Ray Diffraction Studies Research Articles

EXAFS and XANES Study of Layered Double Hydroxides

Structure of Layered Double Hydroxides and the reaction occurring during thermal treatments are investigated. The reaction is supposed to be a grafting reaction of interlamellar species onto layers but its mechanism is not well known. These materials display a very poor level of organisation and the study of their fine structure involves the use of techniques sensitive to the local environments. XANES and EXAFS studies give few information about the grafting process because of the great disorder in the interlayer space. Much more information about the layers local structure are reached, revealing that distorted and regular octahedra coexist which is particular to layers containing copper atoms. It probably creates a local segregation undetectable by X ray diffraction study in anyway. It also highlights the difference of sheet thermal stability in function of the nature of the intercalated anion.

Synthesis and Characterization of Polypropylene Grafted by Acrylamide

Abstract Polypropylene (PP) was grafted with acrylamide using benzoyl peroxide (BP) as an initiator by melt mixture. Effects of various parameters such as monomer and initiator concentration, reaction time, and reaction temperature on degree of grafting were studied. The graft copolymers were characterized by irradiation (IR), electron spectroscopy for chemical analysis (ESCA), wide-angle x- ray diffraction (WAXD), DSC, and contact angle studies.

Investigation of the structure, pyro- and piezoelectric properties of a ferroelectric ceramic of PZT+(fesb)

Abstract X - ray diffraction studies of polycrystalline Pb[(Fe 1/3 Sb 2/3) xTiy Zrz ]O 3 with x + y + z = 1, x = 0.1 and y = 0.43 – 0.47 have been performed in the temperature range between 23°C to 380°C. The results indicate that below 220°C rhombohedral and tetragonal phases coexist; above 220°C the cubic symmetry phase only. The amount of the rhombohedral phase decrease with increasing temperature for all values of y. The pseudo perovskite cell parameters and their temperature dependence were determined. The pyrocurrents in the temperature range from 25°C to 380°C were measured.

X ray diffraction study of Langmuir-Blodgett mono- and multi-layers

Langmuir-Blodgett (LB) films are often proposed as candidates for molecular electronics. In fact, the deposition technique allows an easy and good control of the structure along the normal to the surface (B. Belbeoch, M. Roulliay, M. Tournarie, 82 (1985) 701–706). However, only few information has been obtained about in plane structure of LB films. Mono- and multi-layers of docosanoic acid have been studied by X-ray transmission diffraction and infrared spectroscopy. For that purpose, LB layers have been deposited onto collodion membranes which present good mechanical properties and give rise to low background signal for the two characterisation techniques. Deposition of the layers occurred at room temperature and a surface pressure π = 36 mN/m. No salt was added to the underlying water. Different samples were prepared, either with a single monolayer deposited on the upstroke, with a double layer (with first layer deposited on the down stroke) or with multilayers. X-ray diffraction has been performed on beam line D24 at LURE by using a Weissenberg chamber equipped with image plates and infrared absorption was used to control the quality and the number of deposited layers. X-ray diffraction is known to work well with multilayers. In the present work, good signal has been obtained from only 2 layers (one on each side of the collodion membrane). Several diffraction rings have been obtained in these conditions. The structure of the monolayer is compared to that of the multilayers.

Maximum solubility of FeO in (Mg, Fe)SiO3‐perovskite as a function of temperature at 26 GPa: Implication for FeO content in the lower mantle

We have explored phase relations in the fundamental ternary system MgO‐FeO‐SiO2 at lower mantle pressure (26 GPa) via synthesis experiments on the join MgSiO3‐FeSiO3. The maximum solubility of FeO in (Mg,Fe)SiO3 perovskite as a function of temperature has been determined in the multianvil apparatus in the temperature range of 1150–1740°C. Pure perovskites with 10 and 15 mol % FeSiO3 can only be synthesized above 1525°C and 2072°C, respectively, at 26 GPa. Synthesis experiments were also conducted in a laser‐heated diamond anvil cell to resolve a previous discrepancy concerning the maximum solubility of FeO in (Mg,Fe)SiO3 perovskite determined by different high‐pressure apparatus. Both Mössbauer spectroscopic and X ray diffraction studies revealed that laser‐heated samples with more than 10 mol % FeSiO3 invariably contained magnesiowüstite. The coexistence of magnesiowüstite with relatively lower FeO content perovskite results from chemical disequilibrium process caused by the large temperature gradient in the laser‐heated samples. Finally, we conclude that the maximum FeO content at the top of the lower mantle is about 12 mol % for a perovskite‐dominated lower mantle, along a 2000‐K lower mantle geotherm.

