Showing papers on "Crystal published in 1972"
TL;DR: In this paper, a computer simulation model is described which applies to the molecular processes involved in crystal growth under very general growth conditions, and the transition probabilities used for adding and subtracting molecules from the crystal and for surface diffusion are shown to satisfy microscopic reversibility in equilibrium.
Abstract: A computer simulation model is described which applies to the molecular processes involved in crystal growth under very general growth conditions. The transition probabilities used for adding and subtracting molecules from the crystal and for surface diffusion are shown to satisfy microscopic reversibility in equilibrium. The computer program uses several internal self‐consistency checks, the results of which support the validity of the simulation method. Growth measurements are obtained in a range above and below the surface roughening temperature. The growth rates of the (100) face of a Kossel crystal show a two‐dimensional nucleation barrier at low supersaturations and below the roughening temperature. An almost linear dependence on supersaturation is observed above this temperature. This result is independent of the amount of surface diffusion. A simple step model is described and the resulting growth rates are compared with the simulated rates of faces containing a fixed number of steps. Agreement is...
438 citations
389 citations
343 citations
TL;DR: The presence of ordered atomic steps may be considered as a general structural property of high index surfaces regardless of the chemical bonding in the crystal as mentioned in this paper, and a nomenclature is suggested to identify the surface structures of stepped surfaces.
300 citations
TL;DR: In this paper, the vibrational spectra of diamond and diamond-like crystals of the elements of Group IV (Si, Ge, and gray Sn) were treated on the basis of a valence force potential.
Abstract: Lattice dynamics and the vibrational spectra of diamond and diamondlike crystals of the elements of Group IV (Si, Ge, and gray Sn) are treated on the basis of a valence force potential. Experimental phonon dispersion curves from the literature are satisfactorily fitted by a six‐parameter valence force potential. The one‐ and two‐phonon absorptions are compared with the calculated density of states g(v) and with the density of combined states J(v). The results are satisfactory. The success in reproducing the spectroscopic properties of all four elements with only these parameters is consistent with the highly directional character of the covalent bonds in the crystal and the lack of ionic character. The different information derived from the widely used shell model and the valence force potential are briefly discussed.
267 citations
TL;DR: In this paper, the authors used the most recent ice crystal drag coefficients, aspect ratios, and densities to calculate the terminal velocities of different ice crystal forms, using Doppler radar.
Abstract: Terminal velocities of different ice crystal forms were calculated, using the most recent ice crystal drag coefficients, aspect ratios, and densities. The equations derived were primarily for use in calculating precipitation rates by sampling particles with an aircraft in cirrus clouds, and determining particle size in cirrus clouds by Doppler radar. However, the equations are sufficiently general for determining particle terminal velocity at any altitude, and almost any crystal type. Two sets of equations were derived. The 'general' equations provide a good estimate of terminal velocities at any altitude. The 'specific' equations are a set of equations for ice crystal terminal velocities at 1000 mb. The calculations are in good agreement with terminal velocity measurements. The results from the present study were also compared to prior calculations by others and seem to give more reasonable results, particularly at higher altitudes.
233 citations
TL;DR: In this article, the authors measured the heat capacity of oterphenyl with an adiabatic calorimeter for the crystal from 2°K to Tm (329.35°K) and for the liquid from Tg to 360°K, on a sample with less than 0.005 mole % impurity.
Abstract: The heat capacity of o‐terphenyl has been measured with an adiabatic calorimeter for the crystal from 2°K to Tm (329.35°K), for the glasses from 2°K to Tg (around 240°K) and for the liquid from Tg to 360°K, on a sample with less than 0.005 mole % impurity. The heat of fusion and the entropy of fusion are 17 191 J mole−1 and 52.20 J°K−1· mole−1, respectively. The residual entropy of the glasses at 0°K is about 15 J°K−1· mole−1. Above 170°K, the heat capacity of the o‐terphenyl crystal is nearly proportional to the temperature to within 1%. Configurational entropy of the supercooled liquid, estimated from the result of this investigation, is used to relate the relaxation properties of glass‐forming liquids according to the theory of Adam and Gibbs. Good agreement is found for both viscosity and NMR correlation frequency data.
