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All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

MnEdgeNet for accurate decomposition of mixed oxidation states for Mn XAS and EELS L2,3 edges without reference and calibration

Accurate decomposition of the mixed Mn oxidation states is highly important for characterizing the electronic structures, charge transfer and redox centers for electronic, and electrocatalytic and energy storage materials that contain Mn. Electron energy loss spectroscopy (EELS) and soft X-ray absorption spectroscopy (XAS) measurements of the Mn L2,3 edges are widely used for this purpose. To date, although the measurements of the Mn L2,3 edges are straightforward given the sample is prepared properly, an accurate decomposition of the mix valence states of Mn remains non-trivial. For both EELS and XAS, 2+, 3+, and 4+ reference spectra need to be taken on the same instrument/beamline and preferably in the same experimental session because the instrumental resolution and the energy axis offset could vary from one session to another. To circumvent this hurdle, in this study, we adopted a deep learning approach and developed a calibration-free and reference-free method to decompose the oxidation state of Mn L2,3 edges for both EELS and XAS. A deep learning regression model is trained to accurately predict the composition of the mix valence state of Mn. To synthesize physics-informed and ground-truth labeled training datasets, we created a forward model that takes into account plural scattering, instrumentation broadening, noise, and energy axis offset. With that, we created a 1.2 million-spectrum database with 1-by-3 oxidation state composition ground truth vectors. The library includes a sufficient variety of data including both EELS and XAS spectra. By training on this large database, our convolutional neural network achieves 85% accuracy on the validation dataset. We tested the model and found it is robust against noise (down to PSNR of 10) and plural scattering (up to t/λ = 1). We further validated the model against spectral data that were not used in training. In particular, the model shows high accuracy and high sensitivity for the decomposition of Mn 3 O 4 , MnO, Mn 2 O 3 , and MnO 2 . The accurate decomposition of Mn 3 O 4 experimental data shows the model is quantitatively correct and can be deployed for real experimental data. Our model will not only be a valuable tool to researchers and material scientists but also can assist experienced electron microscopists and synchrotron scientists in the automated analysis of Mn L edge data.

25 ENERGY STORAGE↗
DOE OSTI2024

Magnetic anisotropy in single-crystalline antiferromagnetic Mn 2 Au

Multiple recent studies have identified the metallic antiferromagnet Mn 2 ⁢Au to be a candidate for spintronic applications due to apparent in-plane anisotropy, preserved magnetic properties above room temperature, and current-induced Néel vector switching. Crystal growth is complicated by the fact that Mn 2 ⁢Au melts incongruently. We present a bismuth flux method to grow millimeter-scale bulk single crystals of Mn 2 ⁢Au in order to examine the intrinsic anisotropic electrical and magnetic properties. Flux quenching experiments reveal that the Mn 2 ⁢Au crystals precipitate below 550°⁢C, about 100⁢°⁢C below the decomposition temperature of Mn 2 ⁢Au. Bulk Mn 2 ⁢Au crystals have a room-temperature resistivity of 16–19 µ⁢Ωcm and a residual resistivity ratio of 41. Mn 2 ⁢Au crystals have a dimensionless susceptibility on the order of 10 –4 (SI units), comparable to calculated and experimental reports on powder samples. Single-crystal neutron diffraction confirms the in-plane magnetic structure. The tetragonal symmetry of Mn 2 ⁢Au constrains the ab-plane magnetic susceptibility to be constant, meaning that χ 100 =χ 110 in the low-field limit, below any spin-flop transition. We find that three measured magnetic susceptibilities χ 100 , χ 110 , and χ 001 are the same order of magnitude and agree with the calculated prediction, meaning the low-field susceptibility of Mn 2 ⁢Au is quite isotropic, despite clear differences in ab-plane and ac-plane magnetocrystalline anisotropy. Mn 2 ⁢Au is calculated to have an extremely high in-plane spin-flop field above 30 T, which is much larger than that of another in-plane antiferromagnet, Fe 2 ⁢As (less than 1 T). Finally, the subtle anisotropy of intrinsic susceptibilities may lead to dominating effects from shape, crystalline texture, strain, and defects in devices that attempt spin readout in Mn 2⁢ Au.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Materials Data on Mn(FeO2)2 by Materials Project

