Structural identification of cubic iron-oxide nanocrystal mixtures: X-ray powder diffraction versus quasi-kinematic transmission electron microscopy
Peter Moeck
备注：
7 pages, 3 figures, 1 table, expanded and updated version of a conference paper that has been published in Suppl. Proc. of TMS 2008, 137th Annual Meeting & Exhibition, Volume 1, Materials Processing and Properties, pp. 25-32
Two novel (and proprietary) strategies for the structural identification of a nanocrystal from either a single high-resolution (HR) transmission electron microscopy (TEM) image or a single precession electron diffraction pattern are proposed and their advantages discussed in comparison to structural fingerprinting from powder X-ray diffraction patterns. Simulations for cubic magnetite and maghemite nanocrystals are used as examples. This is an expanded and updated version of a conference paper that has been published in Suppl. Proc. of TMS 2008, 137th Annual Meeting & Exhibition, Volume 1, Materials Processing and Properties, pp. 25-32.
Band alignment effects of anatase and rutile nanocrystals in TiO$_2$ powders lead to an electron hole separation, increasing the photo catalytic efficiency of these powders. While size effects and types of possible alignments have been extensively studied, the effect of interface geometries of bonded nanocrystal structures on the alignment is poorly understood. In order to allow conclusive studies of a vast variety of bonded systems in different orientations, we have developed a new density functional tight binding parameter set to properly describe quantum confinement in nanocrystals. Applyin…
The effect of sintering temperatures (Ts) on the structural and magnetic properties of Ni0.6Zn0.4Fe2O4 (NZFO) ferrites synthesized by conventional double sintering method has been reported. The samples are sintered at 1200, 1250 and 1300 °C. The X-ray diffraction (XRD) analysis reveals the formation of a single phase cubic spinel structure of the sample. The magnetic parameters such as saturation magnetization, Ms; coercive field, Hc; remanent magnetization, Mr and Bohr magneton, μB are determined and well compared with reported values. The obtained values are found to be 71.94 emu/gm and 1.2 …
We use a first-principles based kinetic Monte Carlo simulation to study the movement of a solid iron nanocrystal inside a carbon nanotube driven by the electrical current. The origin of the iron nanocrystal movement is the electromigration force. Even though the iron nanocrystal appears to be moving as a whole, we find that the core atoms of the nanocrystal is completely stationary, and only the surface atoms are moving. Movement in the contact region with the carbon nanotube is driven by electromigration forces, and the movement on the remaining surfaces is driven by diffusion. Results of our…
Under the application of electrical currents, metal nanocrystals inside carbon nanotubes can be bodily transported. We examine experimentally and theoretically how an iron nanocrystal can pass through a constriction in the carbon nanotube with a smaller cross-sectional area than the nanocrystal itself. Remarkably, through in situ transmission electron imaging and diffraction, we find that, while passing through a constriction, the nanocrystal remains largely solid and crystalline and the carbon nanotube is unaffected. We account for this behavior by a pattern of iron atom motion and rearrangem…
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Nanocrystalline metal alloys show great potential as structural materials, but are often only available in small volumes such as thin films or powders. However, recent research has suggested that dopant segregation and grain boundary structural transitions between states known as complexions can dramatically alter grain size stability and potentially enable activated sintering. In this study, we explore strategic consolidation routes for mechanically alloyed Cu-4 at.% Zr powders to capture the effects of amorphous complexion formation on the densification of bulk nanostructured metals. We obse…
We present a simple, scalable synthesis route for producing exchange coupled soft/hard magnetic composite powder that outperforms pure soft and hard phase constituents. Importantly, the composites is iron oxide based (SrFe12O19 and Fe3O4) and contain no rare earth or precious metal. The two step synthesis process consists of first precipitating, an Iron oxide/hydroxide precursor directly on top of SrFe12O19 nano-flakes, ensuring a very fine degree of mixing between the hard and the soft magnetic phases. We then use a second step that serves to reduce the precursor to create the proper soft mag…
