THE ROLE OF OXYGEN IN YBa2Cu3O7−δ

1988 ◽  
Vol 02 (03n04) ◽  
pp. 379-391 ◽  
Author(s):  
JOHN B. GOODENOUGH ◽  
A. MANTHIRAM
Keyword(s):  
Oxygen Atom ◽  
Oxygen Partial Pressure ◽  
Basal Plane ◽  
Redox Reactions ◽  
Orthorhombic Phase ◽  
Near Neighbor ◽  
Oxidation States ◽  
Internal Electric Field ◽  
Phase 3

Five observations concerning the role of oxygen in the high-Tc superconductors YBa 2 Cu 3 O 7−δ are emphasized: (1) An internal electric field parallel to the c-axis constrains the redox reactions associated with the intercalation/disintercalation of oxygen primarily to the [ CuO 3−δ]3− layers located between Ba 2+ layers. (2) Intercalation of O 2− into the tetragonal YBa 2 Cu 3 O 6 phase results in an ordering onto one of the basal-plane axes of the Cu(1) layer, the b-axis of the orthorhombic phase. (3) Ordering between and within b-axis chains gives rise to discrete phases predicted to occur at O 6.875, O 6.75, O 6.5, O 6.25, and O 6.125. (4) An equilibrium oxidation state for the intercalation layer depends not only on the oxygen partial pressure and temperature, but also on the cations of the structure. (5) At higher oxidation states of the intercalation layer, any oxygen atom on the a-axis interacts with a near-neighbor oxygen on the b-axis to trap out holes in a peroxide ion ( O 2)2−.

scholarly journals Factors Affecting the Rate of Breast Cancer; Role of Heavy Metals

2020 ◽  
Vol 11 (3) ◽  
pp. 57-64
Author(s):  
Shabbir Hussain ◽  
Sumra Naseer ◽  
Muhammad Waqas ◽  
Samina Ashraf ◽  
Aisha Saddiqa ◽  
...  
Keyword(s):  
Breast Cancer ◽  
Redox Reactions ◽  
Chemical Structure ◽  
Epidemiologic Studies ◽  
Oxidation States ◽  
International Agency ◽  
Factors Affecting ◽  
Potential Risk Factors ◽  
Breast Cells

Breast cancer is caused by uncontrolled growth of breast cells. It is more common in women as compared tothat in men. The breast cancer may be interlinked with the drinking of alcohol, smoking, sex, hormonal therapy, obesity,family history and age. Various epidemiologic studies suggest the role of metals e.g., nickel (Ni), zinc (Zn), arsenic(As),selenium (Se)and cadmium (Cd)as potential risk factors in breast cancer. Humans are exposed to these metals bymeans of drinking water, food and air. The oxidative theory suspects that the complexes formed from these metals invivo, near the location of DNA, catalyze the redox reactions which results in oxidation of DNA. The metals like arsenic(As), chromium (Cr), aluminum (Al), cadmium (Cd) and chromium (Cr)which exist in trace amount are considered ascarcinogens for organisms by IARC (International Agency for Research on Cancer). The carcinogenicity of these metalsmainly depends upon their chemical structure and oxidation states.

Anti-toxicant Properties of Saffron and Relevance to Protection from Toxins and Drugs

2020 ◽  
Vol 16 (3) ◽  
pp. 265-283
Author(s):  
Kyriaki Hatziagapiou ◽  
George I. Lambrou
Keyword(s):  
Redox Reactions ◽  
Case Reports ◽  
Meta Analysis ◽  
Reactive Oxygen ◽  
Crocus Sativus ◽  
Protective Effects ◽  
Nitrogen Species ◽  
Eligibility Criteria ◽  
Crocus Sativus L

Background: Reactive oxygen species and reactive nitrogen species, which are collectively called reactive oxygen nitrogen species, are inevitable by-products of cellular metabolic redox reactions, such as oxidative phosphorylation in the mitochondrial respiratory chain, phagocytosis, reactions of biotransformation of exogenous and endogenous substrata in endoplasmic reticulum, eicosanoid synthesis, and redox reactions in the presence of metal with variable valence. Among medicinal plants there is a growing interest in Crocus sativus L. It is a perennial, stemless herb, belonging to Iridaceae family, cultivated in various countries such as Greece, Italy, Spain, Israel, Morocco, Turkey, Iran, India, China, Egypt and Mexico. Objective: The present study aims to address the anti-toxicant role of Crocus sativus L. in the cases of toxin and drug toxification. Materials and Methods: An electronic literature search was conducted by the two authors from 1993 to August 2017. Original articles and systematic reviews (with or without meta-analysis), as well as case reports were selected. Titles and abstracts of papers were screened by a third reviewer to determine whether they met the eligibility criteria, and full texts of the selected articles were retrieved. Results: The authors focused on literature concerning the role of Crocus Sativus L. as an anti-toxicant agent. Literature review showed that Saffron is a potent anti-toxicant agent with a plethora of applications ranging from anti-oxidant properties, to chemotherapy protective effects. Conclusion: Literature findings represented in current review herald promising results for using Crocus Sativus L. and/or its active constituents as anti-toxicant, chemotherapy-induced protection and toxin protection.

