Intensities Of X-ray Reflections Research Articles

Specific features of the formation of diffraction patterns of metallofullerene crystals

The specific features of the formation of diffraction patterns of face-centered cubic crystals of metallofullerene clathrates have been investigated. It has been demonstrated that the presence of dopants in holes of fullerite crystals substantially affects the ratio between the X-ray reflection intensities. The regularities in the redistribution of the intensities of diffraction peaks when metal atoms fill interstices and intramolecular cavities of the face-centered cubic fullerite crystal have been established.

Influence of Oxygen Stoichiometry and Cation Ordering on Magnetoresistive Properties of Sr<sub>2</sub>FeMoO<sub>6±δ</sub>

This work investigates the influence of initial compound synthesis prehistory on the phase sequence during formation of single-phase Sr2FeMoO6 (SFMO). Analytical-grade SrCO3, Fe2O3 and MoO3 (sample No.1) and partially reduced precursors of SrFeO3-x (SFO) and SrMoO4-y (SMO) (sample No.2) were used as initial reagents. In the latter case, kinetic limitations of SFMO phase formation are resolved by increasing the diffusivity of both of Fe3+ and Mo5+ and decreasing diffusion lengths to the reaction zone. This enhances the double-perovskite growth rate, lowers synthesis temperature and increases the intensity of X-ray reflections of (011) and (013) planes suggesting a superstructural ordering of Fe3+ and Mo5+ cations. Samples No.1 and No.2 have both a Тс ~ 420K while the magnetization value at 77 K in the sample No.2 is higher by a factor 2.3 compared to that of sample No.1. A decrease of the oxygen vacancy concentration by annealing Sr2FeMoO5.82 lowered magnetization of the samples and promoted the formation of a second magnetic phase with Тс = 700 К. We suppose that an increase of oxygen partial pressure during annealing causes formation of clusters with antiferromagnetic coupling in Fe3+-О2--Fe3+ chains. In order to increase the magnetoresistive effect at temperatures relevant for technical application, weak intergrain bonds should be formed.

Pressure-Induced Phase Transitions on a Liquid Crystalline Europium(III) Complex

The effect of pressure on the phase behavior of the liquid crystalline complex [Eu(bta)(3)L(2)] (bta is benzoyltrifluoroacetonate, and L is the Schiff base 2-hydroxy-N-octadecyl-4-tetradecyloxybenzaldimine) was studied by X-ray diffraction, Raman spectroscopy, and luminescence spectroscopy. The pressure was varied between ambient pressure and 8.0 GPa. [Eu(bta)(3)L(2)] exhibits a smectic A (SmA) phase at room temperature. The complex undergoes a transition from the SmA phase to a solid lamellar structure around 0.22 GPa and another transition from the solid lamellar phase to an amorphous state from 1.6 to 3.5 GPa. At low pressures, the smectic layer spacing increases, and the intermolecular distance decreases. Above 3.5 GPa, both the interlamellar and the intermolecular spacings hardly change, but the intensity of X-ray reflections exhibits a remarkable decrease and eventually vanishes. An interpretation of the changes in the molecular structure is given. It was found that less interdigitation of the alkyl chains situated in adjacent layers and/or a full extension of the alkyl chains occurred at low pressures and that the second phase transition was accompanied by a transfer of the hydrogen atom from the nitrogen atom of the imine group to the oxygen atom of the Schiff base ligand. The effect of applying pressure equals that of the lanthanide contraction on the phase behavior.

Element specific separation of bulk and interfacial magnetic hysteresis loops

We have studied the reversal of the bulk and interfacial magnetizations of the free layer of a spin valve using soft x-ray resonant magnetic scattering. By dusting the interface of the NiFe free layer with a few angströms of Co, we were able to distinguish between the interfacial and bulk magnetisms by tuning the x-ray photon energy. We measured hysteresis loops of reflected x-ray intensity at selected points in reciprocal space. We find no difference in the switching fields, showing that in transition metal ferromagnets, the exchange interactions are sufficiently strong to prevent a separate interfacial coercivity from arising.

Nanosecond Domain Wall Dynamics in FerroelectricPb(Zr,Ti)O3Thin Films

Domain wall motion during polarization switching in ferroelectric thin films is fundamentally important and poses challenges for both experiments and modeling. We have visualized the switching of a Pb(Zr, Ti)O(3) capacitor using time-resolved x-ray microdiffraction. The structural signatures of switching include a reversal in the sign of the piezoelectric coefficient and a change in the intensity of x-ray reflections. The propagation of polarization domain walls is highly reproducible from cycle to cycle of the electric field. Domain wall velocities of 40 m s(-1) are consistent with the results of other methods, but are far less than saturation values expected at high electric fields.

