The magnetic properties of oxygen-hole aluminum centres in crystalline SiO2. VI: A stable AlO4/Li centre

2003 ◽  
Vol 81 (3) ◽  
pp. 583-598 ◽  
Author(s):  
C J Walsby ◽  
N S Lees ◽  
R FC Claridge ◽  
J A Weil
Keyword(s):  
Lithium Atom ◽  
Lithium Ion ◽  
Cryogenic Temperatures ◽  
Oxygen Anion ◽  
Paramagnetic Resonance ◽  
Oxygen Hole ◽  
Fitted Parameter ◽  
Electron Paramagnetic ◽  
Internal Charge Transfer ◽  
Hole Centres

A new study, by electron paramagnetic resonance (EPR) spectroscopy at cryogenic temperatures, of aluminum oxygenic-hole centres in a α-quartz single crystal is reported. The well-known centre [AlO4]0 has been reinvestigated with somewhat improved techniques and computer analysis, confirming previous results in the literature. A previously unreported Al–Li centre has now been well characterized by EPR. From the fitted parameter matrices g, A(27Al), P(27Al), A(7Li), and P(7Li) we have determined not only that the hole resides on a "long-bonded" oxygen anion, as in [AlO4]0, but have also established the position of the near-by interstitial lithium ion. One model for this centre is that it consists of a lithium atom Li0 linked to the diamagnetic centre [AlO4]–, yielding hole-bearing species [AlO4/Li]– via internal charge transfer. PACS Nos.: 7630Da, 7630Mi

Thermally reversible γ-ray-induced redox reaction between substitutional iron and aluminum impurity centers in a silica glass

2001 ◽  
Vol 16 (1) ◽  
pp. 127-131 ◽  
Author(s):  
Radhaballabh Debnath
Keyword(s):  
Silica Glass ◽  
Γ Irradiation ◽  
Paramagnetic Resonance ◽  
Hole Trapping ◽  
Oxygen Hole ◽  
Before And After ◽  
Impurity Centers ◽  
Spin Resonances ◽  
Electron Paramagnetic ◽  
Hole Centers

The magnetic properties of the substitutional iron and aluminum impurity centers in a sintered Vycor silica glass were studied before and after 1.1–1.3 MeV γ irradiation. Observation of two overlapping spin resonances (g ∼ 4.20–4.28) in the spectra of both the irradiated and preirradiated glasses indicated the existence of two types of tetra coordinated substitutional iron centers of the [FeO4−/Na+]0 type. The intensity of these electron-paramagnetic resonance (EPR) signals decreased upon g irradiation of the glass with concomitant generation of aluminum hole center [AlO4]0, which was manifested by the occurrence of a new six-line EPR signal with g 4 2.009, while thermal annealing of these aluminum oxygen hole centers restores the intensity of the iron centers almost to their preirradiation level. This result suggests that if not the whole, a major fraction of the electrons released in the process of g-ray-induced hole trapping at the Al site are captured by the substitutional iron centers. The electron traps, thus formed, are quite stable and can be deactivated by thermal stimulation.

Lithium superoxide encapsulated in a benzoquinone anion matrix

2021 ◽  
Vol 118 (51) ◽  
pp. e2019392118
Author(s):  
Matthew Nava ◽  
Shiyu Zhang ◽  
Katharine S. Pastore ◽  
Xiaowen Feng ◽  
Kyle M. Lancaster ◽  
...  
Keyword(s):  
Solid State ◽  
Lithium Ion ◽  
Spectroscopic Characterization ◽  
Blue Color ◽  
Paramagnetic Resonance ◽  
Deep Blue ◽  
Lithium Peroxide ◽  
X Ray Absorption ◽  
Electron Paramagnetic ◽  
Lithium Air Batteries

