Kinetic effects yield different results on the timescales of laboratory and synchrotron high-pressure experiments.

Temperature dependent X-ray and neutron diffraction study of the liquid–solid and solid–solid equilibria in the Al 29.2Ga 27Zn 43.8 ternary alloy

We have investigated pressure-induced structural transitions in NaBH4 through density-functional theory calculations combined with X-ray and neutron diffraction experiments. Our calculations confirm that the cubic phase is stable up to 5.4 GPa and an orthorhombic phase occurs above 8.9 GPa, as observed in X-ray diffraction experiments. Both the calculations and X-ray diffraction measurements identify an intermediate tetragonal phase that appears between 6 and 8 GPa; that is, between the cubic and orthorhombic phases. This result is also confirmed by high-pressure neutron diffraction experiments performed on NaBD4. Our calculations and X-ray diffraction measurements show that the space group of the orthorhombic phase above 8.9 GPa is Pnma and the orthorhombic phase remains stable up to 30 GPa. The calculated equations of state are in excellent agreement with experiments.

Structural and optical properties of double sodium–bismuth molybdate NaBi(MoO4)2 semiconductor compound was investigated by x-ray diffraction, Raman and transmission experiments. From the x-ray diffraction experiments, the crystal that has tetragonal structure was obtained. Vibrational modes of the crystal were found from the Raman experiments. Transmission experiments were performed in the temperature range of 10–300 K. Derivative spectroscopy analysis and absorption spectrum analysis were performed to get information about the change in band gap energy of the crystal with temperature. It was observed that the band gap energies of the crystal at different temperatures obtained from these techniques are well consisted with each other. By the help of absorption spectrum which was obtained from transmission measurements performed at varying temperatures, absolute zero value of the band gap and average phonon energy as 3.03 ± 0.02 eV and Eph = 24 ± 0.2 meV, respectively. Moreover, based on absorption spectrum analysis the Urbach energy of the crystal was obtained as 0.10 eV.

The amount of data collected during synchrotron X-ray diffraction (XRD) experiments is constantly increasing. Most of the time, the data are collected with image detectors, which necessitates the use of image reduction/integration routines to extract structural information from measured XRD patterns. This step turns out to be a bottleneck in the data processing procedure due to a lack of suitable software packages. In particular, fast-running synchrotron experiments require online data reduction and analysis in real time so that experimental parameters can be adjusted interactively. Dioptas is a Python-based program for on-the-fly data processing and exploration of two-dimensional X-ray diffraction area detector data, specifically designed for the large amount of data collected at XRD beamlines at synchrotrons. Its fast data reduction algorithm and graphical data exploration capabilities make it ideal for online data processing during XRD experiments and batch post-processing of large numbers of images.

In most studies related to milled powders, the grain size1 is analyzed via X-ray diffraction (XRD) experiments, and a transmission electron microscopy (TEM) image with high magnification, if provided, is used primarily to confirm the results obtained by XRD experiments. This widely used approach is reasonable in light of the difficulties associated with TEM sample preparation. The present study, however, addresses the hypothesis that such an approach may not be valid when there is an inhomogeneous distribution of grains present. TEM examination, carried out in carefully prepared Al-7.5 wt% Mg samples, in which a global region is observable by TEM, provided the opportunity for quantitative analysis of grain size in cryomilled powders having an inhomogeneous distribution of grain sizes. The cryomilled Al-7.5 wt% Mg had a bimodal grain microstructure of 77% (area fraction) fine grains in the range of 10 to 60 nm and 23% coarse grains of approximately 1 μm. The results show that the XRD analysis yields a grain size that is close to that present in the fine-grained regions (i.e., 10–60 nm). The present study also systematically investigated the influence of the nine possible combinations of the Cauchy (C) and the Gaussian (G) approximations on the calculated grain size value, and the results show that the CC-CC approximation resulted in the largest calculated grain size, the GG-GG generated the smallest one, and the CG-CG, the approximation recommended by Klug and Alexander [1], led to a calculated grain size that is approximately equal to the average one from the CC-CC and GG-GG approximations. The maximum possible fluctuation of grain size values stemming from the various approximations is 38%.

