Oxygen Stoichiometry and Ordering in HTSC and Other Perovskite-Like Solids

1989 ◽  
Vol 156 ◽  
Author(s):  
Miguel Angel Alario-Franco
Keyword(s):  
Oxidation State ◽  
Oxygen Vacancies ◽  
The Other ◽  
Oxidation States ◽  
Oxygen Stoichiometry ◽  
Tetrahedral Coordination ◽  
Subsequent Work ◽  
Ordered Phases ◽  
Cation Coordination ◽  
Marked Tendency

ABSTRACTAs long ago remarked by WADSLEY, perovskite-like solids have a clear tendency to be non-stoichiometric and both the geometrical requirements of cation coordination and the oxidation state can control the way in which non-stoichiometry is accommodated.For example, in the case of iron, which shows a particular preference for coexisting octaedral and tetrahedral coordination and in which oxidation states ranging formally from 2 + to 4 + are common in oxides, a Family of Phases AnFenO3n−1, has been described. It includes the members n=2,3,4 and ∞. When the stoichiometries are different from these integral n values, disordered 1−D intergrowthhs are observed. Subsequent work has shown that all the intermediate compositions, whether ordered or disordered in 1−D, can still become non-stoichiometric by oxidation at high temperatures (T>1200°C in air) and this originates the formation of 3D microdomains. Of these, up to nine different sets have been shown to coexist in the same crystal.Similarly, the copper based HTSC, which have a lot in common with perovskite, have shown a marked tendency for being oxygen deficient. In particular, Ybacuo, Ba2YCu3O7±6 has been shown to exist in a wide oxygen range extending from, at least RO7.2 to RO6 (R<>Ba2YCu3). Within that range, and in spite of an apparent structurally monophasic, and thermodynamically bivariant, behaviour, a succesion of ordered states of the oxygen vacancies in 1,2 and 3 dimensions has been found. This, again, suggests the existence of intermediate ordered phases which, on the other hand, can also be non-stoichiometric. Results of our work along these lines is presented and discussed.

scholarly journals Selenium– and tellurium–halogen reagents

2018 ◽  
Vol 3 (12) ◽  
Author(s):  
Tristram Chivers ◽  
Risto S. Laitinen
Keyword(s):  
Oxidation State ◽  
Halogen Bond ◽  
The Other ◽  
Oxidation States ◽  
Alkyl Aryl ◽  
Organic Selenium ◽  
Formal Oxidation State ◽  
Wide Range ◽  
Inorganic And Organic

Abstract Selenium and tellurium form binary halides in which the chalcogen can be in formal oxidation states (IV), (II) or (I). They are versatile reagents for the preparation of a wide range of inorganic and organic selenium and tellurium compounds taking advantage of the reactivity of the chalcogen–halogen bond. With the exception of the tetrafluorides, the tetrahalides are either commercially available or readily prepared. On the other hand, the low-valent species, EX2 (E = Se, Te; X = Cl, Br) and E2X2 (E = Se, Te; X = Cl, Br) are unstable with respect to disproportionation and must be used as in situ reagents. Organoselenium and tellurium halides are well-known in oxidation states (IV) and (II), as exemplified by REX3, R2EX2 and REX (R = alkyl, aryl; E = Se, Te; X = F, Cl, Br, I); mixed-valent (IV/II) compounds of the type RTeX2TeR are also known. This chapter surveys the availability and/or preparative methods for these widely used reagents followed by examples of their applications in synthetic inorganic and organic selenium and tellurium chemistry. For both the binary halides and their organic derivatives, the discussion is subdivided according to the formal oxidation state of the chalcogen.

scholarly journals Influence of Physicochemical Properties and Parent Material on Chromium Fractionation in Soils

Processes ◽  
2021 ◽  
Vol 9 (6) ◽  
pp. 1073
Author(s):  
Claudia Campillo-Cora ◽  
Laura Rodríguez-González ◽  
Manuel Arias-Estévez ◽  
David Fernández-Calviño ◽  
Diego Soto-Gómez
Keyword(s):  
Physicochemical Properties ◽  
Contaminated Soils ◽  
Research Work ◽  
Parent Material ◽  
The Other ◽  
Oxidation States ◽  
Diethylenetriaminepentaacetic Acid ◽  
Remediation Strategies ◽  
Exchangeable Aluminum ◽  
Efficient Extraction

Chromium is an element that possess several oxidation states and can easily pass from one to another, so its behavior in soils is very complex. For this reason, determining its fate in the environment can be difficult. In this research work we tried to determine which factors affect the chromium fractionation in natural soils, conditioning chromium mobility. We paid special attention to the parent material. For this purpose, extraction experiments were carried out on spiked soils incubated for 50–60 days, using H2O, CaCl2 and diethylenetriaminepentaacetic acid (DTPA). The most efficient extraction rate in all soils was achieved using water, followed by CaCl2 and DTPA. We obtained models with an adjusted R2 of 0.8097, 0.8471 and 0.7509 for the H2O Cr, CaCl2 Cr and DTPA Cr respectively. All models were influenced by the amount of chromium added and the parent material: amphibolite and granite influenced the amount of H2O Cr extracted, and schist affected the other two fractions (CaCl2 and DTPA). Soil texture also played an important role in the chromium extraction, as well as the amounts of exchangeable aluminum and magnesium, and the bioavailable phosphorus. We concluded that it is possible to make relatively accurate predictions of the behavior of the different Cr fractions studied, so that optimized remediation strategies for chromium-contaminated soils can be designed on the basis of a physicochemical soil characterization.

