Showing papers in "Journal of Applied Crystallography in 1969"
TL;DR: In this paper, a structure refinement method was described which does not use integrated neutron powder intensities, single or overlapping, but employs directly the profile intensities obtained from step-scanning measurements of the powder diagram.
Abstract: A structure refinement method is described which does not use integrated neutron powder intensities, single or overlapping, but employs directly the profile intensities obtained from step-scanning measurements of the powder diagram. Nuclear as well as magnetic structures can be refined, the latter only when their magnetic unit cell is equal to, or a multiple of, the nuclear cell. The least-squares refinement procedure allows, with a simple code, the introduction of linear or quadratic constraints between the parameters.
14,360 citations
TL;DR: In this paper, a new study of the structure of vitreous silica has been made under greatly improved conditions, using Rh Kα radiation with the method of fluorescence excitation, reliable intensity values were measured to 4π sinθ/λ = 20.
Abstract: A new study of the structure of vitreous silica has been made under greatly improved conditions. Using Rh Kα radiation with the method of fluorescence excitation, reliable intensity values were measured to 4π sinθ/λ = 20. The interpretation was in terms of pair functions, thereby eliminating the approximations in earlier work. Each silicon is tetrahedrally surrounded by 4 oxygen atoms, with a Si–O distance which is closely 1.62 A. Each oxygen atom is bonded to 2 silicon atoms. The Si–O–Si bond angle α shows a distribution V(α) extending all the way from 120° to 180°, with a maximum at α = 144°. This wide variation in α is an important distinction between the vitreous and the crystalline forms of silica, and it furnishes an important criterion for any proposed model of vitreous silica. Good agreement with the measured pair function distribution curve was obtained by assuming a random orientation about the Si–O bond directions. The interpretation leads to the familiar random network model, but with the new results the model is more precise.
1,147 citations
TL;DR: A fully automatic program that finds the constants of the reciprocal lattice from powder data by selecting pairs of zones with a common row in order to find reciprocal lattices, which are then reduced in a simple way.
Abstract: A description is given of a fully automatic program, written in ALGOL 60, that finds the constants of the reciprocal lattice from powder data. The progress of the program is illustrated with the (nearly) complete computer output for one selected case. Planes through the origin of the reciprocal lattice (zones) are found first. After evaluating these, the program selects pairs of zones with a common row in order to find reciprocal lattices, which are then reduced in a simple way. Each solution is compared with the experimental data and a figure of merit is calculated. The program is most suited for compounds of orthorhombic or lower symmetry.
874 citations
TL;DR: In this paper, the lattice constants and the atomic position parameter, z, of a high purity, low strain, single-crystal of arsenic have been determined using low extinction reflections of filtered Mo Kα and Ag Kα radiation.
Abstract: The lattice constants and the atomic position parameter, z, of a high purity, low strain, single-crystal of arsenic have been determined. Low extinction reflections of filtered Mo Kα and Ag Kα radiation were used for the determination of z. The Bond precision technique with Mo Kα radiation was used for the determination of the unit-cell dimensions a and c. Average values for a and c in A, and for z are: 4.2°K z = 0.22764 a = 3.7597 c = 10.4412; 78°K z = 0.22754 a = 3.7595 c = 10.4573; 299±3°K z = 0.22707 a = 3.7598 c = 10.5475. The estimated standard deviation of z is ±0.00004 at 4.2°K, ±0.00002 at 78°K and ±0.00005 at 299°K. The precision of a is estimated to be ±0–0001 A and that for c to be ±0.0002 A. The results for As are compared with those reported earlier for Sb and Bi.
208 citations
TL;DR: The theory of single and multiple small-angle scattering of fibres with a two-phase system of densities is revised in this paper, where it is shown that the results of measurements with an ''infinite'' slit parallel to the fibre axis cannot give the specific internal surface directly, but that this information can be obtained by a combination of measurement and measurements with a pinhole system in the case of needle-like pores with preferred orientation.
