Showing papers on "Crystal published in 1968"
TL;DR: An analysis of the solvent content of 116 different crystal forms of globular proteins found that in many cases this range will be sufficiently restrictive to enable the probable number of molecules in the crystallographic asymmetric unit to be determined directly from the molecular weight of the protein and the space group and unit cell dimensions of the crystal.
7,857 citations
TL;DR: In this paper, the electron structure factor for forward scattering for a crystal containing ionized atoms is derived and a parametric fit to these is given in the range of sin θ/λ from 0.0 to 2.0 A−1.
Abstract: Kinematic X-ray and electron scattering factors, found with the use of relativistic Hartree–Fock atomic fields, are tabulated for 76 atoms and ions. Parametric fits to these are given in the range of sin θ/λ from 0.0 to 2.0 A−1. A method is developed to obtain the electron structure factor for forward scattering for a crystal containing ionized atoms.
1,613 citations
TL;DR: In this article, the spontaneous polarization of ferroelectric Bi4Ti3O12 was shown to be monoclinic point group m at 25°C, where m is the number of points in the a−c plane.
Abstract: The symmetry of ferroelectric Bi4Ti3O12 is shown to be monoclinic point group m. The spontaneous polarization PS is approx 50 μC/cm2 at 25°C and lies in the monoclinic a‐c plane at an angle of less than 5 deg from the plane of the crystal sheets. A complete determination of the optical indicatrix as a function of temperature is given. Switching for fields along the c axis occurs by a unique ``rocking'' of the large PS vector and leads to interesting electrical‐optical behavior. The domain structure is quite complex, and observed wall orientations are compared with those predicted theoretically.
760 citations
TL;DR: In this article, a criterion for judging the relative effeciency of excitation of piezoelectric surface waves as a function of crystal plate orientation and propagation direction is developed based on a velocity change upon application of a thin conducting sheet to the surface.
Abstract: A criterion for judging the relative effeciency of excitation of piezoelectric surface waves as a function of crystal plate orientation and propagation direction is developed. This criterion is based on a velocity change upon application of a thin conducting sheet to the surface. Plots of surface wave velocity for various orientations of the crystal surface are presented as a function of propagation direction for the conducting sheet in contact with and infinitely far removed from the crystal surface. A plot of a typical velocity variation as a function of height of the conducting sheet is also presented. Evidence in support of the criterion of using velocity changes as an indicator of efficiency is presented in the form of mechanical displacement and electric potential plots for several orientations and propagation directions. All velocity displacements and potential calculations were carried out under the assumption that the crystal medium was lithium niobate.
641 citations
Book•
01 Jan 1968
TL;DR: Elements of quantum mechanics Elements of group theory Connection of Quantum Mechanics with Group Theory The Hydrogen Atom The Complex Atom - Multiplet Theory The Magnetic Ion in a Crystal - The Role of Symmetry The Weak Field Scheme The Medium Field Scheme the Strong Field Scheme Covalent Bonding and its Effect on Magnetic Ions in Crystals.
Abstract: Elements of Quantum Mechanics Elements of Group Theory Connection of Quantum Mechanics with Group Theory The Hydrogen Atom The Complex Atom - Multiplet Theory The Magnetic Ion in a Crystal - The Role of Symmetry The Weak Field Scheme The Medium Field Scheme The Strong Field Scheme Covalent Bonding and Its Effect on Magnetic Ions in Crystals The Quantum Theory of the Radiation Field Molecular Vibrations Lattice Vibrations The Ion-Photon Interaction - Absorption and Emission of Radiation The Ion-Vibration Interaction - Radiationless Processes - Thermal Shift and Broadening of Sharp Lines Vibrational-Electronic Interaction and Spectra Absorption Spectra of Magnetic Ions in Crystals Fluorescence Spectra of Magnetic Ions in Crystals Elements of Laser Theory
437 citations
TL;DR: In this paper, it was shown that there exists a composition domain for the lithium metaniobate near the stoichiometric compound Nb2O5-Li2O in the vicinity of the NbLiO3 compound.
368 citations
TL;DR: In this paper, the authors measured the width of the metastable zone of concentrations under varying conditions and found that the nucleation rate at the beginning of nucleation will be identical with the supersaturation rate for a limited period of time.
