Powder Crystallites Research Articles

Enhancing optical properties of Ba-Ni ferrite through nonmagnetic ion doping for sustainable green technologies and renewable energy applications

Barium ferrite powder was produced using a standard ceramic procedure, and its structure and optical properties were investigated. X-ray diffraction analysis (XRD) showed that the powder had a w-type hexagonal structure. The crystallite size was at approximately 35–36 nm, with bulk density and lattice constants increasing as zinc concentration rose. Conversely, X-ray density and porosity decreased with the increasing zinc concentration. This material has useful optical properties, as well as the standard ferrimagnetic properties of barium ferrite, which make it suitable for use in recording media. Ferrimagnetic behavior, which is useful for recording media, occurs because the powder's crystallites have their unit cell axes aligned. Up to the near-infrared part of the spectrum, the powder was found to have a very low absorption coefficient. Both of these properties—an arrangement that gives rise to ferrimagnetism and a corresponding low optical density—make barium ferrite very attractive for high-density recording and microwave applications. Fourier transform infrared spectra of the samples were recorded in the wavenumber range of 400–4000 cm−1 and supported the X-ray diffraction findings by confirming the idea of the formation of W-type hexagonal ferrite by the presence of two prominent peaks at 454 and 591 cm−1 in the FTIR spectra. Zinc addition was also found to enhance the optical properties of the material. The UV–VIS analysis confirms that the band gap energy of Ba-Ni ferrite was indeed reduced by zinc doping. Values decrease from 3.34 eV to 3.20 eV for direct transitions and from 2.96 eV to 2.79 eV for indirect transitions, using Tauc equation. That means that zinc doping enhances the optical properties of Ba ferrite without affecting the hexagonal structure of Ba-Ni ferrite. Moreover, key parameters of optical performance such as the dielectric constant, the extinction coefficient, the penetration depth, and the refractive index show a dramatic increase with a rise in zinc concentration. These attributes make zinc-doped Ba-Ni ferrite a promising optoelectronic material. The material also showed high absorbance in the wavelengths ranging from 334 to 338 nm, which makes it good for the solar cell applications. Overall, zinc-doped Ba-Ni ferrite is a good candidate for sustainable and renewable energy applications. Our study of the optical properties of barium ferrite up to the near-infrared part of the spectrum demonstrated that the powdered material has a very low absorption coefficient. Indeed, the combination of ferrimagnetism and low optical density makes barium ferrite particularly appealing for use in high-density recording and microwave technology applications.

Impact of Mn-substitution on crystallographic, optical, and magnetic properties of nanocrystalline Li-Ni-Zn ferrites fabricated by the sol-gel autocombustion technique

The wet-chemical sol-gel autocombustion, which is a faster and inexpensive synthesis technique has been implemented to synthesize Mn-substituted Li–Ni–Zn ferrite nanoparticles with nominal compositions of Li0.15Ni0.30-xMnxZn0.40Fe2.15O4 ranging from x = 0.00 to 0.15 in the step of 0.03. Well-shaped specimens have been sintered at temperatures ranging from 1373 to 1523 K. The patterns of the XRD reveal the internal shape which ensured the growth of the spinel layout for all samples. The Debye-Scherrer formula has been carried out to estimate the as-developed powder's crystallite size which is in the range of 46–52 nm. Both the lattice constant and average grain diameter of the samples have been increased with Mn2+ ions. The topmost value of the real portion of initial permeability and relative quality factor have been observed for Li0.15Ni0.18Mn0.12Zn0.40Fe2.15O4 ferrite sintered at the temperature of 1523 K, which are 7% and 16% larger, respectively, compared to the pristine composition.

Real-space texture and pole-figure analysis using the 3D pair distribution function on a platinum thin film.

An approach is described for studying texture in nanostructured materials. The approach implements the real-space texture pair distribution function (PDF), txPDF, laid out by Gong & Billinge {(2018 ▸). arXiv:1805.10342 [cond-mat]}. It is demonstrated on a fiber-textured polycrystalline Pt thin film. The approach uses 3D PDF methods to reconstruct the orientation distribution function of the powder crystallites from a set of diffraction patterns, taken at different tilt angles of the substrate with respect to the incident beam, directly from the 3D PDF of the sample. A real-space equivalent of the reciprocal-space pole figure is defined in terms of interatomic vectors in the PDF and computed for various interatomic vectors in the Pt film. Furthermore, it is shown how a valid isotropic PDF may be obtained from a weighted average over the tilt series, including the measurement conditions for the best approximant to the isotropic PDF from a single exposure, which for the case of the fiber-textured film was in a nearly grazing incidence orientation of ∼10°. Finally, an open-source Python software package, FouriGUI, is described that may be used to help in studies of texture from 3D reciprocal-space data, and indeed for Fourier transforming and visualizing 3D PDF data in general.

