Showing papers on "Lattice constant published in 1979"
TL;DR: In this paper, the details of the interface region of a molecular beam epitaxially grown Al single crystal on a single-crystal substrate were studied using X-ray diffraction and total external reflection.
Abstract: A new technique utilizing conventional x‐ray diffraction in conjunction with total external reflection has provided a powerful tool for studying ordered interfaces and surface phenomena. It has been used in this work to study the details of the interface region of a molecular beam epitaxially grown Al single crystal on a molecular beam epitaxially grown GaAs single‐crystal substrate. A simple model including variations of the lattice parameter and disorder in the interface region is in agreement with these experimental results.
482 citations
TL;DR: In this paper, a model system composed of identical dielectric spheres ordered in a three-dimensional lattice is derived and the diffraction of uv or visible light is formulated, in which the large lattice constants and hence the low frequency of diffracted electromagnetic waves give rise to a Bragg reflection orders of magnitude stronger than that involved in the x-ray diffraction.
Abstract: For a model system composed of identical dielectric spheres ordered in a three-dimensional lattice, the secular equation of the energy band of photons is derived and the diffraction of uv or visible light is formulated. The model simulates void lattices in irradiated metals or ordered lattices in polystyrene latexes, in which the large lattice constants and hence the low frequency of the diffracted electromagnetic waves give rise to a Bragg reflection orders of magnitude stronger than that involved in the x-ray diffraction. The present formulation is an extension of the theory of Mie and Debye. Also, it is an extension of the Korringa-Kohn-Rostoker formalism for energy-band calculations to Maxwell's equations or to the vector Helmholtz equation. Although the present paper is restricted to developing a formulation, some characteristic aspects anticipated in low-energy photon diffraction are discussed in relation to low-energy electron diffraction.
308 citations
TL;DR: In this article, a computer modeling study has been made of the structure of f.c. boundaries which are defined by {111}f.c∥{110}b.c and a rotation about an axis normal to these conjugate habit planes leading to orientation relationships.
234 citations
TL;DR: In this paper, the structure parameters of the wurtzite type compounds Sic-2H and ZnO were determined using X-ray intensities from single crystals collected with an automatic single crystal diffractometer.
204 citations
TL;DR: In this article, the Invar character disappears after irradiation up to 250°C, in particular the variation of the lattice parameter versus temperature becomes linear around room temperature, and two phases appear in the alloy, one rich in nickel and ordered with FeNi (AuCu) superstructure, the other rich in iron and probably ordered (Fe 3 Ni) The Invar state is therefore shown to be a metastable state.
154 citations
TL;DR: In this article, the long-range pair potentials for the fcc metals Ni, Au, Ag, Pt, Pd, Cu, and Al have been derived for a variety of point-defect properties including self-interstitial geometries and migration energies.
Abstract: Long-range pair potentials are presented for the fcc metals Ni, Au, Ag, Pt, Pd, Cu, and Al. Experimental data considered in deriving the potentials include the sublimination energies and stacking-fault energies as well as the lattice parameters, elastic constants, and vacancy-formation and -migration energies. A volume-dependent energy term has been included in the potentials. By scaling the potentials with respect to lattice spacing and a characteristic binding energy, a striking similarity can be seen between the various potentials. These potentials have been used to calculate a variety of point-defect properties including self-interstitial geometries and migration energies. In addition the migration energy of helium and its binding energy to a vacancy have been calculated.
147 citations
TL;DR: In this article, the dominant disorder in GaAs is Frenkel defect formation on the arsenic sub-lattice with the arsenic vacancy exhibiting donor-like behaviour at high temperatures, and the phase extent of GaAs was mapped and the model shown to account adequately for the density, lattice parameter and internal friction variations in as-grown and heat treated material as well as for the high temperature Hall coefficient behaviour.
138 citations
TL;DR: In this paper, a modified form of the electron-gas approximation is proposed for the calculation of interionic potentials in the solid state, and the results of these potentials are calculated and compared both with experiment and with the results derived from other theoretical methods.
