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Valence (chemistry)

About: Valence (chemistry) is a research topic. Over the lifetime, 24937 publications have been published within this topic receiving 645252 citations. The topic is also known as: valency.


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Journal ArticleDOI
TL;DR: In-depth analysis of operando X-ray pair distribution function (PDF) data is combined with Li NMR spectroscopy to gain comprehensive insights into the electrochemical reaction mechanism of high-performance iron oxyfluoride electrodes.
Abstract: In-depth analysis of operando X-ray pair distribution function (PDF) data is combined with Li NMR spectroscopy to gain comprehensive insights into the electrochemical reaction mechanism of high-performance iron oxyfluoride electrodes. While the full discharge capacity could be recovered upon charge, implying reversibility of the electrochemical reaction, the atomic structure of the electrode formed after cycling (discharge–charge) differs from the pristine uncycled electrode material. Instead, the “active” electrode that forms upon cycling is a nanocomposite of an amorphous rutile phase and a nanoscale rock salt phase. Bond valence sum analysis, based on the precise structural parameters (bond lengths and coordination number) extracted from the in situ PDF data, suggests that anion partitioning occurs during the electrochemical reaction, with the rutile phase being F-rich and the rock salt phase being O-rich. The F- and O-rich phases react sequentially; Fe in a F-rich environment reacts preferentially dur...

122 citations

Journal ArticleDOI
TL;DR: In this paper, the potential energy for the 26 lowest lying states of Li 2 was analyzed and compared with available experimental and quantum mechanical potential energy curves and molecular constants, and the errors in the present calculations are of nearly equal magnitude to, and in the opposite sense of, the optimized valence configuration calculations of Konowalow and Olson.

122 citations

Journal ArticleDOI
TL;DR: Long-range ferromagnetic ordering at 3 K is observed for the title compound, which may be considered as a fully localized mixed-valence species as well as a mixed-spin species (low-spin and high-spin Mn(2+) ions).
Abstract: Long-range ferromagnetic ordering at 3 K is observed for the title compound, which may be considered as a fully localized mixed-valence species (Mo(3+) and Mo(4+)) as well as a mixed-spin species (low-spin and high-spin Mn(2+) ions). Its two-dimensional structure consists of heart-shaped 48-membered rings, and each ring contains 16 metal centers (see picture).

122 citations

Journal ArticleDOI
TL;DR: This work reports a record-high average ZT value of ∼1.6 at 300-793 K with maximum ZT values ranging from 0.8 at 300 K to 2.1 at 793 K in p-type SnSe crystals, which arises from the enhanced power factor and lowered lattice thermal conductivity through crystal structure modification via Te alloying.
Abstract: The simple binary compound SnSe has been reported as a robust thermoelectric material for energy conversion by showing strong anharmonicity and multiple electronic valence bands. Herein, we report a record-high average ZT value of ∼1.6 at 300-793 K with maximum ZT values ranging from 0.8 at 300 K to 2.1 at 793 K in p-type SnSe crystals. This remarkable thermoelectric performance arises from the enhanced power factor and lowered lattice thermal conductivity through crystal structure modification via Te alloying. Our results elucidate that Te alloying increases the carrier mobility by making the bond lengths more nearly equal and sharpening the valence bands; meanwhile, the Seebeck coefficient remains large due to multiple valence bands. As a result, a record-high power factor of ∼55 μW cm-1 K-2 at 300 K is achieved. Additionally, Te alloying promotes Sn atom displacements, thus leading to a lower lattice thermal conductivity. Our conclusions are well supported by electron localization function calculations, the Callaway model, and structural characterization via aberration-corrected scanning transmission electron microscopy. Our approach of modifying crystal structures could also be applied in other low-symmetry thermoelectric materials and represents a new strategy to enhance thermoelectric performance.

122 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20231,521
20222,997
2021616
2020611
2019584
2018577