MnFe2O4 is Spinel-like structured and crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are ten inequivalent Mn2+ sites. In the first Mn2+ site, Mn2+ is bonded to four O2- atoms to form MnO4 tetrahedra that share corners with two equivalent MnO6 octahedra and corners with ten FeO6 octahedra. The corner-sharing octahedra tilt angles range from 56–63°. There are a spread of Mn–O bond distances ranging from 2.06–2.09 Å. In the second Mn2+ site, Mn2+ is bonded to six O2- atoms to form MnO6 octahedra that share corners with two equivalent FeO4 tetrahedra, corners with four MnO4 tetrahedra, and edges with six FeO6 octahedra. There are a spread of Mn–O bond distances ranging from 2.00–2.19 Å. In the third Mn2+ site, Mn2+ is bonded to four O2- atoms to form MnO4 tetrahedra that share corners with three MnO6 octahedra and corners with nine FeO6 octahedra. The corner-sharing octahedra tilt angles range from 56–63°. There are a spread of Mn–O bond distances ranging from 2.05–2.08 Å. In the fourth Mn2+ site, Mn2+ is bonded to four O2- atoms to form MnO4 tetrahedra that share corners with three MnO6 octahedra and corners with nine FeO6 octahedra. The corner-sharing octahedra tilt angles range from 56–60°. There are a spread of Mn–O bond distances ranging from 2.05–2.09 Å. In the fifth Mn2+ site, Mn2+ is bonded to six O2- atoms to form MnO6 octahedra that share corners with three MnO4 tetrahedra, corners with three FeO4 tetrahedra, and edges with six FeO6 octahedra. There are a spread of Mn–O bond distances ranging from 2.01–2.24 Å. In the sixth Mn2+ site, Mn2+ is bonded to four O2- atoms to form MnO4 tetrahedra that share corners with three MnO6 octahedra and corners with nine FeO6 octahedra. The corner-sharing octahedra tilt angles range from 55–64°. There are a spread of Mn–O bond distances ranging from 2.03–2.07 Å. In the seventh Mn2+ site, Mn2+ is bonded to six O2- atoms to form MnO6 octahedra that share corners with three MnO4 tetrahedra, corners with three FeO4 tetrahedra, and edges with six FeO6 octahedra. There are a spread of Mn–O bond distances ranging from 2.08–2.25 Å. In the eighth Mn2+ site, Mn2+ is bonded to four O2- atoms to form MnO4 tetrahedra that share a cornercorner with one MnO6 octahedra and corners with eleven FeO6 octahedra. The corner-sharing octahedra tilt angles range from 58–61°. There are a spread of Mn–O bond distances ranging from 2.06–2.10 Å. In the ninth Mn2+ site, Mn2+ is bonded to six O2- atoms to form MnO6 octahedra that share corners with three MnO4 tetrahedra, corners with three FeO4 tetrahedra, and edges with six FeO6 octahedra. There are a spread of Mn–O bond distances ranging from 2.01–2.18 Å. In the tenth Mn2+ site, Mn2+ is bonded to four O2- atoms to form MnO4 tetrahedra that share a cornercorner with one MnO6 octahedra and corners with eleven FeO6 octahedra. The corner-sharing octahedra tilt angles range from 58–62°. There are a spread of Mn–O bond distances ranging from 2.07–2.10 Å. There are twenty inequivalent Fe3+ sites. In the first Fe3+ site, Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with two equivalent FeO4 tetrahedra, corners with four MnO4 tetrahedra, edges with two equivalent MnO6 octahedra, and edges with four FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 2.05–2.09 Å. In the second Fe3+ site, Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with six MnO4 tetrahedra, an edgeedge with one MnO6 octahedra, and edges with five FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 1.98–2.04 Å. In the third Fe3+ site, Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with two equivalent FeO4 tetrahedra, corners with four MnO4 tetrahedra, edges with two equivalent MnO6 octahedra, and edges with four FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 2.03–2.08 Å. In the fourth Fe3+ site, Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with three MnO4 tetrahedra, corners with three FeO4 tetrahedra, edges with two equivalent MnO6 octahedra, and edges with four FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 2.00–2.14 Å. In the fifth Fe3+ site, Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with three equivalent MnO4 tetrahedra, corners with three equivalent FeO4 tetrahedra, edges with two MnO6 octahedra, and edges with four FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 2.02–2.08 Å. In the sixth Fe3+ site, Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with three MnO4 tetrahedra, corners with three FeO4 tetrahedra, edges with two equivalent MnO6 octahedra, and edges with four FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 1.99–2.15 Å. In the seventh Fe3+ site, Fe3+ is bonded to four O2- atoms to form FeO4 tetrahedra that share corners with three MnO6 octahedra and corners with nine FeO6 octahedra. The corner-sharing octahedra tilt angles range from 55–63°. There are a spread of Fe–O bond distances ranging from 2.01–2.09 Å. In the eighth Fe3+ site, Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with three MnO4 tetrahedra, corners with three FeO4 tetrahedra, edges with two equivalent MnO6 octahedra, and edges with four FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 2.01–2.11 Å. In the ninth Fe3+ site, Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with three equivalent MnO4 tetrahedra, corners with three equivalent FeO4 tetrahedra, edges with two MnO6 octahedra, and edges with four FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 2.03–2.11 Å. In the tenth Fe3+ site, Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with three MnO4 tetrahedra, corners with three FeO4 tetrahedra, edges with two equivalent MnO6 octahedra, and edges with four FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 2.01–2.12 Å. In the eleventh Fe3+ site, Fe3+ is bonded to four O2- atoms to form FeO4 tetrahedra that share corners with three MnO6 octahedra and corners with nine FeO6 octahedra. The corner-sharing octahedra tilt angles range from 53–61°. There are a spread of Fe–O bond distances ranging from 1.92–1.99 Å. In the twelfth Fe3+ site, Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with three equivalent MnO4 tetrahedra, corners with three equivalent FeO4 tetrahedra, edges with two MnO6 octahedra, and edges with four FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 2.00–2.09 Å. In the thirteenth Fe3+ site, Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with three MnO4 tetrahedra, corners with three FeO4 tetrahedra, edges with two equivalent MnO6 octahedra, and edges with four FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 2.02–2.09 Å. In the fourteenth Fe3+ site, Fe3+ is bonded to four O2- atoms to form FeO4 tetrahedra that share corners with three MnO6 octahedra and corners with nine FeO6 octahedra. The corner-sharing octahedra tilt angles range from 58–61°. There are a spread of Fe–O bond distances ranging from 2.02–2.08 Å. In the fifteenth Fe3+ site, Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with three equivalent MnO4 tetrahedra, corners with three equivalent FeO4 tetrahedra, an edgeedge with one MnO6 octahedra, and edges with five FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 2.04–2.08 Å. In the sixteenth Fe3+ site, Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with three MnO4 tetrahedra, corners with three FeO4 tetrahedra, edges with two equivalent MnO6 octahedra, and edges with four FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 2.04–2.09 Å. In the seventeenth Fe3+ site, Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share a cornercorner with one FeO4 tetrahedra, corners with five MnO4 tetrahedra, and edges with six FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 2.01–2.03 Å. In the eighteenth Fe3+ site, Fe3+ is bonded to four O2- atoms to form FeO4 tetrahedra that share corners with two equivalent MnO6 octahedra and corners with ten FeO6 octahedra. The corner-sharing octahedra tilt angles range from 55–62°. There are a spread of Fe–O bond distances ranging from 2.00–2.09 Å. In the nineteenth Fe3+ site, Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share a cornercorner with one FeO4 tetrahedra, corners with five MnO4 tetrahedra, and edges with six FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 2.05–2.10 Å. In the twentieth Fe3+ site, Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share a cornercorner with one FeO4 tetrahedra, corners with five MnO4 tetrahedra, and edges with six FeO6 octahedra. There are a spread of Fe–O bond distances ranging from 2.04–2.08 Å. There are forty inequivalent O2- sites. In the first O2- site, O2- is bonded to two Mn2+ and two Fe3+ atoms to form distorted OMn2Fe2 tetrahedra that share corners with four OMnFe3 tetrahedra, corners with five OMnFe3 trigonal pyramids, and an edgeedge with one OMn2Fe2 trigonal pyramid. In the second O2- site, O2- is bonded to two Mn2+ and two Fe3+ atoms to form a mixture of distorted edge and corner-sharing OMn2Fe2 trigonal pyramids. In the third O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to two Mn2+ and two Fe3+ atoms. In the fourth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to one Mn2+ and three Fe3+ atoms. In the fifth O2- site, O2- is bonded to two Mn2+ and two Fe3+ atoms to form distorted OMn2Fe2 trigonal pyramids that share corners with two equivalent OMnFe3 tetrahedra and corners with three OFe4 trigonal pyramids. In the sixth O2- site, O2- is bonded to four Fe3+ atoms to form distorted OFe4 trigonal pyramids that share corners with two OMnFe3 tetrahedra, corners with four OMn2Fe2 trigonal pyramids, an edgeedge with one OMn2Fe2 tetrahedra, and an edgeedge with one OMnFe3 trigonal pyramid. In the seventh O2- site, O2- is bonded to two Mn2+ and two Fe3+ atoms to form a mixture of distorted edge and corner-sharing OMn2Fe2 tetrahedra. In the eighth O2- site, O2- is bonded in a rectangular see-saw-like geometry to two Mn2+ and two Fe3+ atoms. In the ninth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to two Mn2+ and two Fe3+ atoms. In the tenth O2- site, O2- is bonded in a rectangular see-saw-like geometry to one Mn2+ and three Fe3+ atoms. In the eleventh O2- site, O2- is bonded in a rectangular see-saw-like geometry to one Mn2+ and three Fe3+ atoms. In the twelfth O2- site, O2- is bonded to one Mn2+ and three Fe3+ atoms to form distorted OMnFe3 trigonal pyramids that share corners with three OMnFe3 tetrahedra, corners with four OMn2Fe2 trigonal pyramids, an edgeedge with one OMn2Fe2 tetrahedra, and an edgeedge with one OFe4 trigonal pyramid. In the thirteenth O2- site, O2- is bonded to two Mn2+ and two Fe3+ atoms to form a mixture of distorted edge and corner-sharing OMn2Fe2 trigonal pyramids. In the fourteenth O2- site, O2- is bonded in a rectangular see-saw-like geometry to four Fe3+ atoms. In the fifteenth O2- site, O2- is bonded to one Mn2+ and three Fe3+ atoms to form distorted corner-sharing OMnFe3 tetrahedra. In the sixteenth O2- site, O2- is bonded in a rectangular see-saw-like geometry to one Mn2+ and three Fe3+ atoms. In the seventeenth O2- site, O2- is bonded in a rectangular see-saw-like geometry to two Mn2+ and two Fe3+ atoms. In the eighteenth O2- site, O2- is bonded to two Mn2+ and two Fe3+ atoms to form a mixture of distorted edge and corner-sharing OMn2Fe2 trigonal pyramids. In the nineteenth O2- site, O2- is bonded in a rec