Current-voltage characteristics and X- ray diffraction study of Pd/Si1- xGex schottky contacts

The electrical characteristics of Pd/p-Si1-xGex Schottky contacts have been investigated. The Schottky contacts were formed by depositing Pd metal on substrates at room temperature (RT = 300K) and at low temperature (LT = 77K). Post annealing was performed in nitrogen atmosphere at 450 and 550°C, respectively, to study the effect of silicide formation on contact characteristics. The current-voltage measurements showed that the barrier height, ϕB, decreased with the increase of the gemanium composition. The contact postannealed at 550°C showed a current transport mechanism obviously different from the as-deposited Schottky contacts. Nearly identical characteristics were observed for the low temperature deposited contacts and the room temperature deposited contacts with 550°C post-annealing. They both showed thermionic emission dominated transport mechanism. X-ray diffraction technique was used to characterize the effect of different temperature treatments on the crystal structure. The full width at half maximum of Si1-xGex(400) phase decreased at low temperature deposited sample, while it increased at room temperature deposition.

Thermodynamic properties of α‐quartz, coesite, and stishovite and equilibrium phase relations at high pressures and high temperatures

Isobaric heat capacities of α ‐quartz, coesite, and stishovite were measured by differential scanning calorimetry at 183–703 K. The heat capacity data of coesite represent a significant revision of the previous data. The heat capacities and entropies were also calculated using Kieffer's model. By high‐temperature solution calorimetry, transition enthalpy for the β‐quartz‐coesite at 979 K was measured to be 1.27±0.39 kJ/mol. The enthalpies for the α‐quartz‐coesite and coesite‐stishovite transitions at 298 K were measured to be 3.40±0.56 and 33.62±1.01 kJ/mol, respectively, by differential drop‐solution calorimetry. The enthalpy of the coesite‐stishovite transition obtained in this study is about 10–15 kJ/mol smaller than those in the previous studies. Phase relations in SiO2 at high pressures and high temperatures were calculated using these new thermodynamic data. The calculated boundary for the α‐quartz‐coesite transition is consistent with those determined experimentally. For the coesite‐stishovite transition, the calculated boundary having a slope of 2.5±0.3 MPa/K disagrees with that by Yagi and Akimoto but is generally consistent with that by Zhang et al.'s new in situ X ray diffraction study.

In situ X ray observation of high‐pressure phase transitions of MgSiO3 and thermal expansion of MgSiO3 perovskite at 25 GPa by double‐stage multianvil system

A double‐stage multianvil system was developed to conduct in situ X ray diffraction study at high pressures. The system generates pressures and temperature above 25 GPa and 1200°C and has been used in conjunction with intense synchrotron radiation to study the phase transitions of MgSiO3 and the thermal expansion of MgSiO3 perovskite. At pressures between 20 and 30 GPa, we observed a series of phase transitions from spinel+stishovite through ilmenite to perovskite. Spinel+stishovite transforms into ilmenite at 20.0±1.0 GPa, and ilmenite transforms into perovskite at 24.0±0.5 GPa at 800°C. The phase boundary between ilmenite and perovskite is estimated to be P (GPa) = (24.0±0.5) ‐ (0.0025±0.0025)(T‐800)(°C) by combining the present results and previous constraints on the slope of the phase boundary from the thermodynamic properties. Measured unit cell parameters of MgSiOs perovskite indicate that the average volumetric thermal expansion coefficient of MgSiOs perovskite over 25°–1200°C is 2.0±0.4×10−5 K−1 at 25 GPa. These results provide the phase stability relation of MgSiO3 and the thermal equation of state of MgSiO3 perovskite at pressures corresponding to the boundary between the upper and lower mantle. However, uncertainties involved in extrapolating to the actual mantle temperatures do not allow evaluation of the chemical structure near the 670 km discontinuity in the mantle.

