X-ray Diffractometry Studies Research Articles

Bending Beam Measurement of Moisture Diffusion in Polyimide Films on Silicon Substrate

A theoretical model, correlating the bending curvature variation ratio of a layered structure caused by moisture-induced-swelling in its polymer overcoat with time under Case I diffusion, has been developed. This model has considered the pre-existing intrinsic strain in the polymer film upon deposition. According to this model, any specimen to be studied does not need to be bending or strain free. Furthermore, an useful and relatively simplified formula has been derived therefrom and used in identifying the diffusions of moisture in the films of two rod-like and one semi-flexible polyimides, their blends, and a random copolyimide. In PMDA-ODA (pyromellitic dianhydride-4,4′-oxydianiline), the diffusion constant, D, is 4.64×10−9 cm2 s−1. In PMDA-PDA (p-phenylenediamine), D=1.25×10−9, and in PMDA-B (-benzidine) 0.10×10−9 cm2s−1. The diffusion fastest in PMDA-ODA can be attributed to its amorphous structure, and slowest in PMDA-B to its small interchain spacing. The diffusion in a random copolymer with 50 wt% PMDA-PDA and 50 wt% PMDA-B is faster than in the blend with 60 wt% PMDA-PDA and 40 wt% PMDA-B. This can be attributed that the random copolyimide film is more amorphous according to an X-ray diffractometry study.

4-Isoxazolyl-1,4-dihydropyridines: biological, theoretical, and structural studies

Biological activity was determined for a series of seven isoxazolyldihydropyridines (IDHPs). The highest biological activity was observed for 5-alkyl-3-phenyl-IDHP (1), for which the O-endo conformation at the ring juncture between the heterocyclic rings is known in the solid state. The 3,5-dialkyl-IDHPs were intermediate in overall activity. A theoretical study of rotation about this ring juncture was performed to estimate the relative energy and barrier to rotation for the different conformers as a function of both the ring juncture between the heterocyclic rings and the esters in the 3- and 5-position of the dihydropyridine. Molecular mechanics predicts the minimum energy conformer to be O-exo-ap,ap, while quantum mechanical calculations predict O-exo-sp,sp as the minimum-energy conformer. Both methods indicate that the barrier to rotation about the heterocyclic ring juncture should be relative low, but both methods appear to overestimate the difficulty of ester rotation. A single-crystal X-ray diffractometry study of the (3,5-dimethylisoxazolyl)dihydropyridine 2 was carried out, and shows the O-endo ring juncture and sp,sp ester conformation. 2D NOESY NMR spectroscopy indicates the presence of both conformations about the ring juncture, at room temperature, as evidenced by correlations for both alkyl groups on the isoxazole with the C-2 methyl on the DHP moiety. The ap ester conformer was also evidenced by NOESY, indicating that ester interconversion must take place.

Polymorphic behavior of erucic acid

AbstractPolymorphic behavior of erucic acid was examined by differential scanning calorimetry (DSC), X‐ray diffractometry (XRD) and optical microscopy. Four individual polymorphs were observed, α1, γ1, α and γ. The single crystals of α and α1 were obtained from acetonitrile solutions. DSC and XRD studies exhibited reversible transformations between α and γ, and between α1 and γ1. The two transformations were characterized by an order (γ and γ1)‐disorder (α and α1) transformation due to melting of the aliphatic chain between acis double bond and a methyl end group, as revealed in α and γ of oleic acid. The thermodynamic stability among the four polymorphs was determined based on the transformation features and the solubility data. α1 is most stable above 25.9 C, melting at 34.0 C, α is most stable in a range of temperature between −1.0 and 25.9 C, transforming in a crystalline state to α1 at 31.2 C on heating. γ is most stable below −1.0 C. It can be concluded that the polymorphism of erucic acid is different from that of oleic acid with respect to the thermal and structural behaviors, although some similarities are revealed.

A structural study of the YBa2Cu3O7?x superconductor system

X-ray photoelectron spectroscopy (XPS), X-ray diffractometry (XRD) and analytical scanning electron microscopy have been employed to investigate the structure and microstructure together with the chemical nature of the YBa2Cu3O7−x superconductor system at different stages of preparation. XRD studies showed that the original mixture assumed a structure quite similar to that of the final superconductor phase after being sintered at about 900° C in air. While XPS results showed no evidence for copper in any valency other than 2, X-ray-induced Auger features confirmed the existence of monovalent copper at low temperatures. A small shoulder on the O1s spectrum in the final compound proved to be variant with the temperature. The intensity of this shoulder increased relative to the main O1s peak by lowering the temperature. This is believed to be due to the formation of monovalent copper on the top of the sample. Microstructural studies together with point analysis and X-ray mapping showed the existence of different phases in the final compound.