In-situ single-crystal and powder X-ray diffraction (XRD) experiments were performed on diaspore at high temperatures. The powder XRD experiments showed that the dehydration reaction from diaspore to corundum occurs between 703 and 733 K. The in-situ single-crystal XRD measurements of diaspore could successfully determine the cell parameters, fractional atomic coordinates and anisotropic displacement parameters at high temperatures, i.e., from 295 to 698 K. Temperature variations in the cell parameters indicate that thermal expansion of the a-axis is a little higher than those of the b-axis and the c-axis. However, the axial thermal expansivity is not as anisotropic as was previously suggested. The results of structure refinements indicate that such lattice expansion behavior is the result of thermal expansion of the tunnels through O2–H···O1 hydrogen-bond separation in the diaspore structure. To the best of our knowledge, this is the first time that the thermal expansion of diaspore has been investigated at an atomic level by in-situ single-crystal XRD experiments at high temperatures.

Quantum mechanical (QM)/molecular mechanics (MM) calculations by the use of a large-scale QM model (QM Model V) have been performed to elucidate hydrogen-bonding networks and proton wires for proton release pathways (PRP) of water oxidation reaction in the oxygen evolving complex (OEC) of photosystem II (PSII). Full geometry optimisations of PRP by the QM/MM model have been carried out starting from the geometry of heavy atoms determined by the recent high-resolution X-ray diffraction (XRD) experiment of PSII refined to 1.9 Å resolution. Computational results by the QM/MM calculations have elucidated the hydrogen-bonding O···O(N) and O···H distances and O(N)–H···O angles in PRP, together with the Cl–O(N) and Cl···H distances and O(N)–H···Cl angles for chloride anions. The optimised hydrogen-bonding networks are well consistent with the XRD results and available experiments such as extended X-ray absorption fine structure, showing the reliability of channel structures of OEC of PSII revealed by the XRD experiment. The QM/MM computations have elucidated possible roles of chloride anions in the OEC of PSII. The QM/MM computational results have provided useful information for understanding and explanation of accumulated mutation experiments of key amino acid residues in the OEC of PSII. Implications of the present results are discussed in relation to three steps for theoretical modelling of water oxidation in the OEC of PSII and bio-inspired working hypotheses for developments of artificial water oxidation systems by use of 3d transition-metal complexes.

<p class="Abstract"><span lang="EN-US">The MCX beamline at the synchrotron Elettra is the general purpose diffraction beamline that is well suited for non-destructive and innovative X-ray diffraction (XRD) experiments in the field of cultural heritage. The experimental station houses a large number of instruments facilitating a range of different types of analysis. Recently, a comprehensive study of the alteration products in grisaille paints was performed at the beamline. This type of analysis is very important to understand the complex processes involved in the deterioration of this type of glass decoration. An exhaustive characterization of these products and so a full understanding of the mechanism of their formation may lead to the development of new protective materials for conservation and restoration. XRD experiments at the MCX beamline allowed us to recognize the alteration products on the grisailles surface and to propose a mechanism for the formation of alteration patina. Here we present the beamline, its instrumentation and its capabilities by showing an example of the study on grisaille paints. </span></p>

A gasket is an important constituent of a diamond anvil cell (DAC) assembly, responsible for the sample chamber stability at extreme conditions for X-ray diffraction studies. In this work, we studied the performance of gaskets made of metallic glass Fe0.79Si0.07B0.14 in a number of high-pressure X-ray diffraction (XRD) experiments in DACs equipped with conventional and toroidal-shape diamond anvils. The experiments were conducted in either axial or radial geometry with X-ray beams of micrometre to sub-micrometre size. We report that Fe0.79Si0.07B0.14 metallic glass gaskets offer a stable sample environment under compression exceeding 1 Mbar in all XRD experiments described here, even in those involving small-molecule gases (e.g. Ne, H2) used as pressure-transmitting media or in those with laser heating in a DAC. Our results emphasize the material's importance for a great number of delicate experiments conducted under extreme conditions. They indicate that the application of Fe0.79Si0.07B0.14 metallic glass gaskets in XRD experiments for both axial and radial geometries substantially improves various aspects of megabar experiments and, in particular, the signal-to-noise ratio in comparison to that with conventional gaskets made of Re, W, steel or other crystalline metals.