Optical Properties of BaEu(CO 3) 2 F and Na 3La 2(CO 3) 4F: Eu 3+: Correlations to the Crystallographic Structures

The luminescent properties of trivalent europium are analyzed in Na 3La 2(CO 3) 4F: Eu 3+ at 77 and 9 K and in BaEu(CO 3) 2F at 77 K. In BaEu(CO 3) 2F, the C 3ν, symmetry of the rare earth, deduced from the X ray diffraction study, is confirmed. In Na 3La 2(CO 3) 4F, the spectroscopic technique shows that the order which appears at low temperature implies a single site for the rare earth with a C 3ν or a C 3 symmetry. For both compounds, the energy level scheme of the 7 F J ( J = 0-4) levels is well reproduced (weak RMS standard deviation) from six crystal field (cf) parameters consistent with the C 3ν site symmetry.

STRUCTURAL AND SUPERCONDUCTING PROPERTIES OF Bi4Sr3Ca3CuyOw AND Bi4Sr3Ca3Cu4−xMxOz(M=Fe, Cr AND Mn) GLASS CERAMICS

The synthesis of glass ceramic superconductors of Bi 4 Sr 3 Ca 3 Cu y O w(3≤y≤6) and Bi 4 Sr 3 Ca 3 Cu 4−x M x O z ( M=Fe , Cr , Mn and 0≤x≤0.2) compositions is reported. The 4334 sample is found to be the optimum composition to obtain Bi-2212 superconducting phase. X ray diffraction studies indicate that the solid solubility of 3d metal ions in the 4334 system is limited to x=0.05 in the case of Fe and Cr and x=0.1 in the case of Mn. A systematic decrease in Tc with increasing dopant concentration is observed from resistivity as well as AC susceptibility measurements. Tc depression rates, however, are found to differ for different dopants. XRD studies indicate the decrease in c lattice parameter with increase in dopant content. The systematics of the superconducting transition is discussed in view of Tc depression rates.

Perovskite at high P‐T conditions: An in situ synchrotron X ray diffraction study of NaMgF3 perovskite

The lattice distortion and structural phase transition of NaMgFa perovskite (Neighborite) have been studied using synchrotron X ray powder diffraction at high pressure and temperature. Changes in the unit cell dimensions of the perovskite are determined by conventional peak indexing and least squares routines. The stress field within the high‐pressure cell assembly is analyzed, and the yield strength of the NaMgF3 perovskite is determined at high P and T. The pressure‐ and temperature‐induced dimensional changes of the NaMgF3 perovskite structure are expressed empirically as a combination of compression/expansion of the [Mg‐F] bond length and tilting of the MgF6 octahedral framework. The linear thermal expansions of the NaMgF3 perovskite observed at different pressures show significant anisotropy with αa > αc > αb which reflects the decrease of structural distortion and the development of a phase transition in the perovskite with increasing temperature. The tilting angle of the MgF6 octahedral framework is observed to decrease rapidly toward zero, in a manner expected for a ferroelastic phase transition, as the temperature approaches the transition point Tc. The apparent [Mg‐F] bond lengths of the MgF6 octahedra experience drastic shrinkage with increasing temperature just prior to the transition. Despite a 12% change in volume due to compression, the experimental results on NaMgF3 perovskite show that the thermal expansivity is independent of pressure, i.e., dα/dP ≈ 0, and, compatibly, that the compressibility is independent of temperature, i.e., dβ/dT 0. However, the dominant compression mechanism is the compression of the octahedral bond length, whereas the dominant mechanism for thermal expansion is the diminishing of octahedral tilting. The Earth's mantle may be isochemical if the thermal expansion of MgSiO3 perovskite at high pressure behaves like NaMgF3, of which the Anderson‐Grüneisen parameter is near zero, i.e., δs ≈ 0. It is observed that crystal structure of the NaMgF3 perovskite transforms directly from the orthorhombic Pbnm phase to the cubic phase at all pressures. The transition temperature is observed to increase with increasing pressure with a positive slope of 45 K/GPa.