Abstract: The theory of single and multiple small-angle scattering of fibres with a two-phase system of densities is revised Luzzati's fundamental treatment of multiple scattering has been applied to systems with cylindrical symmetry It is shown that the results of measurements with an `infinite' slit parallel to the fibre axis cannot give the specific internal surface directly, but that this information can be obtained by a combination of `infinite' slit measurement and measurements with a pin-hole system in the case of needle-like pores with preferred orientation The experimental results obtained indicate that the scattering at very small angles is a multiple scattering determined by the filament cross-section It is shown that parameters related to the size and the shape of the filament cross-section as wall as the specific surface of the filaments can be computed from this scattering The scattering at somewhat wider angles is essentially a single scattering and can contain two components The predominant component is a scattering of needle-like pores with diameters in the 10–20 A range and lengths of at least 200–300 A The porosity is around 30% The needle axes show a preferred orientation parallel to the fibre axis The angular distribution of the needle axes is very similar to that of the graphitic layers A second component can be observed, which is produced by density fluctuations in the parallel stacking of graphitic layers Studies on powdered fibres indicate changes in the microstructure due to the grinding
168 citations
TL;DR: In this paper, the axial thermal expansion of monoclinic and tetragonal ZrO2 and of monocallinic HfO2 was studied over the temperature range from room temperature to 1400 °C.
Abstract: The axial thermal expansion of monoclinic and tetragonal ZrO2 and of monoclinic HfO2 was studied over the temperature range from room temperature to 1400 °C. The linear thermal expansion coefficients were calculated. Thermal expansion along (x 106 per °C) a = 10.31 monoclinic ZrO2, 11.60 tetragonal ZrO2, 9.34 monoclinic HfO2; b = 1.35 monoclinic ZrO2, – tetragonal ZrO2, 2.98 monoclinic HfO2; c = 14.68 monoclinic ZrO2, 16.08 tetragonal ZrO2, 13.10 monoclinic HfO2. Some aspects of the present study, such as anisotropy of thermal expansion and a pretransformation vibrational anomaly, are discussed briefly.
165 citations
TL;DR: In this article, the theory of the direct comparison X-ray method of phase analysis is extended to correct for preferred orientation effects and texture parameters are defined to assess the type and intensity of preferred orientation using data from diffractometer patterns.
Abstract: The theory of the direct comparison X-ray method of phase analysis is extended to correct for preferred orientation effects. Texture parameters are defined to assess the type and intensity of preferred orientation using data from diffractometer patterns. The analysis is illustrated with results obtained on three austenitic stainless steels.
159 citations
TL;DR: In this paper, the texture of commercially produced stabilized steel in the temper rolled condition has been represented by a three-dimensional orientation distribution, defined by a set of coefficients of a series of generalized spherical harmonics.
Abstract: The texture of commercially produced stabilized steel in the temper rolled condition has been represented by a three-dimensional orientation distribution, defined by a set of coefficients of a series of generalized spherical harmonics. The coefficients have been used to calculate the elastic and plastic properties in the plane of the sheet and comparison is made between the predicted and experimental values. Errors in the experimental determination of pole figures have been analysed and estimated.
125 citations
TL;DR: In this paper, the lattice constants of yttrium and gadolinium iron and gallium garnets were measured in the temperature range 296-1400°K and the results showed that among these, GdGaG gave the closest match of Δa/a0 vs. T to YIG and to GdIG.
Abstract: Lattice constants of yttrium and gadolinium iron and gallium garnets and of yttrium aluminium garnet have been measured in the temperature range 296–1400°K. The results show that among these, GdGaG gives the closest match of Δa/a0 vs. T to YIG and to GdIG.
118 citations
TL;DR: In this paper, a study of the molecular and crystallographic structures of Langmuir-Blodgett multilayer films of lead stearate has been made, which consists of a large number of three-dimensional ordered lead Stearate crystals arranged in near-perfect alignment, with the longest axes of their unit cell projecting from the plane of the supporting substrate.
Abstract: A study has been made of the molecular and crystallographic structures of Langmuir–Blodgett multilayer films of lead stearate. Electron microscopy and diffraction were used in the examination of such a film which had separated from the glass slide on which it had been formed. The films consist of a large number of three-dimensionally ordered lead stearate crystals arranged in near-perfect alignment, with the longest axes of their unit cell projecting from the plane of the supporting substrate. The unit cell of the lead stearate crystal is either monoclinic with the space group P21/a or orthorhombic with the space group P21212. The former is considered to be rather the more likely. The major lattice spacings are 4.96 A (100), 7.38 A (010) and 47 A (001). The β angle of the monoclinic unit cell is not known but is probably within a few degrees of 90°. The lead atoms are in special positions in the basal plane, regardless of which is the correct unit cell, and the hydrocarbon chains make an angle of 62±5 ° with the basal plane. Any free stearic acid in the films occurs as a separate phase.
