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The three-dimensional structure of oleic acid-capped CdSe and thiol-capped CdTe nanocrystals used as quantum dots has been determined by total synchrotron radiation x-ray diffraction and atomic pair distribution function analysis. Both CdSe and CdTe are found to exhibit the zinc-blende-type atomic ordering. It is only slightly distorted in CdSe implying the presence of nanosize domains and very heavily distorted in CdTe due to the presence of distinct core-shell regions. The results well demonstrate the great potential of the experimental approach and thus encourage its wider application in quantum dot research. [ABSTRACT FROM AUTHOR]

The nanocrystalline fine powders (∼80 nm) of (Ba1− x La x )(Fe2/3W1/3)1− x/4O3, (BLFW) ( x = 0.0, 0.05, 0.10 and 0.15) were synthesized with a combined mechanical activation and conventional high-temperature solid-state reaction methods. Preliminary X-ray structural analysis of pellet samples (prepared from fine powders) showed formation of a single-phase tetragonal system. Detailed studies of dielectric properties (εr and tan δ) exhibit that these parameters are strongly dependent on frequency, temperature and La composition. The La-substitution increases the dielectric constant and decreases the tan δ up to 10% substitutions of La at the Ba-site, and then reversed the variation, and hence this composition is considered as a critical composition. This observation was found valid for structure, microstructures, dielectric constant, electrical conductivity, J– E characteristics and impedance parameters also. Like in other perovskites (PZT, BZT), La substitution plays an important role in tailoring the properties of Ba(Fe2/3W1/3)O3 ceramics. [ABSTRACT FROM AUTHOR]

Microstructure characterization and phase transformation kinetics of a high-energy ball-milled and post-annealed stoichiometric (1:1 mol%) m-ZrO2 and amorphous ( a-) SiO2 powder mixture have been investigated by Rietveld analysis of X-ray powder diffraction data. The experimental results reveal that the ball-milling of stoichiometric powder results in the formation of c-ZrO2/ t-PSZ phases only. The ZrSiO4 phase was not found to form even after 30 h of milling. However, an almost stoichiometric ZrSiO4 (commercially known as zircon) phase is found to form even when a sample that was ball-milled for 5 min was post-annealed at 1473 K for 1 h. It appears that the intermediate t-PSZ phase plays an important role in zircon phase formation. The content of ZrSiO4 phase increases very sharply within 15 min of milling and remains almost unchanged after 30 h of ball-milling. It is also found that nanocrystalline zircon particles are almost free from lattice strain. Contamination by an α-Fe2O3 phase from the milling media results in a colour gradient (white to reddish) in the nanocrystalline ZrSiO4 phase. [ABSTRACT FROM AUTHOR]

The microwave dielectric CaZrO3 has been prepared in nanocrystalline form by high-energy ball milling an equimolar powder mixture of CaO and monoclinic (m) ZrO2. The formation of CaZrO3 is noticed in the X-ray diffraction pattern of 2 h ball-milled powder. At the early stage of milling, up to 4 h, the weight fraction of CaZrO3 increases rapidly and then slowly reaches almost the saturation value of ∼73 wt% within 18 h of milling. It is observed that in the course of milling, the weight fraction of c-ZrO3 increases continuously from its starting value, ∼2.5 wt%, to ∼43 wt% within 2 h of milling, and then reduces slowly to its starting value. It seems that the c-ZrO3 phase has been stabilized by CaO and takes part in the formation of CaZrO3 by mechanochemical reaction of nanocrystalline CaO and c-ZrO3 crystallites. However, post-annealing of 2, 6 and 18 h ball-milled samples results in the formation of ∼95 wt% CaZrO3 phase. The formation mechanism, phase transition kinetics, structure and microstructure changes in terms of lattice imperfections and relative phase abundances of individual phases have been estimated from the analysis of X-ray powder diffraction data of unmilled, ball-milled and post-annealed samples by Rietveld powder structure refinement. [ABSTRACT FROM AUTHOR]

