Bragg Lines Research Articles

Principal Component Analysis (PCA) for Powder Diffraction Data: Towards Unblinded Applications

We analyze the application of Principal Component Analysis (PCA) for untangling the main contributions to changing diffracted intensities upon variation of site occupancy and lattice dimensions induced by external stimuli. The information content of the PCA output consists of certain functions of Bragg angles (loadings) and their evolution characteristics that depend on external variables like pressure or temperature (scores). The physical meaning of the PCA output is to date not well understood. Therefore, in this paper, the intensity contributions are first derived analytically, then compared with the PCA components for model data; finally PCA is applied for the real data on isothermal gas uptake by nanoporous framework γ –Mg(BH 4 ) 2 . We show that, in close agreement with previous analysis of modulation diffraction, the variation of intensity of Bragg lines and the displacements of their positions results in a series of PCA components. Every PCA extracted component may be a mixture of terms carrying information on the average structure, active sub-structure, and their cross-term. The rotational ambiguities, that are an inherently part of PCA extraction, are at the origin of the mixing. For the experimental case considered in the paper, the extraction of the physically meaningful loadings and scores can only be achieved with a rotational correction. Finally, practical recommendations for non-blind applications, i.e., what boundary conditions to apply for the the rotational correction, of PCA for diffraction data are given.

TiO2 thin films on Au/Ti/SiO2/textured Si substrates as high capacity anode materials for Li-ion batteries

In this paper, we investigate the structural and electrochemical properties of TiO2 thin films deposited on multilayered Au/Ti/SiO2/(100) textured-Si substrates by electron-beam evaporation technique at various substrate temperatures in the range 25 ≤ Ts ≤ 350 °C. Phase-pure and well-crystallized TiO2 thin films grown at Ts = 250 °C exhibit the typical (101) Bragg line of the tetragonal anatase structure with crystallite size of about 30 nm. The surface morphological analysis reveals the uniform growth of prismatic shaped grains (40–120 nm in size) deposited on pyramidal architectures of textured substrates. The electrochemical tests show that TiO2 thin films electrodes deposited at Ts of 250 °C deliver a specific discharge capacity of 74 μAh cm−2 μm−1 at a current density of 1 mA cm−2 with 96% capacity retention after 100 cycles. Hence, the experimental results demonstrate that TiO2 thin films can be used as anodes of planar solid-state Li-ion microbatteries.

A Study of Thermal Properties of Au25Pd75 Alloy Using X-Ray Diffraction

Abstract—The structure and thermal properties of Au25Pd75 alloy were studied using X-ray diffraction (XRD) technique. The change in lattice parameter a(T) was measured as a function of temperature using the Bragg line displacement method. The diffraction data obtained in the temperature range of 308–1158 K was utilized to determine the thermal parameters like the characteristic Debye temperature ΘD, mean square amplitude of vibration $$\overline {{{u}^{2}}(T)} $$ , and the coefficient of thermal expansion α(T). The results show that the alloy forms a single phase solid solution having a face centered cubic structure (A1-type) in said temperature range. Further, it is found that the addition of gold to palladium leads to an increase in the value of lattice parameter and reduction in the value of Debye temperature, mean square amplitude of vibration, and the coefficient of thermal expansion. The mean square amplitude of vibration was found to obey the classical Gruneisen relationship, as is seen in the case of most of cubic alloys.

An X-ray powder diffraction study of damage produced in Ca(OH)2 and Mg(OH)2 by electron irradiation using the 2.5 MeV SIRIUS accelerator

Two isomorphous hydrous minerals, Mg(OH)2 and Ca(OH)2, were exposed to the 2.5 MeV electron beam of the SIRIUS accelerator platform. Both compounds remain stable under the beam up to high doses, in the range of 3–3.5 GGy. No decomposition is observed.But contrary to earlier statements, a net difference of reactivity between them is highlighted as a result of the present X-ray powder diffraction study: i) a significant dilatation is observed along the c - axis, more significant in brucite than in portlandite as already reported during thermal decomposition studies, ii) but a contraction is here revealed in the basal plane of brucite, along the a – axis, while a slight dilatation is still being observed in portlandite. Contraction in the basal plane seems a specific feature of electron irradiation only once previously observed by TEM in brucite. Moreover for brucite, the decreasing intensities of Bragg lines together with the appearance of a diffuse scattering over the whole angular range is compatible with the appearance of some static structural disorder induced by electron irradiation. Finally electron irradiation leads to a significant reduction in crystallite size with increasing dose, by a factor of 2 at the intermediate dose of 310 MGy in brucite, while for a comparable effect to occur an absorbed dose of 3.5 GGy should be attained in portlandite.

