Flat Plate Samples Research Articles

Reflection Asymmetric Powder Diffraction with Flat-Plate Sample using a Curved Position-Sensitive Detector (INEL CPS 120)

The reflection flat-sample asymmetric geometry is an attractive set-up for powder diffraction measurements, as compared to either conventional Debye–Scherrer or symmetric Bragg–Brentano geometries. Combined with grazing- or fixed-incidence-angle X-rays, it is suitable for surface-structure or thin-film texture analysis. Furthermore, it allows curved position-sensitive detectors to be used for in situ experiments. In this paper, the major systematic error sources in connection with this geometry are reviewed. It is confirmed that experimental linearization of the curved position-sensitive detector and sample positioning have to be very carefully performed. Simple and automatable procedures are proposed. Then, it is shown that peak-location accuracy leads to satisfactory cell-parameter determination as checked by the use of a silicon international standard reference sample and that structure refinement by the Rietveld method can be performed in very good conditions, as observed with an NaBi2Sb3O11 compound.

Measurement of Resistivity of Conductive Flat Plate Sample by the SRPM Method

Title: Measurement of Resistivity of Conductive Flat Plate Sample by the SRPM Method | Keywords: Resistivity, Permeability, Flat plate, SRPM, Solenoid coil | Author: Yoshihiro Nonaka, Hiroshi Nakane, Kiminori Hasuike, Takao Maeda and Hirohiko Ishikawa

In-situ sampling and characterization of frazil ice deposits

Three new samplers were developed for detailed analysis of the three-dimensional characteristics of frazil ice deposits beneath an ice cover. These samplers obtain in-situ bulk, hollow core and flat plate samples of the deposits through 200-mm-diameter access holes. The samples provide information on a deposit's internal structure, stratigraphy and sedimentology, geometry and physical properties, and lateral and vertical variabilities of each. When used as part of a comprehensive field program, the data provide information required for interpreting mechanisms of frazil transport and deposition, and for analyzing the dynamic interaction of frazil deposits with winter river processes.

Rietveld refinement of Debye–Scherrer synchrotron X-ray data from Al2O3

The application of the Rietveld refinement technique to synchrotron X-ray data collected from a capillary sample of Al2O3 in Debye–Scherrer geometry is described. The data were obtained at the Cornell High Energy Synchrotron Source (CHESS) with an Si(111) double-crystal monochromator and a Ge(111) crystal analyzer. Fits to a number of well resolved individual peaks demonstrate that the peak shapes are very well described by the pseudo-Voigt function, which is a simple approximation to the convolution of Gaussian and Lorentzian functions. The variation of the Gaussian and Lorentzian half widths, ΓG and ΓL, with Bragg angle can be approximated quite closely by the functions V tan θ and X/cos θ which represent the contributions from instrumental resolution and particle-size broadening respectively. Rietveld refinement based on this model yields generally satisfactory results. The refined values of V and X are consistent with the expected vertical divergence (≃0.1 mrad) and the nominal particle size (≃ 0.3μm). In particular, the use of a capillary specimen virtually eliminates preferred orientation effects, which are highly significant in flat-plate samples of this material.

Absorption corrections and digital filtering of X-ray diffraction profiles recorded with a position-sensitive detector

Expressions for the absorption correction function are obtained in the form of integral equations for the case of a flat-plate sample and a position-sensitive detector. It is shown that the absorption correction used for both transmission and reflection geometries with a conventional diffractometer may be applied to a diffractometer equipped with a linear position-sensitive detector. The application of a Savitzky–Golay-type digital filter considerably facilitates the analysis of the data without losing pertinent information.

Viscoelastic creep behavior of filament-wound case materials

The viscoelastic creep behavior of an S-901 glass/epoxy composite used in a solid rocket motor case is examined for a variety of loading conditions. Samples were removed from the forward dome region of a filament-wound motor case at fiber angles of ± 20 and ± 70 deg. They were tested at several stress levels in tension and four-point beam bending to determine the creep response through several creep-recovery cycles. Constant displacement rate tests also were conducted using the four-point beam bending test to evaluate hysteresis at relatively low stress levels. The behavior was found to be similar in many ways to that previously found for autoclaved, flat-plate samples tested at equivalent conditions. The creep behavior was found to follow a power law in time, D = D0 + /)/*, where D is the creep compliance (psi ~*), D0 is the initial elastic compliance, and D2 and n define the viscoelastic response characteristics. In the linear viscoelastic range, n = 0.19 and is in good agreement with data derived from the epoxy resin itself. At higher stress levels, the value of n increases due to microcracking within the composite. The largest difference in the creep-recovery behavior is exhibited between the first and second loading cycles, with n decreasing slightly with subsequent loading.

