Search results for "Powder diffraction"

Nanostructured Alumina from Freeze-Dried Precursors

2010

Nanocrystalline alumina has been obtained on the 100 g scale by thermal decomposition of precursors resulting from the freeze-drying of aqueous solutions of different aluminum-containing products, namely aluminum acetate and aluminum L-lactate. Samples prepared at different temperatures (from 873 to 1573 K in steps of 100 K) were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and surface area measurements. In the acetate case, the transformation sequence involves the formation of θ-Al 2 O 3 as an intermediate phase between γ-Al 2 O 3 and α-Al 2 O 3 , whereas this θ phase is not observed in the lactate case. TEM…

Structural evolution of CO2 filled pure silica LTA zeolite under high-pressure high-temperature conditions

2017

[EN] The crystal structure of CO2-filled pure-SiO2 LTA zeolite has been studied at high pressures and temperatures using synchrotron-based X-ray powder diffraction. Its structure consists of 13 CO2 guest molecules, 12 of them accommodated in the large alpha-cages and one in the beta-cages, giving a SiO2/CO2 stoichiometric ratio smaller than 2. The structure remains stable under pressure up to 20 GPa with a slight pressure-dependent rhombohedral distortion, indicating that pressure-induced amorphization is prevented by the insertion of guest species in this open framework. The ambient temperature lattice compressibility has been determined. In situ high-pressure resistive-heating experiments…

Anomalous Valence Contrast of Metal Transition in Nanocrystalline Ferrite

2001

Electron diffraction tomography and X-ray powder diffraction on photoredox catalyst PDI

2019

N,N-Bis(2,6-diisopropylphenyl)-perylene-3,4,9,10-bis(dicarboximide) (PDI-iPr) is starting to be widely used as a metal-free homogeneous photoredox catalyst. The crystal structure was determined by a combination of electron diffraction tomography and X-ray powder diffraction and further validated by DFT-D calculations. Surprisingly, the molecular geometry of PDI-iPr leads to voids in the packing.

Co-precipitation synthesis of neodymium-doped yttrium aluminium oxides nanopowders: Quantitative phase investigation as a function of joint isotherma…

2007

Abstract Neodymium-doped yttrium aluminium nanopowders with nominal Nd:Y:Al ratio equal to X:3–X:5 (where X = 0, 0.006, 0.012, 0.024, 0.048, 0.081, 0.096, 0.171, 0.192, 0.384, 0.540 and 0.720) were prepared by the co-precipitation method and subjected to five cumulative stages of isothermal treatment in the temperature range from 900 to 1050 °C. The phase evolution of the oxides were investigated quantitatively by the X-ray powder diffraction approach using the Rietveld method of analysis. An almost single phase cubic garnet structure was attained at temperatures as low as 900 °C for specimens with neodymium loading less than ca. 6 at.% with respect to total (Nd + Y) atoms. Isothermal treat…

Novel method of phosphorescent strontium aluminate coating preparation on aluminum

2018

This work was supported by the ERDF , European-Union Project No. 1.1.1.1/16/A/182 .

Insights into the formation of metal carbon nanocomposites for energy storage using hybrid NiFe layered double hydroxides as precursors

2020

[EN] NiFe-carbon magnetic nanocomposites prepared using hybrid sebacate intercalated layered double hydroxides (LDHs) as precursors are shown to be of interest as supercapacitors. Here, the low-temperature formation mechanism of these materials has been deciphered by means of a combined study using complementaryin situ(temperature-dependent) techniques. Specifically, studies involving X-ray powder diffraction, thermogravimetry coupled to mass spectrometry (TG-MS), statistical Raman spectroscopy (SRS), aberration-corrected scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS) have been carried out. The experimental results confirm the early formation o…

Two-component self-assembly with solvent leading to "wet" and microcrystalline organogel fibers

2014

Abstract Hypothesis The microcrystalline fibers of N -(2-aminoethyl)-3α-hydroxy-5β-cholan-24-amide 1 provided a useful model system for studying the complex relationship between morphology, experimental parameters, solvent, and the phenomenon of organogelation. The presence of solvents in the solid forms of 1 along with crystallization behavior suggested solvate formation and polymorphic behavior. Experiments Forty solid state- and xerogel samples of 1 formed in organic solvents and in three categories of experimental conditions were analyzed with single crystal X-ray diffraction (XRD), powder X-ray diffraction (PXRD), Raman microscopy, and attenuated total reflection Fourier-transform infr…

Low-temperature metastabilization of tetragonal V+4-containing ZrO2 solid solutions

2001

Abstract The formation and characterization of tetragonal vanadium–zirconia solid solutions with different vanadium contents have been investigated. Vanadium–zirconia precursors were prepared by gelling mixtures of zirconium n-propoxide and vanadyl acetylacetonate, and studied over the range of temperature up to the tetragonal–monoclinic phase transformation. The formation of the tetragonal phase has been investigated by X-ray powder diffraction (XRD). It was found that it took place after annealing around 450°C for all specimens independently of the vanadium loading. In contrast, the temperature for the subsequent tetragonal to monoclinic transformation was dependent on the nominal vanadiu…

Freeze-dried precursor-based synthesis of new polymetallic oxynitrides, V1−u−zCruMoz(OxNy),V1−u−zCruWz(OxNy), Cr1−u−zMouWz(OxNy) (u, z=0.2, 0.33, 0.4…

2005

Abstract Interstitial polymetallic oxynitrides in the solid solution series V 1− u − z Cr u Mo z (O x N y ), V 1− u − z Cr u W z (O x N y ) and Cr 1− u − z Mo u W z (O x N y ) ( u , z  = 0.2, 0.33, 0.4, 0.6, u  +  z z Cr z Mo z W z (O x N y ) ( z  = 0.25) composition, can be obtained by ammonolysis of precursors resulting from the freeze-drying of aqueous solutions of the simple metal salts NH 4 VO 3 , (NH 4 ) 2 CrO 4 , (NH 4 ) 6 Mo 7 O 24 ·4H 2 O and (NH 4 ) 6 W 12 O 39 ·18H 2 O. A study of the influence of the preparative variables on the outcomes of this procedure is presented. Compounds in the V 1− u − z Cr u Mo z (O x N y ) series have been prepared as single phases by direct ammonolys…