A probabilistic method for the estimation of ocean surface currents from short time series of HF radar data

We present a new method for inverting ocean surface currents from beam-forming HF radar data. In contrast with the classical method, which inverts radial currents based on shifts of the main Bragg line in the radar Doppler spectrum, the method works in the temporal domain and inverts currents from the amplitude modulation of the I and Q radar time series. Based on this principle, we propose a Maximum Likelihood approach, which can be combined with a Bayesian inference method assuming a prior current distribution, to infer values of the radial surface currents. We assess the method performance by using synthetic radar signal as well as field data, and systematically comparing results with those of the Doppler method. The new method is found advantageous for its robustness to noise at long range, its ability to accommodate shorter time series, and the possibility to use a priori information to improve the estimates. Limitations are related to current sign errors at far-ranges and biased estimates for small current values and very short samples. We apply the new technique to a data set from a typical 13.5 MHz WERA radar, acquired off of Vancouver Island, BC, and show that it can potentially improve standard synoptic current mapping.

Study of superparamagnetic nano particles of MnxCo1−xFe2O4 ferrite system prepared by co-precipitation technique

The ferrites with magnetic nano-particles of MnxCo1−xFe2O4 (with x = 0.0 to 1.0, step 0.2) system are prepared by the chemical co-precipitation method. Structural and magnetic properties of Mn2+ doped cobalt nano ferrites have been studied by x-ray diffraction (XRD), scanning electron microscopy (SEM), saturation magnetization and low field AC susceptibility. The crystallite size is determined from the FWMH of the higher angle Bragg line (4 0 0) using the Scherer’s formula. The saturation magnetization at 300 K in the peak field of 5 kOe is measured using B → H loop technique. The observed saturation magnetic moment is found very low compared to the Neel’s magnetic moment. The lower value of observed magnetic moment is explained on the basis of high magneto-crystalline anisotropy and exchange disorder. The Curie temperatures are determined through thermal variation of low field (0.5 Oe) AC susceptibility. All the plots of thermal variation AC susceptibility exhibit large hump due to single domain to superparamagnetic transition which is the characteristic of high anisotropic ion present in the system. The ZFC-FC curves exhibit thermo-magnetic irreversibility. The magnetic behavior observed through Mossbauer spectra also supports the concept of fine particle superparamagnetism.

First order sea clutter cross section for bistatic shipborne HFSWR

This paper studies the development on the first order sea clutter cross section for bistatic high frequency surface wave radar (HFSWR). Based on the received first order electric field expression, a closed-form of cross sections is derived to account for the case of receiving antenna array being mounted on the shipborne platform. The uniform linear motion and sway motion components are assumed to be responsible for the observed differences in comparison with the bistatic fixed antenna case. Correspondingly, simulations are conducted to study the sea clutter spectral characteristics for these two cases versus different system parameters and sea state conditions. It is shown numerically that the forward motion component will spread the Bragg lines severely and the influence triggered by the sway motion can be explained as the Bessel function modulation of the ordinary sea clutter spectra. The obtained results have important implications in the application of shipborne HFSWR technology to ocean remote sensing and target detection.

Anneal Temperature Effect on Crystallite Size and Electric Conductivity of LiMn2O4

Powder samples of LiMn2O4 have been prepared by solid state reaction of LiOH and MnO2. Neutron scattering experiments at room temperature and conductivity measurement have been performed on the samples. Anneal temperature effect on the crystallite size and electric conductivity of LiMn2O4 is analyzed. The average crystallite size is obtained from the full width at half maximum (FWHM) of Bragg lines using Scherrer equation. The average crystallite size increases with the increase of anneal temperature. Activation energy and conductivity prefactor increase with anneal temperature.