Preparation and Characterization of Ni-Containing Aluminophosphate Molecular Sieves

2011 ◽  
Vol 418-420 ◽  
pp. 617-620
Author(s):  
Ying Sun ◽  
Lan Ying Ge
Keyword(s):  
Oxidation State ◽  
Molecular Sieves ◽  
Molecular Sieve ◽  
Crystalline Form ◽  
Spectroscopic Techniques ◽  
Tetrahedral Coordination ◽  
Tetrahedral Geometry ◽  
Nickel Ions ◽  
Aluminophosphate Molecular Sieves

Aluminophosphate molecular sieve and Ni(II)-containing APO-5 materials were synthesized hydrothermally and characterized by various analytical and spectroscopic techniques. It indicates that the nickel ions with a divalent oxidation state can incorporate into the tetrahedral coordination in mesoporous aluminophosphate very well. The better crystallizing temperature is explored. A stronger crystalline form is obtained with the addition of HF. Further, microporous aluminophosphate molecular sieves and Ni(II) ions remain in a tetrahedral geometry even after calcination at 550 °C.

Stable copernicium hexafluoride (CnF6) with an oxidation state of +VI

2021 ◽  
Author(s):  
Shuxian Hu ◽  
Wenli Zou
Keyword(s):  
Oxidation State ◽  
Oxidation States ◽  
Group 12

As the heaviest group 12 element known now, copernicium (Cn) often presents the oxidation states of +I, +II, and rarely +IV as in its homologue mercury. In this work we...

The Defect Structure of BaTiO3 Thin Films

1993 ◽  
Vol 310 ◽  
Author(s):  
L.A. Wills ◽  
B.W. Wessels
Keyword(s):  
Thin Films ◽  
Cross Section ◽  
Defect Structure ◽  
Oxygen Vacancies ◽  
Vacuum Annealing ◽  
Deep Level ◽  
Energy Levels ◽  
The Other ◽  
Optical Cross Section ◽  
Impurity Defects

AbstractThe defect structure of BaTiO3 thin films grown on (100) Si was examined using transient photocapacitance spectroscopy. The concentration, optical cross section and associated energy levels of both native and impurity defects in as-grown and annealed BaTiO3 films were evaluated. Deep level defects withpeak energies of Ev+1.8, Ev+2.4, Ev+2.7, Ev+3.0-3.1 and Ev+3.2-3.3 eV were observed in the as-grown films. Upon vacuum annealing, the concentration of the traps at Ev+3.0 and Ev+3.2 eV increased while the concentration of the traps at Ev+ 1.8 and Ev+2.4 eV decreased. The levels at Ev+3.0-3.1 and Ev+3.2-3.3 eV are attributed to oxygen vacancies. The other levels are tentatively ascribed to Fe and Fe related defects.

Sorption of trivalent plutonium onto UO2 and the effect of the solid phase on the Pu oxidation state

2005 ◽  
Vol 93 (6) ◽  
Author(s):  
Mattias Olsson ◽  
Henrik Glänneskog ◽  
Anna-Maria Jakobsson ◽  
Hans Nilsson ◽  
Yngve Albinsson
Keyword(s):  
Oxidation State ◽  
Solid Phase ◽  
Oxidation States

SummaryA problem with plutonium in sorption studies is its tendency to occur in a mix of oxidation states. This work was a study of the sorption of plutonium on the solid phase UOA comparison is made between the sorption of Th(IV), Pu(III) and Co(II) on UO

scholarly journals Probing the variability in oxidation states of magnetite nanoparticles by single-particle spectroscopy

2018 ◽  
Vol 6 (4) ◽  
pp. 875-882 ◽  
Author(s):  
A. Fraile Rodríguez ◽  
C. Moya ◽  
M. Escoda-Torroella ◽  
A. Romero ◽  
A. Labarta ◽  
...  
Keyword(s):  
Oxidation State ◽  
Absorption Spectroscopy ◽  
Magnetite Nanoparticles ◽  
Single Particle ◽  
Cation Distribution ◽  
Oxidation States ◽  
Magnetic Response ◽  
X Ray ◽  
Single Particle Spectroscopy ◽  
X Ray Absorption

Single-particle X-ray absorption spectroscopy reveals that the oxidation state and cation distribution of individual magnetite nanoparticles may be largely heterogeneous even when the macroscopic structural and magnetic response of the ensembles is uniform.

