A Magnetically Ordered Non-Stoichiometric Zinc Ferrite for the Oxidative Dehydrogenation Reactions.

2001 ◽  
Vol 676 ◽  
Author(s):  
J. A. Toledo ◽  
N. Nava ◽  
X. C. Sun ◽  
X. Bokhimi
Keyword(s):  
Catalytic Activity ◽  
Oxidative Dehydrogenation ◽  
Spinel Structure ◽  
Zinc Ferrite ◽  
Room Temperature ◽  
Annealing Temperature ◽  
Octahedral Sites ◽  
Tetrahedral Sites ◽  
Dehydrogenation Reactions ◽  
Hydrothermal Reduction

ABSTRACTZnFe2O4 nanoparticles were prepared by hydrothermal reduction approach. A considerable amount of α-Fe2O3 was segregated in the as-synthesized sample, which diffused into the tetrahedral and octahedral sites of the ZnFe2O4 spinel structure with increasing the annealing temperature. The introduction of Fe3+ into the tetrahedral positions was observed by Mössbauer spectra. Magnetization measurements showed an unusual ferrimagnetic behavior of the ZnFe2O4 phase, even at room temperature, confirming the introduction of Fe3+ into the tetrahedral sites of the spinel structure. Catalytic activity measured in the oxidative dehydrogenation of 1-butene reaction increased with increasing annealing temperature, indicating that those interactions of Fe3+ in tetrahedral and octahedral positions also promotes the activity and selectivity to butadiene formation.

A Generalized Approach to Adjust the Catalytic Activity of Borocarbonitride for Alkane Oxidative Dehydrogenation Reactions

2021 ◽  
Author(s):  
Xuefei Zhang ◽  
Xueya Dai ◽  
Kuang-Hsu Wu ◽  
Bingjian Su ◽  
Jinming Chen ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Oxidative Dehydrogenation ◽  
Dehydrogenation Reactions

MAGNETIC STRUCTURE OF ZINC-FERRITE APPROACHING NANOMETER SIZES

2001 ◽  
Vol 15 (24n25) ◽  
pp. 3312-3316 ◽  
Author(s):  
A. H. MORRISH ◽  
Z. W. LI ◽  
J. Z. JIANG
Keyword(s):  
Magnetic Structure ◽  
Zinc Ferrite ◽  
Bulk Material ◽  
Spinel Ferrite ◽  
Average Particle Size ◽  
Average Particle ◽  
Octahedral Sites ◽  
Tetrahedral Sites ◽  
Zn Ferrite ◽  
Nanometer Particles

A unit cell of a spinel ferrite is just under 1 nm, actually about 0.8 nm. Particles approaching this size can be expected to possess properties that differ from the bulk material. Bulk polycrystalline Zn-ferrite ( ZnFe2O4 ) has been ball milled; after 50 h the average particle size is about 13 nm. The 57 Fe Mössbauer spectra at T = 4.2 K with and without a large (52 kOe) magnetic field applied longitudinally establish that the antiferromagnetic structure of the bulk has become ferrimagnetic in the ten nanometer particles via the transfer of some Zn cations from the A (tetrahedral) sites to the B (octahedral) sites. In addition, there is a large non-collinearity in the magnetic structure.

Visible and near‐infrared spectra of rocks from chromium‐rich areas

Geophysics ◽  
1979 ◽  
Vol 44 (4) ◽  
pp. 820-825 ◽  
Author(s):  
G. R. Hunt ◽  
J. C. Wynn
Keyword(s):  
Spinel Structure ◽  
Near Infrared ◽  
Ultramafic Rocks ◽  
Ferrous Ions ◽  
Mafic Rocks ◽  
Typical Situation ◽  
Octahedral Sites ◽  
Tetrahedral Sites ◽  
Near Infrared Spectra ◽  
Bidirectional Reflection

Bidirectional reflection spectra are presented from 0.35 to 2.5 μm for a suite of ultramafic rocks collected from chromium‐rich areas in southwestern Oregon and northwestern California. Features due to the presence of chromium are entirely absent from these spectra. However, the massive chromite samples are distinguishable from all others on the basis of spectral features produced by absorptions in ferrous ions located in unique tetrahedral sites afforded by the chromite spinel structure. Chromite samples are also distinguishable by their lack of specific absorption near 1.0 μm, normally caused by ferrous ions located in octahedral sites; absorption in the 1.0 μm region is the typical situation found in ultramafic and mafic rocks. The potential usefulness for remote‐sensing purposes of this unusual spectral regime is suggested.