Stacking fault formation in NiZn f.c.c. alloys

AbstractX‐ray diffraction study of the fault formation in NiZn alloys is carried out. Approximative analyses are performed in order to distinguish the influences of the dispersity and the microdeformations. Correlation between the X‐ray diffraction data and the free molar Gibbs energy is looked for.

Kristallstrukturen von Li6MgBr8 und Li2MgBr4/Crystal Structure of Li6MgBr8 and Li2MgBr4

The crystal structures of the fast ionic conductors Li6MgBr8 and Li2MgBr4 oC 14 and cF 56 were determined by single crystal X -ray diffraction and neutron powder studies, respectively. At ambient temperature, Li6MBr8 (M = Mg, Mn) crystallize in a Suzuki-type structure (space group Fm3̄̄̄ m , Z = 4, Li6MgBr8: a = 1098.0(1) pm, 114 unique reflections, R = 0.037). Li2MgBr4 oC 14 crystallizes in a SnMn2S4-type structure (space group Cmmm , Z = 2, a = 777.94(2), b = 1104.25(4), and c = 386.55(1) pm , RI, = 0.073, 318 K), the high-temperature polymorph (HTM I) in the Li2MnBr4 cF 56 type (space group Fd 3 m , Z = 8, a = 1124.55(4) pm , RI , = 0.052, 673 K). These structure types are more or less ordered NaCl superstructures. The thermal ellipsoids of the lithium ions are discussed in terms of the conduction pathways and the order-disorder phase transitions observed.

Randomly Interstratified Serpentine/Chlorite: Its Detection and Quantification by Powder X-ray Diffraction Methods

AbstractX-ray diffraction studies of the pore-lining chloritic mineral from the Tuscaloosa Formation disclose a marked pattern of odd-order line broadening for the 001 to the 00,16 reflections. The odd-order peaks are approximately twice as broad as the even orders after correction for instrumental broadening effects. These results are consistent with a randomly interstratified 7-Å/14-Å structure, which is most likely serpentine/chlorite. Quantitative analysis of line broadening and model calculations indicate that the serpentine/chlorite contains 7% serpentine layers.A simplified method is proposed for quantifying randomly interstratified serpentine/chlorite. Residual line broadening (βr) is obtained from the half-height widths of uncorrected diffraction profiles for the 004 and 005 “chlorite” reflections by means of the following: βr=(β0051.25−β0041.25)11.25.Percent serpentine in the random interstratification is computed from the empirical expression %S=−0.51+24.27βr, which is valid from about 1 to 20 percent serpentine.

Chemical and Electrical Characterization of the CoGa/GaAs Interface as A Function of Temperature: A Thermally Stable Schottky Barrier up to 500°C

ABSTRACTX-ray diffraction studies and current-voltage measurements have been performed on a (100) oriented single crystal thin film of CoxGa1-x (x = 0.42) grown epitaxially on n-GaAs, from 300°C to 900°C. At this composition, CoxGa1-x, which has a broad range of homogeneity and a variable lattice parameter, is lattice matched to GaAs better than 0.5%. A Schottky barrier height of 0.68eV and an ideality factor of 1.07 have been measured up to 500°C, with significant barrier degradation at 600°C. At 700°C formation of the CoGa3 phase and a shift in CoxGa1-x stoichiometry to its bulk thermodynamically most stable composition of Co.45Ga.55 was observed with x-ray diffraction. At 800°C Co2AS formed, and at 900°C only CoGa3 and Co2As phases remained in contact with GaAs.

