Changes In Crystal Lattice Parameters Research Articles

Effect of electron beam processing on structure of electroexplosion coating of ZnO-Ag system

The structure, phase composition of the composite electroexplosion coating of ZnO- Ag system subjected to the irradiation by the high intense electron beam have been studied for the first time. The combined processing including the electroexplosion spraying of the coating of ZnO-Ag system and its subsequent electron beam processing results in the formation of multilayer structure of the coating. The electron beam melts and homogenizes the surface layer of the composite electroexplosion coating of ZnO-Ag system to the depth of 35-40 μm. The effect of the electron beam leads to the formation of the nanocrystalline phases of Ag, ZnO, Cu, CuZn, Ag5Zn8, Cu2O, Ag2O, Cu0.67Zn0.33, AgZn. The dependences of changes in crystal lattice parameters and coherent scattering regions of the phases being formed depending on the processing regime by high intense electron beam have been found.

Effect of silver coating on electrochemical performance of 0.5Li2MnO3.0.5 LiMn1/3Ni1/3Co1/3O2 cathode material for lithium-ion batteries

In this work, a Li-rich layered 0.5Li2MnO3.0.5LiMn1/3Ni1/3Co1/3O2 (LMNCO) pristine cathode material synthesized with a glycine-nitrate combustion method is further coated with silver. The effects of silver coating on the material structure and performance of the as-prepared cathode are systemically studied with X-ray diffraction (XRD), scanning electron microscope (SEM), galvanostatic charge/discharge, cyclic voltammetry (CV), and electrochemical impedance spectra (EIS). Material characterizations and electrochemical measurements show that the surface modification does not lead to the change of crystal lattice parameter and particle morphology. It is found that the rate capability and cyclability can be significantly improved, which could be attributed to the enhancement of electronic conductivity of the particle surface of the cathode. It has been found that the obtained silver-coated LMNCO cathode exhibits excellent electrochemical characteristics. For example, it can deliver a high initial discharge capacity of 290 mAh g−1 between 2.0 and 4.9 V at a rate of 0.05C at room temperature and a discharge capacity of 159 mAh g−1 at 1 C, 128 mAh g−1at 2 C, and 101 mAh g−1 even at 5 C. EIS result shows that Rsf and Rct values of LMNCO are bigger than those of silver-coated LMNCO cathode.

Properties of arsenic sulphide (β-As4S4) modified by mechanical activation

Arsenic sulphide β-As4S4 has been modified by mechanical activation in a planetary ball mill. As a consequence, the solid-state properties and dissolution yield have been influenced. The following changes were observed: the increase of specific surface area, changes in the morphology (the formation of submicron particles), the occurrence of nanoparticles (21–31 nm), changes in crystal lattice parameters and changes in the Raman shift of particular vibrations. As a consequence of these changes, the dissolution rate of β-As4S4 has been increased, which is a challenge for the application in cancer research.

Size-Controlled Dissolution of Organic-Coated Silver Nanoparticles

The solubility of Ag NPs can affect their toxicity and persistence in the environment. We measured the solubility of organic-coated silver nanoparticles (Ag NPs) having particle diameters ranging from 5 to 80 nm that were synthesized using various methods, and with different organic polymer coatings including poly(vinylpyrrolidone) and gum arabic. The size and morphology of Ag NPs were characterized by transmission electron microscopy (TEM). X-ray absorption fine structure (XAFS) spectroscopy and synchrotron-based total X-ray scattering and pair distribution function (PDF) analysis were used to determine the local structure around Ag and evaluate changes in crystal lattice parameters and structure as a function of NP size. Ag NP solubility dispersed in 1 mM NaHCO(3) at pH 8 was found to be well correlated with particle size based on the distribution of measured TEM sizes as predicted by the modified Kelvin equation. Solubility of Ag NPs was not affected by the synthesis method and coating as much as by their size. Based on the modified Kelvin equation, the surface tension of Ag NPs was found to be ∼1 J/m(2), which is expected for bulk fcc (face centered cubic) silver. Analysis of XAFS, X-ray scattering, and PDFs confirm that the lattice parameter, a, of the fcc crystal structure of Ag NPs did not change with particle size for Ag NPs as small as 6 nm, indicating the absence of lattice strain. These results are consistent with the finding that Ag NP solubility can be estimated based on TEM-derived particle size using the modified Kelvin equation for particles in the size range of 5-40 nm in diameter.

