Showing papers on "Single crystal published in 1969"
TL;DR: Adiabatic elastic stiffness constants of single crystal forsterite measured as function of hydrostatic pressure and temperature, using pulse superposition technique as discussed by the authors, were derived from a single-crystal single crystal FER.
Abstract: Adiabatic elastic stiffness constants of single crystal forsterite measured as function of hydrostatic pressure and temperature, using pulse superposition technique
253 citations
TL;DR: The interface between inorganic crystalline and organic amorphous matter in the skeletal element appears to be the first example reported in nature of a periodic mninimal suirface.
Abstract: X-ray diffraction studies confirm that, with few exceptions, each skeletal element of echtinoderms is a single crystal of magnesium-rich calcite and that a relation exists between the shape of the element and the crystallographic a- and c-axes. The exceptions incluide the teeth of echinoids, and the calcareous ring as well as the anal teeth of holothurians. The tubercles of an echinoid plate begin their growth as parts of the single crystal of the plate; under the mechanical action of the spines that are attached to them, they become partly polycrystalline, as shown by scanning electron microscopy and by x-ray powder diffraction. The interface between inorganic crystalline and organic amorphous matter in the skeletal element appears to be the first example reported in nature of a periodic mninimal suirface.
198 citations
TL;DR: In this paper, a detailed analysis of surface crystallography using low energy electron diffraction (LEED) is presented and discussed in this paper, and the work function and thermal desorption energy studies will be presented elsewhere.
195 citations
113 citations
TL;DR: In this paper, a thermal faceting of tungsten single crystal surfaces in oxygen was performed using vibrating-capacitor work function probe with low energy electron diffraction.
111 citations
TL;DR: An analysis of the crystallographic structure of the principal components of bone and its piezoelectric and pyroelectric behavior showed that bone is a texture that has the same elastic coeffcient matrix as a hexagonal single crystal.
Abstract: The elastic stiffness coefficients of dried bovine phalanx and femur and of fresh bovine phalanx were measured by an ultrasonic technique. An analysis of the crystallographic structure of the principal components of bone and its piezoelectric and pyroelectric behavior showed that bone is a texture that has the same elastic coeffcient matrix as a hexagonal single crystal. The five elastic stiffness coefficients of fresh phalanx are: C 1l, 1.97; C 12, 1.21; C 13, 1.26; C 33, 3.20; and C 44, 0.54 (all in units of 1011 dynes per square centimeter). Value of axial and transverse Young's and shear moduli, compressibility, and the three Poisson's ratios were calculated.
99 citations
03 Dec 1969
TL;DR: Welin this article determined the structure of a related mineral, thaumasite (Ca6H4(SiO4)2(SO4) 2(CO3)2.26H2O), which he found based on chains of Ca2+ and SiO44− ions with the remaining ions and water molecules in between.
Abstract: ETTRINGITE (Ca6[Al(OH)6]2(SO4)3.26H2O) occurs as a natural mineral, and is technically important as a hydration product of Portland and supersulphated cements and in its use, as satin white, for coating paper. It forms hexagonal, prismatic crystals which in synthetic material are often highly elongated. Bannister, Hey and Bernal1 obtained unit-cell data (hexagonal: a 11.26, c 21.48 A, space group P63/mmc, Z = 2). No crystal structure determination based on single crystal evidence has been reported, but Welin2 determined the structure of a related mineral, thaumasite (Ca6H4(SiO4)2(SO4)2(CO3)2.26H2O), which he found to be based on chains of Ca2+ and SiO44− ions with the remaining ions and water molecules in between.
97 citations
TL;DR: In this paper, the decay of the respective dynamic yield points with increasing propagation distance can be predicted as a function of the dislocation mobility and the initial mobile dislocation density, and it is shown that simple dislocation damping models for the mobility are not consistent with the experimental results.
Abstract: Three groups of single‐crystal disks approximately 5‐mm thick with surface normals along [100], [110], and [111] crystallographic directions were prepared from 99.99+ at.% pure copper. These specimens were shock loaded to about 50 kbar in a state of uniaxial strain by nitroguanidine explosive plane‐wave generators, and the propagated wave profiles were measured with quartz gauges. Elastic wavefronts for the single crystals exhibited sharp risetimes (of the order of 10 nsec) to dynamic yield points, and subsequent stress relaxations preceding the plastic wavefronts. For the propagation distances of about 5 mm, the measured yield point normal stresses were about 2.0, 1.3, and 1.3 kbar, respectively, for wave propagation in the [100], [110], and [111] directions. Although the principal stress states at the yield points differed, analysis reveals that the shear stresses on {111} 〈110〉 slip systems were about the same for all orientations. Single‐crystal disks prestrained by about 3½% exhibited essentially zero yield stresses and ramp‐like elastic waves. Similar behavior observed for polycrystalline specimens indicates the importance of initial dislocation density on dynamic yielding. In all cases the plastic wave velocities were the same. Constitutive relations derived on the basis of dislocation dynamics are given for the three single crystal orientations. From these relations the decay of the respective dynamic yield points with increasing propagation distance can be predicted as a function of the dislocation mobility and the initial mobile dislocation density. Within the framework of this theory it is shown that simple dislocation damping models for the mobility are not consistent with the experimental results.