Influence of divalent metals (Zn, Cu and Co) on the synthesis and magnetic properties of spinel ferrite nanopowders

Hematite iron oxide (α-Fe2O3) and spinel ferrite nanopowders were synthesized by hydrothermal technique. The spinel ferrite MFe2O4 is prepared using three divalent metals M = Cu, Zn and Co. In order to investigate the spinel phase formation mechanism, we have used two atomic ratios (M/Fe) between Fe and divalent metal (above and below the stoichiometric ratio) and two preparation times (6 and 10 h). The nanopowder structure and morphology were characterized by mean of X-ray diffraction, scanning and transmission electron microscopies observation. The magnetic properties of the powder were archived using vibrating sample magnetometer. The results reveal that using low divalent metallic concentration yields to a powder composed of hematite and spinel phases. However, increasing the divalent metal concentration leads to the formation of monophasic spinel powder with a metallic oxide secondary phase. The spinel phase formation enthalpy controls the powder crystallite size and the secondary phase formation. The magnetic properties of the powder are altered by the presence of secondary phase. The magnetic exchange between the phase causes the surface spin canting resulting in the magnetic properties deterioration.

Manifold of spin states and dynamical temperature effects in LaCoO3 : Experimental and theoretical insights

The unconventional transport and magnetic properties of perovskitelike lanthanum cobalt oxide ${\mathrm{LaCoO}}_{3}$ have been studied for more than five decades. This highly correlated electron system exhibits a variety of peculiar properties that are desirable for environmentally friendly energy solutions, fuel cell technologies, novel diesel engines, and oxyfuel power plants. However, the true spin state of the ${\mathrm{Co}}^{3+}$ ion is an important but still unresolved issue that underlies these applications. Although many theoretical models have been proposed, finding supporting experimental evidence of spin-state transitions is extremely difficult. Not until recently have new advanced scattering methods emerged allowing unprecedented precision in determining the crystal structure of ${\mathrm{LaCoO}}_{3}$. In this work, we combine high-resolution extended x-ray absorption fine structure, x-ray powder diffraction, and neutron powder and single-crystal diffraction over a broad range of temperatures, from 2 up to 1000 K, as well as quantum mechanical modeling to study the spin-state transition in ${\mathrm{LaCoO}}_{3}$ and in a reference sample of ${\mathrm{LaGaO}}_{3}$. Our results suggest that the Co ions are mainly in a low-spin state at temperatures below 150 K, with a minority of ions in a high-spin state. With an increase in the temperature the gradual transition from low- to intermediate-spin state occurs up until 550 K. At the metal-insulator transition at 550 K, the long-range domains of the intermediate-spin states become a dominant contribution. Above 550 K, a transition from intermediate- to high-spin state is observed. It is established that a slight change in the degree of $pd$ hybridization can lead to the appearance of a spin-state transition which might be induced by both temperature and surface effects in powder crystallites.

Synthesis of silicon carbide nanopowders in free flowing plasma jet with different energy levels

Silicon carbide (SiC) nanopowders were produced by the synthesis in an electrodischarge plasma jet generated by a high-current pulsed coaxial magnetoplasma accelerator. The present work focuses on the experiments where the obtained hypersonic plasma jet flew into space of the reactor chamber without impact on a target. The energy level of experiments was changed from ∼10.0 to ∼30.0 kJ. Four experiments were carried out at different energy levels. The powder products synthesized by the plasmadynamic method were studied by such well-known methods: X-ray diffraction (XRD), transmission electron microscopy (TEM). All the powders mainly contain cubic silicon carbide (β-SiC) particles with clear crystal structures and triangular shapes. SiC content reaches its maximum value 95% at the energy level 21.0 kJ, then SiC content is decreased to 70% the energy level 27.8 kJ. The powder crystallites in different experiments have approximately the same average crystallite size because quasistationary time, which allows growing powder crystallites, is absent.

