Two new experimental diffraction methods for a precise measurement of crystal perfection

Synchrotron x-radiation in a double-crystal geometry has been used for topography and rocking-curve measurements to study imperfections in single-crystal HP/HT synthetic diamonds grown from (111) seeds by the reconstitution technique. The influence that clusters of small opaque particles (sometimes called `pin-point-like inclusions') have upon lattice parameter differences, as well as upon relative lattice tilts within each sample, was of particular interest in this study. Rocking curves measured with a large beam diameter (illuminating entire specimens) gave widths (FWHM) in the range 5 - 30 seconds of arc in a non-dispersive Bragg - Bragg diffraction geometry in which good diamond crystals give and for which the calculated theoretical minimum width is under . Rocking curves were also recorded for small regions of each crystal, using a translatable pin-hole, and these showed that some diamonds had relatively narrow rocking curves in selected areas (of diameter). Epochs of crystal growth were recorded in series of x-ray topographs, taken at intervals of 2.5 seconds of arc. Such series were taken for all four principal azimuths (, 90, 180 and ) of the incident beam by rotating the sample about the normal to the Bragg plane. This procedure yielded important information about lattice parameter distribution and lattice tilt across entire samples. For the samples heavily populated with pin-point-like inclusions it was concluded that there is a possible slight variation in lattice parameter values in some regions of the crystal but most of it falls below the adopted angular step resolution, although better accuracy can be achieved. Relative tilt measurements revealed that there are large misorientations of those parts of the crystal which are close to external outcrops of {111} boundaries. In this case of (111) oriented diamond samples, three separate regions with different tilts can be attributed to the three parts of the crystal close to optically visible {111} growth-sector boundaries.

CuIn1-xAlxSe2 (CIAS) thin films were grown on the flexible stainless steel substrates, by dc co-sputtering from the elemental cathodes. CuInAl alloyed precursor films were selenized both by noble gas assisted Se vapor transport and vacuum evaporation of Se. X-ray diffraction, scanning electron microscopy and UV-visible absorption spectroscopy were used to characterize the selenized films. The composition (x=Al/Al+In) with 0≤x≤0.65 was varied by substituting Al with indium in CuInSe2. Lattice parameters, average crystallite sizes and compact density of the films compared to CuInSe2, decreased and (112) peak shifted to higher Bragg's angle, with Al incorporation. Cells were fabricated with the device structure SS/Mo/CIAS/CdS/iZno-AZO/Al. Best cell showed the efficiency of 6.8%, with x=0.13, Eg=1.17 eV, fill factor 45.04, short circuit current density Jsc 30 mA/cm2.

A novel structure–catalytic activity correlation of platinum and palladium alloys is reported in this study. Metals with similar covalent radius (Pt and Pd) were alloyed with metals of lesser covalent radius (Fe and Co). The ternary alloys namely, PtFeCo and PdFeCo were synthesized by a solvothermal method. The structural properties such as lattice parameters and compressive strain of these electrocatalysts were evaluated by XRD and SAED analysis. Particle size and pattern of dispersion of these catalysts in Vulcan XC-72 carbon were characterized by TEM. The composition of the alloys was identified by ICP-OES and EDX techniques. Electrochemical properties such as ECSA, oxygen reduction reaction activity and kinetic parameters were assessed by CV and RDE studies. Structural and electroactivity of both alloys were compared with their respective bulk metal catalysts (20 wt% Pt/C, 20 wt% Pd/C). The lattice strain was calculated from the decrease in lattice parameters of alloys compared with those of pure metals. It is observed that PdFeCo/C shows more compressive strain than PtFeCo/C which is reflected in the greater improvement in ORR activity than that of PtFeCo/C catalyst. ORR studies revealed that both alloys and their pure metals follow a four electron transfer mechanism. The kinetic parameters such as mass and specific activities are calculated from the Tafel slope of ORR. Pt/C, PtFeCo/C and PdFeCo/C electrocatalysts have Tafel slope values (∼120 mV dec−1) indicative of one electron transfer as the rate determining step. The mass and specific activities of PdFeCo/C show higher increments than those of PtFeCo/C compared to their respective metals. The results of ORR studies reflect that lattice strain is an important factor to improve the catalytic activity of the electrocatalyst. Single cell polarizations were carried out at 60, 70 and 80 °C with PtFeCo/C and PdFeCo/C as cathode electrocatalysts. Both ternary alloy electrocatalysts show higher performance than pure metal catalysts. At 80 °C, PtFeCo/C and PdFeCo/C register a power density of 713 mW cm−2 and 437 mW cm−2 respectively.

