Standard X-ray Diffraction Research Articles

Extended polymorphism in copper(II) imidazolate polymers: a spectroscopic and XRPD structural study.

Copper(II) bisimidazolate affords five different polymorphs; of these, one was structurally characterized 40 years ago by standard single-crystal X-ray diffraction (Jarvis, J. A. J.; Wells, A. F. Acta Crystallogr. 1960, 13, 1027), while the remaining four, selectively prepared as pure polycrystalline phases, have been now studied by X-ray powder diffraction (XRPD) methods. Of the four new (blue, green, olive-green, and pink) phases, three were solved by the ab initio XRPD technique and refined by the Rietveld method, and the fourth phase (pink) could not be structurally characterized. Crystal data for [Cu(imidazolate)(2)](n): blue phase, a = 27.559(3) A, c = 5.3870(9) A, trigonal, R3 macro, Z = 54; green phase, a = 21.139(1) A, b = 19.080(1) A, c = 9.2842(8) A, orthorhombic, Ccca, Z = 20; olive-green phase, a = 11.7556(8) A, b = 23.422(2) A, c = 9.0727(9) A, beta = 104.993(5) degrees, monoclinic, C2/c, Z = 12. All polymorphs contain four-coordinate CuN(4) chromophores and (N,N')-exobidentate imidazolate ligands, but show different spectroscopic and structural properties, the latter ranging from 2D to different 3D networks of the PtS, sodalite, and moganite archetypes. The intermediacy of the [Cu(imidazole)(2)CO(3)]-H(2)O species in the synthesis of the blue polymorph has been confirmed by spectroscopic and thermal analyses. FTIR, Raman, and electronic spectra were correlated with the structural features revealed in the present work, and used to gain insight into the coordination geometry of copper(II) ions of the pink polymorph. In addition, the correct Raman spectrum for copper(II) bisimidazolate, common for all polymorphs, has been definitely determined.

Ultra-thin bi-axially textured IBAD MgO template layers resolved by grazing incidence X-ray diffraction

We describe a method using grazing incidence diffractometry (GID) with a rotating anode X-ray source to measure the in-plane alignment of ∼10-nm thick MgO films deposited by ion beam assisted deposition (IBAD). In conjunction with these measurements, we have calibrated the IBAD film growth process by monitoring the film in situ with reflected high-energy electron diffraction and comparing the intensity versus time curve with results obtained from the ex situ GID measurements. GID has also been used to identify differences in the observed in-plane texture for samples with and without the addition of a homoepitaxial layer. Improvements in texture after the addition of the homoepitaxial layer are attributed to the healing of ion induced damage during growth of the IBAD layer. Further analysis has revealed that standard X-ray diffraction measurements of these overcoated films do not sufficiently quantify the in-plane alignment of the initial IBAD layers.

Crystal Tilts in Epitaxially Laterally Overgrown GaN FilmsDetermined by Four-Circle X-Ray Diffraction

Crystal tilts in epitaxially laterally overgrown (ELO) GaN films via hydridevapour phase epitaxy (HVPE) on sapphire substrates have been investigated byusing the four-circle x-ray diffraction method. Three diffraction peakscorresponding to the (0002) reflection of vertically epitaxial andtilted GaN domains are observable in the x-ray rocking curve. The angleseparations Δω between the main peak and two lobes changewith the azimuth angle ϕ. The dependence of Δω onϕ and the crystal tilt angle θ has beencalculated based on the standard kinetic x-ray diffraction model. Thecrystal tilt angle of a typical HVPE ELO GaN sample has been determined tobe 2.379°.

Determination of Ir consumption during thermal oxidation and PbZrxTi1−xO3 processing using Bragg-peak fringe analysis

Thickness interference fringes can be seen around the Bragg peaks of a variety of polycrystalline thin (10–20 nm) films using standard x-ray diffraction techniques in a conventional Bragg–Brentano geometry. In this article, thickness fringe analysis is used to investigate oxidation and roughening in thin Ir films with and without overlayers of the ferroelectric PbZrxTi1−xO3 (PZT). Changes in fringe spacing were used to determine the Ir thickness consumed by oxidation. Fringe contrast degradation (indicating roughening) was observed both after oxidation anneals (which formed a surface layer of IrO2) and after subsequent reduction anneals (which converted the IrO2 back to Ir). Film overlayers were found to have a protective effect against oxidation and roughening, as evidenced by comparison of postoxidation fringe patterns for bare and PZT-coated Ir films. Overall, our results demonstrate that thickness fringe analysis can be used as a simple, quantitative probe of processing-induced thin film thickness and morphology changes.