Cr3+-substitution induced structural reconfigurations in the nanocrystalline spinel compound ZnFe2O4 as revealed from X-ray diffraction, positron annihilation and Mössbauer spectroscopic studies

RSC Advances ◽  
2015 ◽  
Vol 5 (80) ◽  
pp. 64966-64975 ◽  
Author(s):  
Rahul Mundiyaniyil Thankachan ◽  
Jincemon Cyriac ◽  
B. Raneesh ◽  
Nandakumar Kalarikkal ◽  
D. Sanyal ◽  
...  
Keyword(s):  
Positron Annihilation ◽  
Spinel Structure ◽  
Zinc Ferrite ◽  
Spectroscopic Studies ◽  
X Ray Diffraction ◽  
X Ray ◽  
Tetrahedral Sites ◽  
Normal Spinel

In an earlier work, the substitution of Zn2+ ions at the tetrahedral sites of nanocrystalline zinc ferrite (ZnFe2O4) by Ni2+ ions had been observed to cause a transformation from the normal spinel structure to the inverse one.

scholarly journals Epitaxial growth and structure of cobalt ferrite thin films with large inversion parameter on Ag(001)

2019 ◽  
Vol 75 (1) ◽  
pp. 8-17 ◽  
Author(s):  
Maurizio De Santis ◽  
Aude Bailly ◽  
Ian Coates ◽  
Stéphane Grenier ◽  
Olivier Heckmann ◽  
...  
Keyword(s):  
Photoelectron Spectroscopy ◽  
Spinel Structure ◽  
Room Temperature ◽  
Cobalt Ferrite ◽  
Ex Situ ◽  
X Ray Diffraction ◽  
Step Method ◽  
X Ray ◽  
Octahedral Sites

Cobalt ferrite ultrathin films with the inverse spinel structure are among the best candidates for spin filtering at room temperature. High-quality epitaxial CoFe2O4 films about 4 nm thick have been fabricated on Ag(001) following a three-step method: an ultrathin metallic CoFe2 alloy was first grown in coherent epitaxy on the substrate and then treated twice with O2, first at room temperature and then during annealing. The epitaxial orientation and the surface, interface and film structure were resolved using a combination of low-energy electron diffraction, scanning tunnelling microscopy, Auger electron spectroscopy and in situ grazing-incidence X-ray diffraction. A slight tetragonal distortion was observed, which should drive the easy magnetization axis in-plane due to the large magneto-elastic coupling of such a material. The so-called inversion parameter, i.e. the Co fraction occupying octahedral sites in the ferrite spinel structure, is a key element for its spin-dependent electronic gap. It was obtained through in situ resonant X-ray diffraction measurements collected at both the Co and Fe K edges. The data analysis was performed using FDMNES, an ab initio program already extensively used to simulate X-ray absorption spectroscopy, and shows that the Co ions are predominantly located on octahedral sites with an inversion parameter of 0.88 (5). Ex situ X-ray photoelectron spectroscopy gives an estimation in accordance with the values obtained through diffraction analysis.

Inversion parameter of the CoGa2O4 spinel determined from single-crystal X-ray data

2006 ◽  
Vol 62 (5) ◽  
pp. i109-i111 ◽  
Author(s):  
Akihiko Nakatsuka ◽  
Yuya Ikeda ◽  
Noriaki Nakayama ◽  
Tadato Mizota
Keyword(s):  
Single Crystal ◽  
Single Crystals ◽  
Diffraction Data ◽  
Spinel Structure ◽  
Room Temperature ◽  
Structural Formula ◽  
X Ray Diffraction ◽  
X Ray ◽  
Octahedral Sites ◽  
Normal Spinel