66 citations
TL;DR: In this article, a horizontal diffractometer has been set up for transmission studies of liquid samples, and a high temperature furnace assembly has been constructed which fits on the diffractor.
Abstract: A horizontal diffractometer has been set up for transmission studies of liquid samples. An asymmetric, singly bent LiF monochromator in the primary X-ray beam focuses the radiation on the receiving slit of the diffractometer. The sample rotates at half the angular speed of that of the X-ray detector to retain focusing at all angles of diffraction. A high temperature furnace assembly (camera) has been constructed which fits on the diffractometer. Its heating element consists of a thin-walled, pyrolitic graphite tube 38 mm in diameter. A special sample holder for the liquids is mounted on a boron nitride stool bolted to the bottom plate of the camera. The entire set-up allows the measurement of the diffracted intensity between 2θ = 2° and 2θ = 90° corresponding to K = 4πsinθ/λ = 0.3 A−1 at 12.4 A−1 when Mo Kα radiation is used. Correction procedures to obtain the scattered intensity per atom from the raw data are discussed, and a comparison is made between the transmission and reflection methods with liquid tin.
TL;DR: In this article, the interpretation of small angle scattering data is applied to various concentrated systems, such as polytetrafluoroethylene and cubic microcrystals of MgO, to obtain the ϕ(l) distributions characteristic of particles with or without sharp edges.
Abstract: The method proposed in part I for the interpretation of small angle scattering data is applied to various concentrated systems. For a dilute system, small angle scattering provides the ϕ(l) distribution of chords directly in the scattering units. Two examples of dilute particle suspensions are studied: firstly rounded particles of polytetrafluoroethylene and secondly cubic microcrystals of MgO. Thus we have obtained the ϕ(l) distributions characteristic of particles with or without sharp edges. For concentrated systems, when the ϕ(l) distribution of particle chords is known, small angle scattering provides the f(m) distribution of interparticle spacings. The result, applied to a porous aggregate of the rounded particles, already studied in a dilute state, and to a concentrated suspension of the same particles, gives two f(m) distributions distinctly characteristic of each state.
TL;DR: In this paper, the strain induced phase transformations produced in lead monoxide powders by ball milling at temperatures ranging from −196 to 200°C have been studied by X-ray diffraction methods.
Abstract: The strain induced phase transformations produced in lead monoxide powders by ball milling at temperatures ranging from −196 to 200°C have been studied by X-ray diffraction methods. It has been found that either of the two polymorphs, litharge and massicot, was partially converted to the other at all the temperatures investigated, and that, whichever polymorph was the starting material, the end product, after a sufficiently long time, was a mixture of the two polymorphs, both highly strained. The percentage of each phase present was found to be dependent on the temperature of deformation. The results have been interpreted by consideration of the production of the microstrain energy required to overcome the energy barrier to the transformation, and of the shear generated in the mill on the pressure-temperature phase diagram. It is considered that shear stresses can affect the nature of the pressure-temperature phase diagram, in a manner theoretically postulated by Kumazawa. The commercial importance of the results has been briefly outlined.
TL;DR: X-ray diffraction analyses of polycrystalline samples of Ca3TeO6 and Ca3WO6 have shown these compounds to be isostructural with Ca3UO6 (space group P21) as discussed by the authors.
Abstract: X-ray diffraction analyses of polycrystalline samples of Ca3TeO6 and Ca3WO6 have shown these compounds to be isostructural with Ca3UO6 (space group P21).
TL;DR: In this paper, slightly twinned and untwinned single crystals of Ba2NaNb5O15 have been studied by X-ray techniques and it was shown that the c axis is twice the previously reported value and there are 8 formula units per unit cell.
Abstract: Slightly twinned and untwinned single crystals of Ba2NaNb5O15 have been studied by X-ray techniques. Oscillation and full rotation X-ray photographs show the c axis to be twice the previously reported value; therefore, there are 8 formula units per unit cell. It was also found that Cmm2 (C2v11) is not the correct space group assignment for the crystals studied, and that Ccc2 (C2v13) appears to be likely.
TL;DR: In this paper, the α phase of the silver-magnesium alloy system containing 26.1 atomic per cent magnesium has been studied by X-ray diffraction methods in the temperature range from 20 to 678°C.
