to 3) × 1017 cm−3. On doping silicon carbide crystals with scandium the VLS growth mechanism is possible. The luminescenc…
Ionic force parameters for a soft sphere model have been derived from the known crystal structures and thermodynamic lattice energies of alkaline earth halides. Polarization of the chloride, bromide, and iodide ions has been taken into account by a simple shell-core model. The derived parameters are capable of reprodu…
The reflectivities of single crystals of Mo${\mathrm{O}}_{2}$ and oriented films of Cr${\mathrm{O}}_{2}$ grown on rutile substrates have been measured from 0.1 to 6 eV. A Kramers-Kronig analysis has been performed to obtain the dielectric functions and optical conductivities. A rise in the absorption coefficient above…
Anomalous EPR line intensities observed in the photoexcited triplet state of porphyrins at 100°K are discussed. A kinetic model consisting of the singlet ground state and the first excited triplet state is developed. The EPR signal intensities are expressed in terms of the kinetic rate constants and are given as linea…
An experimental study of the microwave properties of pure crystals of the organic salt tetrathiofulvalene-tetracyanoquinodimethan (TTF-TCNQ) is presented. Included are electron spin resonance and a complete study of the dielectric function, ${\ensuremath{\epsilon}}_{1}\ensuremath{-}i{\ensuremath{\epsilon}}_{2}$, from…
The effect of pressure on the solubility of CaCO 3 (calcite), CaF 2 , and SrSO 4 in water was investigated for temperatures between 0 and 35 °C for pressures up to 1000 atm. It was found that for SrSO 4 at 0 °C, and at 22 °C above 500 atm, and CaCO 3 the high pressure solubility products were appreciably lower than th…
Methyl 5-bromolevulinate (30%) is obtained directly by brominating levulinic acid in methanol. The synthesis of 5-aminolevulinic acid over the 5-phthalimido ester thus becomes a three-step one.
Transformation formulas have been derived for conversions between the various conventional systems for reporting zero field splitting data using the Hamiltonian H = D [Sz2 − (1/3)S(S + 1)] + E(Sx2−Sy2). It is recommended that all future work be reported in the standard system corresponding to the range −1≤3E/D≤0.
The dc resistivity and low-field Hall effect of the transition-metal oxide Re${\mathrm{O}}_{3}$ have been measured as a function of temperature. The samples used were oriented single crystals which were large enough for measurements to be made by a conventional four-point probe method. The samples of Re${\mathrm{O}}_{…
The polarized emission and absorption spectra of single crystals of europium ultra(penta)phosphate, EuP5O14, were measured and interpreted. Most of the observed transitions were identified and the energy level structure of the 7F multiplet defined. The over-all site symmetry is found to be extremely low (C1), but in t…
The spectrum and intensity of depolarized light scattered from binary solutions of the nematic MBBA and carbon tetrachloride have been measured. The results are interpreted in terms of pair correlations in the orientation of MBBA molecules. A systematic approach to the study of the orientational structure in nematic l…
The perovskite PrAl${\mathrm{O}}_{3}$ is known to exhibit an apparently complicated series of structural phase transitions from cubic to rhombohedral orthorhombic to monoclinic and ultimately tetragonal symmetry at temperatures of 1320, 205, and 151 K, respectively. The 1320-K cubic-rhombohedral transition is a simple…
We study the thermoelectric power of a narrow-band Hubbard chain with an arbitrary number of electrons per site. The calculations are carried out to the lowest order in the transfer integral. We find a characteristic electron density ($\ensuremath{\rho}=\frac{2}{3}$) below which the thermoelectric power is negative at…
High-resolution measurements of the Huang diffuse scattering from dislocation loops in neutron-irradiated copper and cobalt precipitates in Cu:1-wt%-Co crystals have been carried out close to the (200) and (111) reflections using a three-axis x-ray diffractometer. These measurements have been compiled in the form of d…
We have measured the luminescence spectrum of Mn-doped GaAs at liquid-He temperatures with and without an applied uniaxial stress. At zero stress we found clearly resolved donor-acceptor (DA) and band-acceptor recombination bands involving Mn. From these measurements we get a precise acceptor binding energy of 113 \if…
The influence of molecular weight (900 to 1.8 × 10 6 ) on the glass transition temperature of low polydispersity polystyrene (anionically prepared) has been studied by differential scanning calorimetry at heating rates of 5 to 80 °C min −1 . Over the range of molecular_weight studied, and at an extrapolated heating ra…