Materials Literature
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The Brillouin-scattering spectrum of K${\mathrm{H}}_{2}$P${\mathrm{O}}_{4}$ has been studied over the temperature range $118\ifmmode^\circ\else\textdegree\fi{}\mathrm{K}<T<300\ifmmode^\circ\else\textdegree\fi{}\mathrm{K}$ with particular emphasis on the region close to the ferroelectric transition at 122\ifmmode…
We introduce a simple model Hamiltonian for the study of phase transitions in perovskite compounds $\mathrm{AB}{\mathrm{O}}_{3}$ involving rotations of $B{\mathrm{O}}_{6}$ octahedra. Depending on the relative magnitude of the anharmonic coefficients, we find a transition to the tetragonal or to the trigonal phase. We…
The electrical resistivity was determined for polycrystalline and single-crystal BeO between 1200°–1700°C. Analysis was made of the effects of oxygen partial pressure, aliovalent impurities, and microstructure. Conductivity and relevant diffusion coefficients were calculated with these data. The results show the BeO s…
The heat capacity of a single crystal of CaWO4 was determined by adiabatic calorimetry from 5° to 350°K and found to be without transitions or thermal anomalies. Deviation of the curve from normal sigmate shape is shown to be due to internal vibrations of the WO4= ions. Apparent Debye θ's for the lattice-only heat cap…
Abstract Single, double and multi-layered dislocation loops have been observed in thin foils of quenched magnesium, and the structure of the loops established by contrast analysis. On annealing in the temperature range 150 to 200°C the loops are observed to grow as a result of the production of vacancies by surface ox…
A series of Ni(II) complexes with methyl-, ethyl-, and sym-dimethyl-, sym-diethyl-, and sym-di-n-butyl- thioureas and halide, perchlorate, and thiocyanate anions have been prepared and characterized. Spectral and magnetic studies show that compounds NiL 4 X 2 (L = N,N′-dimethyl and N,N′-diethylthiourea, X = halide) ar…
The viscosity measurements on 1,3,5-tri-α-naphthylbenzene have been extended to 407°C, in order to establish the limiting high-temperature Arrhenius activation energy. Diverse functions have been used to fit the viscosity results on this material which range over 15 orders of magnitude. From the temperature dependence…
The structure of thiourea nitrate has been determined by three-dimensional X-ray methods. Both Cu Ke and Mo K~ data were obtained with a single-crystal diffractometer and the final R values are 4.9% and 5.5% respectively. The space group is P211m and there are two molecules in the unit cell. All atoms, including hydro…
The ${F}^{\ensuremath{'}}$ band has been produced and measured in the following alkali halides: NaCl, KCl, KBr, KI, RbCl, RbI, CsBr, and CsI. Additively colored samples were optically bleached in the $F$ band at an optimum temperature to produce a maximum $F$-to-${F}^{\ensuremath{'}}$ conversion. The observed spectra…
Polarized far-infrared spectra of aliphatic polyesters [–(CH2)z–CO–O–O]n with z = 1, 2, and 5 (z = 4, nonpolarized) and α-polyamide (nylon 6 and its N-deuteroderivative) have been measured in the region up to 80 cm−1. All these polymers have essentially planar zigzag conformations. The normal vibrations of these polym…
Measurements of the 57Fe Mössbauer spectrum of phthalocyanine iron(II) made at 4.2° and 100°K, with the sample in applied magnetic fields of 30 kOe, show that the electric field gradient at the iron nucleus is of positive sign and that there is no large asymmetry in the electric-field-gradient tensor. The major axis o…
The reflectivity of single-crystal sodium nitrite has been measured as a function of temperature and crystallographic orientation over a wavelength region which spans all the eight infrared-active normal modes. The temperature-dependent dielectric response functions and oscillator parameters have been obtained both by…
Photoluminescence studies were made at liquid-helium temperatures of epitaxial GaAs with ionized-impurity concentrations \ensuremath{\lesssim}${10}^{15}$ ${\mathrm{cm}}^{\ensuremath{-}3}$. Narrow linewidths at half-height were achieved by using material of high purity and perfection, by using low intensities of illumi…
Crystals of ${\mathrm{Ti}}_{2}$${\mathrm{O}}_{3}$ of relatively high purity or doped with various impurities have been grown by the Czochralski method. The semiconductor-metal transition commenced at 435\ifmmode^\circ\else\textdegree\fi{}K with a change of resistivity from 9\ifmmode\times\else\texttimes\fi{}${10}^{\en…
The magnetic properties of phthalocyanine iron (II) have been investigated in the temperature ranges 1.25°–20°K and 100°–300°K. Between 100° and 300°K the magnetic susceptibility obeys the Curie–Weiss law accurately, but the measured value of μeff at 25°C is 3.71 μB, which is intermediate between the theoretical spin-…
A pulsed magnetic-resonance spectrometer is used to measure pure NQR frequencies and relaxation times of the $^{35}\mathrm{Cl}$ and $^{37}\mathrm{Cl}$ nuclei in powdered samples of ${\mathrm{K}}_{2}$Pt${\mathrm{Cl}}_{6}$ over the temperature range $6<T<490\ifmmode^\circ\else\textdegree\fi{}$K. The ratio of frequ…
The experimental dependence of the magnetization on temperature and composition is presented for ${\mathrm{Ga}}_{2\ensuremath{-}x}{\mathrm{Fe}}_{x}{\mathrm{O}}_{3}$. Interpretation is based on a three-sublattice model, giving the $x$ dependence of the iron occupation of the various sites, the variation of the Curie te…
In their paraelectric phases, SrTi${\mathrm{O}}_{3}$ and KTa${\mathrm{O}}_{3}$ crystallize in the cubic perovskite structure (space group ${{O}_{h}}^{1}$) in which the first-order Raman effect is forbidden. We discuss here experiments in which first order Raman scattering has been induced by the application of an exte…
Room-temperature Raman spectra of high-quality single-domain BaTi${\mathrm{O}}_{3}$ crystals are reported. The frequencies of the Raman-active long-wavelength optical phonons are determined and shown to be in reasonable agreement with the Lyddane-Sachs-Teller (LST) relation as well as infrared reflectivity data. The e…
A systematic study has been made of multiphonon orbit-lattice relaxation of excited states of rare-earth ions in crystals. By measuring both excited-state fluorescence lifetimes and multiphonon relaxation quantum efficiencies, pure multiphonon transition rates were determined for the following set of crystals: (1) La$…