Abstract: The α phase of the silver–magnesium alloy system containing 26.1 atomic per cent magnesium has been studied by X-ray diffraction methods in the temperature range from 20 to 678°C. The tetragonal symmetry of the low-temperature phase is confirmed. The temperature variation of the lattice parameters and the volume expansion coefficient have been determined. It seems likely that the order–disorder transformation is a first-order rather than a second-order transformation.
TL;DR: In this article, the wear mechanism of tungsten monocarbide has been investigated, and it was shown that the deformation is an important factor in the wear of Tungsten carbide.
Abstract: The practical importance of tungsten monocarbide prompted an investigation into its wear mechanism. Initial studies on ball-milled tungsten carbide powders revealed considerable plastic deformation, coupled with a reduction in crystallite size. Deformation stacking faults, involving slip on the basal plane, were observed. The work was extended to sintered blocks, tool tips and single crystals. Studies on the worn surfaces of these revealed plastic deformation that extended to a depth of a few microns below the surface. The plastic deformation is an important factor in the wear of tungsten carbide.
TL;DR: In this article, the intensity relationships for the three common silicon carbide polytypes (6H, 4H and 15R) are presented together with the details of a technique by which pure polytype samples may be prepared.
Abstract: Revised intensity relationships for the three common silicon carbide polytypes (6H, 4H and 15R) are presented together with the details of a technique by which pure polytype samples may be prepared
TL;DR: In this paper, it has been observed for the first time that NaU2(PO4)3 single crystals possess ferroelectric properties, and the measurements were performed on very small single-crystal samples with an area of about 1 ǫmm2 and 0.05mm thick.
Abstract: By the application of Sawyer and Tower's method it has been observed for the first time that NaU2(PO4)3 single crystals possess ferroelectric properties. Hysteresis loops were recorded and ferroelectric parameters were determined at room temperature. The measurements were performed on very small single-crystal samples with an area of about 1 mm2 and 0.05 mm thick.
TL;DR: In this article, a typical Bonse-Hart small-angle diffractometer was experimentally investigated for infinite slit-height configuration for a wide range of angular divergence-limiting schemes.
Abstract: Slit smearing effects have been experimentally investigated for a typical Bonse–Hart small-angle diffractometer. This instrument was found to satisfy the criteria for infinite slit-height configuration for a wide range of angular divergence-limiting schemes. Standard mathematical desmearing methods applied to the data show excellent agreement with scattering data obtained from an essentially slit-correctionless instrument.
TL;DR: In this article, the orientation of the individual twin components can be determined from a knowledge of the relative magnitudes of the tilt angles in various twinned lattice planes, and from a study of the widths and contrast of bands in the images from different Bragg reflections from the same crystal face.
Abstract: In Berg–Barrett micrographs of twinned crystals whose structure is slightly distorted from cubic, a characteristic pattern of white and dark bands appears due to small changes of orientation of the reflecting planes; the appearance of these bands depends on which lattice planes are used for reflection. The orientations of the crystallographic axes in the individual twin components can be determined from a knowledge of the relative magnitudes of the tilt angles in various twinned lattice planes, and from a study of the widths and contrast of bands in the images from different Bragg reflections from the same crystal face. This method has been developed for twins appearing in rhombohedral and tetragonal structures, and applied to antiferromagnetic NiO and ferroelectric BaTiO3 crystals in order to identify microscopic domains.
TL;DR: In this article, a method for analyzing satellite reflections in X-ray diffraction patterns in terms of two- or three-dimensional atomic ordering arrangements is presented, which is consistent with the observed location and intensity distribution of the satellite reflections, as confirmed by structure factor calculation and by optical diffraction.
Abstract: A method is presented for analyzing satellite reflections in X-ray diffraction patterns in terms of two- or three-dimensional atomic ordering arrangements. The ordered arrangement of Nd atoms in Nd2(MoO4)3 has been successfully determined by this method. The derived model is consistent with the observed location and intensity distribution of the satellite reflections, as confirmed by structure factor calculation and by optical diffraction.
TL;DR: In this article, the X-ray powder diffraction pattern and precise determination of the lattice parameter of U2C3 (ao = 8.0899±0.0002 A) were given.
Abstract: The X-ray powder diffraction pattern and a precise determination of the lattice parameter of U2C3 (ao = 8.0899±0.0002 A) are given. Further analysis indicates that U2C3 appears to be a stoichiometric compound.
TL;DR: In this article, a commercial pole figure goniometer (Philips) is operated by a process control computer (IBM 1800) with a digital voltmeter to digitize the ratemeter output.