Magnetoresistance and Hall coefficient of inhomogeneous metals

In strong magnetic fields, most metals have highly anisotropic transport coefficients, and these have long been known to be much influenced by sample inhomogeneities. This paper reports a detailed theoretical study of such effects. Various approximations for calculating the effective transport coefficients of inhomogeneous solids are rederived from a unified point of view; these are then used for a variety of model calculations appropriate to metals with open Fermi surfaces. A small concentration of crystallites with open orbits embedded in a free-electron metal is shown to give rise to a strictly linear transverse magnetoresistance (TMR) at strong magnetic fields. The linear coefficient is strongly dependent on the orientation of the open orbit in the plane perpendicular to the magnetic field $\stackrel{\ensuremath{\rightarrow}}{\mathrm{H}}$. Extended-orbit crystallites in a free-electron metal produce a TMR which is initially linear, but saturates at sufficiently strong field. The Hall coefficient ${R}_{H}$ is unchanged from its free-electron value to first order in the concentration of defects. A striking geometrical effect is predicted, the TMR from open-orbit crystallites saturating in geometries such that current distortions are unable to propagate parallel to $\stackrel{\ensuremath{\rightarrow}}{\mathrm{H}}$. The TMR and Hall coefficient of a free-electron metal containing a larger concentration of open-orbit crystallites is calculated in the effective-medium theory (EMT). The TMR is found to saturate at strong fields, in agreement with previous results of Stachowiak, while the Hall coefficient falls off as 1/${\mathrm{H}}^{2}$ at strong fields, except in flat-plate samples with $\stackrel{\ensuremath{\rightarrow}}{\mathrm{H}}$ perpendicular to the plate, in which case it is predicted to saturate at its free-electron value for a sufficiently large concentration of open-orbit crystallites, but to fall off quadratically for lower concentrations. In contrast, calculations within a non-self-consistent approximation give a strictly linear TMR and a Hall coefficient which saturates at a value below the free-electron coefficient. Possible explanations for the discrepancy are discussed. Calculations in the EMT for a model polycrystal with extended-orbit crystallites reveal a broad field region of quasi-linear magnetoresistance, as found previously by Stachowiak, and a reduced Hall coefficient, as well as a conspicuous geometrical effect. The possible relation of these model calculations to experiments of polycrystalline noble metals is examined, but no quantitative theory for these metals is given.

Resistivity Tensor Elements in Silver Measured Using Helicon-Like Waves

Elements of the anisotropic resistivity tensor R of silver were measured for a large range of field directions. Helicon standing-wave resonances in flat plate samples were used to measure the tensor elements Rij. Samples were tipped in the magnetic field. Data were taken for crystallographic directions of B0 which completely outlined the unit stereographic triangle. Measurements were also made for many directions in the interior of the unit triangle. Hall effect and transverse-even voltage terms were measured, as well as the transverse magnetoresistance. Results are presented which can be compared to the predictions provided by Fermi surface shape.

Measurement of the Anisotropic Resistivity Tensor of Silver Using Heliconlike Waves

Standing-wave resonances of heliconlike waves have been used to measure resistivity tensor elements ${R}_{\mathrm{ij}}$ in silver single crystals. Flat-plate samples were used. Data were taken for \ifmmode\pm\else\textpm\fi{} 12\ifmmode^\circ\else\textdegree\fi{} regions near the major directions [100], [111], [110], and [211]. Curves are presented of the variation of the ${R}_{\mathrm{ij}}$ elements with field direction. Data are also presented as functions of field strength with the field direction fixed along major directions. Reversing the field allowed the separation of terms even and odd in field. These data represent a more complete study of resistivity tensor elements in silver for field directions near major axes than has previously been available.