Search results for "STOICHIOMETRY"
showing 10 items of 270 documents
Effect of zinc concentration on the microstructure and relaxation frequency of Mn–Zn ferrites synthesized by solid state reaction
2013
Abstract Mn3Zn polycrystalline ferrites with Mn1−xZnxFe2O4 stoichiometry (x=0.59, 0.61, 0.65) were prepared by solid state reaction. These ferrites were heated at different temperatures. The cubic structure with space group Fd3m (Oh7) No. 227 was confirmed by the refinement of x-ray diffraction (XRD) powders through Rietveld´s method using fullprof. Scanning electron microscopy (SEM) results revealed for all compounds a non-homogeneous grain size and shape distribution, with a mean grain size of 9 μm. The Curie temperature Tc was found to decrease as the Zn concentration increases. The magnetic domain relaxation was investigated by inductance spectroscopy (IS). The relaxation frequency fr s…
Large magnetoresistance at room temperature in the off-stochiometric chalcogenide Cr0.92Te
2006
Abstract We present the electronic and magnetic properties of the transition chalcogenide Cr0.92Te. The compound is the hexagonal counterpart to the hypothetical half-metallic ferromagnet CrTe. The off-stochiometric phase crystallizes in the hexagonal NiAs-type structure P63/mmm. New magnetotransport results show a large magnetoresistance (MR) of 5.5% at room temperature in a magnetic field of 8 T. The remarkable MR-effect can be explained with spin-dependent scattering below the Curie temperature.
Submicrometer CaCuO2 and Ca2CuO3 particles from bimetallic formate precursors
1992
Abstract CaCuO2 and Ca2CuO3 are readily obtained by thermal decomposition of two new calcium and copper formates, CaCu(HCOO)4 and Ca2Cu(HCOO)6. These chemical-precursor based syntheses, while overcoming problems related to the stoichiometry of the final products, involve very short diffusion path lengths. This, in turn, results in soft treatments yielding pure phases constituted by submicrometer (≈0.4 μm) homogeneous particles.
Synthesis and characterization of copper intercalated ZrTe3
1997
Abstract Electrochemical copper intercalation in ZrTe3 yields the new metallic ternary phase CuxZrTe3 with a maximum stoichiometry of x = 1.9. The charge is balanced by filling the σ∗ antibonding Te p bands, as monitored by XANES spectroscopy. The reaction is accompanied by an increase in the a lattice dimension of 9%. This observation is explained by theoretical calculations.
Raman Imaging of Single Carbon Nanotubes
2000
[19] The single crystals of the Bu4NBr0.6I1.4Cl salt, were obtained by addition of IBr to a solution of Bu4NCl in ethanol at a reagent ratio of 1:0.5. Stoichiometry of the anion has been found by EDX. Based on a Raman study the anion consists of the I2Br ‐ (band at 140 cm ‐1 ), IBr2 ‐ (band at 150‐ 176 cm ‐1 ), BrICl ‐ (band at 225 cm ‐1 ), and ICl2 ‐ (band at 250‐263 cm ‐1 ) trihalide anions. [20] The X-ray diffraction data from single crystals for both trihalide salts were measured using an Enraf Nonius CAD4 diffractometer with graphite monochromatic Mo Ka radiation (k = 0.71073 a) at room temperature. Unit cell parameters of the new a¢¢¢- crystal were determined from a leastsquares analy…
Texture and Phase Recognition Analysis of beta-NaYF4 Nanocrystals
2014
Texture and phase recognition analysis (TPRA) based on electron nanodiffraction technique is used to characterize the geometry of up-conversion nanocrystals (UCNCs) synthesized by the common thermal-decomposition protocol in the presence of a stoichiometric amount of NH4F. Here, we confirmed experimentally that despite the apparently different shapes of samples (hexagons, rods, and cubes), all the nanocrystals are actually beta-phase hexagonal prisms. This is of relevance since many biological features of nanostructures, such as cellular internalization and cytotoxicity, are governed by their geometry. In addition, reproducibility in biological experiments is paramount.
High-Yield Growth and Tunable Morphology of Bi2Se3 Nanoribbons Synthesized on Thermally Dewetted Au
2021
The yield and morphology (length, width, thickness) of stoichiometric Bi2Se3 nanoribbons grown by physical vapor deposition is studied as a function of the diameters and areal number density of the Au catalyst nanoparticles of mean diameters 8–150 nm formed by dewetting Au layers of thicknesses 1.5–16 nm. The highest yield of the Bi2Se3 nanoribbons is reached when synthesized on dewetted 3 nm thick Au layer (mean diameter of Au nanoparticles ~10 nm) and exceeds the nanoribbon yield obtained in catalyst-free synthesis by almost 50 times. The mean lengths and thicknesses of the Bi2Se3 nanoribbons are directly proportional to the mean diameters of Au catalyst nanoparticles. In contrast, the me…
High-pressure synthesis of boron-rich chalcogenides B12S and B12Se
2022
The authors thank Drs. I. Dovgaliuk and T. Chauveau for assistance with Rietveld analysis; and Drs. V. Bushlya and A. Jamali for help with EDX/SEM measurements. This work was financially supported by the European Union's Horizon 2020 Research and Innovation Program under Flintstone2020 project (grant agreement No 689279).
Structure and Phase Changes in Natural and Synthetic Magnesium Aluminum Spinel
2015
Natural spinel crystals from Ural and Pamir deposits and synthetic magnesium aluminium spinel single crystals with different stoichiometry (MgO.nAl2O3 ) grown by Verneuil method were used. The photoluminescence (PL), its excitation (PLE) and optical absorption of stoichiometric and nonstoichiometric magnesium aluminium spinel crystals containing the chromium and manganese ions and defects produced by fast neutron irradiation( fluence up to 1020cm-2, E>0.1 MeV) are investigated. The broadening of R- and N-lines takes place in synthetic stoichiometric spinel. Structure of synthetic nonstoichiometric spinels (n>1) has to be more disordered, since in addition to the site exchange …
Are AuPdTM (T = Sc, Y and M = Al, Ga, In), Heusler Compounds Superconductors without Inversion Symmetry?
2019
Heusler compounds with 2:1:1 stoichiometry either have a centrosymmetric Cu 2 MnAl structure or an Li 2 AgSb structure without a centre of inversion. The centrosymmetry is always lost in quaternary Heusler compounds with 1:1:1:1 stoichiometry and LiMgPdSn structure. This presents the possibility of realizing non-centrosymmetric superconductors in the family of Heusler compounds. The objective of this study is to search for and investigate such quaternary derivatives of Heusler compounds, particularly with respect to superconductivity. Several compounds were identified by carrying out calculations from first principles and superconductivity was observed in experiments conducted on AuPdScAl a…