Valence State Of Manganese Research Articles

Developing an in situ environmental TEM set up for investigations of resistive switching mechanisms in Pt-Pr1-xCaxMnO3-δ-Pt sandwich structures

Non-volatile resistance change under electric stimulation in many metal-oxides is a promising path to next generation memory devices. However, the underlying mechanisms are still not fully understood. In situ transmission electron microscopy experiments provide a powerful tool to elucidate these mechanisms. In this contribution, we demonstrate a TEM lamella geometry for in situ biasing with two fixed electrode contacts ensuring low and stable contact resistances. We use Pr1-xCaxMnO3-δ sandwiched by Pt electrodes as model system. The evolution of manganese valence state during electric stimulation in different environments is mapped by means of electron energy loss spectroscopy with high spatial resolution in STEM. Correlation of Mn valence with local oxygen content is found. In addition to electrically driven switching, beam-induced redox reactions in oxygen environment are observed. This effect might be restricted to thin lamellae. In general, our results support that bulk oxygen electromigration is the relevant mechanism for non-volatile resistive switching in PCMO.

Preparation and Electrochemical Properties of High‐Voltage Spinel LiNi0.5Mn1.5O4 Synthesized by using Different Manganese Sources

AbstractThe crystal structure and electrochemical performance of the 4.7 V cathode LiNi0.5Mn1.5O4 (LNMO) are quite dependent on the amount of Mn3+ and ordering of Ni/Mn in the octahedral sites. This work attempts to study LNMO synthesized by using different manganese sources, in which the valence states of manganese are +2, +2/+3, +3 and +4. A small amount of Mn3+ existing in the spinel crystal structures of the obtained LNMO can dramatically affect the material's conductivity and electrochemical performance. Among the four studied samples, LNMO‐1 (with MnCO3 as the manganese source) delivers the highest specific capacity of 138 mAh g−1, higher than LNMO‐2 (Mn3O4 as the manganese source), LNMO‐3 (Mn2O3 as the manganese source), and LNMO‐4 (MnO2 as the manganese source). After 100 cycles at 0.2 C, LNMO‐1 still delivers the highest discharge capacity of 129 mAh g−1. This work provides an insight into the phenomenon of how manganese sources influence the lithium diffusion ability and crystal structure stability of LNMO as a cathode material for highly reversible lithium storage.

Interactional effect of cerium and manganese on NO catalytic oxidation.

To preferably catalyze the oxidation of NO to NO2 in diesel after-treatment system, a series of CeO2-MnO x composite oxides was supported on silica-alumina material by the co-impregnation method. The maximum conversion of NO of the catalyst with a Ce/Mn weight ratio of 5:5 was improved by around 40%, compared to the supported manganese-only or cerium-only sample. And its maximum reaction rate was 0.056μmolg-1s-1 at 250°C at the gas hourly space velocity of 30,000h-1. The experimental results suggested that Ce-Mn solid solution was formed, which could modulate the valence state of cerium and manganese and exhibit great redox properties. Moreover, the strong interaction between ceria and manganese resulted in the largest desorption amount of strong chemical oxygen and oxygen vacancies, leading to the maximum O α area ratio of 62.26% from the O 1s result. These effective oxygen species could be continually transferred to the surface, leading to the best NO catalytic activity of 5Ce5Mn/SA catalyst. Graphical abstract.

Synthesis and electrochemical performance of lithiated manganese oxides Li0.35MnO2 with tetragonal structure

Non-stoichiometric Li0.35MnO2 nanoparticles with tetragonal-structure were successfully synthesized from MnCl2·4H2O and KOH in LiOH aqueous solution, via chemical lithiation under liquid olefin atmosphere at 353K. The microstructure and composition of the nanoparticles were characterized by X-ray diffraction, transmission electron microscopy, and inductively coupled plasma atom emission spectroscopy. The valence state of manganese in the sample was determined by the redox titration method. Further, the electrochemical performance of the sample as a cathode material was evaluated by galvanostatic measurements and cyclic voltammetry. The sample was found to exhibit a tetragonal structure with irregularly shaped grains, and grain diameters between 20 and 40nm. The t-Li0.35MnO2 prepared also exhibited high capacity as lithium ion cathode materials with an initial discharge capacity of 178.8mAhg−1 and retained the discharge capacity at 131.7mAhg−1 after 50 cycles.