Diffraction methods were applied to study irradiation and annealing effects on TlN3. Crystallographic lattice constant and cell volume changes upon x-ray irradiation were determined as function of irradiation time and radiation intensity. From the character of these curves some conclusions were drawn about the physical processes causing the effects. The reversibility of these processes was studied by annealing experiments at various temperatures and in both air and helium atmospheres. Preliminary studies of radiation damage on uv-irradiated samples were carried out in order to relate the diffraction results to the TlN3 absorption spectrum and photoconductivity data.

The effect of annealing on 3-dimensional lattice strain, crystallographic domain structure, magnetic and electrical properties of both 250 Å and 4000 Å thick epitaxial La0.8Ca0.2MnO3 (LCMO(x=0.2)) thin films grown on (001) LaAlO3 substrates have been studied. While short annealing time (∼2hrs. at 950 °C in oxygen of 1 atm. pressure) leads to anomalous increase of the peak temperature (Tp) and Curie temperature (Tc) above room temperature and that of the bulk material, longer annealing time (∼10 hrs.) restores the Tp and Tc to almost the same values as that of the as-grown films. Furthermore, as the annealing time is increased, the lattice strain relaxes with film's lattice parameter approaching the bulk value. In-plane and out-of-plane lattice parameters and strain states of the as-grown and annealed films were measured directly using normal and grazing incidence x-ray diffraction. A clear correlation is observed between Tp and perovskite unit cell volume for both the films. Tp is found to increase with the decrease of perovskite unit cell volume. This is attributed to the enhancement of overlap between Mn d orbitals and oxygen p orbitals leading to increased bandwidth and conductivity. Crystalline quality of the films as determined by the full width at half maximum (FWHM) of the x-ray rocking curves, improves with the annealing time. This work highlights the importance of controlling the 3-dimensional lattice strain for optimizing the properties of CMR films.

Intrinsic crystal defects like metal or oxygen vacancies and extrinsic defects like impurity dopants in a metal oxide semiconductor play a crucial role and alter the several structural and optical properties. In the present work, we have successfully synthesized pure and 5% Nb-doped SnO2 nanocrystalline powder using very convenient and less expensive solid-state reaction route. Influence of Nb incorporation and defects on the structural and optical parameters like lattice constants, lattice strain, average crystallite size, optical band gap, defect energy, etc. has been studied. The average crystallite size, lattice constants, and lattice strain are found to be high in the Nb-doped SnO2 as compared to pure SnO2. The optical bandgap of the pure SnO2 was found to be 3.82 eV and increased to 3.92 eV on the incorporation of the Nb content. Defect energy was found to be 0.26 eV in the pure SnO2 and 0.27 eV in Sn0.95Nb0.05O2.

In this paper, we focus on the effect of processing‐dependent lattice strain on oxygen ion conductivity in ceria based solid electrolyte thin films. This is of importance for technological applications, such as micro‐SOFCs, microbatteries, and resistive RAM memories. The oxygen ion conductivity can be significantly modified by control of lattice strain, to an extent comparable to the effect of doping bulk ceria with cations of different diameters. The interplay of dopant radii, lattice strain, microstrain, anion‐cation near order and oxygen ion transport is analyzed experimentally and interpreted with computational results. Key findings include that films annealed at 600 °C exhibit lattice parameters close to those of their bulk counterparts. With increasing anneal temperature, however, the films exhibited substantial compaction with lattice parameters decreasing by as much as nearly 2% (viz, Δd600–1100 °C: –1.7% (Sc+3) > –1.5% (Gd+3) > –1.2% (La+3)) for the annealing temperature range of 600–1100 °C. Remarkably 2/3rd of the lattice parameter change obtained in bulk ceria upon changing the acceptor diameter from the smaller Sc to larger La, can be reproduced by post annealing a film with fixed dopant diameter. While the impact of lattice compaction on defect association/ordering cannot be entirely excluded, DFT computation revealed that the main effect appears to result in an increase in migration energy and consequent drop in ionic conductivity. As a consequence, it is clear that annealing procedures should be held to a minimum to maintain the optimum level of oxygen ion conductivity for energy‐related applications. Results reveal also the importance to understand the role of electro‐chemo‐mechanical coupling that is active in thin film materials.