On the origin of some red soils from Sardinia (Italy): A neutron activation analysis investigation

In Sardinia, the Italian island in the middle of the MediterraneanSea, there are many red soils developed on limestone or dolomite. Soil andunderlying bedrock samples from 5 different sites have been submitted to chemicaland mineralogical characterization, by using standard X-ray diffraction analysis,spectrochemical methods and instrumental neutron activation analysis. Obtainedresults are presented and discussed in terms of precision and accuracy. Traceelement concentration variation with depth is discussed as well as the enrichment/depletionratios between soils and rocks, and the rare-earth element distribution. Dataanalysis suggests for some soils a formation process based on the evolutionof the underlying bedrock, and for the other soils a formation process partlybased on the evolution of the local rock but with meaningful contributionsof external sources, both eolian and/or alluvial.

In-house low-resolution X-ray crystallography.

It is demonstrated that standard in-house protein crystal X-ray diffraction apparatus can be used to measure very low resolution reflections with only a few modifications. The apparatus and modifications are described in detail and tested on two different macromolecular crystal samples: lysozyme and the 30S ribosomal subunit. Contrast-variation measurements on tetragonal hen egg-white lysozyme demonstrate the potential usefulness of the apparatus in providing accurate data for the determination of macromolecular envelopes. In contrast, the measurement of very low resolution diffraction from crystals of the 30S ribosome subunit illustrates how in-house facilities can provide data from small weakly diffracting crystals of a very large macromolecule.

Compositional heterogeneity in ceria-based mixed oxides observed by x-ray photoelectron spectroscopy

It is argued that compositional heterogeneity in certain reducible mixed oxides, like Ce1−xZrxO2, can be inferred from a variation in the metals ratio, as measured by x-ray photoelectron spectroscopy, between fully oxidized and partially reduced states of the oxide, provided that the characteristic linear dimension of the heterogeneity is at least as large as the typical electron inelastic mean-free path. The argument is supported by experimental results from two examples involving mixed phases, one in which the length scale is 100 nm and the other in which the domains are too small for detection by standard x-ray diffraction.

Stress reduction by ion bombardment in CeO 2 films

We have investigated the influence of deposition parameters on film stress in CeO 2 films grown on biaxially textured nickel (001) substrates using pulsed-laser deposition. The film stress is thought to consist of thermal stress and intrinsic stress. The thermal stress has been calculated at different deposition temperatures. The results reveal that the thermal stress is compressive with MPa order of magnitude and increases with increasing deposition temperature. The intrinsic stress has also been measured by standard X-ray diffraction technique. It has been found that the intrinsic stress is tensile with GPa order of magnitude, and decreases with increasing deposition temperature regardless of whether the films are deposited with ion bombardment or not. Moreover, this is the first time a quantitative confirmation of stress reduction with ion bombardment has been provided. Some possible origins of the influence of deposition parameters on film stress are discussed.

Polymorph Determination for the gp IIb/IIIa Antagonist, Roxifiban, Using a Combination of Electron Diffraction and Synchrotron X-ray Powder Diffraction Techniques

Unit cell parameters of two polymorphs of roxifiban have been determined by a combination of transmission electron microscopy (TEM) single-crystal and synchrotron X-ray powder diffraction techniques. While it was difficult to differentiate the two forms by their standard X-ray diffraction patterns, the high-resolution synchrotron patterns clearly showed striking differences. Unit cells for the two forms required the use of cell parameters derived from TEM diffraction patterns. The two unit cells are, not surprisingly, very similar except for a doubling of one of the axes for form II. The combined use of TEM and synchrotron patterns appears to be a good general approach for characterizing complex (low-symmetry, large unit cell) polymorphs.

Magnetic properties and structure of nanocrystalline Fe-Al and Fe-Ni alloys

Magnetic and structural properties of nanocrystalline Fe-Al and Fe-Ni alloys were investigated. Alloys were prepared by the mechanical alloying process. The standard X-ray diffraction, Mössbauer and magnetic studies were carried out on the powder samples. The structural investigations proved that in the low-energy mechanical alloying process of Fe and Al the disordered bcc solid solution was formed up to 50 at.% Al. Alloys were amorphous for Al content between 50 and 90 at.%. The final products of milling exhibited interesting magnetic properties different as compared with microcrystalline alloys. In the case of Fe-Ni alloys the bcc solid solution was formed during high- energy ball milling for the composition with 20 at.% Ni, while above 35 at.% Ni the fcc solid solutions were obtained. All mechanically synthesized Fe-Ni alloys were ferromagnetic and no Invar effect was observed for 35 at.% Ni.