Morphology of bulk nylon 6 subjected to plane strain compression

Abstract : The mechanics of deformation of nylon 6 is plane strain compression were elucidated by density measurements, differential scanning calorimetry, polarized light microscopy, x ray diffraction and x ray diffraction pole figures. A deconvolution procedure for separating overlapping x ray diffraction peaks and the amorphous halo was used to generate pole figures for the various alpha and gamma phase reflections exhibited by nylon 6. At compression ratios above 1.6, specimens experienced intense shear stresses at -45 deg and +45 deg with respect to the flow direction. Shear bands were formed most frequently at interspherulitic boundaries. This shearing produced a small volume fraction of gamma phase crystals in samples which originally contained only alpha crystallinity. The x ray diffraction studies showed that gamma phase crystals were oriented with their macromolecular chains along the directions of shear bands. The alpha crystals of nylon 6 underwent extensive deterioration in compression by a chain slip mechanism along the (0 0 2) planes containing hydrogen bonds. Slip also caused the rotation of fragmented lamellae that lead, at high compression ratios, to a peculiar bifurcated orientation state resembling a twinned monocrystal.

X‐ray scattering studies of the structure of aqueous hydroxy‐propylcellulose solutions

AbstractX‐ray diffraction studies have been undertaken on aqueous solutions of hydroxy propylcellulose (HPC) over a wide range of the scattering vector Q. The experiments revealed only modest differences in local structure on a distance scale ca. 5–300 Å despite the fact that they covered concentrations generally interpreted as ranging from the isotropic (35.1 wt %) to the anisotropic liquid crystalline (LC) phase (53.5 wt %). Several models were used to interpret the small‐angle scattering data, and each gave similar structural parameters and extrapolated intensities (Q → 0) for both solutions. Peaks were observed with d‐spacings ca. 12–17 Å in both materials. Wide‐angle x‐ray scattering (WAXS) showed slightly increased local order over a size range ca. 5–20 Å for the anisotropic solution, and this is consistent with a greater intensity of the 13 Å peak in this material. It is difficult to reconcile these findings with an interpretation of the LC state involving major differences with the isotropic phase and a high degree of orientational order extending over long length scales.

X–ray Diffraction Studies on Pyrazine Complexes with Copper(II) Chloride, Bromide, and Sulphate

Crystal Research and TechnologyVolume 26, Issue 2 p. K25-K28 Short Note X–ray Diffraction Studies on Pyrazine Complexes with Copper(II) Chloride, Bromide, and Sulphate Prof. I. S. Ahuja, Prof. I. S. Ahuja Chemistry Department, Banaras Hindu University, Varanasi – 221 005, IndiaSearch for more papers by this authorShailendra Tripathi, Shailendra Tripathi Chemistry Department, Banaras Hindu University, Varanasi – 221 005, IndiaSearch for more papers by this author Prof. I. S. Ahuja, Prof. I. S. Ahuja Chemistry Department, Banaras Hindu University, Varanasi – 221 005, IndiaSearch for more papers by this authorShailendra Tripathi, Shailendra Tripathi Chemistry Department, Banaras Hindu University, Varanasi – 221 005, IndiaSearch for more papers by this author First published: 1991 https://doi.org/10.1002/crat.2170260221Citations: 1AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume26, Issue21991Pages K25-K28 RelatedInformation

X–Ray Diffraction Studies on 4,4′‐Bipyridyl Complexes with Cobalt(II)‐, Nickel(II)‐, Zinc(II),‐ and Cadmium(II) Nitrates

X–Ray Diffraction Studies on 4,4′‐Bipyridyl Complexes with Cobalt(II)‐, Nickel(II)‐, Zinc(II),‐ and Cadmium(II) Nitrates

X–ray Diffraction and Thermoanalytical Studies of the Formation of Complex Alkaline Earth Titanates from Precursors

Crystal Research and TechnologyVolume 26, Issue 2 p. K46-K49 Short Note X–ray Diffraction and Thermoanalytical Studies of the Formation of Complex Alkaline Earth Titanates from Precursors Dr. G. Pfaff, Dr. G. Pfaff Chemische Fakultät der Friedrich-Schiller-Universität Jena, August-Bebel-Strasse 2, 0 – 6902 Jena, Bundesrepublik DeutschlandSearch for more papers by this author Dr. G. Pfaff, Dr. G. Pfaff Chemische Fakultät der Friedrich-Schiller-Universität Jena, August-Bebel-Strasse 2, 0 – 6902 Jena, Bundesrepublik DeutschlandSearch for more papers by this author First published: 1991 https://doi.org/10.1002/crat.2170260226AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Volume26, Issue21991Pages K46-K49 RelatedInformation