Nanometre materials, characterized by an ultrafine grain size, have attracted much attention in the past few years because of their unusual chemical, mechanical, optical, electrical and magnetic properties and their wide applicability [1]. Thermodynamically, however, they are metastable. Under certain conditions, the grains comprising the material may grow to a larger scale, which may consequently result in the disappearance of some unique properties of the nanometre material. Therefore, it is important to investigate the thermal stability of a nanostructural material. For the past two decades, sol-gel routes to ultrafine metallic oxide powders have been widely investigated [2]. Among these oxides, titania is a very important material for its humidity [3], hydrogen[4], and oxygen[5] sensitive properties and some catalysis applications [6]. Usually, titania has three different structures: brookite, anatase and futile. The former two phases are both metastable, and the futile phase is of a thermodynamic stable state. Some properties of titania may strongly depend on its microstructure; for example, many studies have suggested that the anatase phase of titania is the superior support of VzOs/TiO4 catalyst for the selective partial oxidation reaction compared to the rutile phase [6]. It is well known that many properties of ceramic materials can be improved by a small amount of doping. For gas-sensitive oxide materials, doping is often necessary to increase the sensitivity and selectivity [7] of the material. In this letter, nanometre titania powders with and without alumina dopant were prepared by a sol-gel method. The structural development of these powders was studied systematically, and the influence of a small amount of alumina dopant on the structural changes was also investigated. Tetrabutyl titanate and aluminium isopropoxide were used as the precursors of titania and alumina, respectively. In preparing TiO2 sol, Ti (OBu)4 was dissolved in ethanol, and then HC1 + H 2 0 solution was dropped into Ti(OBu)4 solution with continuous stirring for an hour. The molar ratio of these reactants was Ti(OBu)4:EtOH:HCl:H20=l:15: 0.3:1. After a week, a transparent orange gel was obtained. To form the alumina-doped titania sol, a given amount of aluminium isopropoxide was added to the Ti(OBu)4 solution (molar ratio AI(C3H70) to Yi(OBu)4, 0.12) and stirred thoroughly using a magnetic mixer and ultrasonic wave successively before the addition of HC1 + H 2 0 solution. The gelation time for alumina-doped titania sol is also about a week. After drying in a vacuum tube (10 -1 Pa) furnace at 333 K for 5 h, the gels were heat treated at different temperatures for 2 h under oxygen atmosphere (O2 flow rate: 40mlmin-1). Changes in the structures of these powders with temperature were investigated by thermogravity analysis (TGA), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) experiments. Both TiO2 dry gels without and with A1203 dopant were confirmed to be of amorphous structure by XRD experiments, as shown in Fig. la and b. For pure titania gel (Fig. la), partial crystallization occurred after annealing at 523 K for 2 h, and the powders annealed at a temperature below 773 K are of anatase structure. A phase transformation from anatase to rutile occurred for annealing temperatures above 823 K and was completed at 1073 K. On the other hand, the alumina-doped TiO2 gel (Fig. lb) remained amorphous after annealing at 623 K for 2 h. When the annealing temperature was 723 K, crystallization began, and the phase transformation from anatase to rutile did not occur until the annealing temperature was elevated to 1073 K. Moreover, a few anatase crystallites still existed at an annealing temperature of 1223 K. This leads to the conclusion that a little alumina addition