Abstract: For pt.I see ibid., vol.10, no.9, p.1431 (May 1977). A modified form of the electron-gas approximation is proposed for the calculation of interionic potentials in the solid state. On the basis of these potentials perfect lattice and defect properties of a number of solids are calculated and compared both with experiment and with the results derived from other theoretical methods. The cohesive energies, lattice constants and compressibilities of a wide range of oxides are considered, while the defect energies for NaCl, MgO, MnO, CaF2 and MgF2 are examined in detail. From the results presented it is concluded that for solids such as the alkali and alkaline-earth halides and the alkaline-earth oxides, which are largely ionic, the modified electron-gas approximation is a reliable non-empirical method for the calculation of interionic potentials.
129 citations
TL;DR: In this paper, the anomalous rise in birefringence with temperature is interpreted in terms of lattice strain and dielectric polarization, and the lattice parameters of PbTiO3 single crystals are described as a function of temperature.
Abstract: Measurements of lattice parameters and birefringence of PbTiO3 single crystals are described as a function of temperature. The anomalous rise in birefringence with temperature is interpreted in terms of lattice strain and dielectric polarization.
128 citations
TL;DR: In this article, a parameter-free calculation of the equation of state for KCl and NaCl is presented which gives an accurate prediction of the equilibrium lattice constant over wide-ranging values of pressure and temperature.
Abstract: A parameter-free calculation of the equation of state for KCl and NaCl is presented which gives an accurate prediction of the equilibrium lattice constant over wide-ranging values of pressure and temperature. The results also show a lattice instability which is consistent with melting.
109 citations
TL;DR: In this paper, a model based on the coexistence of two types of defects, namely, vacancies in the lithium sub-lattice and lithium antistructure atoms in the aluminum sublattices, characterized the defect structure.
TL;DR: In this paper, the authors used neutron diffraction to determine some structural properties of montmorillonite-water systems at low water concentrations, and fitted both the intensities of (00l) reflections and the shape of (001) reflection quantitatively to a model which allows for a Gaussian spread of platelet spacing about a mean value.
Abstract: The use of neutron diffraction to determine some of the structural properties of montmorillonite-water systems at low water concentrations is described. The samples were prepared by compression or suction to give clay samples with between one and three molecular layers of water between the plates. About 10% of the platelets in the clay are randomly oriented. The remainder are partially oriented in the plane of the sample, with an angular spread of 40° about the mean orientation. It is suggested that these oriented domains are formed from the larger platelets present in the system. The Bragg diffraction pattern is better explained by a disordered lattice model rather than by a mixture model with small particles having a well-defined lattice spacing. We have fitted both the intensities of (00l) reflections and the shape of the (001) reflection quantitatively to a model which allows for a Gaussian spread of platelet spacing about a mean value. The half width of the spread is about 10% of the lattice spacing. No significant structural differences are found between Li, Na, K, and Cs montmorillonites. The method of preparation has no effect on the structural properties of the large platelet particles but does affect the randomly oriented fraction. The lattice spacing of the latter appears to be better defined for samples prepared by compression. Experiments on the variation of lattice spacing with humidity indicate that the structural model we have used is adequate except at humidities where the system is changing over from one to two, or two to three water layers.
TL;DR: In this article, the surface vibrational modes of atomic hydrogen adsorbed on W(100), observed by electron energy loss spectroscopy in off-specular directions, indicate bridge-site bonding at all coverages.
TL;DR: In this article, the effects of the [N2]/[Ti] molar ratio of the reactant on the nature of the products were investigated by chemical analysis, X-ray diffraction and electron microscopy.
Abstract: The ultrafine titanium nitride particles with a statistical median size of about 10 nm were prepared by passing pure titanium powder (<25 μm) through a radio-frequency (r.f.) argon-nitrogen plasma. The effects of the [N2]/[Ti] molar ratio of the reactant on the nature of the products were investigated by chemical analysis, X-ray diffraction and electron microscopy. The conversion efficiency was close to 100%. The colour of the product was black, which is attributed to the particle size ranging from 5 to 150 nm. Most of the crystallites were single crystal and showed clear-cut habits of cubic phase. The chemical composition and lattice parameter of the products changed with the [N2]/[Ti] ratio. The thermodynamics of the process were also considered. These results provide evidence to suggest that new materials can be produced by an r.f. plasma process, in particular, the ultrafine refractory nitrides.
