Intensity Of Diffraction Lines Research Articles

Effect of heavy atom disorder on the intensities of powder XRD lines of YBa2Cu3O7-y

Abstract It is shown that heavy atom disorder resulting from Y ↔ Ba, Ba ↔ Cu and Y ↔ Cu interchanges due to local stoichiometric constraints can cause significant changes in the intensities of X-ray powder diffraction lines of YBa2Cu3O7-y . A comparison of the theoretically predicted intensities with published patterns for specimens prepared by the conventional dry route reveals that Ba ↔ Cu interchanges involving copper atoms in the CuO2 planes can occur quite frequently and may be mistaken for (00l) texture.

Isotropic compression of the linear-chain perovskite-type CsCdBr3 up to 20 GPa.

Powder x-ray-diffraction experiments have been performed on 2H-${\mathrm{CsCdBr}}_{3}$ at room temperature up to 20 GPa. Although this compound is usually considered as quasiunidimensional, such a characteristic could not be evidenced for its elastic bulk properties under pressure. No phase transformation occurs in this pressure range, and the a and c lattice parameters steadily decrease with pressure; their ratio lowers by only 2%. As for the bulk modulus, its first and second pressure derivatives have been calculated using Birch's equation of state. The bulk modulus is low (21.3 GPa) and is in good agreement with the bulk-modulus--volume systematics for usual ionic compounds. The value of the first pressure derivative is also typical of ionic compounds. Above 5 GPa increasing intensities of a few diffraction lines were observed; they are consistent with a shift of the bromine anions inside the cell that leaves the structure unchanged. This is also supported by the variations of the Raman frequencies with volume.

Preparation of Bi-Sr-Ca-Cu-O superconductors by the floating-zone melting method

The authors succeeded in obtaining highly oriented crystalline samples of 2212 Bi-Sr-Ca-Ca-O superconductors by the floating-zone melting method. The critical current densities Jc were largely dependent on the degree of crystalline alignment obtained from a ratio of X-ray diffraction line intensities. For a highly oriented crystal, the authors obtained a value for Jc of 14800 A cm-2 at 77.3 K in the absence of a magnetic field.

The Influence of Interstitial Alloying Elements on the Phase Stability and Fracture Toughness of V3Au

AbstractAdditions of the interstitial elements oxygen and carbon to the A15 structure V3Au intermetallic compound resulted in the formation of the L'2 perovskite structure. The composition of the L'12 phase is about 17.5 at.% oxygen. Analysis of x-ray diffraction line intensities indicated that the interstitial stabilized phase was L'12 perovskite structure rather than the L12, Cu3Au structure type. The microhardness of the L'12 phase is about 20% lower than that of the A15 phase and its fracture toughness is 2 to 3.5 times greater. The mechanism for the improved fracture toughness in the L'12 phase is the subject of continued research.

Mechanochemical phenomena of gibbsite, bayerite and boehmite by grinding

Three hydrated aluminas, gibbsite, bayerite and boehmite, were ground in air for 0.25–20 h by a planetary ball mill. The effect of grinding on their texture, structure and thermal behaviors has been examined by means of XRD, TG, DTA, SEM, IR, particle size distribution and nitrogen gas adsorption. It was found that in the initial stages of grinding (within the first 1 h), the specific surface area, S, had increased in the gibbsite, decreased in the bayerite and had a maximum in boehmite, and then proceeded to achieve their respective equilibrium values. These behaviors were correlated with changes in the median size, d 50, as a measure of the aggregate size of the particles. Prolonged grinding times, led to a decrease in the intensity of X-ray diffraction lines and an increase in the half-maximum line breadth. After 4 or 8 h grinding all the hydrated aluminas had been changed to the amorphous phase without mechanochemical dehydration. Moreover, the DTA endotherms attributable to the dehydration of the hydrated aluminas gradually diminished on grinding, and a set of broad endotherms appeared at about 150 or 200 °C for the amorphous phases. Whereas the transformation sequences of the unground hydrated aluminas to α-Al 2O 3 showed gibbsite → χ → κ → α, bayerite → η → θ → α and boehmite → γ → δ → θ → α, all the amorphous phases showed the amorphous hydrated alumina → amorphous alumina → η → α and the temperature of α-transformation had been lowered by more than 200°C.