Effects of the Number of Actin-Bound S1 and Axial Force on X-Ray Patterns of Intact Skeletal Muscle

Effects of the number of actin-bound S1 and of axial tension on x-ray patterns from tetanized, intact skeletal muscle fibers were investigated. The muscle relaxant, BDM, reduced tetanic M3 meridional x-ray reflection intensity (IM3), M3 spacing (dM3), and the equatorial I11/I10 ratio in a manner consistent with a reduction in the fraction of S1 bound to actin rather than by generation of low-force S1-actin isomers. At complete force suppression, IM3 was 78% of its relaxed value. BDM distorted dynamic IM3 responses to sinusoidal length oscillations in a manner consistent with an increased cross-bridge contribution to total sarcomere compliance, rather than a changed S1 lever orientation in BDM. When the number of actin-bound S1 was varied by altering myofilament overlap, tetanic IM3 at low overlap was similar to that in high [BDM] (79% of relaxed IM3). Tetanic dM3 dependence on active tension in overlap experiments differed from that observed with BDM. At high BDM, tetanic dM3 approached its relaxed value (14.34nm), whereas tetanic dM3 at low overlap was 14.50nm, close to its value at full overlap (14.56nm). This difference in tetanic dM3 behavior was explicable by a nonlinear thick filament compliance which is extended by both active and passive tension.

Structure‐Function Relation of the Myosin Motor in Striated Muscle

Force and shortening in striated muscle are driven by a structural working stroke in the globular portion of the myosin molecules-the myosin head-that cross-links the myosin-containing filaments and the actin-containing filaments. We use time-resolved X-ray diffraction in single fibers from frog skeletal muscle to link the conformational changes in the myosin head determined at atomic resolution in crystallographic studies with the kinetic and mechanical features of the molecular motor in the preserved sarcomeric structure. Our approach exploits the improved brightness and collimation of the X-ray beams of the third generation synchrotrons by using X-ray interference between the two arrays of myosin heads in each bipolar myosin filament to measure with A sensitivity the axial motions of myosin heads in situ during the synchronous execution of the working stroke elicited by rapid decreases in length or load imposed during an active isometric contraction. Changes in the intensity and interference-fine structure of the axial X-ray reflections following the mechanical perturbation allowed to establish the average conformation of the myosin heads during the active isometric contraction and the extent of tilt during the elastic response and during the subsequent working stroke. The myosin working stroke is 12 nm at low loads, which is consistent with crystallographic studies, while it is smaller and slower at higher loads. The load dependence of the size and speed of the myosin working stroke is the molecular determinant of the macroscopic performance and efficiency of muscle.

Influence of an admixture of H2 molecules on the structure and parameters of a Ne lattice

X-Ray investigations of solid solutions formed by condensation of mixtures of normal hydrogen and neon gases are performed for concentrations ranging from 2 to 60 mol.% nH2 and temperatures ranging from 5 K to the melting temperature of the sample. The structure of the vacuum condensates Ne-nH2 immediately after the samples are obtained is investigated. The boundary of single-phase solutions of hydrogen in neon is established to be 2 mol.%. At high H2 concentrations a hexagonal hcp2 phase forms in addition to a cubic fcc phase. The lattice volumes of these phases are somewhat larger but close to the volume of a pure-neon cell. The hexagonal hcp2 phase vanishes when the condensates are heated to a temperature of the order of the melting temperature of neon. This metastable hexagonal phase in the neon-rich mixtures studied is probably identical in nature to the previously observed hcp2 phase in hydrogen-rich solid mixtures. Both phases have one symmetry and the same cell volume. Information on the phase composition of the condensates is obtained from data on the concentration and temperature variations of the x-ray reflection intensities. It is shown that as the concentration of hydrogen molecules in the initial gas mixtures increases, the amount of the fcc phase in the condensates decreases almost linearly and the amount of the hcp2 phase increases. A combined analysis of the data obtained in the present work and previous measurements established the phase boundaries in the entire concentration range of the condensates. Evidently, because the molecular parameters of the components are close the Ne-nH2 mixtures do not form gel-like states, which are characteristic for quench-condensed Kr–H2 condensates.

