La marokite, Ca Mn2O4, une nouvelle espèce minérale

Gaudefroy, Christophe; Jouravsky, Georges; Permingeat, François

doi:10.3406/bulmi.1963.5665

Cited by 10 publications

(13 citation statements)

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“…Analysing the phase diagram for the system Ca-Mn-air, 92 we identified CaMn 2 O 4 , the naturally occurring mineral marokite, 93 as an accessible calcium containing Mn oxide with manganese in its +III oxidation state. Microcrystalline marokite could be successfully prepared via a comproportionation reaction of Mn 2+ and MnO 4…”

Section: Manganese Oxides As Catalytically Highly Active Solid State ...mentioning

confidence: 99%

Wateroxidation catalysed by manganese compounds: from complexes to ‘biomimetic rocks’

2012

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One of the most fundamental processes of the natural photosynthetic reaction sequence is the light-driven oxidation of water to molecular oxygen. In vivo, this reaction takes place in the large protein ensemble Photosystem II, where a μ-oxido-Mn(4)Ca- cluster, the oxygen-evolving-complex (OEC), has been identified as the catalytic site for the four-electron/four-proton redox reaction of water oxidation. This Perspective presents recent progress for three strategies which have been followed to prepare functional synthetic analogues of the OEC: (1) the synthesis of dinuclear manganese complexes designed to act as water-oxidation catalysts in homogeneous solution, (2) heterogeneous catalysts in the form of clay hybrids of such Mn(2)-complexes and (3) the preparation of manganese oxide particles of different compositions and morphologies. We discuss the key observations from the studies of such synthetic manganese systems in order to shed light upon the catalytic mechanism of natural water oxidation. Additionally, it is shown how research in this field has recently been motivated more and more by the prospect of finding efficient, robust and affordable catalysts for light-driven water oxidation, a key reaction of artificial photosynthesis. As manganese is an abundant and non-toxic element, manganese compounds are very promising candidates for the extraction of reduction equivalents from water. These electrons could consecutively be fed into the synthesis of "solar fuels" such as hydrogen or methanol.

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Section: Manganese Oxides As Catalytically Highly Active Solid State ...mentioning

confidence: 99%

Wateroxidation catalysed by manganese compounds: from complexes to ‘biomimetic rocks’

2012

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“…Initial studies of CaMn 2 O 4 were published shortly after its discovery in 1963 in Morocco as a naturally occurring mineral. 1 It was subsequently named marokite for its country of origin and was found to crystallize in an orthorhombic structure with space group 2 Pbcm and exhibit antiferromagnetic ͑AFM͒ ordering below 225 K. 3 But in the decades following these preliminary investigations, further studies are completely absent in the literature until 2001, when CaMn 2 O 4 was studied as an impurity phase in the solid-state synthesis of manganese oxides exhibiting colossal magnetoresistance behavior. 4 CaMn 2 O 4 has since enjoyed some renewed interest; however, recently published studies have been primarily limited to reporting on aspects of the magnetic ordering [4][5][6] and crystal structure.…”

Section: Introductionmentioning

confidence: 99%

Magnetic, transport, and thermodynamic properties ofCaMn2O4single crystals

et al. 2009

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Physical properties including magnetic susceptibility, room-temperature electrical resistivity, thermal conductivity, heat capacity, and thermal expansion are reported for high quality single-crystal samples of marokite CaMn 2 O 4. We determined that CaMn 2 O 4 is highly electrically insulating and exhibits long-range antiferromagnetic order below T N = 217.5Ϯ 0.6 K with easy axis along a. Anisotropic thermal expansion, similar to that of crystallographically layered materials, is observed, suggesting that the crystal structure of CaMn 2 O 4 is also assembled from previously undescribed layers. An extensive thermodynamic study of the antiferromagnetic transition was undertaken resulting in a heat-capacity critical exponent ␣ = 0.082Ϯ 0.007 and calculated pressure derivative dT N / dP = 5.154Ϯ 0.174 K / GPa.

