Higher Bragg Angles Research Articles

Chemical vapor deposition-based synthesis of cost-effective binder-free nanostructured Ag/MoS2/Ni–F electrode material for portable energy storage devices

The synthesis of novel electrode materials (E-Ms) is the demand of scientific community to overcome the energy crisis in developing countries. Hereon, the molybdenum disulfide (MoS2) and silver-wrapped MoS2 (Ag/MoS2) E-Ms are synthesized on hierarchical-nickel foam (Ni–F) via a cost-effective chemical vapor deposition technique. The synthesized E-Ms are characterized in terms of structure, chemical bonding, surface morphology, weight percentage of elements, porosity and energy storage capability. The X-ray diffraction analysis is indicated that by wrapping of Ag species, the diffraction peaks associated with MoS2 material not only moved to higher Bragg's angles but their peaks intensities are also lowered which showed the existence of structural defects in the synthesized E-Ms. The surface area of cauliflower like Ag/MoS2/Ni–F E-Ms (170 m2g-1) is higher than the surface area (60 m2g-1) of MoS2/Ni–F E-Ms. The cauliflowers based Ag/MoS2/Ni–F E-Ms is presented supreme specific capacitance of 4200 Fg-1 as compared to MoS2/Ni–F E-Ms (2518 Fg-1) at 1Ag-1. The implementation of power law and Dunn's model is demonstrated that the synthesized E-Ms can behave like a battery and supercapacitor (0.67 < b < 0.92) nature. The diffusive-controlled contribution for cauliflower-based synthesized E-Ms is 97 % at 5 mVs−1 and became 88 % at 70 mVs−1. The assembled asymmetric supercapacitor (ASC) device is exhibited the specific capacitance of 957 Fg-1, energy density of 366–284 Whkg−1 and power density of 1494–14110 Wkg-1. The ASC device could sustain the capacitance retention of 94 %, Coulombic efficiency of 99 % even for 20000 cycles in contrast to capacitance retention of 95 % and Coulombic efficiency of 97.89 % of the synthesized E-Ms.

The effective role of potassium doping in improving the structural, morphological optical, and electrical properties of CdO thin film for optoelectronic application

Aspiring to increase the electrical conductivity, enhance the electron mobility, and widen the band gap, potassium (K) was used as a substitutional dopant in the CdO matrix. Transparent cadmium oxide (CdO) and potassium-doped cadmium oxide (K–CdO) thin films with different K concentrations (0.02, 0.04, and 0.06 mol) were deposited on glass substrates via thermal evaporation technique. A remarkable shift of (111) peak towards high Bragg's angle was noticed as the potassium content was increased, which established the successful incorporation of K into the CdO matrix. The surface became more compacted and denser with a noticeably smaller particle size upon doping with K, as revealed by field emission scanning electron microscopy (FESEM)aand the Willmason-Hall plot. The optical band gap was boosted from 2.5 to 2.79 eV, when the K concentration was increased from 0.0 to 0.06 mol. Moreover, the optoelectronic features, such as transmittance, reflectance, skin depth, refractive index, tailing energy, optical dielectric constants, and optical conductivity were investigated in depth. The Hall experiment was used to determine the DC electrical properties of the K– CdO film including the resistivity (ρ), Carrier concentration, Carrier mobility, and Hall coefficient. The Hall measurement asserted that the film is an n-type semiconductor and electron mobility (μn) was boosted, as the K concentration was raised. The increased optical band gap and enhanced electron mobility achieved by potassium doping reflected the fact that K-doped CdO thin films are promising window layers in photovoltaic applications.

Novel applications of centreless X-ray diffractometers for non-destructive pole figure measurements

Centreless X ray diffractometers are specially designed for non-destructive residual stress measurements. The similarity between the X-ray diffraction-based stress and texture measurement methods led us to introduce a new method on non-destructive (sample cutting-free) stress measurement devices to studies on crystallographic texture. The method that determines texture characteristics from residual stress data has recently been introduced. Afterwards, a method with which pole figures (fully equivalent to conventionally measured pole figures) at high Bragg-angles can be constructed with centreless diffractometers were developed. The paper gives an illustration of the new methods’ utilization on the field of archaeometry. In that area, only non-destructive testing modes are permitted. In the case of archaeological finds, knowing the crystallographic texture assists to reconstruct the ancient process technology (hammering, rolling, annealing) that was applied during the manufacturing. The new methods are suitable to be used on valuable and unique objects both in the automotive industry, archaeometry and in the space applications.