Solid-state behavior of cromolyn sodium hydrates

Cromolyn sodium (CS, disodium cromoglycate) is an antiasthmatic and antiallergenic drug. The solid-state behavior of CS is still not completely understood. CS forms nonstoichiometric hydrates and sorbs and liberates water in a continuous manner, although with hysteresis. The reported continuous changes in crystal lattice parameters of CS, which are associated with the changes in water stoichiometry, renders CS physically variable, which may complicate formulation and processing. In addition, controversies still remain as to whether CS exists as different stoichiometric hydrates, mainly because of its variable powder X-ray diffraction (PXRD) patterns (Cox, J. S. G. et al. J. Pharm. Sci. 1971, 60, 1458?65), which indicates a variable crystal structure. The objectives of this study are (a) to understand this unusual water uptake in the light of the molecular and crystal structures of CS, (b) to understand the relationship between the crystal structure and the PXRD patterns using Rietveld analysis, and (c) to investigate whether CS exists as different stoichiometric hydrates. The crystal structure of CS containing 6.44 molecules of water per molecule of CS was determined at 295 and 173 K. The packing arrangements in these structures (space group P1) are similar to those in a previous report, in which the water stoichiometry is 5 to 6, but the bond lengths, bond angles, and lattice parameters are different, reflecting the different water stoichiometries. In the crystal structure solved at 295 K, the position of only one of the two sodium ions could be determined. In the crystal structure solved at 173 K, the previously undetermined sodium ion is disordered over three sites, while four of eight water positions are partially occupied. The 2-hydroxy-propane chain that links the two cyclic moieties of CS was found to be flexible, perhaps allowing the CS crystal to accommodate variable amounts of water. The lack of a fixed coordination site for the second sodium ion may contribute to the disorder of the water molecules. The nonstoichiometric water content of CS is mainly attributed to the water molecules that are associated with the two unoccupied sodium sites. From the PXRD patterns of CS powder, equilibrated at various relative humidities, the various lattice parameters, including previously unreported α, β, and γ values, were calculated using Rietveld analysis. The peak shifts in these PXRD patterns are quantitatively explained by slight changes in the unit cell parameters. The recently described solid forms of CS were prepared and were found to correspond to the original crystalline CS, described by Cox et al. (1971), but with contamination by the known M mesophase in various proportions. The present results support a variable crystal structure and not the existence of different stoichiometric hydrates of CS.

Modification of shell formation in the giant clam Tridacna gigas at elevated nutrient levels in sea water

The effect on shell formation of Tridacna gigas by sea water supplemented for 3 mo with ammonium (5, 10 μM, N) and phosphate (2, 5, 10 μM, P), separately or in combination, was examined. Exposure to N and N+P significantly enhanced shell-extension rates, but significantly reduced shell weights at equivalent size. Scanning-electron microscopy further revealed structural alterations in the outer shell layer, such as misshapen aragonite crystals, irregular crossed-lamellar orientation, and relatively porous shell microstructure. These observations are consistent with results of X-ray diffractometry on the shells which show distinct shifts in the positions of reflections from the (012) and (200) crystal planes relative to the control, indicating changes in crystal lattice parameters following addition of nutrients

Local photodeformation in crystals of LiNbO3:Fe

The paper is concerned with the first results of the investigation of photorefraction effect by the method of x-ray diffraction. One could observe in the crystal region subjected to He-Ne laser radiation a considerable distortion of the crystal structure, which reveals itself in the disappearance of the Borrman effect, change of crystal lattice parameter, and diffraction maximum broadening.