High-quality Er:ZnO films were grown by the pulsed-laser deposition technique at high temperature followed by in situ annealing. The films demonstrate remarkable crystalline quality and array of self-assembled grains. Although the films show very low electrical resistivity (∼6.41×10-4 Ω cm) at room temperature, a semiconductor-metal transition was observed at 190 K for low doping in contrast to semiconductor behavior for high doping. The films show pronounced room temperature emission at 1.54 μm, illustrating the activation of Er3+ ions in ZnO matrix. Furthermore, no quenching effects in 1.54 μm emission characteristics were observed up to 2 wt % of Er doping in ZnO at room temperature. [ABSTRACT FROM AUTHOR]

We report on the observation of remarkable room-temperature ferromagnetism in nanocrystalline epitaxial Co:TiO2 films grown on sapphire (0001) substrates by a pulsed-laser deposition technique using high-density targets. The films were characterized by x-ray measurements, atomic force microscopy, micro-Raman, electron-paramagnetic resonance, and magnetization studies. The films exhibit three-dimensional islandlike growth that contains nanocrystalline particles. Our experimental results suggest that the remarkable ferromagnetism in Co:TiO2 films is controlled either by the interstitial Co2+ ions or small clusters, which are mainly present at the interface and on the surface of the films. Our work clearly indicates that Co interstitials and nanoclusters cause room-temperature ferromagnetism in Co-doped TiO2. [ABSTRACT FROM AUTHOR]

Abstract: Nanocrystalline NaNbO3 and NaTaO3 have been synthesized by the reverse micellar technique for the first time. The particle size of NaNbO3 was found to be 18nm while that of NaTaO3 was found to be 40nm (much smaller size than most of the earlier reports on NaTaO3). Rietveld refinement of X-ray diffraction data and Raman spectroscopy confirm that the nanoparticles of NaNbO3 and NaTaO3 have orthorhombically distorted structures with Pmc21 and Pbnm space groups, respectively. The dielectric constant at 25°C of NaNbO3 and NaTaO3 was found to be 209 and 147 at 1kHz, respectively. The antiferroelectric transition in NaNbO3 shifts to lower temperature (325°C) in the nanocrystalline solid. [Copyright &y& Elsevier]

The three-dimensional structure of nanocrystalline magnesium ferrite, MgFe2O4, prepared by ball milling, has been determined using synchrotron radiation powder diffraction and employing both Rietveld and atomic pair distribution function (PDF) analysis. The nanocrystalline ferrite exhibits a very limited structural coherence length and a high degree of structural disorder. Nevertheless, the nanoferrite possesses a very well defined local atomic ordering that may be described in terms of a spinel-type structure with Mg2+ and Fe3+ ions almost randomly distributed over its tetrahedral and octahedral sites. The new structural information helps explain the material's unusual magnetic properties. [ABSTRACT FROM AUTHOR]

We report the growth and magnetic characterizations of La0.7Ba0.3MnO3 and La0.7Sr0.3MnO3 films on SrTiO3-buffered Si (100) and Si (111) substrates by pulsed-laser deposition. The structural studies show the epitaxial nature of the films. The microscopic studies show that the films consist of nanocrystalline particles. All films display sharp magnetic and electrical transitions associated with the colossal magnetoresistance behavior at and above room temperature, illustrating the superior quality of the films. [ABSTRACT FROM AUTHOR]

Single phase nanocrystalline biocompatible A-type carbonated hydroxyapatite (A-cHAp) powder has been synthesized by mechanical alloying the stoichiometric mixture of CaCO3 and CaHPO4.2H2O powders in open air at room temperature within 2 h of milling. The A-type carbonation in HAp is confirmed by FTIR analysis. Structural and microstructure parameters of as-milled powders are obtained from both Rietveld's powder structure refinement analysis and transmission electron microscopy. Size and lattice strain of nanocrystalline HAp particles are found to be anisotropic in nature. Mechanical alloying causes amorphization of a part of crystalline A-cHAp which is analogous to native bone mineral. Some primary bond lengths of as-milled samples are critically measured. MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay test reveals high percentage of cell viability and hence confirms the biocompatibility of the sample. The overall results indicate that the processed A-cHAp has a chemical composition very close to that of biological apatite. [ABSTRACT FROM AUTHOR]

