scholarly journals Anion polarity-induced dual oxidation states in a dual-layered purely organic paramagnetic charge-transfer salt, (TTF)3(PO-CON(CH3)C2H4SO3)2, where PO = 2,2,5,5-tetramethyl-3-pyrrolin-1-oxyl free radical

CrystEngComm ◽  
2011 ◽  
Vol 13 (17) ◽  
pp. 5281 ◽  
Author(s):  
Hiroki Akutsu ◽  
Atsushi Kawamura ◽  
Jun-ichi Yamada ◽  
Shin'ichi Nakatsuji ◽  
Scott S. Turner
Keyword(s):  
Charge Transfer ◽  
Free Radical ◽  
Oxidation States

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.

ROLE OF FREE RADICAL QUENCHERS IN THE CHARGE TRANSFER POLYMERIZATION OF STYRENE AND ALKYLMETHACRYLATES

1999 ◽  
Vol 36 (5-6) ◽  
pp. 759-773 ◽  
Author(s):  
R. VIJAYARAGHAVAN ◽  
M. SURIANARAYANAN ◽  
P. GANGADARA RAO ◽  
K. V. RAGHAVAN
Keyword(s):  
Charge Transfer ◽  
Free Radical

scholarly journals The charge percolation mechanism and simulation of Ziegler-Natta polymerizations. Part III. Oxidation states of transition metals

2006 ◽  
Vol 71 (4) ◽  
pp. 357-372 ◽  
Author(s):  
Branka Pilic ◽  
Dragoslav Stoiljkovic ◽  
Ivana Bakocevic ◽  
Slobodan Jovanovic ◽  
Davor Panic ◽  
...  
Keyword(s):  
Charge Transfer ◽  
Oxidation States ◽  
Support Surface ◽  
Active Centers ◽  
Active Centre ◽  
Whole Process ◽  
Oxidation Reduction ◽  
Donor And Acceptor ◽  
Donor Acceptor ◽  
A Charge

The oxidation state of the transition metal (Mt) active centre is the most disputable question in the polymerization of olefins by Ziegler-Natta (ZN) and metallocene complexes. In this paper the importance and the changes of the Mt active centers are presented and discussed on the basis of a charge percolation mechanism (CPM) of olefin polymerization. Mt atoms can exist in different oxidation states and can be easily transformed from one to another state during activation. In all cases, the Mt atoms are present in several oxidation states, i.e., Mt+(n-1), Mt+(n) to Mt+(n+1), producing an irregular charge distribution over the support surface. There is a tendency to equalize the oxidation states by a charge transfer from Mt+(n-1) (donor) to Mt+(n+1) (acceptor). This cannot occur since the different oxidation states are highly separated on the support. However, monomer molecules are adsorbed on the support producing clusters with stacked ?-bonds, making a ?-bond bridge between a donor and an acceptor. Once a bridge is formed (percolation moment), charge transfer occurs. The donor and acceptor equalize their oxidation states simultaneously with the polymerization of the monomer. The polymer chain is desorbed from the support, freeing the surface for subsequent monomer adsorption. The whole process is repeated with the oxidation-reduction of other donor-acceptor ensembles.

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