Ocean surface cross sections for shipborne HFSWR with sway motion

AbstractTo interpret the essential characteristics of the sea echo backscattered from the ocean surface, the first‐ and second‐order ocean surface cross sections are mathematically derived for an omnidirectional receiving sensor in monostatic shipborne high‐frequency surface wave radar (HFSWR), where the uniform linear motion and sway motion are involved simultaneously. The derived cross sections could be reduced to the existing results in HFSWR on a floating platform, shipborne HFSWR with uniform linear motion, and even a stationary land‐based HFSWR. The illustrations and discussions are presented based on the simulated Doppler spectra under different situations. Aside from the Bragg lines broadening due to the uniform linear motion and its variation with wind direction, the sway motion generates additional Doppler spectra, which emerge with the uniform spacing of sway frequency. The theoretical derivations and analyses based on simulations may be of importance to future investigations and applications, not only in target detection but also in ocean remote sensing.

Frequency analysis for modulation-enhanced powder diffraction.

Periodic modulation of external conditions on a crystalline sample with a consequent analysis of periodic diffraction response has been recently proposed as a tool to enhance experimental sensitivity for minor structural changes. Here the intensity distributions for both a linear and nonlinear structural response induced by a symmetric and periodic stimulus are analysed. The analysis is further extended for powder diffraction when an external perturbation changes not only the intensity of Bragg lines but also their positions. The derived results should serve as a basis for a quantitative modelling of modulation-enhanced diffraction data measured in real conditions.

High-Resolution Ocean Clutter Spectrum Estimation for Shipborne HFSWR Using Sparse-Representation-Based MUSIC

The spreading of the dominant first-order Bragg lines in shipborne high-frequency surface wave radar (HFSWR) severely obscures the detection of the slow-moving targets and the measurement of ocean clutter. Space–time adaptive processing (STAP) is an effective tool for solving the problem. It normally requires a large number of independent and identically distributed (i.i.d.) training samples to estimate the ocean clutter spectrum and design the filter to eliminate the ocean clutter from the test cell. However, the training samples are insufficient due to the system limitation of shipborne HFSWR, and the stationarity of training data is destroyed in the nonstationary and nonhomogeneous ocean environment, which result in decreased performance. Thus, the estimation of the ocean clutter spectrum with small training samples or even only the test cell is an important work for shipborne HFSWR. In this paper, by exploiting the intrinsic sparsity of the ocean clutter in shipborne HFSWR, the multiple signal classification (MUSIC) algorithm based on the sparse representation technique, called SR–MUSIC, is introduced to estimate the ocean clutter spectrum. The correctness of the ocean clutter sparsity and the validity of the SR–MUSIC algorithm for the high-resolution ocean clutter spectrum estimation are verified by the simulation results.

Burgers Vector Analysis of Vertical Dislocations in Ge Crystals by Large-Angle Convergent Beam Electron Diffraction.

By transmission electron microscopy with extended Burgers vector analyses, we demonstrate the edge and screw character of vertical dislocations (VDs) in novel SiGe heterostructures. The investigated pillar-shaped Ge epilayers on prepatterned Si(001) substrates are an attempt to avoid the high defect densities of lattice mismatched heteroepitaxy. The Ge pillars are almost completely strain-relaxed and essentially defect-free, except for the rather unexpected VDs. We investigated both pillar-shaped and unstructured Ge epilayers grown either by molecular beam epitaxy or by chemical vapor deposition to derive a general picture of the underlying dislocation mechanisms. For the Burgers vector analysis we used a combination of dark field imaging and large-angle convergent beam electron diffraction (LACBED). With LACBED simulations we identify ideally suited zeroth and second order Laue zone Bragg lines for an unambiguous determination of the three-dimensional Burgers vectors. By analyzing dislocation reactions we confirm the origin of the observed types of VDs, which can be efficiently distinguished by LACBED. The screw type VDs are formed by a reaction of perfect 60° dislocations, whereas the edge types are sessile dislocations that can be formed by cross-slips and climbing processes. The understanding of these origins allows us to suggest strategies to avoid VDs.

A method for the monitoring of metal recrystallization based on the in-situ measurement of the elastic energy release using neutron diffraction.

