Materials Literature
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It is shown by an analysis similar to that for the spinodal decomposition of a supersaturated solution that an array of dislocations, modelled by parallel screw dislocations, of uniform density, is unstable; the dislocations move to form a structure having a modulated dislocation density. It is suggested that the inst…
Abstract The fluorescence yield of europium chelates in several solutions varies, through its maximum value, with the increase in the energy difference between the triplet state of a ligand and the emitting level of an europium ion. The time-resolved spectroscopic measurements show that the excitation energy is transf…
The nature of the chemical bond in crystals is discussed. The general theories of L. Pauling based on thermochemical data and of C. A. Coulson based on valence bond concepts are compared with a recent spectroscopic theory. Particular emphasis is placed on binary crystals of formula ${\mathrm{A}}^{N}{\mathrm{B}}^{8\ens…
Abstract A transmission electron micrograph is essentially a projection of the specimen in the direction of view. In order to reconstruct a three-dimensional image of the specimen, it is necessary to be able to combine data from a number of different views. A formal solution of this problem is given in terms of Fourie…
We have observed that liquid crystals of the $p$-azoxyanisole type exhibit macroscopic rotational motion above a threshold voltage. The vortex motion of the birefringent liquid results in a lattice of cylindrical lenses whose focal lengths are voltage variable. These experiments are in excellent agreement with the dyn…
Scattering of electrons from surfaces of ZnO single crystals has been studied in ultrahigh vacuum with a high-resolution electron-impact spectrometer ($\ensuremath{\Delta}E<20$ meV, impact energy ${E}_{0}=1\ensuremath{-}100$ eV). The energy-loss spectrum in specular reflection shows a series of equally spaced loss…
The critical temperatures, T c, and critical current density, J c were measured for ZrV alloys containing 6 and 9 at% V at various stages of aging at 500 °C. The microstructure of the samples was determined by metallographic and X-ray diffraction techniques in conjunction with previously reported studies. The alloys…
Prestraining of iron prior to shock-loading inhibits the formation of shock twins because in the presence of mobile dislocations fewer twins are needed to complement slip in accommodating the imposed strain rate, i.e., fewer twins nucleate when mobile dislocations are present. The propagation characteristics of a twin…
The theory of kinematic X-ray diffraction from dislocated crystals as developed in [1] is extended to crystals containing more than one set of straight parallel dislocations. The Bragg reflexion line broadening is expressed by two parameters of the dislocated crystal, the dislocation density, ϱ, and the effective oute…
Energy bands are calculated for hexagonal NiS using lattice constants and crystal potential appropriate to the metallic phase. Group theoretic results for $s$, $p$, and $d$ bands in the NiAs structure are obtained, and the calculation is performed using a first-principles tight-binding method. The energy band structur…
The infrared absorption in $n$-type InP was studied as a function of free-carrier concentration from 3.5\ifmmode\times\else\texttimes\fi{}${10}^{17}$ to \ensuremath{\sim} ${10}^{19}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ in the spectral range of 10 \ensuremath{\mu} to the fundamental absorption edge. The Burstein shifted…
The optical absorption of vanadate glasses based on the system V2O5–P2O5 was measured in the range 20 cm−1 to 25 000 cm−1 at room and liquid-nitrogen temperatures. The samples were blown films of thickness about 1–2 μ and of composition 70.0, 80.0, and 87.5 mole % V2O5. Vibrational absorption peaks were observed at ab…
Amorphous alloys having the composition ${({\mathrm{Ni}}_{x}{\mathrm{Pt}}_{1\ensuremath{-}x})}_{0.75}{\mathrm{P}}_{0.25}$, where $0.20\ensuremath{\le}x\ensuremath{\le}0.60$, were obtained by rapid quenching from the liquid state. X-ray diffraction measurements indicate a high degree of structural disorder in these all…
A proton magnetic resonance spin–lattice relaxation and second moment study of the ferroelectric transitions in diglycine nitrate (DGN), trissarcosine calcium chloride (TSCC), and its deuterated analog has been performed. The results support the order–disorder model of the ferroelectric transition in these compounds a…
The crystal structure of [OCr3(CH3COO)6.3H20]+C1 -. 6H20 has been determined from three-dimensional diffractometer data using Cu Ke radiation. The configuration of the complex cation consists of three chromium atoms linked to a central oxygen atom in a planar configuration. Each chromium atom is coordinated octahedral…
A comparison between the ultraviolet-reflectivity spectrum and the characteristic energy-loss spectrum of ZnO has been carried out. Reflectivity measurements made over an energy range of band gap to 22 eV yielded a spectrum with structure at 3.34, 5.0, 7.3, and 8.4 eV, and in the region 11-15 eV. Energy-loss measureme…
The theory of dielectric relaxation in a model polar liquid is developed and applied to experimental data. The model is a spherical Onsager cavity, with a uniform dielectric background described by the high frequency limit ε∞ and containing a permanent point dipole. The dipole moment undergoes rotational Brownian moti…
The 5D emissions of Eu3+ in Y2O2S, La2O2S, and LaOCl quench sequentially with increasing temperature in the simple order 5D3, 5D2, 5D1, 5D0. These 5D quenchings are attributed to thermally activated resonance crossovers from the 5D states to the charge-transfer states (CTS). The activation energies for the 5D quenchin…
The electronic band structure of graphite has been calculated from an ab initio variational approach using a linear-combination of atomic-orbitals (LCAO) basis of Bloch states, including nonspherical terms in the one-electron crystal potential. Matrix elements of the Hamiltonian are evaluated directly without any tigh…
El presente trabajo comprende el estudio taxonómico de catorce especies de equinoides, de las que diez son regulares y cuatro son irregulares. Entre las irregulares, dos especies son nuevas: Heteraster aguilerai n. sp. y Heteraster alencasterae n. sp. La colección de equinoides estudiada proviene de las formaciones Za…