299 citations
287 citations
TL;DR: In this article, a schematic band model for the ferromagnetic phase is presented, where localized ''3d'' electrons occur at thermally excited highspin Co3+ ions, from strontium-rich regions, where the ''3D'' electrons are collective and give ferromagnetism at low temperatures.
Abstract: Crystallographic, magnetic, and electrical studies of the system La1−xSrxCoO3.00±0.01 for 0≤x≤0.5 give indirect evidence for the presence of chemical inhomogeneities separating strontium‐free regions, where localized ``3d'' electrons occur at thermally excited high‐spin Co3+ ions, from strontium‐rich regions, where the ``3d'' electrons are collective and give ferromagnetism at low temperatures. These different regions occur within the same rhombohedral perovskite crystal and appear to represent two different electronic phases within the same crystallographic phase. A schematic band model for the ferromagnetic phase is presented.
220 citations
TL;DR: In this article, the binding energies of excitons to single nitrogen impurities and to double nitrogen impurity were calculated using the complete structure of the GaP conduction bands.
Abstract: Isoelectronic impurities in semiconductors are investigated using a Koster-Slater one-band---one-site approximation. Good agreement with experiment is found for the optical absorption induced by nitrogen in gallium phosphide. Binding energies of excitons to single nitrogen impurities and to double nitrogen impurities are calculated using the complete structure of the GaP conduction bands. Very limited success is achieved in these calculations, which ignore correlation effects and the lattic relaxation and electronic polarization of the host crystal. The indications are that the response of the host to the impurity is of crucial importance in the short-range-interaction problem in semiconductors.
184 citations
TL;DR: In this paper, the effects of polarization on the Raman spectra of single crystals of naphthalene and anthracene have been measured by the use of an argon ion gas laser as an exciting light source.
TL;DR: In this paper, the flow stress distribution below the surface of previously deformed large copper single crystals is obtained when these are sliced into smaller component crystals, measured along the slip direction.
Abstract: The flow stress distribution below the surface of previously deformed large copper single crystals is obtained when these are sliced into smaller component crystals. It is found that a considerable flow stress gradient extends for a distance of about 2 mm below the surface, measured along the slip direction. Electron microscope studies show that there is an increase in the cell size of dislocation structures near the surface and a decrease in dislocation density. On the basis of flow stress distribution measurements the stress–strain curves of single crystals of the same orientation but different sizes are shown to be consistent with the complete absence of a stage II in an infinitely large crystal. It is further shown experimentally that for very large crystals the value of τ111 is reduced considerably. This leads to the conclusion that τ111 should not be related to a fundamental physical phenomenon such as the stacking-fault energy of a metal.
TL;DR: In this paper, a single crystal platelet of uranium dioxide has been prepared with one side very nearly parallel to the (111) plane and the other side inclined approximately 11.4° from the ( 111) plane.
TL;DR: In this paper, a series of vanadium dioxide single crystals containing small concentrations of different impurity ions were grown by a thermal decomposition technique, and it was expected that these ions would produce a systematic change in the semiconductormetallic transition exhibited by the VO 2 phase.
01 Oct 1968
TL;DR: In this paper, the structural changes during the melting process of polyethylene, polypropylene and polybutene-1 were studied making use of direct measurements, including diameter, birefringence and surface temperature.
Abstract: The structural changes during melt spinning process of polyethylene, polypropylene and polybutene-1 were studied making use of direct measurements. A model spinning apparatus was devised for this purpose. Measurements of diameter, birefringence and surface temperature were carried out. Wide and small angle x-ray photographs were taken at the successive points below the spinneret, moreover, the change in crystallinity of polyethylene was measured along the spinning way. In the case of polyethylene, thec-axis of woundup filament tilts against the fiber axis and the crystalline reflections observed in the intial stage of the crystallization are already nearly the same as those of the woundup filament in their features. There is a sudden change in birefringence in the region of crystallization. Crystallization takes place very fast and crystallinity reaches a saturated value in a fraction of a second. The rate of crystallization in melt spinning process is much higher than that of the unoriented state at the same crystallization temperature. The crystallization temperature decreases as take-up velocity increases. As for polypropylene, the structure of the filament consists ofc-axis anda*-axis oriented crystallites, and the process of structural formation is discussed. The transition from tetragonal to hexagonal form of polybutene-1 crystal is very rapid in oriented state.