Magnetic field alignment of high-T c superconductorsRBa2Cu3O7?? (R=rare earth)

Finely ground powders ofRBa2Cu3O7 − δ (R=Y, Nd, Sm, Eu, Dy, Ho, Er, Tm, Yb) have been mixed at dilute 3%-by-volume concentrations into epoxy matrices which were then allowed to harden in applied magnetic fieldsH A=18 kOe. X-ray diffractometry studies and 4.3 K measurements of supercurrent-induced magnetization hysteresisΔM are interpreted as indicating at least partial alignment of single-crystal-grain c-axes (1) parallel toH A forR=Y, Nd, Sm, Dy, Ho (as earlier found by Farrell et al. forR=Y), and (2) perpendicular toH A forR=Eu, Er, Tm, Yb. With a few exceptions (Y, Sm, Eu) the alignment direction correlates with the sign of the second-order Stevens factorα J of the crystalline electric field Hamiltonian in the manner suggested by Livingston et al. For the best aligned specimens (Ho, Dy) critical current densitiesJ c (4.3 K, 5 kOe) for individual grains are estimated fromΔM and the Bean model to be of order 107 A/cm2 for the measuring fieldH parallel to the original alignment fieldH A, and of order 106 A/cm2 forH perpendicular toH A.

Formation and chemical stability of metallic glass particles prepared by thermolysis of Fe (CO)5

A ferrofluid has been prepared by thermal decomposition of Fe(CO)5 in an organic liquid. Mossbauer spectroscopy and x-ray diffractometry studies show that the ferrofluid contains small particles of a metallic glass. The particles are only partly oxidized even after exposure of the ferrofluid to air at room temperature for 30 days.

Structural and Orientational Characteristics of the Disodium/Cromoglycate-Water Mesophases by Deuterium NMR and X-Ray Diffraction

Abstract Deuterium NMR and X-ray diffractometry studies of the lyomesophases of the disodium/cromoglycate-water system are reported. The deuterium NMR studies were made on three specifically labelled compounds, viz. disodium cromoglycate-6,8,6′,8′-d4, disodium cromoglycate-3,3′-d2 and disodium cromoglycate-10-d1. The deuterium spectra of these species consist of doublets caused by the corresponding average quadrupolar interaction in the N and M phases; however, in phase III only the methine deuteron of disodium cromoglycate-10-d1 could be seen. The splittings of the chromone moiety deuterons, 3,6 and 8, are essentially identical over the whole temperature and concentration range of the N and M phases, ranging between 50 and 65 kHz. The methine deuteron splitting in the M phase is similar to that of the chromone deuterons, but is considerably higher (115 to 117 kHz) in phase III. The X-ray diffraction studies were made on a 20 wt% solution as a function of temperature between −15°C and 60°C. Two diffraction bands were observed corresponding to approximately 37 Å and 3.4 Å d-values at room temperature. Distinct changes in the diffraction pattern have been observed in the phase transition regions, Isotropic → N → M → III → solid. The results are consistent with a model in which the N and M phases consist of highly ordered cylindrical micelles of stacked disodium cromoglycate molecules whose chromone planes lie perpendicular to the cylinder axes. The 37 Å and 3.4 Å spacings are identified with respectively the intermicellar and intramicellar stacking distances, and from the NMR results the effective orientational order parameter of the micelles is calculated to be between 0.75 and 1.0 depending on the concentration.

An X-ray diffractometry study of LaB6 single crystals, prepared by high-temperature solution growth

Article An X-ray diffractometry study of LaB6 single crystals, prepared by high-temperature solution growth was published on November 1, 1984 in the journal Zeitschrift für Kristallographie - Crystalline Materials (volume 168, issue 1-4).

An X-ray diffractometry study of LaB6single crystals, prepared by high-temperature solution growth

An X-ray diffractometry study of LaB₆single crystals, prepared by high-temperature solution growth

In situ X-ray diffractometry study of the hydride in the intermetallic compound Mg2Ni

The crystal symmetry of the reaction product of hydrogen with the intermetallic compound Mg2Ni has been determined to be tetragonal with unit cell dimensions: a=6.533 AA and c=7.499 AA, by in situ X-ray diffractometry at about 623K and under 4.6 MPa hydrogen pressure. The resultant hydride phase transforms at 503K to an orthorhombic structure with lattice dimensions: a=11.394 AA, b=11.196 AA and c=9.165 AA. This phase transition is of polymorphic type as is evident from the well defined exothermic (endothermic) peak in the pressure-differential scanning calorimetry curves obtained during cooling (heating) after the formation of the nearest stoichiometric hydride Mg2NiH4. The results are briefly compared with previously reported data.