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mn(BO4)4 by Materials Project

Mn(B2O7)2O2 crystallizes in the triclinic P-1 space group. The structure is zero-dimensional and consists of two water water molecules and two Mn(B2O7)2 clusters. In each Mn(B2O7)2 cluster, Mn is bonded in a 5-coordinate geometry to five O atoms. There are a spread of Mn–O bond distances ranging from 1.59–2.04 Å. There are four inequivalent B sites. In the first B site, B is bonded in a trigonal planar geometry to three O atoms. There are a spread of B–O bond distances ranging from 1.36–1.39 Å. In the second B site, B is bonded in a trigonal planar geometry to three O atoms. There are a spread of B–O bond distances ranging from 1.37–1.39 Å. In the third B site, B is bonded to four O atoms to form corner-sharing BO4 tetrahedra. There are a spread of B–O bond distances ranging from 1.45–1.50 Å. In the fourth B site, B is bonded to four O atoms to form corner-sharing BO4 tetrahedra. There are a spread of B–O bond distances ranging from 1.45–1.49 Å. There are fourteen inequivalent O sites. In the first O site, O is bonded in a single-bond geometry to one Mn atom. In the second O site, O is bonded in a 2-coordinate geometry to one Mn and one O atom. The O–O bond length is 1.31 Å. In the third O site, O is bonded in a single-bond geometry to one Mn atom. In the fourth O site, O is bonded in a single-bond geometry to one O atom. The O–O bond length is 2.01 Å. In the fifth O site, O is bonded in a single-bond geometry to one B atom. In the sixth O site, O is bonded in a bent 120 degrees geometry to two B atoms. In the seventh O site, O is bonded in a bent 120 degrees geometry to two B atoms. In the eighth O site, O is bonded in a single-bond geometry to one B atom. In the ninth O site, O is bonded in a bent 120 degrees geometry to two B atoms. In the tenth O site, O is bonded in a distorted bent 150 degrees geometry to one Mn and one B atom. In the eleventh O site, O is bonded in a bent 120 degrees geometry to two B atoms. In the twelfth O site, O is bonded in a single-bond geometry to one B atom. In the thirteenth O site, O is bonded in a bent 120 degrees geometry to two B and one O atom. In the fourteenth O site, O is bonded in a 1-coordinate geometry to one Mn and one O atom.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Fate of arsenic during the interactions between Mn-substituted goethite and dissolved Fe(II)

Geogenic arsenic has become a globally-distributed groundwater contaminant, liberated from the weathering of arsenic-bearing sulfide minerals and often transported to aquifer sediments adsorbed to iron oxides. Among the iron oxides, goethite (α-FeOOH) is uniquely important for the fate of arsenic because of its widespread abundance, stability, and high affinity for binding arsenic. Goethite is ubiquitous in soils and sediments and often contains substituted elements, including manganese. Structural manganese may affect the surface reactivity and redox capacity of goethite and alter the mechanisms of recrystallization catalyzed by dissolved Fe(II), potentially affecting arsenic adsorption. Here, this study examined the fate of As(V) during the interactions between dissolved Fe(II) and Mn-substituted goethites at pH 4 and 7 as well as associated changes in arsenic speciation. At pH 7, the addition of dissolved Fe(II) initially increases the adsorption of As(V) onto Mn-bearing and Mn-free goethites. For the Mn-substituted goethites, the adsorbed As(V) slowly releases to solution at longer aging times. Fe(II) addition at pH 4 slightly increases As(V) uptake by Mn-substituted goethites, with differences in total sorption correlating with the Mn content in goethite. The addition of Fe(II) releases substantial dissolved manganese but the amount solubilized is higher at pH 4 compared to 7, suggesting that the presence of adsorbed As(V) may substantially promote the Mn release at pH 4. X-ray absorption fine structure spectroscopy shows that arsenic is stabilized as As(V) in all the samples and adsorbed on goethite via a bidentate binuclear mechanism. Fitting results show that the binding distance and coordination numbers are stable in Mn-free goethite and Mn-substituted goethite samples; the effect of substituted Mn on the surface complex structure is minor. High resolution transmission electron microscopy and X-ray diffraction confirm that no secondary ferrous arsenate minerals precipitate under both pH conditions. This study improves our understanding of the Fe(II)-As(V) interactions on iron oxides, and demonstrates that the substituted cations such as manganese may quantitatively alter the geochemical fate of arsenic during the reaction of dissolved Fe(II) with Fe(III) oxides.

