Nonstoichiometric structures during dehydroxylation of goethite

1989 ◽  
Vol 189 (3-4) ◽  
Author(s):  
Emilia Wolska ◽  
Udo Schwertmann
Keyword(s):  
Crystal Lattice ◽  
Infrared Spectra ◽  
Chemical Formula ◽  
Oh Groups ◽  
X Ray ◽  
Lattice Constants ◽  
General Chemical ◽  
Iron Deficient ◽  
Oxygen Anions ◽  
Integrated Intensities

AbstractThermal dehydration of goethite (The variations of band positions in the infrared spectra and the specific changes in relative integrated intensities of X-ray lines with the increase of dehydration temperature suggested that OH-groups replace oxygen anions in the hematite crystal lattice, while the electroneutrality is preserved by the cation vacancies.Comparison of integrated intensities observed with intensities calculated on this assumption fully confirms that the hematite-like phase is an iron deficient species with a general chemical formulaThe accurate measurements of lattice constants reveal that while the crystallographic

scholarly journals Mathematical modeling of perspective structures of metal oxides

2020 ◽  
Vol 22 (4) ◽  
pp. 268-271
Author(s):  
P. A. Sechenykh
Keyword(s):  
Metal Oxides ◽  
Crystal Lattice ◽  
Structural Characteristics ◽  
Elementary Cell ◽  
Group Symmetry ◽  
Cubic Symmetry ◽  
Lattice Constants ◽  
General Chemical ◽  
Crystalline Metal ◽  
Chemical Formulas

Information about the structure and properties of materials is especially important when working with micro-and nanoscale objects due to the high complexity of their obtaining. This makes it relevant to use computer modeling to predict the required characteristics of materials. Electronic, magnetic, mechanical, and other properties of crystalline substances are determined by their structure-the periodicity of the lattice and the symmetry of the unit cell. This article discusses metal oxides with the general chemical formulas MeO (metals: Ca, Cd, Mg), MeO2 (metals: Hf, Ce, Zr), Me2O3 (metals: Er, Nd, Sc, Mn, Tl) and Me3O4 (using Fe as an example) and a cubic symmetry type crystal lattice — structural types NaCl (rock salt), Fluorite, Bixbyite, Spinel accordingly. The paper describes the model of ion-atomic radii, which is widely used in the modeling of crystalline metal oxides. The application of the annealing simulation algorithm for calculating the metric parameters of the compounds under consideration is shown. The software implementation of the algorithm presented in this paper allows us to determine the coordinates of the atoms that are included in the elementary cell of the crystal lattice, calculate the lattice constant and the density of the packing of atoms in the crystal cell using the specified chemical formula and the space group symmetry. These structural characteristics can be used as input parameters for determining electronic, magnetic, and other properties. The article compares the values of lattice constants obtained as a result of modeling with experimental data.

Crystal Structure of ζ2' Martensite in Au-49.5at%Cd Alloy

1991 ◽  
Vol 246 ◽  
Author(s):  
Yutaka Emura ◽  
Takuya Ohba ◽  
Kazuhiro Otsuka
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
Crystal Lattice ◽  
Least Squares ◽  
Least Squares Method ◽  
Diffraction Method ◽  
X Ray Diffraction ◽  
Full Matrix ◽  
X Ray ◽  
Lattice Constants

AbstractCrystal structure of the ζ2' martensite in a Au-49.5at%Cd ally has been analyzed by the single crystal x-ray diffraction method. The crystal lattice was trigonal and the lattice constants were a:0.8095(3) and c=o.57940(6) nm. There were 18 atoms in a unit cell. The space group was P3, which was different from that previously determined by Vatanayon and Hehemann. The structure was refined by the full matrix least squares method to a final R factor of 7.8% and a weighted R factor of 4.1%.

scholarly journals Fabrication and study of the structural and spectral properties of the composites (y) Mn0.6 Zn0.4 Fe2O4 + (1-y) PZT prepared by the powder technology method

2019 ◽  
Vol 23 (10) ◽  
pp. 81
Author(s):  
Ismaeal K. Jasem1 ◽  
Abdul-Samee Fawzi Abdul-Aziz2 ◽  
Nibras Malallah Ibrahim1
Keyword(s):  
Particle Size ◽  
Apparent Density ◽  
Spectral Properties ◽  
Annealing Temperature ◽  
Powder Technology ◽  
Chemical Formula ◽  
X Ray Diffraction ◽  
X Ray ◽  
Lattice Constants ◽  
Ray Density