93 citations
90 citations
TL;DR: In this paper, it was shown that the graphite nucleates preferentially at substrate grain boundaries and kink sites, and evidence was provided which indicates that precipitation from solution in the substrate cannot be involved.
86 citations
TL;DR: In this paper, the electron spin resonance (ESR) of a γ-irradiated single crystal of L-tyrosine-HCl reveals a free radical formed by loss of an H from the hydroxyl group attached to the ring.
Abstract: Analysis of the electron spin resonance (ESR) of a γ-irradiated single crystal of L-tyrosine-HCl reveals a free radical formed by loss of an H from the hydroxyl group attached to the ring. Principal g values of the radical are gx = 2.0023 ± 0.0005, gy = 2.0067 ± 0.0005, and gz = 2.0045 ± 0.0005, with gx perpendicular to the plane of the ring and gy along the CO bond to the ring. Analysis of the hyperfine structure of the spectra shows electron spin density on C(2) and C(6) to be 0.24 and on C(4) to be 0.32. Corresponding spin densities calculated from molecular orbital theory are 0.26 and 0.31, respectively.
TL;DR: In this article, the results of the inelastic cold neutron scattering experiments on polycrystalline quartz and cristobalite specimens of different degrees of crystal perfection were obtained at room temperature.
Abstract: Coherent inelastic cold neutron scattering experiments have been carried out at room temperature on polycrystalline quartz, on three polycrystalline cristobalite specimens of different degrees of crystal perfection, and on vitreous silica. The results for quartz show marked coherence effects, and it was possible to derive the form of the directionally averaged lowest‐energy acoustic branch of the spectrum. Coherence effects at higher energies are too complex to be interpreted in detail, but the results show the presence of a maximum in the vibrational frequency distribution [G(ω)] at ≈ 130 cm−1 and a broad maximum extending from ≈ 250–500 cm−1. These results are in excellent agreement with recent neutron scattering experiments on a single crystal and detailed calculations of the dispersion relations for a model of quartz. For cristobalite, the scattering was shown to be largely independent of crystal perfection so that the results obtained are characteristic of perfect cristobalite. The form of the direct...
TL;DR: In this article, the epitaxial growth of copper vapour deposited onto the surface of a tungsten single crystal has been studied using low energy diffraction, Auger electron emission and electron energy loss spectra, while in a separate apparatus, work function changes have been measured.
TL;DR: In this paper, the single-crystal elastic constants of Ni3Al were determined by a rod resonance technique, and their values and standard deviations at 25°C in units of 10−12 m2/N were s11=9.27±0.15, s44=8.25± 0.27, and s12=−3.19±0.50.
Abstract: The single‐crystal elastic constants of Ni3Al were determined by a rod resonance technique. Their values and standard deviations at 25°C in units of 10−12 m2/N are s11=9.27±0.15, s44=8.25±0.27, and s12=−3.19±0.50.
TL;DR: In this article, a new method was employed to measure the change of lattice parameters of single crystal SrTiO3 as a function of temperature from 77 to 150 °K, and a clear indication of a phase transition at 108 °K was observed.
Abstract: A new method was employed to measure the change of lattice parameters of single crystal SrTiO3 as a function of temperature from 77 to 150 °K. A clear indication of a phase transition at 108 °K was observed. The line splitting below 108 °K is consistent with tetragonal symmetry, the axial ratioc/a of the crystal lattice being 1.0004 at 77 °K. When comparing our results with recently performed measurements of the rotating angleϕ of the TiO6 octahedra, good agreement is obtained by assuming an additional tetragonal deformationc/a′=1.0001 of the oxygen octahedra. There was no indication of a temperature hysteresis of the lattice parameters, formerly observed with x-rays.
TL;DR: In this paper, the selfdiffusion coefficient of Al3+ and Cr3+ ions in MgO was calculated and the interdiffusion coefficients increased with the mole fraction of cation vacancies.
TL;DR: In this article, it was shown that the surface regions of gallium arsenide become non-crystalline (i.e. amorphous) after bombardment at 21 °C with Ne20 ions of energies between 40 and 100 keV.
Abstract: Transmission electron microscopy studies of thin films of gallium arsenide have shown that the surface regions become non-crystalline (i.e. amorphous) after bombardment at 21 °C with Ne20 ions of energies between 40 and 100 keV. This effect occurs after ion doses of about 1 × 1015 ions cm−1 and the damaged material recrystallizes onto the underlying single crystal in an apparently epitaxial manner during post-bombardment annealing at temperatures between 270 °C and 300 °C. Annealing at temperatures up to ∼700°C in an inert atmosphere causes growth of dislocation loops which result from the initial damage structure. These dislocations have not been studied in detail due to the occurrence of complicating structure which results from the dissociation of GaAs at temperatures above ∼400 °C. GaAs which was bombarded with ∼3 × 1016 60 keV Ne20 ions cm−2 while held at different temperatures between 35° and ∼200 °C contained a dense network of dislocations and dislocation loops, but did not become amorpho...