TL;DR: In this paper, the spontaneous polarization in gadolinium molybdate was shown to arise from an elastic instability which gives rise to a spontaneous strain in the original piezoelectric paraelectric phase.
Abstract: Ferroelectric properties in gadolinium molybdate are shown to originate from a new mechanism completely different from that in conventional ferroelectric materials. In this crystal the spontaneous polarization results from an elastic instability which gives rise to a spontaneous strain in the original piezoelectric paraelectric phase. The dielectric permittivity of the clamped crystal ($\ensuremath{\epsilon}_{33}^{x}$) is low and independent of temperature, while the elastic constant ($c_{66}^{E}$) shows a strong temperature dependence with a marked anomaly at the Curie point.
TL;DR: In this paper, a new empirical size-dependent growth rate model is proposed which has properties superior to those of previous models, and experimental steady state data are presented to illustrate the application of the model to actual CMSMPR crystallization systems.
Abstract: Empirical size-dependent growth rate models are studied for their effect on the population density distributions from a continuous, mixed suspension, mixed product removal (CMSMPR) crystallizer. The growth rate models and/or their corresponding population density distributions are examined for continuity, convergence of moments, versatility, and their ability to fit experimental data.
A new empirical size-dependent growth rate model is proposed which has properties superior to those of previous models. Experimental steady state data are presented to illustrate the application of the model to actual CMSMPR crystallization systems.
TL;DR: In this article, single crystals of MnSb with various Mn compositions in e phase were prepared successfully with Bridgeman method and magnetization and torque measurements were made on these crystals in temperatures ranging from 4.2°K to 800°K.
Abstract: Single crystals of MnSb with various Mn compositions in e phase were prepared successfully with Bridgeman method. Magnetization and torque measurements were made on these crystals in temperatures ranging from 4.2°K to 800°K. The temperature dependence of saturation magnetization on the sample with 48.2 at. % Mn was in good agreement with Brillouin function of J =3/2∼2, but the samples with Mn rich composition exhibited slight discrepancies from this function. The saturation magnetization per Mn atom at 0°K in Bohr magneton decreases with increasing Mn composition, and these values are well explained quantitatively as excess Mn atoms with 2.2µ B occupy the B site and these spins are arranged antiparallel to those of A site Mn with 3.5µ B . The temperature dependences of the first order crystal magnetic anisotropy of various Mn compositions exhibit analogous function with those of cobalt and nickel derived from Carr's theory.
TL;DR: In this paper, the role of the intermolecular potential in determining the spin alignments in the crystal has been discussed, and it is shown that the interactions V and the projections of spins from one molecule onto those of another, determine the crystal spin quantization in the absence of external fields.
Abstract: The theory of the Zeeman and Stark effects in molecular crystal exciton bands is presented. The development emphasizes the role of the intermolecular potential in determining the spin alignments in the crystal, and it is shown that the interactions V, and the projections of spins from one molecule onto those of another 〈Tα | Tβ〉, determine the crystal spin quantization in the absence of external fields through matrix elements of the type V 〈Tα | Tβ〉. A complete anisotropic Zeeman study in weak and strong fields is presented for the benzophenone crystal. It is shown that relatively low‐resolution optical studies can be used to determine zero‐field splitting parameters to about 5% accuracy. The higher resolution studies have led to the assignments, and relative ordering of the twelve k = 0 exciton components of the 3nπ* state of benzophenone crystals. These results are confirmed by Stark and Stark–Zeeman experiments which demonstrate the applicability of the theory outlined. The final best set of molecular ...
TL;DR: The chemical implications of single crystal Raman spectroscopy by means of laser excitation are briefly outlined in this article, where the results of a site-factor group analysis are applied to the first-order spectra of centrosymmetric crystals and rely on the validity of the Raman tensor predictions resulting from factor group analysis.