58 GEOSCIENCES↗
DOE OSTI2020

Epitaxial growth mechanism of heterogeneous catalytic oxidation of Mn(II) on manganite under oxic conditions

Manganese oxides are ubiquitous in soils and sediments, and their formation and transformation processes affect the migration and transformation of heavy metals and organic pollutants. Most previous work has been focused the oxidation of Mn(II) on Mn(IV) oxide surface, but it remains poorly understood how Mn(II) interacts with manganite under oxic conditions. Here, the interactions between manganite and dissolved Mn(II) within pH 5.0–9.0 under oxic conditions were systematically studied. The results indicated that adsorbed Mn(II) was directly oxidized to manganite on the surface, and the oxidation rate increased with increasing pH and oxygen partial pressure. Electrons are likely transferred in bulk manganite during the oxidation process of Mn(II). Although manganite induced Mn(II) oxidation and the epitaxial growth of bulk particles, there was no obvious change in mineral phase. Dissolved oxygen accelerated the growth of manganite in Mn(II) solution. Compared with the absence of manganite, the presence of manganite inhibited the formation of hausmannite from Mn(II) oxidation by oxygen in air. Furthermore, this study reveals the catalytic oxidation process and mechanism of Mn(II) on manganite surface, and improves the understanding of manganite crystal growth in supergene environments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Crystal structure and magnetic properties of Gd 8 Mn 3 Sb 19

Here, in this study, a novel magnetic semimetal compound, Gd 8 Mn 3 Sb 19 , was synthesized successfully via high-temperature solid-state reaction. The crystal structure of Gd 8 Mn 3 Sb 19 was determined using both single crystal and powder X-ray diffraction techniques, revealing a non-centrosymmetric orthorhombic space group, Pmn2 1 (No. 31). The Sb atoms in Gd 8 Mn 3 Sb 19 form five-atom-wide Sb 5 7− ribbons, narrower three-atom-wide Sb 3 5− ribbons, and single Sb 3− anions. On the other hand, both Gd 3+ and Mn 2+ ions form the distorted Gd 3 and Mn 3 triangular lattices, respectively. The magnetic measurements suggest the complex magnetic interactions contributed by both Gd 3+ and Mn 2+ ions. A sharp peak observed in the magnetic susceptibility plot at approximately 25 K corresponds to the antiferromagnetic-type transition in Gd 8 Mn 3 Sb 19 . Furthermore, the magnetic measurements along different directions indicate the strong magnetic anisotropy present in Gd 8 Mn 3 Sb 19 , which is likely due to the complex magnetic interactions arising from the existence of Gd and Mn ions. Finally, the electrical resistivity measurements of Gd 8 Mn 3 Sb 19 indicate semimetallic behavior with a positive magnetoresistance.

Chemistry↗
DOE OSTI2024

Structure and tunable temperature coefficient of magnetization of Mn 4-x Ga x C alloys prepared by induction melting method

The magnetization of most magnetic materials decreases monotonically with increasing temperature. In this work, we found that the temperature coefficient of magnetization of Mn 4-x Ga x C alloys can be tuned from negative values to positive values by controlling the composition x. The antiperovskite type Mn 4-x Ga x C (0.05 ≤ x ≤ 0.75) alloys were prepared by using induction melting method, which is more efficient in large-scale production and obtaining full-density alloys in comparison with the traditional solid-state-reaction method. The values of the temperature coefficient of magnetization of Mn 4-x Ga x C change continuously from negative to positive with decreasing x. The Mn 4-x Ga x C alloys with highly thermal-stable magnetization is expected to present in the composition range of 0.15 < x < 0.25. The saturation magnetization of Mn 4-x Ga x C increases with increasing x, owing to the reduced number of antiferromagnetically coupled Mn atoms at the cubic corner with the face centered Mn atoms. Most Mn 4-x Ga x C alloys with varying x display near-zero remanent magnetization and coercivity at room temperature. The Currie temperature of Mn 4-x Ga x C decreases with increasing x. The x-ray photoelectron spectra of Mn 2p, Ga 2p, and C 1 s reveal distinct splitting due to the diverse chemical states of these atoms at different lattice positions and/or phases. Our work has developed a class of alloys capable of offering a desired temperature coefficient of magnetization across a broad temperature range, thereby offering a method to manipulate the thermodynamics of magnetization.

Magnetic properties↗
DOE OSTI2022

Effects of C/Mn Ratios on the Sorption and Oxidative Degradation of Small Organic Molecules on Mn-Oxides

We report manganese (Mn) oxides have a high surface area and redox potential that facilitate sorption and/or oxidation of organic carbon (OC), but their role in regulating soil C storage is relatively unexplored. Small OC compounds with distinct structures were reacted with Mn(III/IV)-oxides to investigate the effects of OC/Mn molar ratios on Mn–OC interaction mechanisms. Dissolved and solid-phase OC and Mn were measured to quantify the OC sorption to and/or the redox reaction with Mn-oxides. Mineral transformation was evaluated using X-ray diffraction and X-ray absorption spectroscopy. Higher OC/Mn ratios resulted in higher sorption and/or redox transformation; however, interaction mechanisms differed at low or high OC/Mn ratios for some OC. Citrate, pyruvate, ascorbate, and catechol induced Mn-oxide dissolution. The average oxidation state of Mn in the solid phase did not change during the reaction with citrate, suggesting ligand-promoted mineral dissolution, but decreased significantly during reactions with the other compounds, suggesting reductive dissolution mechanisms. Phthalate primarily sorbed on Mn-oxides with no detectable formation of redox products. Mn–OC interactions led primarily to C loss through OC oxidation into inorganic C, except phthalate, which was predominantly immobilized in the solid phase. Together, these results provided detailed fundamental insights into reactions happening at organo–mineral interfaces in soils.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Materials Data on Mn(O2F)2 by Materials Project