Application of Nuclear Quadrupole Resonance Relaxometry to Study the Influence of the Environment on the Surface of the Crystallites of Powder

Abstract The results of the experimental study of the influence of the environment surrounding the surface of the crystallites of a KClO3 powder on the distribution of the spin–spin and spin–lattice relaxation times for 35Cl nuclear quadrupole resonance are described. It was found that the distributions of the spin–lattice relaxation times are unimodal and distributions of the spin–spin relaxation times are bimodal for all samples we studied. T 1 – T 2 and T 1ρ – T 2 correlations by means of the two-dimensional (2D) inverse Laplace transform are obtained. The efficiency of the method for the study of surface phenomena in solids is demonstrated.

Effect of hydroxyapatite particle size, morphology and crystallinity on proliferation of colon cancer HCT116 cells

The aim of the present work is to chemically and physically characterize the synthesized Hydroxyapatite (HAp) micro and nanoparticles and to explore the inhibitory effect of nano-HAps on the in vitro growth of human colon cancerous cells HCT116. HAp powder was synthesized using three different routes to achieve micro and nanosized powders, with different morphologies and crystallinity. The synthesized powders were characterized using X-ray diffraction, FTIR spectroscopy and scanning electron microscope. The results showed that the average crystallite size of HAp powder varies from 11nm to 177nm and respective crystallinity of powder found to be in the range of 0.12 and 0.92. The effect of these physico-chemical properties of HAp powders on human colon cancer HCT116 cells inhibition was determined in vitro. It was found that decreasing the HAp powder crystallite size between 11nm and 22nm significantly increases the HCT116 cell inhibition. Our results demonstrate that apart from HAp powder size their crystallinity and morphology also play an important role in cellular inhibition of human colon cancer cells.

X-ray diffraction study of a pseudo single crystal prepared from a crystal belonging to point group 2

A pseudo single crystal (a composite of matrix resin and powder crystallites, wherein the individual crystallites are aligned three-dimensionally) was prepared from a powder of sucrose, and its X-ray diffraction pattern was studied. A powder of sucrose crystals suspended in a UV-curable resin precursor was subjected to magnetic alignment in order to align the individual crystallites three-dimensionally, and then the resin precursor was photopolymerized to maintain this orientation. The pseudo single crystal thus obtained produced a well resolved X-ray diffraction profile that is similar to that produced by a twin crystal. The origin of the twin orientation was explained in terms of the interplay between the symmetry of magnetic susceptibility axes and the crystal symmetry (point group 2) of sucrose. The crystal structure of sucrose solved using the pseudo single crystal was in excellent agreement with that solved using a single crystal.

The role of surfactant in synthesis of magnetic nanocrystalline powder of NiFe2O4 by sol–gel auto-combustion method

In this work, a new sol–gel auto-combustion method has been performed to synthesize single phase nickel ferrite nanocrystalline powders by using n-cetyltrimethylammonium bromide, as a cationic surfactant. The gels were prepared from ferric and nickel nitrates and citric acid. Ammonia was used as pH adjusting agent as well. The effects of the surfactant on the after combustion calcination process and the reduction of the resulting powder crystallite size which affects the magnetic properties of the material were investigated by XRD and DTA/TGA techniques. The results showed that the ignition of the gels in air have a self-propagating behavior. Addition of surfactant to the starting solution affected the crystallite size of the synthesized powders and their phase constitution. The crystallite size of nickel ferrite powder in sample with surfactant was obtained 31.2 nm. The other important result of this study was production of single phase nickel ferrite directly after combustion while without surfactant the nickel ferrite single phase was obtained only after a post-calcination process at 1000 °C.

Magnetic alignment to convert powder crystallites into a pseudo single crystal

Magnetic alignment to convert powder crystallites into a pseudo single crystal

Growth and characterization of Nd, Yb – yttrium oxide nanopowders obtained by sol‐gel method

AbstractNanopowders of Y2O3 pure, doped and codoped by Nd3+, Yb3+ were obtained by sol‐gel method. Solution with ethylene glycol was choosed as the proper solution where crystallites of powder with Nd and Yb dopants had the same size. Finally the one‐phased compounds of Y2O3 doped 0.5 at% Nd and 1, 2 or 4 at% Yb were obtained. Grain growth and their morphology were investigated in various temperature and time of heating. The changes of crystallite sizes and lattice constants in relation to the heating time and temperature for the composition Y2O3 doped 0.5 at% Nd and 2 at% Yb are presented. Y2O3 containing 0,5 at% of Nd exhibits intense luminescence bands centered at 920 nm, 1100 nm and 1360 nm whereas a single band at about 1020 nm appears in samples co‐doped with neodymium and ytterbium. Luminescence spectra recorded did not depend on the sample preparation procedure and size of grains. OH impurity affects critically the relaxation dynamics of luminescent ion in nanopowders. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Alignment of Powder Crystallites Under High Magnetic Field

