Materials Literature
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Abstract The mechanism of alternating copolymerization of propylene oxide with phthalic anhydride catalyzed by dialkylzinc is discussed. Dialkylzinc and phthalic anhydride form a complex which exhibits reactivity with propylene oxide to form alkylzinc alkoxide. Alkylzinc alkoxide thus formed reacts preferentially with…
The crystal-field splittings and hyperfine-structure constants of Eu 2+ in CaWO 4 have been accurately measured at 4.2 °K and at 78 °K using the method of electron paramagnetic resonance. These measurements were intended to provide liquid-helium temperature parameters for ENDOR experiments presently in progress but sh…
Au-Cd alloys in the range between 25 and 34 at. per cent Cd have been investigated by electron and X-ray diffraction as well as by calorimetry. The existence of a series of close packed structures with periodic stacking modulations and atomic order has been established. The order of appearance of the stacking variants…
The Raman spectra of the molten nitrates of lithium, sodium, and silver change as the temperature is raised. Close to the melting point well-developed low-frequency modes can be distinguished close to the exciting line while at higher temperature these have become somewhat broader but still quite distinct. There are a…
The oscillatory photoconductivity spectrum associated with the acceptor center in semiconducting diamond has been measured over the spectral energy range 0.35-2.6 eV (3.5-0.47 \ensuremath{\mu}). The energy separation between the acceptor ground state and the top of the valence band is more than twice the longitudinal…
Switching phenomena take place in thick bulk samples of semiconducting glass, once a path of devitrified material is established. Potential probe and infrared microradiometer measurements reveal that the switching action takes place in a small region somewhere along this path. Application of voltage pulses can move th…
This paper reports data on the luminescence spectra associated with $F$ and ${F}^{+}$ centers in calcium oxide. Irradiation in the $F$ band excites emission bands at 500 and 627 nm, which we identify with the transitions $^{1}P\ensuremath{\rightarrow}^{1}S$ and $^{3}P\ensuremath{\rightarrow}^{1}S$, respectively, of th…
Inelastic-neutron-scattering measurements have been performed on the high-temperature cubic perovskite phase of LaAl${\mathrm{O}}_{3}$. Dispersion curves for phonons with q along [111] establish that near the zone corner ($R$ point), the frequency of the lowest branch is both anomalously low and temperature-dependent.…
The mechanisms relating to infrared-pumped visible and ultraviolet emission observed from Yb3+–Er3+ and Yb3+–Ho3+ ions in BaYF5 and Y3OCl7 (reported in the companion papers) are discussed. An analysis is given of the material parameters required for efficient conversion and the limiting performance which can be expect…
A sample of uranium diboride was prepared and characterized as UB1.979±0.006 with 0.06 ± 0.03 wt % of identified impurities. The standard enthalpy of combustion in fluorine was determined to be − 1021.2 ± 1.1 kcal mole−1. The heat capacity was measured from 0.84° to 350°K. At 298.15°K the heat capacity CP°, entropy S°…
The Ge–Se phase diagram was determined in the composition range 0–66.67 at. % Se by the method of differential thermal analysis. The diagram differs totally from the one reported by Liu etal. (1) but is in good agreement with the diagram recently reported by Karbanov etal. (13). In its broad features the Ge–Se phase d…
The crystal structure of the interstitial solid solution of alpha titanium-oxygen system has been investigated by a combined method of electron, neutron and X-ray diffraction as functions of composition and annealing temperature. The existence of two-types of interstitial superstructure has been established over nearl…
When pumped by radiation from a Si–GaAs diode, the luminous efficiency of Y3OCl7:Yb3+, Er3+ is comparable to that of visible emitting GaP diodes. By varying the Yb3+ concentration, phosphors have been made which produce a red or yellow visual response.
The dielectric theory of electronegativity differences is used to calculate second- and third-order nonlinear susceptibilities of covalent crystals. With no adjustable parameters excellent agreement is obtained for ${\ensuremath{\chi}}^{(2)}$ when allowance is made for Coulombic correlations. The experimental values $…
In a nematic system, the molecular axes tend to be aligned parallel to each other, but there are some fluctuations in the alignment. They give rise to a strong scattering of light. By a frequency analysis of the outgoing light, one can measure the power spectrum of these fluctuations, i.e., their dynamical behavior. T…
Efficient infrared-to-visible conversion by Yb3+–Er3+ and Yb3+–Ho3+ ions in BaLuF5 and BaYF5 is reported. When pumped by radiation from a Si–GaAs diode, the power conversion efficiency for green emission from BaYF5:Yb3+, Er3+ is equal to that for green emitting GaP diodes.
Behavior of individual dislocations is investigated by stretching the foil single crystals of Fe-3% Si inside a 500 kV electron microscope. Formation of dislocation dipole trails and loops are continuously observed under the microscope, and is attributed to jogs caused by cross glide. Slip traces of individual disloca…
The Raman spectra of LaAl${\mathrm{O}}_{3}$, PrAl${\mathrm{O}}_{3}$, and NdAl${\mathrm{O}}_{3}$ have been observed at temperatures from 10 to 1135\ifmmode^\circ\else\textdegree\fi{}K. Each of these materials evidences a nominally second-order trigonal cubic phase transition; that in LaAl${\mathrm{O}}_{3}$ has previous…
The appearance of phase-contrast, Fresnel fringes and various forms of diffraction contrast in images produced by transmission scanning electron microscopes can be understood simply by invoking the principle of reciprocity to equate the imaging conditions to those relevant to a conventional electron microscope.
Expressions are derived for the voltage and current in insulators under charge limited conditions using running wave expression for the charge carriers, taking into account displacement and field induced currents. Using these the frequency characteristics of the voltage, current and impedance is derived. It is seen th…