Analysis of Sn Concentration Effect on Morphological, Optical, Electrical and Photonic Properties of Spray-Coated Sn-Doped CdO Thin Films

Tin-doped cadmium oxide (Sn:CdO) transparent thin films with different Sn concentrations were deposited on glass and p-silicon substrates by the chemical spray method at 250 °C. Different concentrations of stannic chloride were used to prepare Sn:CdO thin films. The prepared doped and un-doped CdO films were subjected to X-ray diffraction (XRD), scanning electron microscopy and atomic force microscopy, optical absorption, and electrical analyses to characterize their structural, morphological, optical, and electrical properties, respectively. XRD analysis demonstrated the growth of polycrystalline and cubic CdO with preferential orientation along the (111) plane. Sn-doping shifted the XRD peaks slightly towards a higher Bragg angle and increased the band gap of CdO thin films. Variation in doping concentration also affected the morphology of the films. Optimum Sn-doping increased the electrical conductivity of CdO thin films. Furthermore, to the best of our knowledge, the photoresponse analyses of the fabricated un-doped and doped n-CdO/p-Si heterostructures were performed for the first time in this study.

Bandgap tuning in GaAs1−xSbx axial nanowires grown by Ga-assisted molecular beam epitaxy

In this work we present a comprehensive study on the effects of Sb incorporation on the composition modulation, structural and optical properties of self-assisted axial GaAs1−xSbx nanowires of 2–6 μm in length grown on (111) Si substrate by molecular beam epitaxy. The Sb composition in the GaAs1−xSbx axial nanowire (NW) was varied from 2.8–16 at.%, as determined from energy dispersive x-ray spectroscopy. Lower Sb composition leads to thinner nanowires and inhomogeneous Sb composition distribution radially with a depleted Sb surface region inducing weak type-II optical emission, the presence of an additional peak at higher Bragg angle in the x-ray diffraction spectra and an electric-field-induced strong Raman LO mode. Higher Sb composition of 16 at.% leads to a more uniform Sb compositional distribution radially leading to type-I optical transitions exhibiting the lowest PL peak energy occurring at 1.13 eV. In addition, the high quality of these nanowires exhibiting pure zinc blende crystal structure, largely free of any planar defects, is borne out by high resolution transmission electron microscopy and selected area diffraction patterns. The shift and broadening of the Raman LO and TO modes reveal evidence of increased Sb incorporation in the nanowires. Significant improvement in optical characteristics was achieved by the incorporation of a Al0.2Ga0.8As passivating shell. The results are very promising and reveal the potential to further red shift the optical emission wavelength by fine tuning of the fluxes during growth.

Damage studies on tungsten due to helium ion irradiation

Energetic and high fluence helium ions emitted in a plasma focus device have been used successfully to study the radiation induced damage on tungsten. The reference and irradiated samples were characterized by optical microscopy, field emission scanning electron microscopy, X-ray diffraction and by hardness testers. The micrographs of the irradiated samples at lower magnification show uniform mesh of cracks of micrometer width. However at higher magnification, various types of crystalline defects such as voids, pinholes, bubbles, blisters and microcracks are distinctly noticed. The prominent peaks in X-ray diffraction spectrum of irradiated samples are seen shifted toward higher Bragg angles, thus indicating accumulation of compressive stress due to the heat load delivered by helium ions. A marginal reduction in hardness of the irradiated sample is also noticed.

Advances in X-ray diffraction contrast tomography: flexibility in the setup geometry and application to multiphase materials

Diffraction contrast tomography is a near-field diffraction-based imaging technique that provides high-resolution grain maps of polycrystalline materials simultaneously with the orientation and average elastic strain tensor components of the individual grains with an accuracy of a few times 10−4. Recent improvements that have been introduced into the data analysis are described. The ability to process data from arbitrary detector positions allows for optimization of the experimental setup for higher spatial or strain resolution, including high Bragg angles (0 &lt; 2θ &lt; 180°). The geometry refinement, grain indexing and strain analysis are based on Friedel pairs of diffraction spots and can handle thousands of grains in single- or multiphase materials. The grain reconstruction is performed with a simultaneous iterative reconstruction technique using three-dimensional oblique angle projections and GPU acceleration. The improvements are demonstrated with the following experimental examples: (1) uranium oxide mapped at high spatial resolution (300 nm voxel size); (2) combined grain mapping and section topography at high Bragg angles of an Al–Li alloy; (3) ferrite and austenite crystals in a dual-phase steel; (4) grain mapping and elastic strains of a commercially pure titanium sample containing 1755 grains.