TL;DR: In this paper, a double point of view of mean lattice parameter variation (uniform strain) and lattice microstrains (non-uniform) was compared from the double point-of-view.
Abstract: Twelve samples of three kinds of highly divided nickel oxide, prepared from nickel hydroxide at low temperature, have been compared from the double point of view of mean lattice parameter variation (uniform strain) and lattice microstrains (non-uniform strain). These samples are black non-stoichiometric NiO with a mosaic texture, a green stoichiometric NiO with the same mosaic texture and black non-stoichiometric NiO made up of tiny quasi-perfect single crystals (monolithic NiO). The textures of the three kinds of oxides have been inferred from electron microscopy and diffraction and X-ray diffraction. Crystallite sizes and microstrain values have been obtained from X-ray line broadening analysis. Deviations from stoichiometry have been obtained from chemical analysis. Correlations between uniform strain, non-uniform strain, texture and stoichiometry have been researched. It appears from the comparison of the results that uniform and non-uniform strains are insensitive to the extent of deviation from stoichiometry. The non-uniform strain is mainly due to the mosaic texture of the grains. The uniform strain related to the mean lattice parameter variation appears to be related to the small crystallite size. These two aspects are related to the mechanism of the oxide formation from the hydroxide.
TL;DR: In this article, a phase diagram has been constructed of the various two-dimensional phases of C${\mathrm{D}}_{4}$ physisorbed on graphite and the lattice constant, intensity, and cluster size have been measured as functions of temperature and coverage.
Abstract: Neutron-diffraction studies have been carried out of the various two-dimensional phases of C${\mathrm{D}}_{4}$ physisorbed on graphite and a phase diagram has been constructed. Registered, expanded, and compressed solid phases and a disordered fluidlike phase have been identified. The lattice constant, intensity, and cluster size have been measured as functions of temperature and coverage and the nature of the transitions between the phases has been investigated.
TL;DR: In this article, a model potential consisting of a crystalline field (onebody potential), octopole-octopole type and hexadecapole-hexadecapoles type was used to elucidate the structure of methane solids in phase III, where carbon atoms are fixed at sites of a fcc lattice, and the orientational order has the period not larger than twice the lattice constant of the carbon fcc.
Abstract: In order to elucidate the structure of methane solids in phase III, orientational orderings of molecules are studied on the basis of a model potential consisting of a crystalline field (one‐body potential), octopole–octopole type, octopole–hexadecapole type, and hexadecapole–hexadecapole type potentials, which are obtained through a multipole expansion of the sum of interatomic Lennard‐Jones type potentials. It is assumed that carbon atoms are fixed at sites of a fcc lattice, and that the orientational order has the period not larger than twice the lattice constant of the carbon fcc lattice. In the framework of classical molecular field approximation, we solve consistency equations for molecular fields, and examine stabilities of various solutions which branch off from phase I (disordered phase) or from phase II (partially ordered phase). To this end, Landau’s theorem on the phase transition of second order is extended such that it allows us to determine possible space groups for the lower temperature pha...
TL;DR: In this paper, the structural changes of single crystals of the mixed-valence compound Cs2AuIAuIIICl6 under high hydrostatic pressure were studied using a gasketed diamond-anvil high-pressure cell, which has been adapted to the automatic four-circle diffractometer.
Abstract: Using a gasketed diamond-anvil high-pressure cell, which has been adapted to the automatic four-circle diffractometer, we have studied the structural changes of single crystals of the mixed-valence compound Cs2AuIAuIIICl6 under high hydrostatic pressure. Measurements with a modified measuring procedure at different pressures show a continuous decrease in the lattice constants. The changes in the relative volume are about 19% in the pressure range up to 52 x 108 Pa while the a/c ratio remains constant. The Cl atoms, which coordinate with the different gold atoms in the form of strongly distorted octahedra, move towards the symmetrical position between the AuI and AuIII atoms as the pressure increases. At about 52 x 108 Pa the gold atoms become indistinguishable, this means only formal Au2+ atoms are present.