A method is proposed for the monitoring of metal recrystallization using neutron diffraction that is based on the measurement of stored energy. Experiments were performed using deformed metal specimens heated in-situ while mounted at the sample position of the High Resolution Powder Diffractometer, HRPD (ISIS Facility), UK. Monitoring the breadth of the resulting Bragg lines during heating not only allows the time-dependence (or temperature-dependence) of the stored energy to be determined but also the recrystallized fraction. The analysis method presented here was developed using pure nickel (Ni270) specimens with different deformation levels from 0.29 to 0.94. In situ temperature ramping as well as isothermal annealing was undertaken. The method developed in this work allows accurate and quantitative monitoring of the recrystallization process. The results from neutron diffraction are satisfactorily compared to data obtained from calorimetry and hardness measurements.

Space‐time adaptive processing‐based algorithm for meteor trail suppression in high‐frequency surface wave radar

Meteor trail arises as a result of meteorites burning in the Earth's atmosphere at far altitudes with the characteristics of short lifetime and the ability of scattering high-frequency (HF) signal. It is a classical universal interference for high-frequency surface wave radar, which can provide the capabilities of target monitoring and ocean remote sensing by working on HF band. In this study, the authors propose the superiorities of utilising the space-time adaptive processing-based algorithm for meteor trail suppression. They modify the calculation of the covariance matrix based on the distribution and characteristics of meteor trail aiming to fit for meteor trail better. Finally, they verify the effectiveness of the modified algorithm by measured data. The results show that the modified algorithm can not only detect targets better, but can also make Bragg lines buried in meteor trail visible.

X‐ray and neutron scattering on disordered nanosize clusters: a case study of lead‐zirconate‐titanate solid solutions

Defects and frequently used defect models of solids are reviewed. Signatures for identifying the disorder from x‐ray and neutron scattering data are given. To give illustrative examples how technologically important defects contribute to x‐ray and neutron scattering numerical method able to treat non‐periodical solids possessing several simultaneous defect types is given for simulating scattering in nanosize disordered clusters. The approach takes particle size, shape, and defects into account and isolates element specific signals. As a case study a statistical approximation model for lead‐zirconate titanate [Pb(ZrxTi)O3, PZT] is introduced. PZT is a material possessing several defect types, including substitutional, displacement and surface defects. Spatial composition variation is taken into account by introducing a model in which the edge lengths of each cell depend on the distribution of Zr and Ti ions in the cluster. Spatially varying edge lengths and angles is referred to as microstrain. The model is applied to compute the scattering from ellipsoid shaped PZT clusters and to simulate the structural changes as a function of average composition. Two‐phase co‐existence range, the so called morphotropic phase boundary composition is given correctly. The composition at which the rhombohedral and tetragonal cells are equally abundant was . Selected x‐ray and neutron Bragg reflection intensities and line shapes were simulated. Examples of the effect of size and shape of the scattering clusters on diffraction patterns are given and the particle dimensions, computed through Scherrer equation, are compared with the exact cluster dimensions. Scattering from two types of 180° domains in spherical particles, one type assigned to Ti‐rich PZT and the second to the MPB and Zr‐rich PZT, is computed. We show how the method can be used for modelling polarization reversal. image

Synthesis, structural characterization and magnetic properties of Fe/Pt core-shell nanoparticles

Structural and magnetic properties of Fe/Pt core-shell nanostructure prepared by a sequential reduction process are reported. Transmission electron microscopy shows nearly spherical particles fitting a lognormal size distribution with Do = 3.0 nm and distribution width λD = 0.31. In x-ray diffraction, Bragg lines only from the Pt shell are clearly identified with line-widths yielding crystallite size = 3.1 nm. Measurements of magnetization M vs. T (2 K–350 K) in magnetic fields up to 90 kOe show a blocking temperature TB = 13 K below which hysteresis loops are observed with coercivity HC increasing with decreasing T reaching HC = 750 Oe at 2 K. Temperature dependence of the ac susceptibilities at frequencies fm = 10 Hz–5 kHz is measured to determine the change in TB with fm using the Vogel-Fulcher law. This analysis shows the presence of significant interparticle interaction, the Neel-Brown relaxation frequency fo = 5.3 × 1010 Hz and anisotropy constant Ka = 3.6 × 106 ergs/cm3. A fit of the M vs. H data up to H = 90 kOe for T > TB to the modified Langevin function taking particle size distribution into account yields magnetic moment per particle consistent with the proposed core-shell structure; Fe core of 2.2 nm diameter and Pt shell of 0.4 nm thickness.