A large size single crystal is required for the crystallographic analyses by diffractometry. However, it is often difficult to obtain a large one; we just obtain a powder sample. We have recently developed a novel magnetic technique that enables alteration of powder crystallites to a pseudo-single crystal (PSC). Magnetic alignment of feeble magnetic materials including organic, polymeric, and inorganic materials is well known for many years. However, the alignment was limited so far to a uniaxial one: only the easy or hard magnetization axis is aligned uniaxially. The uniaxial alignment is not sufficient for crystallographic analyses by diffractometry. It only provides a fiber pattern. With our novel technique, powder crystallites belonging to the biaxial crystal system are aligned biaxially to form a PSC that gives rise to an X-ray diffraction pattern equivalent to the real single crystal.

Magnetic Alteration of Crystallite Alignment Converting Powder to a Pseudo Single Crystal

The powder crystallites of L-alanine, selected for demonstration purposes, suspended in a photocurable resin were subjected to a frequency-modulated rotating magnetic field, and the achieved three-dimensional alignment was fixed by photopolymerization of the resin. The obtained sample exhibited the X-ray diffraction pattern that was comparable to the pattern of an equivalent actual original single crystal. This was achieved for the first time by the simultaneous alignment of the two magnetic axes, i.e., the easy and hard magnetization axes with respect to the space coordinates. A theoretical estimation indicates that a better alignment of the sample can be obtained if the sample preparation conditions are improved.

Investigation of the Microstructure of SiC-Zn Nanocomposites by Microscopic Methods: SEM, AFM and TEM

SiC-Zn nanocomposites with about 20% volume fraction of metal were fabricated by infiltration process under the pressure of 2-8 GPa and at the temperature of 400_1000oC. SiC nanopowders used in the experiments formed loosely agglomerated chains of single crystal nanoparticles. The dimension of the agglomerates was in the micrometer range, the mean grain size was up to tens of nanometers. Microstructural investigations of the nanocomposites were performed at a different resolution levels using scanning, transmission electron microscopy and atomic force microscopy techniques (SEM, TEM, AFM, respectively). SEM observations indicate a presence of nano-dispersed, uniform (on the micrometer scale) mixture of two phases. TEM observations show that distribution of SiC and Zn nanocrystallites is uniform on the nanometer scale. High-resolution TEM images demonstrate an existence of thin (on the order of tens of Angstroms) Zn layers separating SiC grains. AFM images of the mechanically polished samples show a smooth surface with the roughness on the order of the SiC grain size (10-30 nm). After ion etching of some samples the AFM topographs show surface irregularities: periodically spaced hillocks 50-100 nm in height. The size of the SiC grains remains equal to that of the initial powder crystallites. The size of the Zn grains varies in the range of 20-100 nm depending on the initial SiC grain size and the composite fabrication conditions.

Current limits to wire technology

High-temperature superconductors could be a boon to the power industry, carrying large currents with virtually no energy loss. Unfortunately, these brittle materials are difficult to make into wires, so in practice they are powdered and encased in silver strips, and drawn out to align the powder crystallites. But the current capacity of these tapes is still severely limited. That is probably due to misalignment of the crystallites, according to new magnet-optical imaging studies. So for commercial applications, slightly different processing strategies may be needed — or an entirely different type of tape.