Annealing Effect on the Structure and Electronic Transport Properties in La5/8Ca3/8MnO3/ErMnO3 Multilayer Thin Films

Ferromagnetic La5/8Ca3/8MnO3 (LCMO) and Ferroelectric ErMnO3 (EMO) multilayer thin films with sandwich structure (LCMO/EMO/LCMO) were grown on (LaAlO3)0.3(Sr2AlTaO6)0.7 (001) [LSAT (001)] substrates by pulsed laser deposition (PLD) method. For these films, the structural characterization was carried out by X-ray diffraction (XRD), and the temperature-dependence resistivity (p-T) showing the metal-insulator transition (Tp) also was measured. In the multilayer thin films the LCMO (002) peak move to lower Bragg angles after annealing at 900 degrees C for 30 hours under 1atm Oxygen pressure, and this condition is much different from the LCMO single layer films where the (002) peak moves to higher Bragg angle after annealing due to the lattice mismatch between the LCMO layer and the substrate. By increasing the thickness of LCMO, the multilayer samples show two MR peaks in a wide temperature range during the process of M-l transition. This phenomenon is attributed to a new (La5/8Ca3/8)xEr(1-x)MnO3 layer produced by the solubility between LCMO and EMO layers after high-temperature annealing. In this paper, we provide some evidence of dissolution between LCMO and EMO layers, and discuss the influence on structure and electronic transport properties in the composite thin films by annealing.

A High Power, High Resolution LDA/PDA System Applied to Gasoline Direct Injection Sprays

A new generation LDA/PDA transmitter system has been designed and constructed. The heart of the optical system is a new type of Bragg cell. Advances in laser power handling and symmetrical splitting at high Bragg angles of the shifted and unshifted beams have made it possible to construct a simple yet elegant LDA/PDA transmitter. The optical system integrates the Bragg cell with a laser beam expander to offer variable beam separation and high beam expansion ratios to produce a measurement volume with a high spatial resolution and at high power levels. The transmitter is proving to be a significant contribution to LDA/PDA optical system design and, not only applicable as a research tool for use in flows of a demanding nature but, due to its simplicity, flexibility and cost, an asset to teaching. The LDA/PDA system is being applied to characterise the atomization of fuel by high pressure automotive injectors as found in Gasoline Direct Injection (GDI) engines. Although the PDA system was configured to measure two orthogonal velocity components (2D) and size, its operation was not restricted to this configuration. An analysis of the spray with the PDA system in 1D and size and the LDA system in 2D and 1D configurations indicated the complexity of the atomization and break-up processes occurring in the spray. Single-shot imaging was used to study the spatial structure of the spray as a function of time. Use of the light sheet imaging technique alone could lead to false impressions of the atomization process.

The influence of microstructure on the measurement of γ-γ′ lattice mismatch in single-crystal Ni-base superalloys

Lattice mismatch in multicomponent high refractory single-crystalline Ni-base superalloys has been measured in situ by hot-stage X-ray diffraction. Prior to X-ray examination, all samples were subjected to long-term aging treatments at 1120 °C to relieve coherency stresses. The resolution of the individual γ and γ′ peaks at high Bragg angles in the X-ray spectra and the magnitude of the misfit was found to be sensitive to the microstructure of the material. When the precipitation of coherent γ′ during cooling from the aging temperature could largely be suppressed, the corresponding matrix peaks were narrower and of higher intensity as compared with samples where cooling γ′ was present. Also, a slightly larger misfit, 0.04%, was measured in the microstructures where the cooling γ′ was not present. Procedures for deconvoluting X-ray data are outlined in detail, and the experimental results are discussed in terms of changes in phase compositions and misfit strains produced by the cooling γ′.