Second-Order Ocean Surface Cross Section for Shipborne HFSWR

To investigate the characteristics of sea clutter in monostatic shipborne high-frequency surface-wave radar (HFSWR) with uniform linear motion, the second-order patch scatter cross section is derived. With the previously proposed first-order ocean surface cross section, both cross sections could be reduced to the existing results in land-based HFSWR. Illustrations and discussions are provided on the basis of the simulation results for different situations. Although the spread Bragg lines vary with the ocean surface wind direction, the second-order contributions contaminate the energies of the Bragg lines in the high sea state, which may affect the application of shipborne HFSWR to wind direction extraction from the ratio of the positive and negative Bragg line energies. The derivations and analyses would be of importance to future investigations and applications, not only for target detection but also for ocean remote sensing.

Electrical characteristics of β-Ga2O3 thin films grown by PEALD

In this work, 7.5nm Ga2O3 dielectric thin films have been deposited on p-type (111) silicon wafer using plasma enhanced atomic layer deposition (PEALD) technique. After the deposition, Ga2O3 thin films were annealed under N2 ambient at 600, 700, and 800°C to obtain β-phase. The structure and microstructure of the β-Ga2O3 thin films was carried out by using grazing-incidence X-ray diffraction (GIXRD). To show effect of annealing temperature on the microstructure of β-Ga2O3 thin films, average crystallite size was obtained from the full width at half maximum (FWHM) of Bragg lines using the Scherrer formula. It was found that crystallite size increased with increasing annealing temperature and changed from 0.8nm to 9.1nm with annealing. In order to perform electrical characterization on the deposited films, Al/β-Ga2O3/p-Si metal–oxide–semiconductor (MOS) type Schottky barrier diodes (SBDs) were fabricated using the β-Ga2O3 thin films were annealed at 800°C. The main electrical parameters such as leakage current level, reverse breakdown voltage, series resistance (RS), ideality factor (n), zero-bias barrier height (ϕBo), and interface states (NSS) were obtained from the current–voltage (I–V) and capacitance–voltage (C–V) measurements at room temperature. The RS values were calculated by using Cheung methods. The energy density distribution profile of the interface states as a function of (ESS–EV) was obtained from the forward bias I–V measurements by taking bias dependence of ideality factor, effective barrier height (ϕe), and RS into account. Also using the Norde function and C–V technique, ϕe values were calculated and cross-checked. Results show that β-Ga2O3 thin films deposited by PEALD technique at low temperatures can be used as oxide layer for MOS devices and electrical properties of these devices are influenced by some important parameters such as NSS, RS, and β-Ga2O3 oxide layer.

Pressure dependence of crystal structure of Cu2O by TOF powder neutron diffraction

Abstract Neutron diffraction measurements were performed on powder Cu 2 O with different samples that are pressure released after a pressing force of 295 K with iMATERIA (IBARAKI Materials Designed Diffractometer) installed at MLF in J-PARC. Peak widths of Bragg lines increased depending on the pressing force. To clarify the relation between the crystallite size and the microstrain effect, Rietveld refinement analysis on a TOF neutron diffraction pattern of Cu 2 O was performed by assuming a cubic cuprite type structure (space group Pn-3m ). Strain and crystallite size effects were estimated from Lorentzian terms in the Pseudo-Voigt profile function with a pair of Back-to-Back exponential types based on the Stephenes model. It is considered that the increasing peak width according to the dependence of pressing force is mainly derived from strain effects. And this result is consistent with the previous studies of Ag 2 O where the Williamson–Hall plot method by X-ray diffraction was applied.

A Study of Structure and Thermal Parameters of Biomedical Used Ni<sub>20</sub>Pd<sub>80</sub> Alloy

The structure and thermal parameters of biomedical used Ni20Pd80 alloy were studied using X-ray diffraction (XRD) technique. The diffraction experiments performed in the temperature range of 308-1100 K revealed that the alloy forms a face centered cubic (fcc) A1-type structure. The temperature dependence of the lattice parameters was investigated using the Bragg line displacement method shows that the lattice parameter increases with the increase of temperature. The mean linear thermal expansion (MLTE (%)), coefficient of thermal expansion (CTE) α, the characteristic Debye temperature (ΘD) and mean square amplitudes of vibration were determined from the XRD data. The value of Debye temperature was found to be 253 K. It was found that temperature factor was independent of the static displacements.