TL;DR: In this article, the relation between the stability and the structural mismatch in layered bismuth compounds, (Bi 2 O 2 ) 2+ (A n−1 B n O 3n+1 ) 2−, was formulated on the basis of an elastic model.
TL;DR: In this article, the phase boundary was determined from the variation of the lattice parameter with hydrogen concentration, and the thermal expansion coefficient increases with hydrogen concentrations and shows an anomalous behaviour just above the alpha - alpha '' phase transition.
Abstract: The incoherent phase transitions of H and D in Nb have been studied by X-ray scattering. For all investigations Nb was loaded with hydrogen in situ in order to prevent precipitation of the new phase, before starting the experiment, which irreversibly changes the crystal lattice and gives misleading results. The incoherent phase boundary was determined from the variation of the lattice parameter with hydrogen concentration. The lattice parameter varies linearly with concentration at least up to 0.34 H/Nb. The thermal expansion coefficient increases with hydrogen concentration and shows an anomalous behaviour just above the alpha - alpha ' phase transition. For the alpha - alpha ' transition of H and D in Nb the critical temperature is Tc=171+or-1 degrees C and the critical concentration cc=0.31+or-0.01 H/Nb. The triple point temperature of the alpha + beta to alpha + alpha ' transition is 88 degrees C for H and 99 degrees C for D in Nb.
TL;DR: In this paper, the formation of spinel Li[Mn2]O4 from Li2CO3 and Mn3O4 by solid state reaction was examined as a function of temperature.
TL;DR: In this article, the phonon frequencies of gallium phosphide were measured along the Delta, Sigma, Lambda and Z-lines and a valence-force-field overlap shell model was used to explain them.
Abstract: The phonon frequencies of gallium phosphide were measured along the Delta -, Sigma -, Lambda - and Z-lines and a valence-force-field overlap shell model, which reproduces the considerable dispersion observed along the Z line, is used to explain them.
TL;DR: In this article, the first isotypic compounds with three-valent rare earth metals have been prepared for the first time and their crystal structure corresponds to that of Ce2O2S (ordered “anti-La2O3 or CaAl2Si2-type structure).
TL;DR: In this paper, the cubic form of indium trihydroxide was obtained by hydrothermal methods at varied concentrations and temperatures. But the final refinement based on 106 independent reflections yields a conventional R value of 1.48%.
TL;DR: In this paper, the lattice spacing and orientation of Y-cut plates were determined from X-ray topographs taken successively at various angular positions around the Bragg position using the double crystal arrangement of parallel setting.
TL;DR: In this paper, the X-ray-crystal structures of both (η5-C5H5)Cr(CO)2(NO) (I) and ( η5C13H9)Cr (CO) 2 (NO)2 (II) are described, where the carbonyl and nitrosyl groups are disordered in I, but the nitro-syl ligand in II occupies a position in the electron-rich C(9) of the fluorenyl system.
TL;DR: In this article, the temperature of transition to a zero-tilt phase was investigated in the perovskite-like layer structures of (C n H 2 n +1 NH 3 ) 2 MnCl 4 with n = 1-10.
TL;DR: In this article, the lattice parameter of SmS single crystals has been measured under hydrostatic pressure up to 70 kbar and the fit for the metallic phase by means of the Birch equation gives an unusually large pressure derivative of the bulk modulus B' = 11 and hence a large pressure dependence of B. No change in the nonmagnetic intermediate valence state of Sm is observed up to 24 kbar.
TL;DR: The lattice constants for the trihydroxides of Pr, Er and Tm are a 0 = 6.456(1), 6.352(1, and 6.769(1) A and c 0 = 3.503(2) A.
TL;DR: In this article, the phase relations in the system HfO2-Sm2O3 were studied by high-temperature and room temperature X-ray diffraction and a tentative phase diagram was proposed.
Abstract: The phase relations in the system HfO2-Sm2O3 were studied by high-temperature and room-temperature X-ray diffraction. The areas of existence of the solid solutions based on HfO2, Sm2Hf2O7, and Sm2O3 were determined using the lattice parameter method. Also, the influence of small additions of Sm2O3 on the monoclinic-tetragonal transformation temperature of hafnia was studied. A tentative phase diagram is proposed.