TL;DR: The structure of CH3MgBr·3C4H8O was solved by single crystal X-ray diffraction techniques as mentioned in this paper, where the five-coordinate magnesium is at the center of a trigonal bipyramide.
TL;DR: In this paper, single crystals of Ni ferrites and Ni-Zn ferrites having good uniformity were prepared by a new floating zone technique, where the initial molten zone was made from the material having a composition different from that of seed crystal.
Abstract: Single crystals of Ni ferrites and Ni-Zn ferrites having good uniformity were prepared by a new floating zone technique. In the preparation of the Ni-ferrite single crystal the initial molten zone was made from the material having a composition different from that of seed crystal. This made the composition of precipitate from molten zone the same as that of the seed, and the composition of crystal uniform throughout the entire body. In the apparatus a halogen lamp and the sample were placed, respectively, on the two focal points of a closed elliptical reflector. Under an oxygen pressure of 30 atm, the vaporization of ZnO and the precipitation of another phase in Ni-Zn ferrite single crystals can be almost eliminated.
TL;DR: In this paper, single crystal octahedra of HgCr2Se4 of up to 1.5mm on an edge were grown by chemical transport in a closed system.
TL;DR: In this article, the diffusion constants of oxygen in nickel and α-iron were calculated from experimentally determined internal oxidation rates in dilute silicon-bearing alloys, and the activation energy required for oxygen diffusion was found to be 39.9 kcal/g atom in the range 700 to 850° C.
Abstract: The diffusion constants of oxygen in nickel and α-iron are calculated from experimentally determined internal oxidation rates in dilute silicon-bearing alloys. A single crystal alloy of composition 0.058 wt % silicon in nickel and polycrystalline alloys of composition 0.48 wt % silicon in nickel and 0.072 wt % silicon in iron were oxidised and allowance is made for the absorption of oxygen in the reaction with silicon. For nickel the values of activation energy Q=73.9 kcal/g atom in the range 800 to 1200° C and Q=74.4 kcal/g atom in the range 900 to 1300° C are in good agreement with a previous result. The activation energy required for oxygen diffusion in α-iron was found to be 39.9 kcal/g atom in the range 700 to 850° C.
TL;DR: In this article, the I-IlI-VI 2 ternary semiconductors CuAlS 2 and CuAlSe 2 have been prepared by vapour transport with iodine and optical transmission measurements give energy gaps of about 3.35 eV (sulphide) and 2.5 eV(selenide).
TL;DR: In this article, it was shown that at a critical thickness (∼200-300 A), there is a transformation from the fcc phase to the normal hcp phase in deposits on the (001) and (111) substrate surfaces.
Abstract: Single crystal thin films of titanium have been epitaxially grown on NaCl substrates of three different orientations [(001), (110), (111)]. At thicknesses above 500 A, the normal hexagonal close-packed structure is obtained. Below approximately 350 A, the metal is seen to grow in a previously unreported face-centered cubic structure with the lattice parameter, ao = 4.33 A. This structure is thought to result from pseudomorphic type growth on the NaCl substrate in keeping with proposed misfit theories. At a critical thickness (∼200–300 A), there is a transformation from the fcc phase to the normal hcp phase in deposits on the (001) and (111) substrate surfaces. The deposit on the (110) NaCl surface demonstrated a coexistence of fcc and hcp material at all thicknesses.
TL;DR: A defect diffusion coefficient was determined in single crystal aluminum oxide from 1400° to 1850°C by measuring the movement of the color boundary in a Ti3+− doped single crystal heated in air as mentioned in this paper.
Abstract: A defect diffusion coefficient was determined in single crystal aluminum oxide from 1400° to 1850°C by measuring the movement of the color boundary in a Ti3+− doped single crystal heated in air. In this temperature range the experimental data can be represented by
The interpretation developed is that this equation represents the diffusivity for a defect which contributes to aluminum self-diffusion.
TL;DR: In this article, single crystals of cytosine monohydrate have been irradiated and analyzed with electron spin resonance spectroscopy at 77°K. Two types of radicals have been observed and identified as the cytosinesine cation and anion radicals.
Abstract: Single crystals of cytosine monohydrate have been irradiated and analyzed with electron spin resonance spectroscopy at 77°K. Two types of radicals have been observed and identified as the cytosine cation and anion radicals. The hyperfine splittings of the 14N and 1H nuclei for the cation radical are found to be in fairly good agreement with the predictions of the molecular orbital theory. The anion‐radical hyperfine splittings could not be resolved in all crystal orientations. Both types of radicals rapidly disappear upon heating, probably via mutual recombination.
TL;DR: In this article, the ESR spectrum of a paramagnetic species in a single crystal is considered and the relationship between the Laue symmetry of the species, the LSA of the crystal, and the number of species observable in specific directions is derived.
Abstract: The ESR spectrum of a paramagnetic species in a single crystal is considered. Relationships between the Laue symmetry of the species, the Laue symmetry of the crystal, and the number of species observable in specific directions is derived. The application to experiment is discussed.