Molybdenum ditelluride (MoTe2), which is stabilized in both semiconducting hexagonal (2H) and metallic distorted octahedral (1T’) phases, has attracted increasing attention owing to their attractive properties for promising wide applications. Exploring the full potential of this emerging material requires a reliable synthesis approach to precisely control its phase structure. Here, we report on the growth of high crystallinity MoTe2 nanosheets with a controlled phase via the tellurization of chemical vapor deposition-grown MoO2 nanosheets. The single crystal MoO2 nanosheets with rhombus shape were converted into MoTe2 single crystal nanosheets with morphology maintained well through the tellurization process. The phase structure of as-grown MoTe2 is determined by the synergetic effect of thermodynamics and kinetics in the crystal growth process, which is based on the difference in the thermodynamic stability and the lattice strain between 2H and 1T’ phases. Low growth temperature combined with a slow tellurization rate (low Te content) is favorable for growing 2H-MoTe2, while high growth temperature together with a fast tellurization rate (high Te content) is beneficial to grow 1T’-MoTe2. A phase diagram based on the thermodynamics and kinetics of MoTe2 growth was drawn, which provides significant guidance for future synthesizing of two-dimensional materials with a controlled phase structure.

Interface, lattice strain and dislocation density of SiCp/Al composite consolidated by equal channel angular pressing and torsion

It is important to use the best combination of characteristic X-rays and adiffraction plane for the X-ray stress measurements. Hence following diffractionprofile is required; 1) Higher Bragg angle near in 90°, 2) High intensity with low background, 3) An isolated diffraction peak. It can’t be especially emphasized enough these points on the stressmeasurement of ceramics. The reason is that many diffraction lines are apt to appear at small angle intervals by use of conventional X-rays excited from metal target because lattice constant of ceramics is generally larger than wavelength of such X-rays.

Freestanding nanowires have been found to exhibit ultra-large elastic strains (4 to 7%) and ultra-high strengths, but exploiting their intrinsic superior mechanical properties in bulk forms has proven to be difficult. A recent study has demonstrated that ultra-large elastic strains of ~6% can be achieved in Nb nanowires embedded in a NiTi matrix, on the principle of lattice strain matching. To verify this hypothesis, this study investigated the elastic deformation behavior of a Nb nanowire embedded in NiTi matrix by means of in situ transmission electron microscopic measurement during tensile deformation. The experimental work revealed that ultra-large local elastic lattice strains of up to 8% are induced in the Nb nanowire in regions adjacent to stress-induced martensite domains in the NiTi matrix, whilst other parts of the nanowires exhibit much reduced lattice strains when adjacent to the untransformed austenite in the NiTi matrix. These observations provide a direct evidence of the proposed mechanism of lattice strain matching, thus a novel approach to designing nanocomposites of superior mechanical properties.

GaAs layers were grown on 2°-off (100) GaP substrates by metal-organic vapor phase epitaxy with various intermediate buffer layer structures. GaAsP and InGaAs were used for the buffer layers, and their As/P and In/Ga ratios were altered to control their lattice constants. The crystal properties of the GaAs layers were evaluated on the basis of double-crystal X-ray diffraction rocking curves, low-temperature photoluminescence spectra, and etch-pit densities using molten KOH. The results suggested that a GaAs layer is relatively relaxed but contains a greater number of dislocations when the change in the lattice constant of the buffer layer structure is larger. In contrast, a GaAs layer has a smaller number of dislocations but greater lattice deformation when the change in lattice constant is smaller.