Valence and electronic trap states of manganese in SrTiO3-based colossal permittivity barrier layer capacitors

Valence and trap level of manganese in the (Mn, Nb)-doped SrTiO3 internal barrier layer capacitor was revealed by EELS and Q-DLTS, explaining macroscopic properties.

Phase Stability of Lithium Manganese Oxide Stored at High Temperatures

Capacity degradation of the LiMn2O4 cathode during high-temperature storage was investigated for various lithium contents. The capacity recovery rate was determined after the storage test, and the phases and valence state of manganese ions were investigated by X-ray diffraction and X-ray absorption fine structure. The storage characteristics depend on the state of charge (SOC); a significantly low recovery rate was found for the shallow SOC region of LiMn2O4. The phase changes determined after the deterioration were as follows. (i) The lattice parameters decrease with an increase in manganese valence, caused by the formation of defects at the 16d site due to manganese dissolution. (ii) A new phase forms as a second phase. This phase has higher manganese valence and a larger amount of manganese vacancies. The same type of phase was produced by a high-temperature treatment of the shallow SOC phase at 150°C, which indicates that the phase was stable at high temperatures. (iii) A lower manganese valence state was observed at the spinel surface, which is related to manganese dissolution. Deterioration in the shallow SOC region during high-temperature storage is related to the phase stability of the de-intercalated spinel phases.

Reduction in the Band Gap of Manganese-Doped Zinc Oxide: Role of the Oxidation State

Manganese-doped zinc oxide powders were synthesized by solid state reaction of the respective oxides. The high-temperature conditions were chosen such that multiple valence states of manganese were doped in the host zinc oxide lattice. Structural characterization was carried out to confirm the doping and to find the maximum amount of manganese that can be incorporated. Diffuse reflectance spectroscopy was used to measure the optical band gap of the doped sample and the lowering with respect to pure ZnO was attributed to the presence of higher oxidation states of manganese. The presence of these oxidation states was confirmed using x-ray photoelectron spectroscopy. The study shows that a solid state reaction is a viable route for synthesizing doped metal oxides with desired optical properties.

Synthesis of diluted magnetic semiconductor Bi2−xMnxTe3 nanocrystals in a host glass matrix

Diluted magnetic semiconductors of manganese doped in bismuth-telluride nanocrystals (Bi2−xMnxTe3 NCs) were grown in a glass matrix and investigated by Transmission Electron Microscopy, X-Ray Diffraction, Atomic Force Microscopy/Magnetic Force Microscopy, and Electron Paramagnetic Resonance. TEM images showed that the nanocrystals formed within the glass matrix were nearly spherical, with average sizes between 4 and 5 nm, and d015-spacing of approximately 0.322 nm, which corresponds to the (015) interplanar distance in Bi2Te3 bulk. The diffraction patterns showed that the diffraction peak associated with the (015) plane of the Bi2−xMnxTe3 nanocrystals shifts to larger diffraction angles as manganese (Mn) concentration increases, suggesting that the Mn2+ ions are substitutional defects occupying Bi sites (MnBi). AFM and MFM measurements showed magnetic phase contrast patterns, providing further evidence of Mn2+ ion incorporation in the nanocrystal structure. EPR signal of manganese ion incorporation and valence states in the crystalline structure of the Bi2Te3 nanocrystals confirmed the presence of the Mn2+ state.

Valence state of manganese and iron ions in La1−xAxMnO3 (A = Ca, Sr) and Bi1−xSrxFeO3 systems from Mn2p, Mn3s, Fe2p and Fe3s X-ray photoelectron spectra. Effect of delocalization on Fe3s spectra splitting