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The crystallization and magnetic behavior of yttrium iron garnet (YIG) prepared by metallo-organic decomposition (MOD) method are discussed. The chemistry and physics related to synthesis of iron and yttrium carboxylates based on 2-ethylhexanoic acid (2EHA) are studied, since no literature was found which elucidates synthesis of metallo-organic precursor of YIG in spite of the literatures of doped YIG samples such as Bi-YIG. Typically, the metal carboxylates used in preparation of ceramic oxide materials are 2-ethylhexanoate (2EH) solvents. Herein, the synthesis, thermal behavior and solubilit…
We report neutron diffraction and transport results on the newly discovered superconducting nitride ThFeAsN with $T_c=$ 30 K. No magnetic transition, but a weak structural distortion around 160 K, is observed cooling from 300 K to 6 K. Analysis on the resistivity, Hall transport and crystal structure suggests this material behaves as an electron optimally doped pnictide superconductors due to extra electrons from nitrogen deficiency or oxygen occupancy at the nitrogen site, which together with the low arsenic height may enhance the electron itinerancy and reduce the electron correlations, thus…
We use neutron powder diffraction to study on the non-superconducting phases of ThFeAsN$_{1-x}$O$_x$ with $x=0.15, 0.6$. In our previous results on the superconducting phase ThFeAsN with $T_c=$ 30 K, no magnetic transition is observed by cooling down to 6 K, and possible oxygen occupancy at the nitrogen site is shown in the refinement(H. C. Mao \emph{et al.}, EPL, 117, 57005 (2017)). Here, in the oxygen doped system ThFeAsN$_{1-x}$O$_x$, two superconducting region ($0\leqslant x \leqslant 0.1$ and $0.25\leqslant x \leqslant 0.55$) have been identified by transport experiments (B. Z. Li \emph{e…
Using neutron inelastic scattering, we investigate the role of interstitial iron on the low-energy spin fluctuations in powder samples of Fe_{1+x}Te_{0.7}Se_{0.3}. We demonstrate how combining the principle of detailed balance along with measurements at several temperatures allows us to subtract both temperature-independent and phonon backgrounds from S(Q,ω) to obtain purely magnetic scattering. For small values of interstitial iron (x=0.009(3)), the sample is superconducting (T_{c}=14 K) and displays a spin gap of 7 meV peaked in momentum at wave vector q_{0}=(π,π) consistent with single crys…
To reduce the emission of greenhouse gases by the steel industry, particularly for ironmaking, the production of DRI (Direct Reduced Iron) using hydrogen as the reducing gas instead of carbon monoxide is being considered. In this context, the reduction of pure hematite by hydrogen was studied at the laboratory scale, varying the experimental conditions and observing the rate and the course of the reaction. All the reduction experiments were performed in a thermobalance and supplementary characterization methods were used like scanning and transmission electron microscopy, X-ray diffraction, an…
X-ray powder diffraction using a synchrotron light source reveals significant modifications to both morphology and strain state in Palladium nanocubes after oxidation. Short-range strain measured by the static component of the Debye-Waller coefficient is observed to be higher in the oxidized nanoparticles; while long-range strain related to the line broadening of the diffraction peaks is seen to decrease. Using multiscale modelling with classical molecular dynamics and density functional theory, we connect the decrease in long-range strain to the increased truncation of the oxidized nanocubes,…
Our searches for new oxide chalcogenides of rare earths and Fe, Co, Ni, and Zn resulted in preparation of two new compounds Ce2Fe2O3S2 and Pr2Fe2O3S2 which are isostructural to La2Fe2O3Se2 and Sm2Ti2O3Sb2. Crystal structures of the new compounds Ce2Fe2O3S2 and Pr2Fe2O3S2 were determined from powder X-ray diffraction data. Magnetic measurements were performed for Ce2Fe2O3S2 and revealed behavior very similar to that of isostructural oxide chalcogenides of iron and pnictides of titanium. In particular, no superconductivity was observed down to 4 K. Crystal chemical factors determining the stabil…
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Diamond nanocrystals containing highly photoluminescent color centers are attractive non-classical and near-field light sources. For near-field applications the size of the nanocrystal is crucial since it defines the optical resolution. NV (Nitrogen-Vacancy) color centers are efficiently created by proton irradiation and annealing of a nanodiamond powder. Using near-field microscopy and photon statistics measurements, we show that nanodiamond with size down to 25 nm can hold a single NV color center with bright and stable photoluminescence.