耐候性鋼のさび定量X線分析から算出した成分比率指標活用法に関する考察

耐候性鋼のさび定量X線分析から算出した成分比率指標活用法に関する考察

A structural study of Sr metaphosphate glass by anomalous X-ray scattering and EXAFS spectroscopy

Anomalous X-ray scattering (AXS) and extended X-ray absorption fine structure (EXAFS) spectroscopy have been used to investigate the structure of Sr metaphosphate glass. While the interpretation of standard neutron and X-ray diffraction data is complicated by the overlapping of peaks in the radial distribution functions, the combination of these two techniques allow a more precise interpretation of the structure. The resulting model is consistent with a description of the structure in terms of Sr2+ ions interposed between phosphate chains.

X-ray diffraction analysis of YBaCuO ultra-thin film growth

The initial growth stages of YBaCuO films deposited by sputtering in the thickness range of 0.6 to 5 nm on (100) SrTiO 3 and MgO substrates have been studied by standard X-ray diffraction. A comparison of film thicknesses estimated from line breadth with the nominal values indicates layered growth in a unit cell by unit cell mode on SrTiO 3 while island growth occurs on MgO until full coverage is reached at 5 nm. Pseudomorphic growth appears to be present on both substrates but restricted to different film thicknesses, i.e., about 4 nm on SrTiO 3 and one unit cell on MgO. In films with thicknesses up to two unit cells the YBaCuO “123” phase coexists with oxides of the cations, an appearance which also was observed in the BiSrCaCuO “2223” phase. The growth characteristics are in agreement with observations made by high resolution backscattering on similar films.

Epitaxial Pb–Fe–O film with large planar magnetic anisotropy on (0001) sapphire

Epitaxial films (1.7 μm thick) with the composition PbFe12.9O22.9 and hexagonal lattice parameters a=5.12 Å and c=23.67 Å have been pulsed laser deposited at 600 °C in 50 mTorr of O2 onto single-crystal (0001) sapphire substrates. Epitaxy was determined using standard powder x-ray diffraction (XRD) and grazing incidence XRD. The films were deposited using a single-phase polycrystalline PbFe12O19 target. The composition of the films is PbFe12.9O22.9, which was measured using Rutherford backscattering spectrometry. Static magnetic measurements were performed using a vibrating sample magnetometer and SQUID magnetometer in order to measure magnetic anisotropy, magnetic remanence (Mr), coercive field (Hc), and saturation magnetization (4πMs) of the films. The PbFe12.9O22.9 films exhibit magnetically isotropic behavior in the film plane with remanence ratio (Mr/Ms) and Hc values of 88±2.9% and 2500±97 Oe, respectively. However, the films are anisotropic with respect to the film normal such that the c axis is a magnetically hard direction and all directions normal to the c axis are magnetically easy (i.e., a planar anisotropy field, HA, with an estimated magnitude of 77.5 kOe). The 4πMs value for the films is 630 Gauss at room temperature.

Magnetoresistance of Al90Y10 and Al90La10: Strong enhancement due to small crystalline precipitates in Al90La10.

The normal-state magnetoresistance, \ensuremath{\Delta}\ensuremath{\rho}/\ensuremath{\rho}, was measured for ${\mathrm{Al}}_{90}$${\mathrm{La}}_{10}$ and ${\mathrm{Al}}_{90}$${\mathrm{Y}}_{10}$ alloys in the temperature region from four to eight times the superconducting ${\mathit{T}}_{\mathit{c}}$ and in magnetic fields up to 12 T. These samples were amorphous in standard x-ray diffraction. An accurate description of the ${\mathrm{Al}}_{90}$${\mathrm{Y}}_{10}$ data in terms of quantum interference effects (QIE) was obtained only when the Maki-Thompson contribution was excluded. Two samples of ${\mathrm{Al}}_{90}$${\mathrm{La}}_{10}$ were studied. \ensuremath{\Delta}\ensuremath{\rho}/\ensuremath{\rho} was anomalously enhanced in sample I, reaching above 1%, and too large to be accounted for by QIE also in sample II. Measurements of the magnetic susceptibility and further structural investigations were made, including high-resolution x-ray diffraction, analytical transmission electron microscopy, and high-resolution electron microscopy (HREM). Small crystallites of ${\mathrm{Al}}_{11}$${\mathrm{La}}_{3}$ were observed in all improved structural analyses of sample I, and only in HREM for sample II. Implications for amorphous metals are discussed. \textcopyright{} 1996 The American Physical Society.