Lithium peroxide is the crucial storage material in lithium–air batteries. Understanding the redox properties of this salt is paramount toward improving the performance of this class of batteries. Lithium peroxide, upon exposure to p–benzoquinone (p–C6H4O2) vapor, develops a deep blue color. This blue powder can be formally described as [Li2O2]0.3 · [LiO2]0.7 · {Li[p–C6H4O2]}0.7, though spectroscopic characterization indicates a more nuanced structural speciation. Infrared, Raman, electron paramagnetic resonance, diffuse-reflectance ultraviolet-visible and X-ray absorption spectroscopy reveal that the lithium salt of the benzoquinone radical anion forms on the surface of the lithium peroxide, indicating the occurrence of electron and lithium ion transfer in the solid state. As a result, obligate lithium superoxide is formed and encapsulated in a shell of Li[p–C6H4O2] with a core of Li2O2. Lithium superoxide has been proposed as a critical intermediate in the charge/discharge cycle of Li–air batteries, but has yet to be isolated, owing to instability. The results reported herein provide a snapshot of lithium peroxide/superoxide chemistry in the solid state with redox mediation.

Copper–lithium ion exchange in LiNbO3

2000 ◽  
Vol 15 (5) ◽  
pp. 1120-1124 ◽  
Author(s):  
F. Caccavale ◽  
C. Sada ◽  
F. Segato ◽  
L. D. Bogomolova ◽  
N. A. Krasil'nikova ◽  
...  
Keyword(s):  
Ion Exchange ◽  
Optical Waveguides ◽  
Secondary Ion Mass Spectrometry ◽  
Exchange Process ◽  
Lithium Ion ◽  
X Ray Diffraction ◽  
Paramagnetic Resonance ◽  
Ion Exchange Process ◽  
Optical Modes ◽  
Electron Paramagnetic

Copper-doped LiNbO3 waveguides were prepared by Cu–Li ion-exchange process. Compositional, structural, and optical analyses were performed by secondary ion mass spectrometry, x-ray diffraction, and m-line spectroscopy, respectively. The chemical state of Cu2+ ions was studied by electron paramagnetic resonance, and the results were correlated with structural modification of the LiNbO3 matrix. Copper incorporation in the crystal took place under different regimes, and it induced a lattice rearrangement with the formation of new crystalline phases. Cu2+ ions were surrounded by tetragonally compressed octahedra with rhombic distortions. Cu:LiNbO3 optical waveguides were formed supporting two optical modes.

scholarly journals Lithium Ion Battery Materials as Tunable, Redox Non-Innocent Catalyst Supports

2021 ◽  
Author(s):  
Alon Chapovetsky ◽  
Ryan J. Witzke ◽  
Robert Kennedy ◽  
Evan Wegener ◽  
Fulya Dogan ◽  
...  
Keyword(s):  
Lithium Ion ◽  
Catalyst Supports ◽  
Paramagnetic Resonance ◽  
Battery Materials ◽  
X Ray ◽  
Electronic Tuning ◽  
Microscopy Techniques ◽  
Nickel Species ◽  
X Ray Absorption ◽  
Electron Paramagnetic

The development of general strategies for the electronic tuning of a catalyst’s active site is an ongoing challenge in heterogeneous catalysis. To this end we report the application of cathode and anode materials as redox non-innocent catalyst supports that can be continuously modulated as a function of lithium intercalation. A zero valent nickel complex was oxidatively grafted onto the surface of lithium manganese oxide (Li<sub>x</sub>Mn<sub>2</sub>O<sub>4</sub>) to yield single-sites of Ni<sup>2</sup><sub>­</sub><sup>+</sup> (Ni/Li<sub>x</sub>Mn<sub>2</sub>O<sub>4</sub>). Its activity for olefin hydrogenation was found to be a function of the redox state of the support material, with the most lithiated variant showing the most activity. X-ray absorption, X-ray photoelectron, solid-state nuclear magnetic resonance and electron paramagnetic resonance spectroscopies, and electron microscopy techniques established the nature of the nickel species on Li<sub>x</sub>Mn<sub>2</sub>O<sub>4</sub>. Catalyst control through support redox non-innocence was extended to an organotantalum complex on lithium titanium oxide (Li<sub>x</sub>TiO<sub>2</sub>), demonstrating the generality of this phenomenon.

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