X-ray diffraction study of mineral components in calcareous algae (Corallinaceae, Rhodophyta)

The mineral composition of nine species of red calcareous algae (Corallinaceae, Rhodophyta) collected in the Adriatic Sea in 1987 and 1988 was examined by X-ray powder diffraction (counter diffractometer, monochromatized CuKα radiation). In addition, a comparison between the calcareous algae from the north Adriatic (Rovinj area) and the central Adriatic (Kornati Islands) with regard to genus, species and environmental factors was undertaken. All analyzed samples contained magnesium calcite, which was dominant in all but in two cases, where aragonite was the main phase. Diffraction lines of magnesium calcite were broadened and shifted toward higher Bragg angles in relation to pure calcite. Supposing that in the calcite crystal lattice only magnesium replaces calcium, it follows that the fraction of magnesium in magnesium calcite, found from diffraction line shifts, would be 18 molar % (M%). Aragonite was dominant (75 to 80 M%) in two samples of Pseudolithophyllum expansum collected at Kornati Islands in 1987 and 1988. These two samples also contained magnesium calcite and a small fraction of calcite (5 to 10 M%). In other studied samples aragonite was detected in small fractions, up to 10 M%. The elemental analysis of corallinacean algae obtained by X-ray spectroscopy showed that the fraction of the metals Sr, Fe, Mn, Zn, Pb, Br, Cu and Rb was very small (15 to 2000 ppm). In most samples other expected minerals were detected in small fractions, such as sylvite (KCl, up to 2 M%), quartz (α-SiO2, up to 2 M%) and magnesite (MgCO3, only in one sample, 1 M%). The results show that calcareous algae are able to deposit a mixture of magnesium calcite, calcite and aragonite. Such a large molar fraction of aragonite in the alga P. expansum, or in any other corallinacean algae, has not been noted in recent literature. It seems that a complexity of microclimatic and oceanographic factors may influence the diversity of two localities and cause some exchange in living organisms. In addition, the fact that under certain conditions the same organism is capable of forming different minerals from the same tissue (McConnaughey 1989) confirms our opinion that environmental effects are imprinted in the skeletal composition of calcareous algae P. expansum.

Thermogravimetry and Rietveld analysis for the high-temperature X-ray powder diffraction pattern of Y4Al2O9

Y4A1209 has a monoclinic crystal structure, space group P21/c [1]. The atomic parameters of this structure were refined by single crystal X-ray and neutron diffraction and by Rietveld analysis for the X-ray synchrotron powder diffraction pattern [2, 3]. Recently, we revealed the high-temperature phase transformation of Y4AIzO9 at 1377 °C by high-temperature differential scanning calorimetry (DSC), high-temperature dilatometry and hightemperature X-ray powder diffraction (XRD) [4, 5]. The low-temperature phase transformed to the high-temperature phase with a small change in endothermic enthalpy and small volume shrinkage. Thermal hysteresis and athermal phenomena were observed at this phase transition. Judging from these results, the phase transition was thought to be martensitic. Takizawa et al. reported a stress induced phase transition from a tetragonal structure to a monoclinic structure for (Hol_xLax)4Al209 and (Yl_xLax)4AlzO9 at room temperature [6]. In our previous study, peaks in the XRD of the high-temperature phase were indexed with a monoclinic cell [4]. However, the crystal structure of the high-temperature phase has not been clarified. This letter describes the thermogravimetric analysis of Y4AI209 and analysis of the crystal structure of the lowand high-temperature phases by the Rietveld method for XRD patterns obtained at room temperature, 1300 °C and 1400 °C. Y4A1209 was prepared from powders of Y203 (99.9% purity) and A1203 (99.9% purity). Stoichiometric amounts of powders were weighed and mixed in an agate mortar. The mixture was pressed into pellets and heated on a Pr 60%-Rh 40% plate in a molybdenum silicide furnace at 1600 °C for 10 h. The obtained pellets were powdered for thermogravimetry (TG) and XRD. TG was carried out with a high-temperature thermobalance (TG-DTA 2200, Mac Science). The rate of heating was 10 °Cmin -1. The XRD pattern was obtained at room temperature using CuKo~ radiation with a pyrolitic graphite monochromator and a diffractometer (RAD-C, Rigaku; tube voltage and current: 40kV and 20 mA). High-temperature XRD patterns were obtained with a graphite monochromator using a diffractometer with a high-temperature furnace attached (MXP18, Mac Science, tube voltage and current: 45 kV and 360 mA). The temperature was measured with a Pt-Rh13% thermocouple set into a Pt sample holder. Since the phase transition had the thermal hysteresis [4, 5], high-temperature XRD was performed at 1300 °C on heating and at 1400 °C on cooling f rom 1500 °C. The intensity data were collected from 10 to 70 ° in 20 with a sampling step width of 0.04 °. Rietveld analysis of the XRD data was carried out using the RIETAN program [7]. A weight loss of about 0.18% was detected for the powdered Y4A1209 sample from room temperature to 350 °C. This was probably due to detachment of adsorbed water. Above this temperature to 1500 °C, the weight change of the sample was less than 0.005%. This result indicated that oxygen atoms and other elements did not transfer from or into the sample within this weight range. Fig. 1 shows the profile fit and difference patterns of Rietveld analysis for the XRD data of Y4AI209 at room temperature, 1300 °C and 1400 °C. The solid lines are calculated intensity profiles and the dots crossing the profiles are observed intensities. The short vertical lines show the positions of possible Bragg reflections. The differences between observed and calculated intensities are plotted below the profiles. Table I lists the refined lattice p0rameters of the primitive monoclinic cells and R faqtors of the Rietveld analysis [8]. In the Rietveld refinement for the XRD pattern at room temperature, the calculated pattern fits the observed one well. The lattice parameters of the present study were almost equal to those reported by Lehmann et al. [2] for the a-axis and /3, and were slightly smaller than those for the band c-axes. The relative intensities of the main diffraction peaks of the high-temperature phase at 1400 °C were not so different from those of the low-temperature phase at room temperature and 1300 °C (Fig. 1). Since the peaks overlapped at higher Bragg angles, the relative intensities of the peaks at 20 from 10 to 25 ° were compared. For the high-temperature phase, peaks of 10 0 and i 12 became very small, and the relative intensities of 1 10 and i 02 were larger than those of the low-temperature phase. Based on the peaks of the powder diffraction pattern of the high-temperature phase, we were not able to adopt any space group except P21/c. Therefore, we analysed its crystal structure with the space group of P21/c. The lattice parameters of the face-centred cell are also listed in Table I; they were calculated from the refined primitive lattice parameters with the conversion proposed by Brandle and Steinfink [9]. The/3' angle of the face-centred cell was close to 90 ° but the lattice of the high-temperature phase did not become orthorhombic.