MnO4F2 crystallizes in the orthorhombic Pca2_1 space group. The structure is two-dimensional and consists of one MnO4F2 sheet oriented in the (1, 0, 0) direction. Mn is bonded in a 4-coordinate geometry to four O and two F atoms. There are a spread of Mn–O bond distances ranging from 2.08–2.75 Å. There is one shorter (1.83 Å) and one longer (1.84 Å) Mn–F bond length. There are four inequivalent O sites. In the first O site, O is bonded in a bent 120 degrees geometry to one Mn and one O atom. The O–O bond length is 1.28 Å. In the second O site, O is bonded in a bent 150 degrees geometry to one Mn and one O atom. The O–O bond length is 1.23 Å. In the third O site, O is bonded in a bent 120 degrees geometry to one Mn and one O atom. In the fourth O site, O is bonded in a bent 120 degrees geometry to one Mn and one O atom. There are two inequivalent F sites. In the first F site, F is bonded in a single-bond geometry to one Mn atom. In the second F site, F is bonded in a single-bond geometry to one Mn atom.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Annealing in Argon Universally Upgrades the Na‐Storage Performance of Mn‐Based Layered Oxide Cathodes by Creating Bulk Oxygen Vacancies

Abstract Manganese‐rich layered oxide cathodes of sodium‐ion batteries (SIBs) are extremely promising for large‐scale energy storage owing to their high capacities and cost effectiveness, while the Jahn–Teller (J–T) distortion and low operating potential of Mn redox largely hinder their practical applications. Herein, we reveal that annealing in argon rather than conventional air is a universal strategy to comprehensively upgrade the Na‐storage performance of Mn‐based oxide cathodes. Bulk oxygen vacancies are introduced via this method, leading to reduced Mn valence, lowered Mn 3 d‐ orbital energy level, and formation of the new‐concept Mn domains. As a result, the energy density of the model P2‐Na 0.75 Mg 0.25 Mn 0.75 O 2 cathode increases by ≈50 % benefiting from the improved specific capacity and operating potential of Mn redox. The Mn domains can disrupt the cooperative J–T distortion, greatly promoting the cycling stability. This exciting finding opens a new avenue towards high‐performance Mn‐based oxide cathodes for SIBs.

Chemistry↗
DOE OSTI2024

Combining solution-, precipitation- and load-transfer strengthening in a cast Al-Ce-Mn- Sc -Zr alloy

Here, a cast Al-9Ce-0.75Mn-0.18Sc-0.12Zr (wt%) alloy is designed to combine three strengthening phases: (i) micron-scale Al 11 Ce 3 platelets formed during eutectic solidification, (ii) nano-scale L1 2 -Al 3 (Sc,Zr) precipitates formed during aging, and (iii) Mn in solid solution in the α-Al matrix. Microstructural analyses by SEM, TEM, and atom-probe tomography reveal that Mn remains in solid solution in the as-cast alloy, providing solution strengthening with no influence on the eutectic Al-Al 11 Ce 3 microstructure, which provides precipitation- and load-transfer strengthening. During long-term over-aging at 400 °C, Mn-rich precipitates grow at the Al-Al 11 Ce 3 interface, with no effect on the microhardness. However, after short aging at 350 °C, a high number density of fine L1 2 -Al 3 (Sc,Zr) nanoprecipitates form in the Al matrix (with a coarser size at the Al-Al 11 Ce 3 interface), providing precipitation strengthening. The synergistic combination of the three strengthening mechanisms (solution, precipitation, and load transfer) in our Al-Ce-Mn-Sc-Zr alloy results in higher microhardness after aging at 350 and 400 °C, and higher creep resistance at 300 °C, as compared to alloys with two strengthening mechanisms: an Al-10Ce-0.93Mn control alloy (without precipitation strengthening from Sc and Zr), Al-Ce-Sc-Zr (without solution strengthening from Mn), and Al-Mn-Zr-Er (without load-transfer strengthening from Ce). Furthermore, these dual-strengthened alloys are more creep resistant than alloys with a single strengthening mechanism (Al-Ce, Al-Mn, and Al-Sc-Zr), confirming that the three mechanisms can be combined in pairs or all together.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Sorption and oxidation of Co(II) at the surface of birnessite: Impacts of aqueous Mn(II)