Ferrite-ferroelectric composites holds following chemical formula (y) Mn0.6 Zn0.4 Fe2O4 + (1-y) PZT with different weight rations (y=0.15, 0.30 and 0.45) are prepared by the powder technology method at annealing temperature (1000 °C) for (12hrs). The structural properties are also studied representing by the lattice constants (a, c), particle size (Dt), apparent density (ρa), and X-ray density (ρx). It has been shown that increasing the concentration of the ferrite phase contributes to an increase in the lattice constant, apparent density and X-ray density which in turn contribute in decreasing porosity that plays a role in improving the physical properties of the samples as well as the weight ratios of the mixture after the final sintering with reference to x-ray diffraction technique. In addition, the spectral properties were also studied represented by the vibration force constant and regions of optical absorption in terms of IR technique.     http://dx.doi.org/10.25130/tjps.23.2018.174  

A reinvestigation of mayenite from the type locality, the Ettringer Bellerberg volcano near Mayen, Eifel district, Germany

2012 ◽  
Vol 76 (3) ◽  
pp. 707-716 ◽  
Author(s):  
E. V. Galuskin ◽  
J. Kusz ◽  
T. Armbruster ◽  
R. Bailau ◽  
I. O. Galuskina ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Raman Spectroscopy ◽  
Single Crystal ◽  
Electron Microprobe ◽  
Partial Substitution ◽  
Chemical Formula ◽  
Oh Groups ◽  
X Ray ◽  
Ray Methods ◽  
Original Formula

AbstractNew electron-microprobe analyses of mayenite from the Ettringer Bellerberg volcano near Mayen in the Eifel district, Germany have high Cl contents and Raman spectroscopy indicates the presence of OH groups. Neither of these components is included in the generally accepted chemical formula, Ca12Al14O33. A refinement of the crystal structure by single-crystal X-ray methods reveals a previously unrecognized partial substitution. The O2 site which forms one of the apices of an AlO4 tetrahedron (with 3 × O1 sites) is replaced by 3 × O2a sites, which change the coordination of the central Al atom from tetrahedral to octahedral. This substitution is related to partial hydration of Ca12Al14O32Cl2 according to the isomorphic scheme (O2– + Cl–) ↔ 3(OH)–. The revised composition of Eifel mayenite is best described by the formula Ca12Al14O32–xCl2–x(OH)3x (x ∼0.75); the original formula, Ca12Al14O33, is inadequate. The analysed mineral can be considered to consist of endmember Ca12Al14O32Cl2 (62.5 mol.%) and endmember Ca12Al14O30(OH)6 (37.5 mol.%).

The mystery of birefringent garnet: is the symmetry lower than cubic?

2013 ◽  
Vol 28 (4) ◽  
pp. 281-288 ◽  
Author(s):  
Sytle M. Antao
Keyword(s):  
Crystal Structure ◽  
Phase Transitions ◽  
Rietveld Method ◽  
Chemical Formula ◽  
X Ray Diffraction ◽  
X Ray ◽  
Garnet Phase ◽  
Cubic Phases ◽  
General Chemical ◽  
Monochromatic Synchrotron

The cause of birefringence in several garnet-group minerals with general chemical formula, [8]X3[6]Y2[4]Z3[4]O12, which was observed over 100 years ago, is unknown, although many different reasons were proposed, including symmetry lower than cubic. In this study, electron microprobe analyses (EMPA) were obtained for a Ti-rich andradite, ideally Ca3(Fe23+)Si3O12, from Magnet Cove, Arkansas, USA, and the results show that the sample is inhomogeneous with two distinct compositions. The crystal structure was refined by the Rietveld method, cubic space group $Ia\overline 3 d$, and monochromatic synchrotron high-resolution powder X-ray diffraction (HRPXRD) data, which shows a mixture of three distinct cubic phases that are intergrown together and cause birefringence because of strain arising from small structural mismatch. This mixture of three cubic phases was not observed by any other experimental technique. These results have many implications, including garnet phase transitions from cubic to lower symmetry in the mantle, which has important geophysical consequences.

scholarly journals CONTRIBUTION CONCERNING THE PROBLEM OF THE INTRAMOLECULAR HYDROGEN BONDS IN ORTHO HALOPHENOLS

1963 ◽  
Vol 41 (9) ◽  
pp. 2240-2244 ◽  
Author(s):  
Henriette Bourassa-Bataille ◽  
P. Sauvageau ◽  
C. Sandorfy
Keyword(s):  
Carbon Tetrachloride ◽  
Hydrogen Bonds ◽  
Infrared Spectra ◽  
Alternative Methods ◽  
Intramolecular Hydrogen Bonds ◽  
Oh Groups ◽  
Integrated Intensities ◽  
Intramolecular Hydrogen ◽  
Hydrogen Bonded

The infrared spectra of the four ortho halophenols were measured in carbon tetrachloride solutions containing variable amounts of ether. The integrated intensities of the stretching band corresponding to the intermolecularly hydrogen-bonded OH groups were determined and plotted against ether concentration. From the curves obtained in this manner it was possible to deduce the relative strengths of the intramolecular hydrogen bonds which are present in these molecules. They are, in order of increasing strength: F < I < Br < Cl. This result is compared to others, published in the literature, obtained using alternative methods.