The grammaticalization of SIC

2021 ◽  
pp. 350-369
Author(s):  
Verner Egerland
Keyword(s):  
Old French ◽  
The Other ◽  
Functional Elements ◽  
Subsequent Work ◽  
The Third ◽  
Sequence Of Events

The Old Romance continuations of Latin sic, such as Old French si and Old Italian sì, involve four different functions, all of which are referred to here as sic. The first one, which is closest to the original Latin usage, is that of a lexical adverbial, while the other three are functional elements introducing main clauses: the second sic follows elements preposed to the verb, the third one introduces clauses in a narrative sequence of events, while the fourth usage of sic has been described as a ‘weak consequential’ (Salvi 2002) . In this article, it is shown that these instantiations of sic in Old Romance, and in particular the third one, are parallel to the grammaticalized usages of svá in Modern Scandinavian. Furthermore, it is argued that the distribution of these functional elements in Old Romance, here represented by French and Italian, as well as Modern Scandinavian, represented by Swedish, can be successfully accounted for in a theory of syntax that incorporates certain notions of ‘narrative’, building on intuitions originating in Labov (1972) and subsequent work.

A STRUCTURAL CHEMICAL MODEL FOR HIGH Tc CERAMIC SUPERCONDUCTORS

1987 ◽  
Vol 01 (07n08) ◽  
pp. 275-288 ◽  
Author(s):  
S.R. OVSHINSKY ◽  
S.J. HUDGENS ◽  
R.L. LINTVEDT ◽  
D.B. RORABACHER
Keyword(s):  
Electronic Properties ◽  
Oxygen Vacancies ◽  
Oxygen Removal ◽  
Bose Condensation ◽  
Oxidation States ◽  
Chemical Model ◽  
Electrically Conductive ◽  
High Tc ◽  
Ceramic Superconductors ◽  
Mixed Oxidation

A structual chemical model for high Tc ceramic superconductors is proposed in which carriers pairs, coupled through a superexchange process, undergo Bose condensation. In the Y-Ba-Cu-O system, Cu atoms on “chain” sites and “sheet” sites are initially assigned formal oxidation states of +3 and +2, respectively, and “sheet”/“chain” interactions are then introduced to bring about the electrically conductive mixed oxidation state. This model explains the presence of labile oxygen in the “chain” structures, describes the structure of deoxygenated phases exhibiting ordered oxygen vacancies in the “chains”, and allows interpretation of the effects of oxygen removal on magnetic and electronic properties of the material.

scholarly journals Atomic-scale determination of spontaneous magnetic reversal in oxide heterostructures

2019 ◽  
Vol 116 (21) ◽  
pp. 10309-10316 ◽  
Author(s):  
M. Saghayezhian ◽  
Summayya Kouser ◽  
Zhen Wang ◽  
Hangwen Guo ◽  
Rongying Jin ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Charge Transfer ◽  
Oxidation State ◽  
Density Functional ◽  
Magnetic Hysteresis ◽  
Atomic Scale ◽  
Oxidation States ◽  
Internal Electric Field ◽  
Magnetic Reversal ◽  
State Changes

Interfaces between transition metal oxides are known to exhibit emerging electronic and magnetic properties. Here we report intriguing magnetic phenomena for La2/3Sr1/3MnO3 films on an SrTiO3 (001) substrate (LSMO/STO), where the interface governs the macroscopic properties of the entire monolithic thin film. The interface is characterized on the atomic level utilizing scanning transmission electron microscopy and electron energy loss spectroscopy (STEM-EELS), and density functional theory (DFT) is employed to elucidate the physics. STEM-EELS reveals mixed interfacial stoichiometry, subtle lattice distortions, and oxidation-state changes. Magnetic measurements combined with DFT calculations demonstrate that a unique form of antiferromagnetic exchange coupling appears at the interface, generating a novel exchange spring-type interaction that results in a remarkable spontaneous magnetic reversal of the entire ferromagnetic film, and an inverted magnetic hysteresis, persisting above room temperature. Formal oxidation states derived from electron spectroscopy data expose the fact that interfacial oxidation states are not consistent with nominal charge counting. The present work demonstrates the necessity of atomically resolved electron microscopy and spectroscopy for interface studies. Theory demonstrates that interfacial nonstoichiometry is an essential ingredient, responsible for the observed physical properties. The DFT-calculated electrostatic potential is flat in both the LSMO and STO sides (no internal electric field) for both Sr-rich and stoichiometric interfaces, while the DFT-calculated charge density reveals no charge transfer/accumulation at the interface, indicating that oxidation-state changes do not necessarily reflect charge transfer and that the concept of polar mismatch is not applicable in metal−insulator polar−nonpolar interfaces.

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