Crystalline imperfections in 4H SiC grown with a seeded Lely method

Commercially available 4H SiC wafers have been studied concerning their crystal quality. A variety of structure sensitive techniques has been utilized to reveal specific macro-defects in the material. Microscopy examination combined with preferential chemical etching have imaged dislocation networks, micropipes, basal plane defects and cracks. Synchrotron X-ray topographs have shown defect-associated strain and lattice misorientation arising in the vicinity of some micropipes. High resolution X-ray diffractometry and Bragg angle topography were used to provide evidence of existing domains and their misorientation. The results obtained are discussed in the context of defect origin and formation mechanisms. A comparison with 6H SiC is made to derive possible similarities of defect appearance in both polytypes.

On the dilatation of synthetic type Ib diamond by substitutional nitrogen impurity

Sequences of high Bragg-angle (0 B = 74°) double-crystal X-ray topographs taken at the SRS (Daresbury, U.K.) have yielded precise measurements of lattice parameter differences between growth sectors of different crystallographic forms in a large undoped synthetic diamond whose type Ib infrared absorption spectrum (principal peak at 1130 cm -1 ) indicated atomically dispersed nitrogen, singly substituting for carbon, as the only detectable impurity. The plate-shaped specimen, polished parallel to (110), 5.0 x 3.2 mm 2 in area, 0.7 mm thick, possessed an unusually well developed (110) growth sector containing nitrogen impurity concentration of only ca. 10 -6 , which served as an internal standard of pure-diamond lattice parameter with which lattice parameters of nitrogen-containing growth sectors were compared. The specimen’s suitability for precision diffractometry was checked by comprehensive tests using optical microscope techniques, cathodoluminescence and single-crystal X-ray topography. The double-crystal combination was silicon reference crystal, asymmetric 175 reflection, with diamond specimen symmetrical 440 reflection. The principal measurement was the increase of the lattice parameter, a 0 , of the (111) growth sector (nitrogen content 88 + 7 parts per 10 6 atomic) relative to that of the (110) sector: Aa 0 / a 0 = 1.18 + 0.07 x 10 -5 . In terms of measured infrared absorption coefficient at 1130 cm -1 , this gives Aa 0/a 0 = (2.95 + 0.27) x 10 -6 [p(1130 cm -1 )/cm -1 ], which is believed to hold for growth sectors of all crystallographic forms. Combination with the nitrogen assay findings of Woods, van Wyk &amp; Collins ( Phil. Mag. B 62. 589-595 (1990)) provides a direct relation to c N , the fractional atomic concentration of substitutional nitrogen, as A a 0 / a 0 = (0.14 + 0.02) c N , which indicates that the effective volume of a single substitutional nitrogen atom in diamond is 1.41 +0.06 times that of the carbon atom it replaces. This substantial dilatation conflicts with several models for the substitutional nitrogen structure.