218 citations
TL;DR: The mechanism of microhardness print forming in diamond-structure crystals is considered to be the result of a local phase transition under the indenter with the formation of a metallic phase due to the high hydrostatic pressure generated in this case as mentioned in this paper.
Abstract: The mechanism of microhardness print forming in diamond-structure crystals is considered to be the result of a local phase transition under the indenter with the formation of a metallic phase due to the high hydrostatic pressure generated in this case. It is shown that at the temperature T < 0.3 to 0.4 Tml, where the microhardness Hv is weakly temperature-dependent, one has Hv ≈ Pc(Pc transition pressure). In GaAs crystals, where Hv ≪ Pc, the athermal part in the hardness-temperature curve was not observed. It is shown as well that at the moment when the indenter entering the crystal is stopped there is a thin layer around it which still contains the metallic phase with high electrical conduction. The estimated thickness of the layer is ≈ 0.05 μm. The plastic deformation is supposed not to proceed at this moment because of the friction forces which oppose the squeezing-out of the metallic layer.
[Russian text ignored].
212 citations
212 citations
TL;DR: In this article, the authors compared the predictions of a simple point charge model with and without corrections for polarization and repulsion for the removal of various electrons from the alkali chlorides and the sodium and cesium halides.
Abstract: We have measured ionization potentials for the removal of various electrons from the alkali chlorides and the sodium and cesium halides. These binding energies are compared with the predictions of a simple point charge model with and without corrections for polarization and repulsion. The simple model predicts and the data show that the spacings of the energy levels for a given ion are independent of what crystal it is in and are the same as for the free ion. The point charge model also allows us to calculate the difference between cation and anion energy levels in the same crystal. There is, however, a disagreement between the predicted and experimental values of this difference that ranges from about 1.8 eV for LiCl to −0.2 eV for RbCl. This discrepancy is markedly reduced by inclusion of polarization effects. The point charge model with polarization and repulsion corrections predicts absolute ionization potentials for the alkali and halide ions that differ in a systematic way from those observed. For the sodium halides, the difference between calculated and experimental energies decreases monotonically from about −4 eV for NaF to about 0.9 eV for NaI. The origin of these discrepancies is apparently due to charging of the samples and their trend is directly attributable to the size of the respective bandgaps. We show that the electrostatic model can be used to provide a comparison between experimental binding energies for inner electrons in a crystal and Hartree‐Fock calculations for binding energies of inner electrons in free atoms. Finally, using the point charge model we show that the binding energy of an electron on a highly charged ion in an ionic crystal is only slightly different from the binding energy of the same electron in the neutral atom.
169 citations
TL;DR: The acoustic properties and low-temperature specific heat of a dense metallic glass in bulk form have been studied for the first time in this article, where a large softening of long-wavelength transverse acoustic phonons in the glass, relative to the crystal, is observed which is not simply attributable to the small density difference between the two states.
Abstract: The acoustic properties and low-temperature specific heat of a dense metallic glass in bulk form have been studied for the first time. A large softening of long-wavelength transverse acoustic phonons in ${\mathrm{Pd}}_{0.775}$${\mathrm{Si}}_{0.165}$${\mathrm{Cu}}_{0.06}$ glass, relative to the crystal, is observed which is not simply attributable to the small density difference between the two states.
DSM1
TL;DR: In this paper, the effect of the metal particle size on the properties of a metal-on-carrier catalyst was discussed, and infrared spectra were recorded with a Grubb-Parson single-beam grating spectrometer provided with a GS 4-type monochromator.