scholarly journals Spotlight on Alkali Metals: The Structural Chemistry of Alkali Metal Thallides

Crystals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1013
Author(s):  
Stefanie Gärtner
Keyword(s):  
Crystal Structure ◽  
Alkali Metal ◽  
Crystal Structures ◽  
Alkali Metals ◽  
Valence Electron ◽  
Oxidation States ◽  
Valence Electron Concentration ◽  
Base Metals ◽  
Charge Balancing

Alkali metal thallides go back to the investigative works of Eduard Zintl about base metals in negative oxidation states. In 1932, he described the crystal structure of NaTl as the first representative for this class of compounds. Since then, a bunch of versatile crystal structures has been reported for thallium as electronegative element in intermetallic solid state compounds. For combinations of thallium with alkali metals as electropositive counterparts, a broad range of different unique structure types has been observed. Interestingly, various thallium substructures at the same or very similar valence electron concentration (VEC) are obtained. This in return emphasizes that the role of the alkali metals on structure formation goes far beyond ancillary filling atoms, which are present only due to charge balancing reasons. In this review, the alkali metals are in focus and the local surroundings of the latter are discussed in terms of their crystallographic sites in the corresponding crystal structures.

scholarly journals More than redox, biological organic ligands control iron isotope fractionation in the riparian wetland

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Elaheh Lotfi-Kalahroodi ◽  
Anne-Catherine Pierson-Wickmann ◽  
Olivier Rouxel ◽  
Rémi Marsac ◽  
Martine Bouhnik-Le Coz ◽  
...  
Keyword(s):  
Redox Reactions ◽  
Isotope Fractionation ◽  
Isotopic Fractionation ◽  
Isotopic Signature ◽  
Organic Ligands ◽  
Riparian Wetland ◽  
Fe Isotopes ◽  
Preferential Binding ◽  
Isotope Systematics

AbstractAlthough redox reactions are recognized to fractionate iron (Fe) isotopes, the dominant mechanisms controlling the Fe isotope fractionation and notably the role of organic matter (OM) are still debated. Here, we demonstrate how binding to organic ligands governs Fe isotope fractionation beyond that arising from redox reactions. The reductive biodissolution of soil Fe(III) enriched the solution in light Fe isotopes, whereas, with the extended reduction, the preferential binding of heavy Fe isotopes to large biological organic ligands enriched the solution in heavy Fe isotopes. Under oxic conditions, the aggregation/sedimentation of Fe(III) nano-oxides with OM resulted in an initial enrichment of the solution in light Fe isotopes. However, heavy Fe isotopes progressively dominate the solution composition in response to their binding with large biologically-derived organic ligands. Confronted with field data, these results demonstrate that Fe isotope systematics in wetlands are controlled by the OM flux, masking Fe isotope fractionation arising from redox reactions. This work sheds light on an overseen aspect of Fe isotopic fractionation and calls for a reevaluation of the parameters controlling the Fe isotopes fractionation to clarify the interpretation of the Fe isotopic signature.

A Pictorial Tracking of Basal Plane Dislocations in SiC Epitaxy

2010 ◽  
Vol 645-648 ◽  
pp. 271-276 ◽  
Author(s):  
Robert E. Stahlbush ◽  
Rachael L. Myers-Ward ◽  
Brenda L. VanMil ◽  
D. Kurt Gaskill ◽  
Charles R. Eddy
Keyword(s):  
Epitaxial Growth ◽  
Basal Plane ◽  
Reduction Process ◽  
Epitaxial Layers ◽  
In Situ Growth ◽  
Half Loop ◽  
Insight Into

The recently developed technique of UVPL imaging has been used to track the path of basal plane dislocations (BPDs) in SiC epitaxial layers. The glide of BPDs during epitaxial growth has been observed and the role of this glide in forming half-loop arrays has been examined. The ability to track the path of BPDs through the epitaxy has made it possible to develop a BPD reduction process for epitaxy grown on 8° offcut wafers, which uses an in situ growth interrupt and has achieved a BPD reduction of > 98%. The images also provide insight into the strong BPD reduction that typically occurs in epitaxy grown on 4° offcut wafers.

Role of internal electric field on suppression of superconductivity by Pr in copper oxides

1989 ◽  
Vol 161 (5-6) ◽  
pp. 574-580 ◽  
Author(s):  
X.X. Tang ◽  
A. Manthiram ◽  
J.B. Goodenough
Keyword(s):  
Electric Field ◽  
Copper Oxides ◽  
Internal Electric Field
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