In Ayurveda, Lauha (Iron) bhasma is primarily used to cure diseases related with iron deficiency in humans. It is produced from purified raw metallic iron using a combination of multi-step traditional preparation processes described in the Ayurveda literature. Here, we present results of structural investigation performed on the medicinal grade Lauha bhasma using various X-ray based techniques. Our results indicate that after several rounds of heating and cooling in specific conditions following the Ayurvedic preparation procedure, metallic iron eventually converts to a natural iron-oxide mine…
Crystal Shape and Lattice Deformation in Powder Diffraction
Saudi Aramco（沙特阿美）；Diamond Light Source (United Kingdom)（英国钻石光源）；Indiana University Bloomington（印第安纳大学布鲁明顿分校）；Friedrich-Alexander-Universität Erlangen-Nürnberg（埃尔朗根-纽伦堡弗里德里希·亚历山大大学）
The aim of this comment is to show that anisotropic effects and image fields should not be omitted as they are in the publication of A. Leonardi, S. Ryu, N. M. Pugno, and P. Scardi (LRPS) [J. Appl. Phys. 117, 164304 (2015)] on Pd <011> cylindrical nanowires containing an axial screw dislocation. Indeed, according to our previous study [Phys. Rev. B 88, 224101 (2013)], the axial displacement field along the nanowire exhibits both a radial and an azimuthal dependence with a twofold symmetry due the <011> orientation. As a consequence, the deviatoric strain term used by LRPS is not suitable to an…
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Thanks to the remarkable developments of ultrafast science, one of today's challenges is to modify material state by controlling with a light pulse the coherent motions that connect two different phases. Here we show how strain waves, launched by electronic and structural precursor phenomena, determine a macroscopic transformation pathway for the semiconducting-to-metal transition with large volume change in bistable Ti$_3$O$_5$ nanocrystals. Femtosecond powder X-ray diffraction allowed us to quantify the structural deformations associated with the photoinduced phase transition on relevant tim…
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The deposition of nano-crystalline ZnS/diamond composite protective coatings on silicon, sapphire, and ZnS substrates, as a preliminary step to coating infrared transparent ZnS substrates from powder mixtures by the aerosol deposition method is presented. Advantages of the aerosol deposition method include the ability to form dense, nanocrystalline films up to hundreds of microns thick at room temperature and at a high deposition rate on a variety of substrates. Deposition is achieved by creating a pressure gradient that accelerates micrometer-scale particles in an aerosol to high velocity. Up…
The intrinsic iron(III) impurity center in polycrystalline lead titanate was investigated by means of high-frequency electron paramagnetic resonance (EPR) spectroscopy in order to determine the local-environment sensitive fine structure parameter D. At a spectrometer frequency of 190 GHz, spectral analysis of a powder sample was unambiguously possible. The observed mean value D = +35.28 GHz can be rationalized if Fe3+ ions substitute for Ti4+ at the B-site of the perovskite ABO3 lattice forming a directly coordinated iron - oxygen vacancy defect associate. A consistent fit of the multi-frequen…
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We generalize and systematize basic experimental data on optical and luminescence properties of ZnO single crystals, thin films, powders, ceramics, and nanocrystals. We consider and study mechanisms by which two main emission bands occur, a short-wavelength band near the fundamental absorption edge and a broad long-wavelength band, the maximum of which usually lies in the green spectral range. We determine a relationship between the two luminescence bands and study in detail the possibility of controlling the characteristics of ZnO by varying the maximum position of the short-wavelength band. …