Abstract: Publisher Summary This chapter discusses the effect of the metal particle size on the properties of a metal-on-carrier catalyst. To relate the adsorptive and catalytic properties of metal crystals to the crystal size, the structure of the crystal surface on an atomic scale must be known. This information is obtained from studies on crystal models. A surface atom has a smaller number of nearest neighbors than an atom in the interior of the crystal. The chapter illustrates the infrared studies on the adsorption of N2, CO, and CO2. The infrared spectra were recorded with a Grubb–Parson single-beam grating spectrometer provided with a GS 4-type monochromator. From thermodynamic considerations, it is evident that bulk nickel cannot be oxidized by CO2. In addition, the reaction of benzene with deuterium is an excellent means for studying the influence of the particle size on the catalytic activity.
TL;DR: In this paper, the authors observed on a NiO single crystal two superlattice X ray diffraction peaks, which disappear above the Neel point, and their intensities, 4 × 10 -8 smaller than normal ones, agree with those evaluated from photon-electron spin interaction.
TL;DR: In this article, a two-stage chain extended crystallization is shown to proceed by a two stage mechanism. Crystal thickening at the triple point may be kinetically controlled, but it is not shown in this paper.
Abstract: Chain extended crystallization is shown to proceed by a two-stage mechanism. Crystal thickening at the triple point may be kinetically controlled.
TL;DR: In this article, the structural influences of misfit, bonding and crystal dimension in epitaxial bicrystals are reviewed and a model in which the inter-action between the crystal halves is represented by a periodic force acting at the interface, the crystals are approximated by elastic continua and the structure is assumed to be governed by lowest energy principles.
TL;DR: In this paper, the magnetic properties of these phases are discussed in relation to crystal field effects and a possible band structure.Magnetic measurements from 1.5 to 300 K on the complete series of Cu3Au-type R Pd3 phases have been made.
Abstract: Magnetic measurements from 1.5 to 300 K on the complete series of Cu3Au-type R Pd3 phases have been made. LaPd3 and LuPd3 are diamagnetic at room temperature. CePd3 shows Pauli-type paramagnetism indicative of a nonmagnetic virtual bound state. PrPd3 and NdPd3 are affected at low temperatures by the presence of the crystal field. The magnetic properties of SmPd3 and EuPd3 are determined by the energy levels of the lowest multiplet. GdPd3 and (possibly) TbPd3 become antiferromagnetic at 7.5 and 2.5 K respectively. DyPd3-ErPd3 obey the Curie law. The magnetic properties of these phases are discussed in relation to crystal field effects and a possible band structure.
TL;DR: In this paper, a detailed study of the temperature dependence of this process, coupled with conductivity measurements, suggests a model in which the fixed holograms are associated with ionic charge patterns formed by drift of thermally activated ions in the electric field pattern of the original hologram, which would have an activation energy of ∼ 1.1 eV and a concentration in excess of 2 × 1013 cm-3 in fair agreement with previous measurements of ionic conductivity.
Abstract: Normally recorded phase holograms in undoped LiNbO3 can be made optically stable, i.e. fixed, by heating the crystal to roughly 100°C. A detailed study of the temperature dependence of this process, coupled with conductivity measurements, suggests a model in which the fixed holograms are associated with ionic charge patterns formed by drift of thermally activated ions in the electric field pattern of the original hologram. These ions would have an activation energy of ∼ 1.1 eV and a concentration in excess of 2 × 1013 cm-3 in fair agreement with previous measurements of ionic conductivity. The room temperature conductivity of the LiNbO3 used in our experiments is concluded to be less than 10-17 Ω cm)-1.
TL;DR: In this paper, the authors present a review of the state-of-the-art work in the field of thermal Neutron Diffraction, focusing on the use of the Aeta Cryst.