Radiation-induced damage and strain in AlxGai-xAs (x=5 to 1) were investigated by measurements of the lattice parameter using x-ray diffraction. Irradiations employed MeV C, Ar and Au ion beams with a substrate temperature of 80 K. For samples with high Al content, the out-of-plane lattice parameter increased with fluence at low doses, saturated, and then decreased to nearly its original value. The in-plane lattice parameter did not change, throughout. These results were independent of the irradiation particle when scaled by damage energy. For the Al.5Ga.5As samples, however, the out-of-plane lattice parameter increased monotonically with dose to large strains until the layer amorpnized. Selected samples were examined by high resolution and conventional transmission electron microscopy (TEM). Channeling Rutherford backscattering spectrometry (CRBS) was also employed to monitor the buildup of damage in many samples. Recovery of the lattice parameter during subsequent thermal annealing was also investigated.

Magnetic skyrmions are nanosized magnetization whirls that exhibit topological robustness and nontrivial magnetoelectrical properties, such as emergent electromagnetism and intriguing spin dynamics in the microwave-frequency region. In chiral magnets, skyrmions are usually found at a pocket in the phase diagram in the vicinity of the ordering temperature, wherein they order in the form of a hexagonal skyrmion lattice (SkL). It is generally believed that this equilibrium SkL phase is a uniform, long-range-ordered magnetic structure with a well-defined lattice constant. Here, using high-resolution small-angle resonant elastic x-ray scattering, we study the field and temperature dependence of the skyrmion lattice in FeGe and Cu2OSeO3 membranes. Indeed, Cu2OSeO3 shows the expected rigid skyrmion lattice, known from bulk samples, that is unaffected by tuning field and temperature within the phase pocket. In stark contrast, the lattice constant and skyrmion size in FeGe membranes undergo a continuous evolution within the skyrmion phase pocket, whereby the lattice constant changes by up to 15% and the magnetic scattering intensity varies significantly. Using micromagnetic modeling, it is found that for FeGe the competing energy terms contributing to the formation of the skyrmion lattice fully explain this breathing behavior. In contrast, for Cu2OSeO3 this stabilizing energy balance is less affected by the smaller field variation across the skyrmion pocket, leading to the observed rigid lattice structure.

In this study, regarding to the wide applications of spinel ferrites in various fields such as Li ion-batteries, photocatalysts, and optoelectronics, the structural and morphological properties of tin ferrite oxide (SnFe2O4) nanoparticles are investigated using X-ray diffraction (XRD) analysis and field emission scanning electron microscopy (FESEM). The sol–gel, solvothermal, and co-precipitation methods were used to synthesize the SnFe2O4 nanoparticles, and the effect of annealing temperatures at T = 350 °C, 450 °C, and 550 °C was investigated. The XRD results confirmed the formation of tin ferrite spinel phase at an annealing temperature of 350 °C with a preferred peak (311). Crystallite size (D) and strain (ε) of SnFe2O4 nanoparticles was determined in region 20–45 nm and 2–4 × 10–4, respectively, using the Scherer, Williamson–Hall, and Rietveld computational methods. The results showed that the crystallite size in the samples increased with increasing annealing temperature. This increase is attributed to the reduction of defects, imperfections and lattice strain, which leading to an increase in the lattice constants and unit cell volume in the nanocrystalline structure. The Rietveld method determine smaller crystal sizes compared to the Williamson–Hall and Scherer methods because it can correct for peak broadening by taking into account all instrumental factors. The FESEM images of the synthesized nanostructures of SnFe2O4 showed cubic and polyhedral grains with cluster growth and an average grain size of 50–80 nm. According to the crystal structure of tin ferrite spinel, the cubic morphology confirmed the formation of this structure. The average crystallite size and grains in the synthesized samples was determined using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) analysis, respectively. The formation conditions of the SnFe2O4 spinel phase and other phases in the synthesis process at different temperatures and dependence of structural parameters was studied by various structural models for the samples.