Size effect of the guest cation on the AlO4 framework in aluminate sodalite-type oxides M 8[Al12O24](SO4)2 (M = Sr2+ and Ca2+) in the I 43m phase

2021 ◽  
Vol 77 (2) ◽  
pp. 186-192
Author(s):  
Yuki Nakahira ◽  
Genta Kawamura ◽  
Toru Wakamatsu ◽  
Ichiro Terasaki ◽  
Hiroki Taniguchi ◽  
...  
Keyword(s):  
Probability Density ◽  
Probability Density Distribution ◽  
Chemical Formula ◽  
Ionic Radii ◽  
Interatomic Distances ◽  
Tetrahedral Framework ◽  
X Ray ◽  
General Chemical ◽  
The Ideal

Sr8[Al12O24](SO4)2 (SAS) and Ca8[Al12O24](SO4)2 (CAS) are members of the aluminate sodalite-type oxides with the general chemical formula M 8[Al12O24](XO4)2 (M 2+ is the guest cation and XO4 2− is the guest anion). To discuss the role of the guest cations (M 2+ = Sr2+ and Ca2+) on the rotation of AlO4 in the oxygen tetrahedral framework in the I 43m phase, the crystal structure parameters and the probability density function of the guest ions in SAS and CAS have been investigated via synchrotron radiation X-ray powder diffraction by considering Gram–Charlier expansions. The interatomic distances between the M 2+ and O2− ions evaluated from the maximum positions in the probability density distribution are almost equal to the sum of the ideal ionic radii of the M 2+ and O2− ions. This result suggests that the geometry of the AlO4 tetrahedral framework and the fluctuation of the guest ions are mainly caused by steric effects between the M 2+ and O2− ions.

X-ray Structure Refinement and Vibrational Spectroscopy of Ca8Gd2 (PO4)6 O2

2013 ◽  
Vol 12 (10) ◽  
pp. 719-726
Author(s):  
R. Ayadi ◽  
Mohamed Boujelbene ◽  
T. Mhiri
Keyword(s):  
Solid State ◽  
General Formula ◽  
Vibrational Spectroscopy ◽  
Powder Diffraction ◽  
Infrared Spectra ◽  
Solid State Reaction ◽  
Structure Refinement ◽  
Unit Cell ◽  
Cell Group ◽  
X Ray

The present paper is interested in the study of compounds from the apatite family with the general formula Ca10 (PO4)6A2. It particularly brings to light the exploitation of the distinctive stereochemistries of two Ca positions in apatite. In fact, Gd-Bearing oxyapatiteCa8 Gd2 (PO4)6O2 has been synthesized by solid state reaction and characterized by X-ray powder diffraction. The site occupancies of substituents is0.3333 in Gd and 0.3333 for Ca in the Ca(1) position and 0. 5 for Gd in the Ca (2) position.  Besides, the observed frequencies in the Raman and infrared spectra were explained and discussed on the basis of unit-cell group analyses.

STRUCTURAL EVOLUTION OF EXCEPTIONALLY IRON-DEFICIENT HEMATITE NANOCRYSTALS AS OBSERVED BY IN SITU SYNCHROTRON X-RAY DIFFRACTION

2019 ◽  
Author(s):  
Si Athena Chen ◽  
◽  
Peter Heaney ◽  
Jeffrey E. Post ◽  
Peter J. Eng ◽  
...  
Keyword(s):  
Structural Evolution ◽  
X Ray Diffraction ◽  
X Ray ◽  
Iron Deficient

Infrared spectroscopic study of the YPO4-YCrO4 system

1985 ◽  
Vol 50 (10) ◽  
pp. 2139-2145
Author(s):  
Alexander Muck ◽  
Eva Šantavá ◽  
Bohumil Hájek
Keyword(s):  
Spectroscopic Study ◽  
Infrared Spectra ◽  
Point Of View ◽  
Mixed Crystals ◽  
Crystal Symmetry ◽  
Infrared Spectroscopic Study ◽  
X Ray Diffraction ◽  
X Ray ◽  
Infrared Spectroscopic ◽  
Diffraction Patterns

The infrared spectra and powder X-ray diffraction patterns of polycrystalline YPO4-YCrO4 samples are studied from the point of view of their crystal symmetry. Mixed crystals of the D4h19 symmetry are formed over the region of 0-30 mol.% YPO4 in YCrO4. The Td → D2d → D2 or C2v(GS eff) correlation is appropriate for both PO43- and CrO43- anions.

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