Grain size and strain in thin sputter-deposited Ni 0.8Fe 0.2 and Cu films

The average grain size and strain in the direction parallel to the surface of thin Ni 0.8Fe 0.2 and Cu films, sandwiched between Ta layers, have been determined as a function of layer thickness by grazing incidence X-ray diffraction. The in-plane grain size and grain size distribution were also assessed by plan-view transmission electron microscopy. Standard θ-2θ X-ray powder diffraction was used to determine the uniform strain in the direction perpendicular to the surface. Both for Ni 0.8Fe 0.2 and Cu, an elongation of the lattice parameter perpendicular to the surface and a compression of the lattice parameter in the plane of the film is observed, which decreases with increasing film thickness. Additionally, for Ni 0.8Fe 0.2 a non-uniform elongation of the perpendicular interactomic distance at the Ta interfaces is deduced by fitting a kinematical model to the θ-2θ diffraction spectrum. This study illustrates the strength and the complementary character of standard powder X-ray diffraction, grazing incidence X-ray diffraction and transmission electron microscopy for the structural analysis of thin metal films.

Technical calcium nitrate as set accelerator for cement pastes at low temperatures

Technical calcium nitrate (CN) is tested as a set accelerator for five French cements by Vicat needle and isothermal calorimetry at both 5°C and 20°C. All five cements were characterized by standard test methods and X-ray diffraction. CN works as a set accelerator for all five cements tested (but poorly for cement no. 2). The CN dosages tested at 5°C were 0·00%, 1·55%, 3·86% and 7·73% of the cement weight. The optimum dosage was found to be 1·55%, 1·55%, 3·86%, 3·86% and 1·55% CN for cements nos 1, 2, 3, 4 and 5, respectively. However, optimum CN dosages less than 1·55% cannot be excluded for cements nos 1, 2 and 5. The accelerating efficiency of CN is higher at 5°C than at 20°C. In addition to shortening the overall setting time, the CN accelerator often reduced the time gap between initial and final set, indicating a more rapid strength build-up. Isothermal calorimetry revealed a good correlation between the extra heat output during the first five hours and the effectiveness of 1·55% CN (fixed dosage) in accelerating initial set at 5°C. The efficiency of CN as set accelerator for the different cements seems to increase with increasing β-CsS, as partly confirmed by X-ray diffraction, or other cement characteristics promoting belire formation in the clinker process.

Quantitative XRD measurement of mineral matter in Gondwana coals using the Rietveld method

Organic matter behaves as amorphous material to X-rays and the presence of organic matter is manifested as an 'organic hump' on a standard X-ray diffraction trace. Empirical calibration curves can be used to determine the weight of organic matter from the trace. The subsequent weights of the organic matter can be input data for the Rietveld method and used to calculate the mineral contents, weighted to the organic content in the respective samples. The Rietveld quantitative method is a standardless, non-destructive technique that relies on crystal unit cell parameters of the minerals being analysed. Rietveld parameters, or variables causing intensity aberrations in the data, are adjusted theoretically, by refinement, to fit a synthetic (or calculated) profile to the measured pattern. In this paper, the mineralogy of a suite of African and Australian coal samples, calculated by the Rietveld method, ash analyses and other coal quality data are presented to test the validity of the methodology for Gondwana coals.

Raman Spectroscopy of Local Structure and Reordering Processes in YBa2Cu3O7-δ-Type Compounds

The real structure of RBa2Cu3O7-δ (R=Y, rare earth) at intermediate values of δ (0<δ<1) is characterized by an inhomogeneous distribution of oxygen atoms in the basal (Cu1—O1) planes. At a microscopic level the sample can be considered as a multi-phase system, the relative weight of co-existing stable and unstable microphases being determined by the value of δ and the history of the sample. Standard x-ray and neutron diffraction techniques fail in distinguishing co-existing microphases as the typical size of corresponding ordered domains (10–100 lattice constants) is below the detection limit of these techniques. In contrast, the phonon frequencies (in particular of the Raman-active modes involving vibrations of mainly one type of atoms) are sensitive to the local atomic-site coordination which may differ significantly for the different microphases. Thus, Raman spectroscopy provides an opportunity to analyse the microphases in RBa2Cu3O7-δ and their mutual transformations with δ and/or under different treatments.

Microstructural Characterization of an Oriented Silicalite Film

ABSTRACTThe crystal orientation of a submicron silicalite membrane is examined using standard x-ray diffraction and pole-figure analyses. Results indicate that the crystals in the molecular sieving layer are preferentially oriented with both straight and sinusoidal channel networks of the zeolite parallel to the membrane surface. This requires that transport across the membrane proceed down the c-axis of the crystals which can occur by jumping between the two channel networks. EDAX data confirms that the molecular sieving layer is the pure silica zeolite silicalite.