Materials Literature
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If the distance between atoms in a crystalline lattice is increased, an energy gap appears, which in a divalent material will separate occupied from unoccupied states of an electron. In a non-crystalline substance, a minimum is expected in the density of states (a ‘pseudogap’). An approximate theoretical estimate is g…
Abstract By using a high speed rotating mirror camera combined with a microscope, the rapid initial lengthening of twins and their subsequent broadening have been studied. In zinc, twins of up to 1·9 mm appeared in crystal surfaces within 1 μs and subsequently the tips of such twins were observed to move at up to 780…
The fluorescence efficiency of tetracene single crystals may be enhanced by as much as 38% in a magnetic field $H>2000$ G. The enhancement is anisotropic with respect to the orientation of $H$ in the $\mathrm{ab}$ plane. It is shown that a magnetically sensitive coupling of singlet states to a double-triplet-excito…
The glass-transition temperature of water (T(g)) has been calculated by use of the Tammann-Hesse viscosity equation with the viscosity equal to 10(13) poise at T(g). The derived value of T(g),162 +/- 1 degrees K, is significantly higher than previous estimates.
The absorption spectrum of blue, γ-irradiated CaF2: Y3+ crystals shows several bands in the visible region whose intensity is roughly proportional to the yttrium concentration. Bleaching into the individual bands indicates that more than one center is responsible for the whole spectrum. Inconsistent color response of…
Measurements of quantum yield of Al–Al2O3 films were made at photon energies between 7 and 22 eV. The photoelectric threshold for intrinsic photoemission from amorphous Al2O3 appeared to be about 8 eV. Approximately 1 eV was estimated for the electron affinity of Al2O3. The yield of anodic oxide film on aluminum at 10…
Experiments on directed atom motions in $\ensuremath{\beta}\ensuremath{-}\mathrm{Zr}$ have been carried out with a view to bringing additional experimental evidence to bear on the current conflicting theories of the anomalous diffusion behavior in this and other bcc refractory metals. Thermomigration and electromigrat…
Optical scattering data have been used to investigate molecular order in certain cholesteric mixtures. When films of these materials are deposited on a reflecting substrate, their colors can be shifted by several thousand angstroms for any condition of illumination and observation by a mechanical disturbance. The disp…
A model descriptive of the growth of precipitates which nucleate at grain boundaries and grow pre ferentially along them (grain-boundary allotriomorphs) is studied. The sequential processes during growth are presumed to be volume diffusion of solute to the grain boundary, transport along the grain boundary to the prec…
The efficiency of production of electrons emitted by the Auger process from the surface of a solid irradiated with a beam of electrons in the energy region below 2 keV is estimated. It is shown that the probability of photon production is negligible and that to a first approximation the optimum primary energy required…
The ternary alloy MnAlGe has been studied by diffraction techniques using both neutrons and x rays. The unit cell is found to be tetragonal with a0 = 3.914±0.001 Å and c0 = 5.933±0.001 Å. The space group is D4h7-P4/nmm. The intensities in the neutron-diffraction patterns agree with a ferromagnetic spin alignment of th…
N,N-Dimethyl formamide (DMF) and N,N-diphenyl formamide (DPF) complexes of six lanthanide perchlorates of the composition M(DMF) 8 (ClO 4 ) 3 and M(DPF) 6 (ClO 4 ) 3 where M = La, Ce, Pr, Nd, Sm, or Y have been prepared and characterized. The infrared spectra show that the amide is bonded to the metal through oxygen.…
Chlorine ligand hyperfine structure has been observed in the EPR spectrum of the octahedral complex ion (MnCl6)4−1, in dilute solution in a single crystal of K4CdCl6 at room temperature. From the isotropic and anisotropic components of the spectrum, it is estimated that fs = 0.40%, and (fσ − fπ) = 3.9%, respectively.…
In the infrared absorption spectra of thiosemicarbazide (I), aldehyde thiosemicarbazones (II), and N-methyl derivatives of these compounds, the following assignments are proposed: ν a (N d H 2 ) absorbs in the vicinity of 3400 cm −1 ; N a H 2 vibrations are observed in the region of 1630 cm −1 ; there is a significant…
The energy transfer in amorphous polyvinyl carbazole (PVCA) has been studied by fluorescence quenching experiments using perylene, trinitrofluorenone, and hexachloro-p-xylene as guest molecules. The PVCA shows excimer fluorescence. The results are discussed in terms of exciton diffusion and competition between excimer…
Using Gärtner's equations, effect of sample thickness on the Cember potential (VD) for strong and weak absorption is discussed. It has been found that for strong absorption, as the thickness of the sample increases, VD tends to a saturation value which decreases as the front-surface recombination velocity increases. F…
From measurements of magnetization in the approach to saturation region of the hysteresis loop, a semiempirical method has been developed for determining reasonably accurate values of | K1 |/Ms and peff, the fraction of nonmagnetic volume of polycrystalline ferrimagnetic materials. The technique involves the precise m…
The mechanism of alkali ion movement in glasses during electron-probe analysis must include a dependence on the temperature of the volume irradiated. Experimental results of the composition changes of binary oxide glasses of Na2O and K2O with SiO2 during electron bombardment indicate that there is a critical temperatu…
A number of compositions A 2 3+ Ti 2 4+ O 7 and of related mixed phases were prepared and investigated. For the trivalent lanthanons from Sm to Lu, and for Y, the homogeneous A 2 Ti 2 O 7 phases were of the cubic pyrochlore type. Their lattice parameters gave a very good linear relationship when plotted against the Te…
Abstract Cellulose has been irradiated by ultraviolet light. The degradation was followed viscometrically and by weight loss measurements. The changes in the degree of Polymerization and weight of the irradiated material indicated that the degradation is random and follows first order kinetics. It is suggested that ch…