The dehydration process in the zeolite laumontite: a real-time synchrotron X-ray powder diffraction study

The dehydration process of the natural zeolite laumontite Ca4Si16Al8O48 · 18 H2O has been studied in situ by means of powder diffraction and X-ray synchrotron radiation. Powder diffraction profiles suitable for Rietveld refinements were accumulated in time intervals of 5 minutes using a position sensitive detector (CPS-120 by INEL), while the temperature increased in steps of about 5 K. The synchronization of accumulation time and temperature plateau allowed collection of 62 temperature-resolved powder patterns in the range 310–584 K, whose analysis produced a dynamic picture of the laumontite structure response to dehydration. The first zeolitic water molecules diffusing out of the channels are those not bonded to the Ca cations and located in the W(1) site, whose occupancy drops smoothly to 10% during heating to 349 K, while the sample in the capillary is still submerged in water. The remaining W(1) and 60% of W(5) water molecules are expelled rather sharply at about 370 K. At this temperature all remaining water submerging the powder crystallites is lost, the structure contains about 13 water molecules/cell, and the crystal structure is that of leonhardite. On continued heating 80% of the water molecules from the W(2) site are lost between 420 and 480 K, while a small amount of the diffusing water is reinserted in the W(5) site. The occupancy factor of the W(8) site decreases starting at 480 K, and reaches a maximum loss of 20% at 584 K. The combined occupancy of the Ca-coordinated W (2) and W (8) water sites never falls much below two, so that the Ca cations in the channels, which are bonded to four framework oxygen atoms, are nearly six-coordinated in the explored temperature range. The water loss is accompanied by large changes in the unit cell dimensions. Except at 367 K, where the excess surrounding water is leaving, all changes in cell dimensions are gradual. The loss of the hydrogen bonded W(1) and W(5) water molecules is related to most of the unit cell volume reduction below 370 K, as shown by the contraction of the a-, b- and c-axes and the increase in the monoclinic angle. Loss of the Ca-coordinated W(2) and W(8) water molecules has a small effect on the unit cell volume as the continued contraction of the a- and c-axes is counter-balanced by a large expansion in the b-axis and a decrease in the monoclinic β angle.

Change in activation energy of surface conduction in polycrystalline zinc oxide upon irradiation by electrons

The dependence of activation energy EA of surface conduction σs in polycrystalline ZnO upon dosage Φ of irradiation by electrons with energy of 30 keV is studied. It is found that the function σs = f(T) is composed of three segments with EA values in unirradiated ZnO approximately equal to 0.77, 0.12, and 0.048 eV, which are ascribed to a surface potential barrier ϕ between the powder crystallites and donor levels of interstitial Zn+i and Znoi atoms, respectively. With increase in radiation dosage EA decreases on all segments, which is explainable by reduction in ϕ with increase in the concentrations of Zn+i and Znoi due to radiation desorption and lattice radiolysis.

Improving the Diffracting Properties of LiF: Comparison with Graphite

The integral reflection coefficient R was measured for the (200) planes in LiF using a double crystal spectrometer over the wavelength range 0.7–2.1 Å. For cleaved LiF, R was about 0.7 × 10−4 rads compared to 0.3 × 10−4 calculated for the theoretically perfect crystal case. After abrading with 1.5–20 μ carborundum, R increased to 2.90 × 10−4 at the 0.7-Å end of the range and to 3.68 × 10−4 at the 2.1-Å end. For a flexed and reflattened crystal, R increased further to 9.45X10−4 at the 0.7-Å end of the range but was not improved over the abraded crystal at the 2.1-Å end. Theoretical R values for mosaic graphite were compared with LiF. The value for graphite at 1.66 Å was 4.5 times higher than that calculated for mosaic LiF and 1.3 times higher than the measured graphite values of Gould, Bates, and Sparks. It appears that one can approximate theoretical mosaic crystals by either distorting a nearly perfect crystal such as LiF or by orienting powder crystallites as in the case of graphite.

Etch Pits in Electroluminescent Zinc Sulfide Crystallites

Through suitable etching techniques, triangular etch pits are developed on the surfaces of electroluminescent ZnS:Cu,Cl powder crystallites at densities in the range 106−108/cm2. These pits, seen by means of the electron microscope, are essentially absent in similarly etched nonelectroluminescent ZnS:Cu,Cl crystallites. Also present on the electroluminescent particles are surface striations. The etch pits appear physically related to the striations in that the pits from only on those faces bearing the striations. All triangular pits on a given face point in the same direction, which is normal to the striation direction. This direction is one of the crystallographic polar axes in sphalerite and the c axis in wurtzite. The pits have also been found in other electroluminescent compositions such as ZnS:Cu,Al; ZnS:Cu, Cl–Pb; and ZnS:Cu, Cl–Mn. The possible interpretations of the pits and striations are discussed in terms of defect structures (e.g., dislocations and stacking faults) which may be of importance to the nature of the barriers believed to reside within the volume of electroluminescent particles. Some experiments with large crystal specimens are reported.