Quasicrystalline Ti-Ni-Fe-Si: Mössbauer indications for high transition-metal-site symmetry.

Melt-spun ${\mathrm{Ti}}_{56}$${\mathrm{Ni}}_{28\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Fe}}_{\mathrm{x}}$${\mathrm{Si}}_{16}$ shows the icosahedral phase recently reported for other rapidly quenched Ti-Ni-based alloys. $^{57}\mathrm{Fe}$ M\"ossbauer measurements in this alloy yield a quadrupole splitting \ensuremath{\Delta}\ensuremath{\sim}0. The value of \ensuremath{\Delta} indicates a highly symmetric Fe site in the icosahedral structure. The relative intensities of the x-ray diffraction lines suggest a structure based on a three-dimensional Penrose tiling in which some of the transition-metal atoms occupy sites with icosahedral symmetry. This is the first experimental indication that a transition metal may occupy the icosahedral site in any quasicrystal.

High-symmetry transition-metal sites in Ti56Ni28−xFexSi16 quasicrystals

Rapidly solidified Ti-Ni-Fe-Si alloys are found to form a metastable phase with x-ray diffraction patterns which can be indexed to a structure with icosahedral symmetry. 57 Fe Mössbauer effect spectra show a negligible quadrupole splitting for the icosahedral phase. This observation, along with a comparison of the measured x-ray diffraction line intensities with calculated values, suggests a structure based on a decoration of a three-dimensional Penrose tiling, with transition-metal atoms in sites with local icosahedral symmetry. Magnetic susceptibility measurements show that a local moment of ∼0.2 μB forms on the Fe atom. These results are discussed in terms of possible local Fe environments.

A study of the YxBa1-xCuOysuperconductors for 0.3<x<0.42

A series of compositions in the region of the YBa2Cu3O7- delta superconducting phase have been studied exhaustively. These materials show significant changes in the X-ray diffraction line intensities which are closely correlated with variations in both the electrical conductivity and the thermoelectric properties as a function of composition. Evidence exists to suggest that these changes may correspond to a change in the hole concentration with increasing x. It is proposed that these effects are associated with the continuous introduction of yttrium planar stacking faults which automatically compensate for the yttrium-barium imbalance and at the same time generate an increased oxygen concentration.

Ion Induced Quasicrystalline Transformation in the Al-Cr-Er System

ABSTRACTThe Aluminum-rich end of the Al-Cr-Er ternary system was investigated in an effort to find new quasicrystalline alloys. Composition, dose dependence and substrate temperatures during ion irradiation were varied. A quasicrystal alloy with the Al-Cr intensity pattern was found at low Er content. Another phase was observed that did not index to any known equilibrium structure. This new phase has d spacings and diffraction line intensities which are similar to those of the Al-Li-Cu quasicrystalline phase.

Accuracy in Temperature Factor Determination in Powder Diffractometry

The discrepancy between the temperature factors derived from X-ray powder diffraction and those derived from X-ray single crystal or neutron powder diffraction led us to look for additional causes of systematic intensity errors for powders. Integrated intensities of powder diffraction lines were carefully measured for selected materials using a Bragg-Brentano powder diffractometer equipped with an automatic divergence slit and a graphite monochromator. The measured intensities were compared with calculated intensities and significant systematic effects were observed which could not be related to structural sources, but were traced to instrumental sources. Use of an empirical angular dependence correction factor resulted in acceptably low R values. The instrumental factor couples strongly to the temperature factor by virtue of a similar angular dependence. Thus, reliable temperature factors cannot be obtained from commercial powder diffractometers unless the instrumental contributions are first removed.