Theory of Coupled Multipole Moments Probed by X-ray Scattering in CeB6

A minimal model for multipole orders in CeB$_6$ shows that degeneracy of the quadrupole order parameters and strong spin-orbit coupling lead to peculiar temperature and magnetic-field dependences of the X-ray reflection intensity at superlattice Bragg points. Furthermore, the intensity depends sensitively on the surface direction. These theoretical results explain naturally recent X-ray experiments in phases II and III of CeB$_6$. It is predicted that under weak magnetic field perpendicular to the (111) surface, the reflection intensity should change non-monotonically as a function of temperature.

Intensity of X-ray reflections from skeletal muscle thin filaments partially occupied with myosin heads: effect of cooperative binding

For quantitative analysis of contractile proteins of muscle by means of X-ray diffraction, it is important to know how the intensities of individual reflections are related to the number of diffracting objects, i.e., the amount of constituent contractile protein in the muscle cell. Here we diffused various amounts of exogenous myosin subfragment-1 (S1) into overstretched skinned skeletal muscle fibers, either in the presence or absence of Ca2+ , and derived the relationship between the S1 content and the intensities of reflections arising from the S1. In theory, the intensities should be proportional to the square of the S1 content (square law). However, the intensity-content relation deviated systematically from the square law as the S1 content was lowered, and it was better described as a linear function at the lower end of the S1 contents (<20% of saturation level). Model calculations show that the way of deviation is explained by the cooperative manner of S1 binding to the regulated thin filament.

Crystal structure of di-(L-serine) phosphate monohydrate [C3O3NH7]2H3PO4H2O

The crystal structure of di-(L-serine) phosphate monohydrate [C3O3NH7]2H3PO4H2O is determined by single-crystal x-ray diffraction. The intensities of x-ray reflections are measured at temperatures of 295 and 203 K. The crystal structure is refined using two sets of intensities. It is established that, in the structure, symmetrically nonequivalent molecules of L-serine occur in two forms, namely, the monoprotonated positively charged molecule CH2(OH)CH(NH3)+COOH and the zwitterion CH2(OH)CH(NH3)+COO−, which are linked with each other and with the H2PO4− ion through a hydrogen-bond system involving water molecules.

Investigation of diffusion and crystallization processes in thin ITO films by temperature and time resolved grazing incidence X-ray diffractometry

Oxygen diffusion into metallic In/Sn films and crystallite growth of thin indium tin oxide (ITO) films were investigated by in situ high temperature grazing incidence X-ray diffractometry (HT-GIXRD) at temperatures ranging from 100 to 300 °C. The investigated films were deposited by dc magnetron sputtering from a metallic target at different oxygen flows and bias voltages. The deposition process influences not only the film properties but also the film reactions during the post-deposition annealing process. The ITO formation is determined by two processes: the diffusion of oxygen into the metallic grains and a fast crystallization process. Kinetic parameters for both processes were derived. A model was developed which allows the determination of the diffusion coefficient D from the time dependence of the integral intensity of the ITO X-ray reflection. Diffusion coefficients as well as the activation energies are influenced by the bias voltage but not by the oxygen flow. According to the Johnson–Mehl–Avrami theory, the crystallization can be described as a two-dimensional process.

Synchrotron X-ray Microdiffraction Images of Polarization Switching in Epitaxial PZT Capacitors with Pt and SrRuO3 Top Electrodes

ABSTRACTThe evolution of stored ferroelectric polarization in PZT thin film capacitors was imaged using synchrotron x-ray microdiffraction with a submicron-diameter focused incident x-ray beam. To form the capacitors, an epitaxial Pb(Zr,Ti)O3 (PZT) thin film was deposited on an epitaxially-grown conductive SrRuO3 (SRO) bottom electrode on a SrTiO3 (STO) (001) substrate. Polycrystalline SRO or Pt top electrodes were prepared by sputter deposition through a shadow mask and subsequent annealing. The intensity of x-ray reflections from the PZT film depended on the local ferroelectric polarization. With 10 keV x-rays, regions of opposite polarization differed in intensity by 26% in our PZT capacitor with an SRO top electrode. Devices with SRO electrodes showed just a 25% decrease in the remnant polarization after 107 switching cycles. In devices with Pt top electrodes, however, the switchable polarization decreased a by 70% after only 5×104 cycles.