Abstract: A commercial pole figure goniometer (Philips) is operated by a process control computer (IBM 1800) with a digital voltmeter to digitize the ratemeter output. The pole density data are stored on disk, and, after processing, are recorded in the pole figure by a plotter attached to the computer. Automatic 2θ–θ powder scans can also be performed without hardware modification.
TL;DR: In this paper, a method combining the analysis of X-ray absorption profiles and selected area Xray topographs is presented for the elucidation of anisotropic effects and inhomogeneities of defect structures.
Abstract: A method is presented which combines the analysis of X-ray absorption profiles and selected area X-ray topographs. The method is based on X-ray divergent beam patterns obtained in transmission. The absorption profiles are obtained by unfolding the spectral distribution fi'om the profiles of the deficiency conics, whereas the selected area topographs derive from the corresponding diffraction conics. The synergy of the two techniques makes the method particularly useful for the elucidation of anisotropic effects and inhomogeneities of defect structures. An example is given for the room temlcerature deformaticn of ber:yllium.
TL;DR: In this article, a new application of small-angle scattering of X-rays to the determination of particle size distributions is discussed, without any hypothesis concerning the shape of these distributions.
Abstract: A new application of small-angle scattering of X-rays to the determination of particle size distributions is discussed, without any hypothesis concerning the shape of these distributions. The practical utilization of this method is described for the case of carbons. In the discussion, a comparison with the results of nitrogen adsorption on an oxidized pile-grade graphite sample is presented.
TL;DR: NiCd has been shown to be a η-carbide (E93) type, with a 0 (typically) = 11.387 µm and X-ray density 9.18 µm−3 as discussed by the authors.
Abstract: The constitution of the Ni–Cd phase-diagram has been explored by X-ray diffraction and microscopy, principally at its high-nickel end, but also with reference to the overall system. No primary solid solubility of Cd in Ni exists. The NiCd (β) compound equilibrates directly with nickel, with no further compound intervening. The unknown crystal structure of NiCd has been determined as being of the η-carbide (E93) type, with a0 (typically) = 11.387 A and X-ray density 9.18 g.cm−3. NiCd has a small homogeneity range and decomposes peritectically at about 680°C. The only other compound occurring in the system is Ni5Cd21 (γ). An earlier reported `Ni2Cd5' (γ) could not be confirmed, though γ′ could compositionally be a dimorph to γ. Three-phase coexistence of Ni, NiCd and Ni5Cd21 can occur unstably or in segregation, the constitution being sensitive to heat-treatment and to the large vapour-pressure differences. NiCd seems to represent a new class of η-carbide type intermetallic phases, in containing a non-transition metal and excluding any early-Group transition metal (e.g. IVA) so far thought to be essential. The wider implications of NiCd having this type structure are discussed briefly, and the (high Fe, Co, Ni, Cu)–(Cd, Zn) phase relations compared in series.
TL;DR: In this article, electron microscopy experiments show that the mechanism of electron-induced decomposition of tin(IV) sulfide differs from that of thermal decomposition, which is controlled by epitaxy and not by a three-dimensional relation between the two lattices.
Abstract: Electron microscope experiments show that the mechanism of electron-induced decomposition of tin(IV) sulfide differs from that of thermal decomposition. Hexagonal tin(IV) sulfide is converted to tetragonal tin in three equivalent orientations with [100]Sn parallel to [100]SnS2 and [001]Sn parallel to [001]SnS2. Experiments on epitaxic growth of tin on tin(IV) sulfide (001) surfaces and theoretical considerations of relative interface energies show that the reaction is controlled by epitaxy and not by a three-dimensional relation between the two lattices.
TL;DR: In this paper, X-ray diffraction measurements have been made at three compositions in the Bi-In system, each alloy was investigated in the liquid phase at two temperatures, 10°C above the liquidus and 499°C. Partial density functions were calculated by assuming that the like partial interference functions are the same as those of the pure components.
Abstract: X-ray diffraction measurements have been made at three compositions in the Bi–In system. Each alloy was investigated in the liquid phase at two temperatures, 10°C above the liquidus and 499°C. Partial density functions were calculated by assuming that the like partial interference functions are the same as those of the pure components. Partial coordination numbers obtained from these density functions lead to the conclusion that the liquid alloys are very similar to a disordered mixture of Bi and In atoms.