Results of the JCPDS-ICDD Intensity Round Robin

Last year at this conference we submitted a preliminary report on an X-ray powder diffraction round robin sponsored by the JCPDS-ICDD. This round robin was designed primarily to study the intensities of diffraction lines found by users in routine work. At that time only a portion of the data had been analyzed, and we reported initial findings on the α-Al2O3, and Zn0 /CaCO3 samples. These included studies on counting statistics, resolution, and the effect of software on intensity precision. Since that time, all the data from the round robin has been entered into Lotus 1-2-3 (*) spread-sheets and numerous additional tests have been carried out. This paper discusses some of the more interesting findings. A complete paper on all of the tests performed is in preparation for submission to the "Methods and Practices Manual" published by the JCPDS-ICDD.

The compositional and structural properties of sprayed SnO 2:F thin films

Thin films of SnO 2 doped with fluorine were produced by the conventional spraying method using Corning 7059 glass substrates. The electrical and optical properties of these films were determined as a function of the substrate temperature T s and dopant concentration in the basic spraying solution. The visible and near-IR transmittance as well as the electrical resistivity of the films decreased with an increase in the fluorine concentration. The best electro-optical properties (an average transmittance of 75% and an electrical resistivity of 10 −3 Ω cm) were achieved for 250°C⩽ T s⩽350°C and fluorine concentrations (relative to tin) in the spraying solution of around 2 at.%. The surface texture of the films was investigated by scanning electron microscopy and optical microscopy. The fluorine content of the samples was analysed by secondary ion mass spectroscopy, Auger electron spectroscopy and electron spectroscopy for chemical analysis. Structural changes were studied using X-ray diffractometry. A systematic change in the intensity of the X-ray diffraction lines as a function of the fluorine content was observed. Theoretical calculations of the structure factors associated with the SnO 2 lattice if fluorine atoms are introduced into substitutional and interstitial positions were performed.

Observed and Calculated XRPD Intensities for Single Substance Specimens

One of the areas of X-ray powder diffraction receiving considerable attention in recent years is quantitative analysis. This analysis depends on an accurate measurement of integrated diffraction line intensities. In order to study the accuracy of these measurements we have calculated integrated intensities from single crystal data for single substance powders and compared them to experimental data obtained in our laboratory.

High T c superconducting NbN films deposited at room temperature

Thin films of niobium nitride with superconducting transition temperature (Tc ) of 15.7 K have been deposited on a variety of amorphous as well as crystalline substrates including glass, glazed ceramic, fused quartz, and sapphire, maintained at room temperature, by dc reactive magnetron sputtering in a mixture of Ar and N2 gases. The effects of the deposition conditions, particularly the carrier gas pressure and composition, on the film crystal structure, orientation, and resistivity have been studied in an effort to maximize the superconducting transition temperature. A study of the variation of nitrogen consumption with nitrogen injection pressures for constant background argon pressures is conducted and found to be an absolute indicator of the NbN formation systematics. Initially, the consumption increases linearly with the injection pressure but beyond a certain threshold, it shows a distinct drop. The desired high Tc NbN with B1 crystal structure is formed in the vicinity of this turning point of the reactive gas consumption-injection characteristic. High Tc films possess B1 (fcc, NaCl-type) crystal structure as revealed by their x-ray diffraction patterns. An initial increase in the injection pressure of the reactive gas (N2) results in a remarkable increase in the (111) diffraction line intensity along with an increase in the film Tc. This trend continues up to the turning point of consumption-injection characteristic, beyond which the crystal structure distorts into the substoichiometric tetragonal phase with a consequent reduction in the transition temperature. A general protocol for studying the formation systematics of transition metal nitrides has thus emerged.

STUDIES ON ALKALINE EARTH SULFITES. VII. HYDROGEN BONDING AND THE LOCATION OF HYDROGEN ATOMS IN THE CRYSTAL STRUCTURE OF CaSO3·4H2O AND Ca3(SO3)2SO4·12H2O

Abstract The location of the hydrogen atoms in the crystal structure of CaSO3·4H2O and Ca3(SO3)2SO4·12H2O was calculated using structural considerations. The results were confirmed by the agreement in the intensities of the X-ray powder diffraction lines between the calculated and the measured patterns. The orientation of the water molecules is such as to allow maximal hydrogen bonding of all oxygens belonging to SO32− or SO42− groups. Also, the coordination of the caatoms is shown to be eight and not six as previously reported.