Residual Stress Analysis in Steels Having Preferred Orientation by Use of Synchrotron Radiation Source

In the field of X-ray stress analysis, a diffraction plane at a high Bragg angle region has to be selected in order to determine the precise value of stress. But stress analysis using a most desired (hkl)- plane is not always possible. The use of synchrotron radiation (SR) enables the stress analysis using many (hkl)-planes with high accuracy by providing a perfectly monochromaticed X-ray beam having an optional wave length. Such features of SR ate most suitable for the stress analysis on materials having preferred orientation.

THE ANOMALOUS BACK DIFFRACTION PSEUDO-KOSSEL PATTERNS OF LiNbo3 CRYSTAL IN THE VICINITY OF 75℃

It is found that the diffraction, obtained by using X-ray divergent beam technique-back reflection Kossel method, of pure and Ti-diffused LiNbO3 crystals become abnormal in the vicinity of 75℃.The Pseudo-Kossel lines of such crystal planes as (11010), (01110), (0118), (1108), (03312), (33012), are found to be severely distorted but still continuous. The pattern's distortion shows approximately two-fold symmetry about x-plane and therefore the crystal's triad axis of symmetry along x-direction is destroyed.It is also found that the distortions of pseudo-Kossel lines arising from high Bragg angle diffraction planes are smaller than those arising from lower angle diffraction planes.

Relationship of the structure of the pseudobinary Laves phase compounds Sm-Er-Fe to their intrinsic magnetostriction

A series of pseudo-binary Laves phase compounds Sm1−xErxFe2 (x=0.1, 0.2...0.85) have been prepared and investigated. Using the method of x-ray diffractometry, the samples are step scanned with monochromatic Cu radiation at Bragg angle 2θ ranging from 50° to 110°. A detailed report is presented here on the broadening and splitting of the line profiles in some specimens at higher Bragg angles, like the cubic (533), (622), (642), and (731) reflections. The results are discussed in connection with the intrinsic magnetostriction of the material. The Curie temperatures and the room temperature saturation magnetization of the compounds have also been studied.

2層ワイセンベルグ写真の回折斑点の解析法

In order to process the diffraction spots on the two-slits Weissenberg photograph (Mito et al. 1981), two computer programs have been pre-pared. One program is for construction of a chart by drawing the axial reciprocal lattice lines. The chart is available for interpretation of the general-inclination Weissenberg photographs taken on a camera with any diameter and any translation constant. The failure in indexing of high Bragg angle reflections can be prevented by using the chart. The other program is for refinement of the lattice constants and the orientation angles of crystallographic axes to the rotation axis. The reflections are indexed from the initial values of unit cell parameters, camera parameters and crystal orientation parameters. The parameters are optimized by the nonlinear least-squares method. The determination of crystal orientation parameters allows us to dispense with the procedure of the crystal alignment on the goniometer. These programs have been employed for the synthetic diamond crystals of the spineltype twin to refine the cell dimensions and obliquity angle.

A study of the rhombohedral distortion of the magnetostrictive samarium-iron compounds with addition of molybdenum or vanadium

The mechanical hardness and magnetostriction of annealed pseudo-binary compounds, based on the binary Laves phase, SmFe2 compound with additions of small percentage of Cu, Ni, V or Mo, have been studied. It is found that the compounds containing Mo have optimum hardness and values of magnetostriction. The pseudo-binary compounds SmFe2−xMox and SmFe2−xVx (x = 0.05, 0.1 and 0.2) have been studied by using X-ray counter diffractometer. Owing to the broadening and the splitting of line profiles at higher Bragg angles, a precision determination of lattice parameters becomes difficult. From the data the angles of rhombohedral cells and the relative change in lattice spacings of cubic (400) reflections in these compounds have been calculated.

An analysis of volume phase gratings at higher Bragg angle incidence

Coupled wove differential equations are derived showing that under certain conditions a plane wave incident at the nth Bragg angle can completely transfer its power to the — n mode. The analytical approximations are compared with the numerical solution.