The sorption of aqueous Mn(II) (1 mM) and Co(II) (50 and 200 μM) onto hexagonal birnessite (0.1 g L –1 ) was studied under anoxic conditions at pH 6.5 and 7.5 in binary and ternary experiments using batch kinetic experiments and XRD, ATR-FTIR, and Co K-edge EXAFS analyses. In the binary systems, sorption of Co(II) was accompanied by partial oxidation to Co(III) yielding a mixture of corner-sharing Co(II) and edge-sharing Co(III) complexes at both pH values, while Mn(II)-birnessite interaction resulted in coordination of Mn(II/III) at layer vacancy sites at pH 6.5, and led to reductive transformation of birnessite into feitknechtite at pH 7.5. In the ternary systems, strong mutual interferences between Co(II) and Mn(II) co-sorbates reduced the rate and extent of sorption relative to the binary experiments. The introduction of Mn(II) aq into the high-Co systems (200 μM) halted the slow sorption of Co(II) that was attributed to the incorporation of Co(III) into layer vacancies, while Co(II) aq prevented Mn(II)-driven transformation of birnessite into feitknechtite at pH 7.5. In the low-Co system (50 μM), reductive transformation of birnessite by Mn(II) aq at pH 7.5 produced Co(II)-substituted feitknechtite, a conversion that was accompanied by reduction of sorbed Co(III) to Co(II) which was partially released to solution. The strong effects of co-sorption are attributed to the similarity in sorption mechanisms of Co(II) and Mn(II), which both sorb as a mixture of di- and trivalent species. Finally, the results of this work demonstrate that aqueous Mn(II) may significantly affect the reactivity of phyllomanganate sorbents towards dissolved Co(II), and therefore impact the speciation and solubility of this trace metal in anoxic and suboxic geochemical environments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Chemical Modulation of Local Transition Metal Environment Enables Reversible Oxygen Redox in Mn-Based Layered Cathodes

Oxygen redox plays a prominent role in enhancing the energy density of Mn-based layered cathodes. However, understanding the factors affecting the reversibility of oxygen redox is nontrivial due to complicated structural and chemical transformations. Here in this paper, we show that local Mn–O symmetry induced structural/chemical evolutions majorly dictate the reversibility of oxygen redox of Na x Li y Mn 1–y O 2 in Na cells. Na x Li y Mn 1–y O 2 with Jahn–Teller distorted MnO 6 octahedra undergoes severe Mn dissolution during cycling, which destabilizes the transition metal layer resulting in poor Li retention and irreversible oxygen redox. Jahn–Teller distortion of MnO 6 octahedra can be suppressed by modulating the local charge of Mn and Mn–O distance through Mg/Ti dual doping. This leads to reduced Mn dissolution and more reversible oxygen redox. Such stabilization significantly improves the electrochemical performance of Mg/Ti dual doped Na x Li y Mn 1–y O 2 . Through this work, we show that local structural stabilization through local chemical environment modification can promote reversible oxygen redox in layered cathodes.

25 ENERGY STORAGE↗
DOE OSTI2025

Cambered Bipyridyl Ligand with Extended Aryl System Enables Electrochemical Reduction of Carbon Dioxide and Bicarbonate by Mn(bpy)(CO) 3 Br-type Catalyst Immobilized on Carbon Nanotubes

Heterogeneous materials containing molecular catalytic sites show promise for electrocatalytic reduction of CO 2 to energy-enriched carbon products. Interactions between the catalyst and the heterogeneous support increasingly are recognized as important in governing product selectivity and rate. Recent work on Mn(R-bpy)(CO) 3 Br type catalysts immobilized on multiwalled carbon nanotubes (MWCNT) demonstrated control of electrocatalytic behavior with steric modification of the molecular catalyst. Phenyl groups installed in the 4,4' positions of the bipyridine ligand (ph-bpy) maximized performance through π–π interactions with the MWCNT support. Herein we report the outcome of extending the ligand π system with Mn(nap-bpy)(CO) 3 Br (nap-bpy = 4,4'-di(naphthalen-1-yl)-2,2'-bipyridine) and Mn(pyr-bpy)(CO) 3 Br (pyr-bpy = 4,4'-di(pyren-1-yl)-2,2'-bipyridine) immobilized on MWCNT. We demonstrate exceptional electrocatalysis with Mn(nap-bpy)(CO) 3 Br/MWCNT (FE CO > 92%; J CO = 16.5 mA/cm 2 ) and find that this catalyst electrochemically reduces bicarbonate in the absence of deliberately added CO 2 at a remarkable overall selectivity of >80% for carbon products (FE HCOO – = 52% and FE CO = 29%). We show diminishing returns to simply adding aromatic character to the bipyridyl ligand with Mn(pyr-bpy)(CO) 3 Br/MWCNT and observe a unique cambering of the Mn(nap-bpy)(CO) 3 Br bipyridyl ligand that we believe enables selective catalysis. Mechanistic studies were carried out on Mn(nap-bpy)(CO) 3 Br/MWCNT using a novel thin-film infrared spectroelectrochemical (IR-SEC) technique. These experiments observe the immobilized Mn(nap-bpy)(CO) 3 Br undergo single electron reduction to a Mn-centered radical that binds CO 2 in a reduction-coupled process.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Jahn–Teller-driven phase segregation in Mn x Co 3–x O 4 spinel thin films

Transition metal spinel oxides comprised of earth-abundant Mn and Co have long been explored for their use in catalytic reactions and energy storage. However, understanding functional properties can be challenging due to differences in sample preparation and the ultimate structural properties of the materials. Epitaxial thin film synthesis provides a novel means of producing precisely controlled materials to explore the variations reported in the literature. In this work, Mn x Co 3–x O 4 samples from x = 0 to x = 1.28 were synthesized through molecular beam epitaxy and characterized to develop a material properties map as a function of stoichiometry. Here, films were characterized via in situ x-ray photoelectron spectroscopy, x-ray diffraction, scanning transmission electron microscopy, and polarized K-edge x-ray absorption spectroscopy. Mn cations within this range were found to be octahedrally coordinated, in line with an inverse spinel structure. Samples largely show mixed Mn 3+ and Mn 4+ character with evidence of phase segregation tendencies with the increasing Mn content and increasing Mn 3+ formal charge. Phase segregation may occur due to structural incompatibility between cubic and tetragonal crystal structures associated with Mn 4+ and Jahn–Teller active Mn 3+ octahedra, respectively. Our results help in explaining the reported differences across samples in these promising materials for renewable energy technologies.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Molecular structure and catalytic promotional effect of Mn on supported Na 2 WO 4 /SiO 2 catalysts for oxidative coupling of methane (OCM) reaction