Single crystals of cobalt digallium tetraoxide, CoGa2O4, have been grown by cooling slowly a 1:1 mixture of CoO and Ga2O3 from 1473 K to room temperature under the presence of a PbF2 flux. The compound crystallizes with the cubic spinel structure (space group Fd\overline{3}m). The occupancy refinement based on single-crystal X-ray diffraction data shows CoGa2O4 to be a largely normal spinel with an inversion parameter of 0.575 (4), resulting in a structural formula of IV(Co0.425Ga0.575)VI[Co0.575Ga1.425]O4, where IV() and VI[] represent the tetrahedral and the octahedral sites, respectively.

scholarly journals FTIR and Electrical Study of Dysprosium Doped Cobalt Ferrite Nanoparticles

2014 ◽  
Vol 2014 ◽  
pp. 1-10 ◽  
Author(s):  
Hemaunt Kumar ◽  
Jitendra Pal Singh ◽  
R. C. Srivastava ◽  
P. Negi ◽  
H. M. Agrawal ◽  
...  
Keyword(s):  
Dielectric Constant ◽  
Spinel Structure ◽  
Room Temperature ◽  
Cobalt Ferrite ◽  
Spinel Phase ◽  
Ferrite Nanoparticles ◽  
Absorption Bands ◽  
Octahedral Sites ◽  
Electrical Study

We have studied the role of Dy3+ doping on the XRD, TEM, FTIR, and dielectric and electrical properties of CoFe2O4 at room temperature. Cubic spinel phase of CoFe2−xDyxO4 (x = 0.00, 0.05, 0.10, and 0.15) was synthesized by using different sintering temperatures (300, 500, 700, and 900°C). The two absorption bands ν1 and ν2 are observed in Fourier transform infrared spectroscopy (FTIR) spectra corresponding to the tetrahedral and octahedral sites, which show signature of spinel structure of the sample. For the sample sintered at 300°C, the dielectric constant is almost unchanged with the frequency at the particular concentrations of x = 0.00 and 0.05. Similar result is obtained for the sample sintered at 500°C (x = 0.10, 0.15), 700°C (x = 0.05, 0.10, and 0.15), and 900°C (x = 0.05, 0.10). An increase in the dielectric constant was observed for the undoped cobalt ferrite sintered at 500, 700, and 900°C. The values of electrical resistivity of the materials vary from ~105 to 109 Ω-cm.

Electron Crystallography of Room Temperature Charge Ordering in Fe3O4

2000 ◽  
Vol 6 (4) ◽  
pp. 400-402
Author(s):  
M.L. Rudee ◽  
David J. Smith ◽  
D.T. Margulies
Keyword(s):  
Thin Films ◽  
Room Temperature ◽  
Tetrahedral Site ◽  
Charge Ordering ◽  
Electron Crystallography ◽  
Octahedral Sites ◽  
Tetrahedral Sites ◽  
Unknown Form ◽  
Diffraction Patterns ◽  
Best Fit

Abstract A previously unknown form of charge ordering has been observed in dislocation free thin films of magnetite, Fe3O4. This charge ordering exists on tetrahedral sites and is unrelated to the well known low temperature ordering on octahedral sites that occurs below 120K. From modeling of electron diffraction patterns we deduce that the best fit to the observed diffraction patterns was obtained by reducing the scattering power on one tetrahedral site per unit cell by about 80%.

Electron Crystallography of Room Temperature Charge Ordering in Fe3O4

2000 ◽  
Vol 6 (4) ◽  
pp. 400-402 ◽  
Author(s):  
M.L. Rudee ◽  
David J. Smith ◽  
D.T. Margulies
Keyword(s):  
Thin Films ◽  
Room Temperature ◽  
Tetrahedral Site ◽  
Charge Ordering ◽  
Electron Crystallography ◽  
Octahedral Sites ◽  
Tetrahedral Sites ◽  
Unknown Form ◽  
Diffraction Patterns ◽  
Best Fit

AbstractA previously unknown form of charge ordering has been observed in dislocation free thin films of magnetite, Fe3O4. This charge ordering exists on tetrahedral sites and is unrelated to the well known low temperature ordering on octahedral sites that occurs below 120K. From modeling of electron diffraction patterns we deduce that the best fit to the observed diffraction patterns was obtained by reducing the scattering power on one tetrahedral site per unit cell by about 80%.

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