Abstract: ABRAHAMS, S. C. 8~ PRINCE, E. (1962). J. Chem. Phys. 36, 50. BACON, G. E. (1969). Acta Cryst. A25, 391. BINAS, H. (1966). Z. anorg, allg. Chem. 347, 133. BUSING, W. R. & LEVY, H. A. (1964). Acta Cryst. 17, 142. CALLERI, M. t~ FERRARIS, G. (1967). Per. Mineral, 36, 1. CASSIEN, M., HERPIN, P. & PERMINGEAT, F. (1966). Bull. Soc. franc. Min~r. Crist. 89, 18. CHIDAMBARAM, P., SEQUEIRA, A. • SIKKA, S. K. (1964). J. Chem. Phys. 41, 3616. COOPER, M. J. (1969). Acta Cryst. A25, 488. COPPENS, P. (1970). Chap. 6 in Thermal Neutron Diffraction. Edited by B. T. M. WILLIS. Oxford Univ. Press. COULSON, C. A. (1970). Chap. 5 in Thermal Neutron Diffraction. Edited by B. T. M. Wn.Lm. Oxford Univ. Press. CURRY, N. A., DENNE, W. A. & JONES, D. W. (1968). Bull. Soc. Chim. France, p. 1748. DENNE, W. A. & JONES, D. W. (1969). Aeta Cryst. A25, S 125. FERRARIS, G., JONES, D. W. & YERKESS, J. (1971a). Acta Cryst. B27, 349. FERRARIS, G., JONES, D. W. 8¢. YERKESS, J. (1971b). Acta Cryst. B27, 354. FISCHER, E. (1960). Chem. der Erde, 20, 162. GUI~RIN, H. (1941). Ann. Chim. 16, 101. MARTIN, C., DURIF, A. & AVERBUCH-POUCHOT, M.-T. (1970). Bull. Soc. fi'anf. MinOr. Crist. 93, 397.
IBM1
TL;DR: In this paper, high purity single crystals of PbZrO3 suitable for electrical measurements were grown from solutions in the PbO-ZRO2-PbF2-B2O3 system.
Abstract: High-purity single crystals of PbZrO3 suitable for electrical measurements were grown from solutions in the PbO-ZrO2-PbF2-B2O3 system. Dielectric, hysteresis-loop, and optical measurements confirmed the existence of an intermediate ferroelectric (FE) form, previously observed only in ceramics, just below the transition temperature (Tc#232°C). The temperature stability range of the FE phase, which cooling curve measurements show to vary from 12° to 26°C, appears to be related to crystal stoichiometry. The maximum value of spontaneous polarization is P8(max)#24 μC/cm2, assuming that the FE phase possesses rhombohedral symmetry.
TL;DR: In this article, the authors used the scattering spectra from adsorbed xenon to investigate the surface structures of Ir (100) 1 × 1 and 1 × 5 type substrates at 55°K.
TL;DR: In this paper, the integrated Raman scattering cross-section in BaTiO3 has been measured near and above the ferroelectric phase transition as a function of temperature and the results indicate that there is disorder which breaks the crystal inversion symmetry in the cubic phase of Ba TiO3.
TL;DR: Particle size spectra were measured during 20 hr of sampling in cirrus generating cells (uncinus, stratus, spissatus, thunderstorm anvil) and the particle concentration, mean crystal length, ice water content, reflectivity factor, and precipitation rate were calculated from these spectra as discussed by the authors.
Abstract: Particle size spectra were measured during 20 hr of sampling in cirrus generating cells (uncinus, stratus, spissatus, thunderstorm anvil) and the particle concentration, mean crystal length, ice water content, reflectivity factor, and precipitation rate were calculated from these spectra. Average values of the physical properties in the generating cells were: Ice crystal concentration: 10,000–25,000m−3 Mean crystal length: 0.6–1.0 mm Particle habit: bullet, rosette, column (75%)-plate (25%) Ice crystal density. 0.6–0.9 gm m−3 Ice water content. 0.15–0.25 gm −3 Reflectivity factor: 5.0–20.0 mm6−3 Precipitation rate. 0.5–0.7 mm hr−1 Growth was found to be downward, reaching a maximum ice water content just below the base of the generating cell. The maximum ice water contents (not including the thunderstorm anvil) were found in cirrus uncinus. Liquid water was not found throughout the cirrus sampling by measurement with the Johnson-Williams hot wire liquid water meter; however, we believe that liqui...
TL;DR: In this article, a new bulk crystallization process is described in which the supersaturation in the crystalliser is maintained by feeding very small subcritical crystals, which grows at the expense of the dissolving sub-critical crystals.