Structural analysis of R 2Ni 17− xAl x intermetallic compounds

The isostructural compounds R 2Ni 17− x Al x (R=Gd, Tb and x=0 to 17) crystallize in the hexagonal structure of the Th 2Ni 17 type. X-ray diffraction patterns were obtained from finely powdered samples. From the intensity of the X-ray diffraction lines a structure model for each investigated compound was deduced. In general, the Ni atoms are replaced by Al atoms in the equivalent positions corresponding with the number of the substituted atoms. In this way the least symmetry operations are effected. The spatial group is changing from one compound to another as a function of the occupied equivalent positions and of the number of the substituted atoms. Te energy bands of the Gd atoms in the Gd 2Ni 2Al 15 compound were identified by using the local symmetry of Gd and Ni atoms.

Semiquantitative X-ray diffraction method for phase analysis using additions of a foreign component

A method is described for semiquantitative X-ray diffraction phase analysis, which involves the addition to the investigated multicomponent system of known large (about 80–95%) amounts of a crystalline substance originally not contained in the system. This results in a decrease of the diffraction line intensities of the components to be measured to small but detectable values. The weight fraction of a component is related to the added fraction of the doping substance and to the fraction of that component remaining in the doped sample. The method is very simple and yields the weight fractions of the major components in the system with a typical error of a few percent. The weight fractions of the minor components cannot be determined with fair accuracy in this way. The method is appropriate in cases where only a small amount of the investigated system is available. Optimum conditions to attain maximum accuracy of the method are discussed.

Thermal effects induced by grinding in dolomite

Differential Scanning Calorimetry (DSC) curves of ground samples of dolomite show an exothermic peak at ca . 300°C. Analysis of the released energy, ΔH, shows that the maximum is reached at 35 h of milling ( ca . 5 J/g) with a subsequent declination as grinding time progresses. No significant loss of specific surface is observed when the ground samples are heated at temperatures above the peak, and therefore the exothermic peak cannot be ascribed to a surface reordering. On the other hand, a recovery of crystallinity, as shown by the intensity of the X-ray diffraction lines and changes in crystallite size and microstrains calculated from the variance of the (104) line profiles, takes place between 200 and 300°C, the interval of temperature at which the exothermic peak appears. Thus, the energy released during heating is due to a restoration of ground dolomite crystallinity.

The doping method in quantitative X-ray diffraction phase analysis. Addendum

A specific case of the doping method [Popović & Gržeta-Plenković (1979). J. Appl. Cryst. 12, 205–208] is elaborated, in which the weight fraction of a crystalline component in the multicomponent system can be determined from the measurement of diffraction line intensities of that component only. Optimum conditions to attain maximum accuracy of the doping method are discussed.

Sarcomere dynamics in single myocardial cells as revealed by high-resolution light diffractometry

A specially designed diffractometer with a high spatial and temporal resolution recorded the diffraction of a laser beam by single enzymatically isolated myocardial cells. The fine structures within the first-order diffraction were resolved and each structure was interpreted as the diffraction from a group of sarcomeres of nearly equal length. During activation of the cell dynamics of each discrete group of sarcomeres was uniform and independent of the other groups. However, a small nonuniform component in the sarcomere dynamics was observed and attributed to the coupling between the shortening tension and the radial stress resulting from the expansion of the myofibrillar cross-section. The time-course of the diffraction fine structures during contractile activity revealed (1) the period of the contraction-relaxation cycle, (2) the latent period, (3) the shortening and relengthening speeds and (4) the variation in the line width and intensity of the fine structure. Measurements showed that the latent period was dependent on the free Ca2+ of the cell's bathing solution while the initial shortening speed was not. The diffraction line width and intensity of the shortening cell were explained by the grating model.