Powder diffraction nanocrystalline powders

The defective structure in nanocrystalline ceria based catalysts proved to have strong effect on the OSC. Mamontov et al. (2000) reported the neutron diffraction studies of the atomic structures of nanocrystalline powder of ceria and ceria-zirconia solid solution. They found that the concentration of vacancy-interstitial oxygen defects has a direct correlation with the OSC. This effect is stronger than the correlation of surface area with OSC. Zirconia reduces ceria and preserves oxygen defects to retard the degradation of ceria-zirconia in OSC. Yan et al. observed the strong correlation between OSC and the lattice strain in nanosized ceria-zirconia, which could be measured via XRD (Si et al., 2004 Figure 11). 

Lithium Niobate Lithium niobate (LiNbOj) is widely used as a photonic material, and has a wide range of applications in lasers, nonlinear optics, optical communications, optical memories, and diffractive optics [25O[. It is not generally considered as an ionic conductor. However, since Li NMR measurements first revealed a rapid Li ion motion in nanocrystalline powders prepared by ball-milling [251], the material has attracted considerable interest and has proved to be a good model system [ 169]. As stated earlier, it is now known that the ball-milled material has a considerable amorphous content, as shown by EXAFS [169,252] and HRTEM [169],... 

Nanocrystalline metal (silver and copper) and metal sulfide (silver sulfide, cadmium sulfide, and lead sulfide) particles were prepared via RESOLV (Rapid Expansion of a Supercritical Solution into a Liquid SOLVent) with water-in-carbon dioxide microemulsion as solvent for the rapid expansion. The nanoparticles were characterized using UV/vis absorption. X-ray powder diffraction, and transmission electron microscopy methods. The results of the different nanoparticles are compared and discussed in reference to those of the same nanoparticles produced via RESOLV with the use of conventional supercritical solvents. 

Fig. 6 Illustration of the common characteristics of powder diffraction patterns collected with micro-XRD. Notice that the individual spots are from larger, micron-sized crystallites while the spotted rings are indicative of micro-crystalline particles (a). The spottiness of the rings is an indication of insufficient number of grains in the dif aetion volume of the sample. The continuous rings indicate that all lattice planes hkl are simultaneously present in all orientations relative to the incident X-ray beam. In micro-diffraction with spot sizes on the micron-scale this usually occurs only with nanocrystalline particles (b)...

Large-angle X-ray powder diffraction (XRD) has been one of the most versatile techniques utilized for the structural characterization of nanocrystalline metal powders. The modern improvements in electronics, computers, and X-ray sources have allowed XRD to become an indispensable tool for identily-ing nanocrystalline phases as well as crystal size and crystal strain. The comparison of the crystallite size obtained by the XRD difffactogram using the Scherrer formula with the grain size obtained from the TEM image allows us to establish if the nanoparticles have a mono- or polycrystalline nature. 

Gal] Neutron diffraction, SANS, magnetic measurements, extended X-ray absorption fine structure spectroscopy Coi4CugoFc6, structural and magnetic properties of ball milled nanocrystalline powders... 

Ultrafme pure BaTi03 powders were obtained by a modified oxalate precipitation method as described previously [13], The powders had a specific surface area of 57 m g and the particle size was nearly spherical from 20 to 30 nm. The main impurities contained in the powders were at the following levels 0.04 wt% Sr, 0.02 wt% Na, and 0.006 wt% K. The Ba/Ti atomic ratio was 1 0.003 for all the powders. The X-ray diffraction (XRD) patterns of nanocrystalline powders apparently correspond to a pseudo-cubic structure without peak splitting of lines such as (002) and (200). We also used Raman spectra to detect local symmetry of the nanocrystalline powder samples. It showed that the local symmetry in the nanopowder appears to be a cubic structure even at a very low temperature of 123 K. Therefore, XRD patterns and Raman spectra revealed that the BaTiOs powder exhibited the commonly reported pseudocubic perovskite structure. 

X-ray powder diffraction measurements have revealed that the metal powders obtained by the deoxygenation of metal oxides are generally nanocrystalline. The grain size of the nickel and cobalt powders was determined by TEM to range between 6 -10 nm and 1 - 5 nm. 

Nanocrystalline CaF2 powder specimens were prepared and examined by ssNMR and powder XRD by Abdellatief et al. The specimen homogeneity and a detailed picture of the lattice defects can be assessed by the simultaneous analysis of the X-ray powder diffraction pattern and of the solid-state F MAS NMR relaxometty data. The relationship between linewidths, structure and defects were discussed. ... 

Finally, the use of a GA to fit the powder X-ray diffraction patterns of nanocrystalline materials, for example, SiC, GaN and diamond nanocrystals, has also been reported [110]. 

We finally note that after 40 hours of milling the powder mixture contains 81% of XRD-amorphous phase (inset of Fig. 4b). According to this large amount and based on the fact that we did not detect any new crystalline phase during 40 hours of milling we can conclude that the carbonato complex is amorphous or eventually nanocrystalline to an extent that is undetectable with X-ray diffraction methods. This example illustrates that enriched information on a local structural scale can only be achieved by appropriate selection of analytical tools. The amorphous carbonato complex has recently been confirmed using Raman and nuclear magnetic resonance (NMR) sp>ectroscopies (Rojac et al., to be published). 

R. Harrington, M. Michel, J. Parise, D. Hausner, D. Strongin, Powder neutron diffraction studies of ferrihydrite, a nanocrystalline material. Geochim. Cosmochim. Acta 74(Suppl 1), A383-A383 (2010)... 

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