La1−xCaxMnO3 (x = 0.5, 0.7, 0.85, 0.95) ceramic samples are synthesized by solid state reaction method. Mn3s and Mn2p X-ray photoelectron spectra (XPS) of La1−xCaxMnO3, and Fe3s-spectra of Bi1−xSrxFeO3 (0 ≤ x ≤ 1) are measured at room temperature. Both Mn3+ and Mn4+ ions are discovered in La1−xCaxMnO3 similarly to the case of Fe3+ and Fe4+ found earlier in Bi1−xSrxFeO3 ceramics. Relative Mn3+/Mn4+ contents are determined by fitting measured Mn2p spectra with combinations of Mn2p spectra of compounds containing tri- and quadrivalent Mn ions. Relative portion of Mn4+ is shown to increase with the increase of x. Fe3s spectrum splitting in Bi1−xSrxFeO3 increases with x in contrast to the Mn3s-spectrum splitting in La1−xCaxMnO3 and La1−xSrxMnO3. Anomalous behavior of Fe3s splitting is explained in the frame of the model of partly itinerant 3d-electrons by strong effect of 3d electron delocalization on electron correlation interaction in final state of 3s photoabsorption.

Microstructure and electrical properties of manganese borosilicate glasses

The structure, optical and electrical properties of manganese borosilicate glasses of the composition xMnO–(80−x)SiO2–20B2O3 (x=40, 50, and 60mol%) were investigated. The dependence of the glass structure on its composition was discussed and related to electrical properties. A separation of two amorphous phases was observed. It was suggested that one phase is MnO-rich and the other is SiO2-rich. It was found that the conductivity of MnO-rich phase is much higher than the conductivity of the other phase. The analysis of the valence states of manganese suggest that the transition metal ions are mainly present at second oxidation state. Magnetic susceptibility measurements show antiferromagnetic interactions in samples.

Electrochemical Properties of Composite Electrodes, Prepared by Spontaneous Deposition of Manganese Oxide into Poly-3,4-ethylendioxythiophene

In the present work, a simple cost-effective method of synthesis of composite PEDOT/MnO2 with dispersed manganese oxide particles was investigated. The composites were obtained by spontaneous reduction of permanganate ions in contact with PEDOT film. The morphology of highly dispersed manganese oxide in PEDOT film was characterized by SEM. XPS spectroscopy was employed for identification of valence states of manganese in composites at different oxidation states. FTIR spectra also confirm the presence of MnO2 in the composite.Electrochemical properties of composites, obtained with variation of synthesis conditions, were investigated using cyclic voltammetry and electrochemical impedance spectroscopy. The capacitive parameters of composites with different ratio between PEDOT and MnO2 layers were systematically investigated and analyzed. Specific capacitance of composites Cs,PEDOT/MnO2 was in the range of 148–221Fg−1 and increased with the increase of MnO2 loading (from 27 to 72wt%) into PEDOT film. The calculated values of capacitance related to contribution of manganese oxide Cs,MnO2 were in the range 274–310Fg−1.The enhanced capacitive properties of composites can be mainly attributed to 3-D distribution of disperse MnO2 in the porous structure of PEDOT film with high surface area. The presence of conducting porous matrix facilitates ion diffusion and electron transfer, leads to the lowering the internal resistance of composite material and improves the electrochemical utilization of manganese oxide. The stability of composite materials was shown by means of long-term cycling, where the low reduction in capacitance values was observed.

X-ray fluorescence determination of the manganese valence state and speciation in manganese ores

This work concerns determination of the manganese valence state and speciation by wavelength-dispersive X-ray fluorescence analysis. The authors investigated the effect of the manganese valence state and speciation on the intensity of some К-series lines of the X-ray emission spectrum for the samples of manganese compounds. The intensities of MnKβ5 line and MnKβ′ satellite are least influenced by speciation, and they may be used for evaluating the manganese valence state for the samples containing low iron. The intensities of MnKβ″ and MnKβx satellites may be employed for assessing the manganese speciation. The results of X-ray fluorescence determination of the manganese valence state and speciation in the manganese ores of the South Ural deposits agree with the X-ray diffraction data. The X-ray fluorescence method is definitely advantageous, because it does not require a complicated process of sample preparation and allows to receive fast information on the manganese valence state and speciation with the purpose to assess the quality of manganese ores. Copyright © 2015 John Wiley & Sons, Ltd.