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“…To the best of our knowledge, this compound has not been prepared to date, which might be related to the difficulty of placing Ca ions in Tetrahedral (T) sites. In the nature, the composition CaMn 2 O 4 forms the marokite mineral 15 , whose structure is commonly denoted post-spinel structural type and hereafter denoted as CM. This comes from the well-known transformation under pressure of some spinellike compounds to the CaMn 2 O 4 marokite-structure [16][17][18][19] .…”

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A Joint Computational and Experimental Evaluation of CaMn₂O₄ Polymorphs as Cathode Materials for Ca Ion Batteries

et al. 2016

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The identification of potential cathode materials is a must for the development of a new calcium-ion based battery technology. In this work, we have firstly explored the electrochemical behaviour of marokite-CaMn 2 O 4 but the experimental attempts to deinsert Ca ion from this compound failed. First principles calculations indicate that in terms of voltage and capacity, marokite-CaMn 2 O 4 could sustain reversible Ca deinsertion reactions; half decalciation is predicted at an average voltage of 3.7 V with a volume variation of 6%. However, the calculated barriers for Ca diffusion are too high (1 eV), in agreement with the observed difficulty to deinsert Ca ion from the marokite structure. We have extended the computational investigation to two other CaMn 2 O 4 polymorphs, the spinel and the CaFe 2 O 4 structural types. Full Ca extraction from these CaMn 2 O 4 polymorphs is predicted at an average voltage of 3.1 V, but with a large volume variation of around 20%. Structural factors limiting Ca diffusion in the three polymorphs are discussed and confronted with a previous computational investigation of the virtual-spinel [Ca] T [Mn 2 ] O O 4 . Regardless the potential interest of [Ca] T [Mn 2 ] O O 4 as cathode forCa ion batteries, calculations suggests that the synthesis of this compound would hardly be feasible. The present results unravel the bottlenecks associated to the design of feasible intercalation Ca electrode materials, and allow proposing guidelines for future research. IntroductionSecondary (i.e. rechargeable) batteries are a power source widely used in portable devices (such as personal computers, camcorders and cellular phones) and are also increasingly present in transport and stationary applications. While the current state-of-the-art technology is Li-ion, research efforts are intensified towards the development of alternative technologies to satisfy the ever increasing demands for enhanced energy density 1 . Indeed, the use of lithium metal anodes with high electrochemical capacities (3860 mAh/g) is only possible under certain specific conditions to avoid safety issues and the most used negative electrode material is graphite (372 mAh/g). Efforts to develop successful magnesium anodes (2210 mAh/g) have culminated in proof of concept of this technology. Yet, the high charge-to-radius ratio for magnesium ions has resulted only in very covalent hosts such as Mo 6 S 8-y Se y (y=1,2) Chevrel phases fulfilling the requirements to be used as cathode materials. 2 We have recently reported on the feasibility and reversibility of calcium plating in conventional alkyl carbonate electrolytes at moderate temperatures 3 which opens the way to the development of a new rechargeable battery technology using calcium anodes. This is especially attractive given the abundance of calcium on the earth crust 4 , the high capacity of calcium anodes (1340 mAh/g), its negative reduction potential (only 170 mV above that of lithium metal) and the lower charge to radius ratio for calcium ions which holds promise of better kin...

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La marokite, Ca Mn2O4, une nouvelle espèce minérale

Cited by 10 publications

References 0 publications

Wateroxidation catalysed by manganese compounds: from complexes to ‘biomimetic rocks’

Wateroxidation catalysed by manganese compounds: from complexes to ‘biomimetic rocks’

Magnetic, transport, and thermodynamic properties ofCaMn2O4single crystals

A Joint Computational and Experimental Evaluation of CaMn₂O₄ Polymorphs as Cathode Materials for Ca Ion Batteries

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La marokite, Ca Mn2O4, une nouvelle espèce minérale

Cited by 10 publications

References 0 publications

Wateroxidation catalysed by manganese compounds: from complexes to ‘biomimetic rocks’

Wateroxidation catalysed by manganese compounds: from complexes to ‘biomimetic rocks’

Magnetic, transport, and thermodynamic properties ofCaMn2O4single crystals

A Joint Computational and Experimental Evaluation of CaMn2O4 Polymorphs as Cathode Materials for Ca Ion Batteries

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A Joint Computational and Experimental Evaluation of CaMn₂O₄ Polymorphs as Cathode Materials for Ca Ion Batteries