硬Ｘ線用斜入射平面ミラーの形状誤差が反射Ｘ線強度・位相分布に及ぼす影響の波動光学的評価

硬Ｘ線用斜入射平面ミラーの形状誤差が反射Ｘ線強度・位相分布に及ぼす影響の波動光学的評価

Crystal structure of diserinesulfate monohydrate

The crystal structure of DL-Serine H2SO4 · H2O is determined by single-crystal x-ray diffraction. The intensities of x-ray reflections are measured at three temperatures, namely, 295, 343, and 233 K. The crystal structure of the studied compound is refined using all three sets of intensities. It is demonstrated that, at a temperature of 233 K, the structure transforms into an incommensurately modulated state. This transformation is assumed to be responsible for the disappearance of the piezoresponse at this temperature.

Multiple phase transitions of leonite-type compounds: optical, calorimetric, and X-ray data

Low-temperature phase transitions of leonite-type compounds, K2Me2+(SO4)2 · 4H2O (Me = Mg, Mn, Fe), are investigated by temperature dependent measurements of single-crystal X-ray reflection intensities and lattice parameters. The transition temperatures and the progress of the transitions are determined by birefringence data and differential scanning calorimetry. The cause for the phase transitions of leonite-type compounds is a dynamic disorder of sulphate groups at room temperature (C2/m), that freezes in to an ordered structure (I2/a) at −4(1) °C in leonite, K2Mg(SO4)2 · 4H2O. At −153(1) °C the crystal structure switches to another ordered phase (P21/a). The Mn analogue shows the same succession with transition temperatures at −68(1) °C and −104(1) °C. The disordered room temperature structure of the isotypic mineral mereiterite, K2Fe(SO4)2 · 4H2O, transforms directly to the ordered P21/a structure at 3(2) °C. Analysis of X-ray intensities and of excess birefringence reveals that the displacive I2/a ⇔ P21/a phase transition of leonite and Mn-leonite is first order. According to Landau theory the C2/m ⇔ I2/a (leonite, Mn-leonite) and C2/m ⇔ P21/a (mereiterite) order-disorder transitions are almost tricritical.

The father of us all.

The father of us all.

Epitaxial growth of Cr on Ag(001)

The growth morphology and structure of ultrathin films of Cr deposited on Ag (001) have been studied in situ by surface x-ray diffraction. The reflected x-ray intensity at the anti-Bragg position along the $(00l)$ rod was monitored during growth at temperatures between 100 and 473 K. At room temperature, there is a steady decay of the intensity, indicative of disordered growth. At higher temperatures the variation of the intensity with time is consistent with the coating of monolayer platelets of Cr with Ag. At 100 K weak oscillations were observed, which decayed relatively quickly. Scans along the reciprocal-lattice vectors perpendicular to the surface were recorded for three different coverages. Expanded interface spacings were found in all of the films. For the two films grown at 100 K analysis of the scans indicated that a fraction of the films were disordered. The Cr film grown at a temperature of 430 K was found to intermix with the layer of Ag that covers it.

Frequency-Dependent Distortion of Meridional Intensity Changes during Sinusoidal Length Oscillations of Activated Skeletal Muscle

Bundles of intact, tetanized skeletal muscle fibers from Rana temporaria were subjected to sinusoidal length oscillations in the frequency domain 100 Hz to 3 kHz while measuring force and sarcomere length. Simultaneously, intensity of the third-order x-ray reflection of the axial myosin unit cell ( I M3) was measured using synchrotron radiation. At oscillation frequencies <1 kHz, I M3 was distorted during the shortening phase of the sinusoid (i.e., where bundle length was less than rest length). Otherwise, during the stretch phase of oscillations at all frequencies, during the shortening phase of oscillations above 1 kHz, and for bundles in the rigor state, I M3 was approximately sinusoidal in form. Mean I M3 during oscillations was reduced by 20% compared to the isometric value, suggesting a possible change in S1 disposition during oscillations. However, the amplitude of length change required to produce distortion (estimated from the phase angle at which distortion was first evident) corresponded to that of a step release sufficient to reach the maximum I M3, indicating a mean S1 disposition during oscillations close to that during an isometric tetanus. The mechanical properties of the bundle during oscillations were also consistent with an unaltered S1 disposition during oscillations.

X-ray magneto-optics in lanthanides.

Magneto-optical methods in the visible light regime generally lack element specificity, which has become a considerable shortcoming in research on advanced heteromagnetic systems. Using circularly polarized soft x rays tuned to a 4d-4f core-level transition of a lanthanide element, the specularly reflected x-ray intensity changes proportionally to the magnetization of this element and, e.g., hystereses are easily measured element specifically. In contrast to the case of visible light, temperature dependent 4d-4f magneto-optical signals are not influenced by the thermal lattice expansion.