Melt crystallization of zinc alkali phosphate glasses

Vibrational and elastic properties of the $R$Fe$_{4}$Sb$_{12}$ skutterudites are investigated by, respectively, temperature $(T)$ dependent extended X-ray absorption fine structure (EXAFS) and pressure $(P)$ dependent x-ray diffraction (XRD) experiments. The Fe $K$-edge EXAFS experiments of the $R=$ K, Ca and Ba materials were performed in the $T$-interval $6<T<300$ K and XRD experiments of the $R=$ Na, K, Ca, Sr and Ba materials were performed in the $P$-interval $1\text{ atm }<P<16$ GPa. From EXAFS, we obtained the correlated Debye-Waller parameters that were thus analyzed to extract effective spring constants connected with the Fe-$Y$ (where $Y=$ either $R$, Fe or Sb) scattering paths. Our findings suggest that in the case of the light cations, $R=$ K or Ca, the $R$ atoms are relatively weakly coupled to the cage, in a scenario reminiscent to the Einstein oscillators. From the XRD experiments, we obtained the bulk modulus $B_{0}$ for all $R=$Na, K, Ca, Sr and Ba materials, with values ranging from $77$ GPa ($R=$ K) to $R=99$ GPa ($R=$ Ba) as well as the compressibility $\beta$ as a function of $P$. The trend in $\beta$ as a function of the $R$ filler is discussed and it is shown that it does not correlate with simple geometrical considerations but rather with the filler-cage bonding properties.

Two kinds of materials, sprayed-on crocidolite and sprayed-on amosite, containing crocidolite and amosite respectively, were treated with aqueous acetic acid solution, the pH of which was adjusted with an ammonium acetate buffer at 5, in order to remove soluble components of cement. The liquids were filtrated with a membrane filter, and the residue collected as crocidolite samples and amosite samples, respectively. The Crocidolite and amosite thus obtained were heated up to 600-1300°C for 1h. Then, power X-ray diffraction (XRD) experiment, scanning electron microscopic (SEM) observation, and thermal analysis (TG/DTA) were carried out for these burned specimens in order to observe the change of the burned materials and melting behaviors together with their thermal properties. In addition, CaCO3 and CaCl2 were mixed with the respective sprayed-on asbestos and sprayed-on crocidolite, and a TG/DTA measurement was conducted on these mixtures. Based on the SEM observation and XRD experiment on the specimens used in the TG/DTA measurements, we tried to decompose the crocidolite and amosite, applying the method of low-temperature decomposition, the applicability of which was previously confirmed in the study on the case of chrysolite. The temperature of the TG/DTA measurement could be raised up to 1000°C, and it became evident that in the cases of specimens where CaCl2 was added, all the asbestos fibers had decomposed, but not in any other specimen. The crocidolite specimen became rounded in shape when it was heated up to 1000°C, and it looked as if it was densified due to burning. CaCO3 and CaCl2 were added to this burned crocidolite, and decomposition of the material after burning was examined. In a DTA thermogram, an endothermic peak was recognized, which corresponds to the formation of a melt of CaCO3-CaO-CaCl2 as summarized in the previous report. Thus it is experimentally verified that burned crocidolite decomposes at high temperatures.

Multi-scale mechanisms of twinning-detwinning in magnesium alloy AZ31B simulated by crystal plasticity modeling and validated via in situ synchrotron XRD and in situ SEM-EBSD

The structure of a mechanically alloyed Ti-45at%Al powder and its decomposition behavior during sintering have been investigated by X-ray diffraction (XRD) and analytical transmission electron microscopy (TEM). By the XRD experiments, the powder after 200 hr mechanical alloying is shown to be consisted of two phases, Ti3A1 and TiAI. The volume fraction of Ti3Al is estimated to be larger than that of TiAI, while for the sintered compact of the powder this tendency was reversed. The mechanically alloyed powder is composed of strain free fine grains (grain size ranging from 10 to 20 nm in diameter). The average composition of the grains are approximately Ti-45at%Al. Therefore, the powder may be assumed to be composed mainly of Al supersaturated Ti3Al. The results of XRD and analytical TEM experiments suggest that the decomposition of the supersaturated Ti3AI to equilibrium Ti3Al and TiAI took place during sintering.