The structure and promotional effect of Mn in supported Mn-Na 2 WO 4 /SiO 2 catalysts for the oxidative coupling of methane (OCM) reaction has been debated for a longtime in the literature. In the current investigation, with the aid of multiple in-situ characterization studies, we show that the freshly calcined supported 1.2Mn-5Na 2 WO 4 /SiO 2 catalyst possesses crystalline Na 2 WO 4 , Mn 2 O 3 and SiO 2 (cristobalite phase) along with surface MnO x and Na-WO x sites at low temperature and oxidizing environments. Under the OCM reaction environment (T>800°C), the crystalline Na 2 WO 4 phase melts and Mn 2 O 3 phase reduces. In contrast, the surface MnO x and Na-WO x sites exhibit excellent thermal and chemical stability. Exposure of the 1.2Mn-5Na 2 WO 4 /SiO 2 catalyst to the OCM reaction environment redisperses the molten Na 2 WO 4 phase on the SiO 2 support to form new surface WO x sites. Interestingly, the stable MnO x species interacts with both molten Na 2 WO 4 phase and surface Na-WO x sites during OCM reaction. Controlled transient kinetic experiments in TAP and detailed steady state OCM fixed-bed reaction studies reveal the role and promotional effect of Mn in the 1.2Mn-5Na 2 WO 4 /SiO 2 catalyst. The W-oxides (both molten Na 2 WO 4 and surface Na-WO x sites) are the active sites for the catalytic OCM reaction and the MnO x species only function as promoters. The promotion of MnO x strongly depends on the gas phase O 2 partial pressure and the MnO x species act as mediators for oxygen exchange between the gas phase molecular O 2 and catalyst lattice oxygen. In conclusion, the temperature dependent MnO x promotion reveals that the MnO x species selectively promote the molten Na 2 WO 4 phase at lower reaction temperature and the surface Na-WO x sites at higher temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mn(BO4)4 by Materials Project

Mn(BO4)4 crystallizes in the triclinic P-1 space group. The structure is zero-dimensional and consists of two Mn(BO4)4 clusters. Mn is bonded to four O atoms to form MnO4 tetrahedra that share a cornercorner with one BO4 tetrahedra. There are a spread of Mn–O bond distances ranging from 1.59–1.92 Å. There are four inequivalent B sites. In the first B site, B is bonded in a trigonal planar geometry to three O atoms. There are a spread of B–O bond distances ranging from 1.36–1.39 Å. In the second B site, B is bonded in a trigonal planar geometry to three O atoms. There is two shorter (1.37 Å) and one longer (1.39 Å) B–O bond length. In the third B site, B is bonded to four O atoms to form corner-sharing BO4 tetrahedra. There are a spread of B–O bond distances ranging from 1.43–1.57 Å. In the fourth B site, B is bonded to four O atoms to form BO4 tetrahedra that share a cornercorner with one MnO4 tetrahedra and a cornercorner with one BO4 tetrahedra. There are a spread of B–O bond distances ranging from 1.46–1.51 Å. There are sixteen inequivalent O sites. In the first O site, O is bonded in a single-bond geometry to one B atom. In the second O site, O is bonded in a bent 120 degrees geometry to two B atoms. In the third O site, O is bonded in a bent 120 degrees geometry to two B atoms. In the fourth O site, O is bonded in a single-bond geometry to one B atom. In the fifth O site, O is bonded in a bent 120 degrees geometry to two B atoms. In the sixth O site, O is bonded in a distorted bent 120 degrees geometry to one Mn and one B atom. In the seventh O site, O is bonded in a bent 120 degrees geometry to two B atoms. In the eighth O site, O is bonded in a distorted single-bond geometry to one B and one O atom. The O–O bond length is 1.43 Å. In the ninth O site, O is bonded in a water-like geometry to two B and one O atom. The O–O bond length is 2.04 Å. In the tenth O site, O is bonded in a single-bond geometry to one O atom. The O–O bond length is 1.24 Å. In the eleventh O site, O is bonded in a single-bond geometry to one O atom. The O–O bond length is 1.27 Å. In the twelfth O site, O is bonded in a single-bond geometry to one Mn atom. In the thirteenth O site, O is bonded in a distorted single-bond geometry to one Mn and one O atom. In the fourteenth O site, O is bonded in a single-bond geometry to one Mn atom. In the fifteenth O site, O is bonded in a bent 120 degrees geometry to two O atoms. In the sixteenth O site, O is bonded in a single-bond geometry to one O atom.

36 MATERIALS SCIENCE↗