Abstract: The chemical implications of single crystal Raman spectroscopy by means of laser excitation are briefly outlined. Unambiguous assignments are presented for PdCl 2- 4 , PtCl 2- 4 , PtCl 2- 6 , PdCl 2- 6 , GeCl 2- 6 and TeCl 2- 6 species. Detailed scattering equations are applied to mercurous chloride. The vibrational spectra of cassiterite, anataseand rutile are discussed in terms of the factor group. Gallium trichloride and aluminium tribromide spectra are discussed from the viewpoint of a perturbed D 2h Raman tensor. The complex spectrum of molybdenum trioxide is interpreted in terms of a site-factor group analysis. Problems of birefringence, crystal imperfection, dichroism, the resonance Raman effect, twinning, enantiomorphism, internal reflexion and dependence of relative intensity on physical state are noted. The methods discussed are applied to the first-order spectra of centrosymmetric crystals and rely on the validity of the Raman tensor predictions resulting from factor group analysis.
TL;DR: In this article, the crystal structures of I^Mn^Oio (BiMn205), Βί2Α14θ9, and Bi2Fe4C>9 have been analyzed.
Abstract: The crystal structures of I^Mn^Oio (BiMn205), Βί2Α14θ9, and Bi2Fe4C>9 have been analyzed. Single crystals of these compounds were grown from the melt of the composition B12O3 · 2M2O3 (M = Mn,Al,Fe) with excess B12O3 added as a flux. These crystals are all orthorhombic, and their unit-cell dimensions are: BioMiuOio: a = 7.540 Ä, b = 8.534 Ä, c = 5.766 Ä B12AI4O9: a = 7.712 Ä, 6 = 8.112 A, c = 5.708 Ä Bi2Fe409: a = 7.905 Ä, 6 = 8.428 A, c = 6.005 Ä. * Present address: Department of Chemistry,Tokyo University, Bunkyo-ku, Tokyo, Japan . 174 N OBUKAZIT N I I Z E K I a n d M A S A T A D A W A C H I These unit cells contain two formula units. Space groups are all Pbam. Threedimensional intensity data was collected by multiple-film integrating Weissen berg photography. The structures were analyzed by interpretation of Patterson sections at ζ = 0, and J, and refined by the least-squares method. The absorption and dispersion corrections were included in data processing. The final R value are O.li, 0.12, and 0.10 for Mn, Al, and Fe compound respectively. Two compounds B12AI4O9 and B12FC.4O3 are isostructural. One kind of Al (Fe) is octahedrally coordinated by six oxygen atoms, and the other kind tetrahedrally by four oxygen atoms. The structure of the Mn compound differs from the other two only in that one oxygen atom located at 00 J in the others is replaced by two oxygen atoms at 0,0, 0.281, and as the result, Mn(2) is coordinated by five oxygen atoms in a square-pyramidal configuration. The coordination of oxygen atoms around Bi is similar to that of sulfur in sulfosalts containing Bi; there are three short Bi—Ο bonds mutually orthogonal, and five more longer bonds.
TL;DR: The second-harmonic phase-matching temperature of nonstoichiometric LiNbO3 crystals has been found to vary by as much as 75°C from crystal to crystal and 10°C within an individual crystal.
Abstract: The second‐harmonic, phase‐matching temperature of ``stoichiometric'' LiNbO3 crystals, for fundamental radiation at 1.06 μ, has been found to vary by as much as 75°C from crystal to crystal and 10°C within an individual crystal. Measurements on crystals grown in a controlled manner from nonstoichiometric melts have shown that the phase‐matching temperature, T, is an approximately linear function of melt composition, x, obeying the equation T = 50.5 + 32 × 102 (x − 0.50). Crystals with phase‐matching temperatures of as high as 186°C have been grown from melts containing excess lithia. Such a crystal has been operated as a second harmonic generator without damage, whereas a comparable radiation produced by a crystal with a low phase‐matching temperature damaged the crystal. A mechanism involving lithium ion vacancies is proposed to explain the results.
TL;DR: In a limited temperature range above the clearing point of crystal suspensions, submicroscopic entities representing unmeasurably small portions of the original crystal population may survive whose existence is revealed by crystals nucleated on subsequent cooling.
Abstract: In a limited temperature range above the clearing point of crystal suspensions, submicroscopic entities representing unmeasurably small portions of the original crystal population may survive whose existence is revealed by crystals nucleated on subsequent cooling [1]. Factors influencing the number of these nuclei and the nature of these nuclei themselves were explored in the case of polyethylene.
Journal Article•