We have demonstrated the fabrication of highly continuous and smooth CdSe semiconductor films containing self-assembled nanocrystals (NCs) using a simple, low cost solution-processed deposition technique. The impact of thermal annealing and ethanedithiol (EDT) treatment on oleate capped CdSe NCs films is illustrated. Post deposition EDT treatment enhances strong electron coupling between NCs by reducing the inter-particle distance, which enhances four orders of magnitude of photocurrent in the pn-device. Mild thermal annealing of NC films cause large redshift and significant broadening. Our findings suggest that NCs with short-range organic ligands are suitable for high-performance Thin-Film-Transistors and next generation high-efficiency photovoltaics. [ABSTRACT FROM AUTHOR]

The detailed understanding of the crystal structure and microstructure of nanomaterials is useful to predict the properties of nanomaterials. SnO2 nanocrystals of different shapes like particles, spheres, rods and pyramids are chemically synthesized. Here, we report the crystal structure and microstructure of SnO2 nanocrystals of different morphologies using X-ray diffraction and high-resolution transmission electron microscopy (HRTEM). It is interesting to note that the tetragonal phase is found in particle, sphere and rod shaped SnO2 nanocrystals and pyramid shaped nanocrystals are composed of two types of orthorhombic phases. The Rietveld method has been used for refining simultaneously the atomic structure and microstructure of different SnO2 nanocrystals, and the growth mechanisms in different shapes are found to be different due to different preferential growth. Structural defects such as oxygen vacancies, deformation of unit cell and more importantly texturing effects are associated with change in bond length, bond angle and crystallite morphology. Size and lattice strain of different kinds of SnO2 nanocrystals are also studied in detail by using the Rietveld method of analysis and transmission electron microscopy (TEM). [ABSTRACT FROM AUTHOR]

The photocatalytic properties of SnO 2 nanocrystals are tuned by varying their morphology and microstructure. SnO 2 nanoparticles and nanowedges have been synthesized using hydrothermal methods, while microwave irradiation techniques have given nanospheres. Detailed structural and chemical characterization of these different morphologies has been accomplished. The influence of SnO 2 morphology on photocatalytic activity has been examined by monitoring the degradation of aqueous methylene blue dye. Results demonstrate that changing the morphology of the SnO 2 modulates both surface area and levels of surface defects and that these alterations are reflected in the photocatalytic properties of the materials. The degradation of methylene blue dye (98%) in the presence of SnO 2 nanoparticles under simulated solar irradiation is superior to previously reported photocatalyst performance and is comparable to that of standard TiO 2 (Degussa P-25). The SnO 2 nanoparticles perform better than both the nanowedges and nanospheres and this is attributed to the number of surface defects available to the high surface area material. They also reveal outstanding recyclability and stability. SnO 2 nanoparticles, nanowedges and nanospheres have been synthesized and the influence of morphology on the photocatalytic degradation of methylene blue investigated. Structure elucidation explains how the change of morphology modulates both surface area and levels of surface defects and how these alterations are reflected in the photocatalytic properties. Good catalyst recyclability is demonstrated. Image 1 • We report a facile approach to SnO 2 nanoparticles, nanowedges and nanospheres. • Our new route to SnO 2 nanostructures is environmentally benign and cost-effective. • A detailed understanding of structure, morphology and stability is developed. • Nanoparticulate SnO 2 show brilliant activity in the degradation of methylene blue. • Correlation of the oxygen vacancies and surface defects with photocatalyst properties. [ABSTRACT FROM AUTHOR]