Probing local site environments and distribution of manganese in SrZrO3:Mn; PL and EPR spectroscopy complimented by DFT calculations

In order to understand the local environment, valence state and distribution of manganese; a combined experimental and theoretical approach based on PL, EPR and DFT is reported for Sr(1−x)Zr(1−y)Mn(x+y)O3, also explaining the origin of various defect related emissions.

On-chip lithium cells for electrical and structural characterization of single nanowire electrodes

We present a transmission electron microscopy (TEM)-compatible, hybrid nanomachined, on-chip construct for probing the structural and electrical changes in individual nanowire electrodes during lithium insertion. We have assembled arrays of individual β-phase manganese dioxide (β-MnO2) nanowires (NWs), which are employed as a model material system, into functional electrochemical cells through a combination of bottom-up (dielectrophoresis) and top-down (silicon nanomachining) unit processes. The on-chip NWs are electrochemically lithiated inside a helium-filled glovebox and their electrical conductivity is studied as a function of incremental lithium loading during initial lithiation. We observe a dramatic reduction in NW conductivity (on the order of two to three orders in magnitude), which is not reversed when the lithium is extracted from the nanoelectrode. This conductivity change is attributed to an increase in lattice disorder within the material, which is observed from TEM images of the lithiated NWs. Furthermore, electron energy loss spectroscopy (EELS) was employed to confirm the reduction in valence state of manganese, which occurs due to the transformation of MnO2 to LixMnO2.

Enhanced ferroelectric properties and thermal stability of nonstoichiometric 0.92(Na0.5Bi0.5)TiO3-0.08(K0.5Bi0.5)TiO3 single crystals

Bi deficient, Mn doped 0.92(Na0.5Bi0.5)TiO3-0.08(K0.5Bi0.5)TiO3 single crystals were grown by carefully controlled top-seeded solution growth method. Local structures were investigated by transmission electron microscopy. The site occupation and valence state of manganese were characterized by electron paramagnetic resonance spectrum. The leakage current density in the as-grown single crystals is effectively depressed. The introduced defect complexes suppress the temperature induced phase transformation, increasing the depolarization temperature (165 °C) and thermal stability of ferroelectric properties.

Structural and magnetic inhomogeneities, phase transitions, 55Mn NMR, and magnetoresistive properties of La0.6Sr0.2Mn1.2 − x Nb x O3 ceramics

Ceramic samples of lanthanum strontium manganite perovskites La0.6Sr0.2Mn1.2 − xNbxO3 (x = 0–0.3) annealed at temperatures of 1260 and 1500°C have been investigated using the X-ray diffraction, electron microscopic, resistive, magnetoresistive, and magnetic (χac, 55Mn NMR) methods. It has been found that there is a correlation between the increasing unit cell parameter a of the rhombohedral R\(\bar 3\)c structure and the average ionic radius with increasing niobium concentration x and annealing temperature for the case where the lattice contains anion vacancies, cation vacancies, and nanostructured clusters. The observed increase in the electrical resistivity and decrease in the temperatures of metal-semiconductor phase transition Tms and ferromagnetic-paramagnetic phase transition TC with an increase in the niobium concentration x and the annealing temperature have been explained by the decrease in the content of the ferromagnetic phase, as well as by changes in the ratio Mn3+/Mn4+, the oxygen nonstoichiometry, and the concentration of defects weakening the high-frequency electronic exchange of the ions Mn3+ ↔ Mn4+. The presence of nanostructured clusters in the lattice has been confirmed by an anomalous hysteresis associated with the unidirectional exchange anisotropy of the interaction between the ferromagnetic matrix and antiferromagnetic clusters with Mn2+ and Nb3+ in distorted A-positions. An analysis of the asymmetrically broadened 55Mn NMR spectra and their computer decomposition have revealed a high-frequency electronic exchange and an inhomogeneity of the magnetic and valence states of manganese due to the nonuniform distribution of all ions and defects. Two types of magnetoresistive effects have been found: one effect, which is observed near the phase transition temperatures TC and Tms, is caused by scattering at intracrystalline nanostructured heterogeneities of the imperfect perovskite structure, and the other effect, which is observed in the low-temperature range, is induced by tunneling through intercrystalline mesostructured boundaries. The phase diagram has demonstrated that there is a strong correlation between the composition, structure, resistive and magnetic properties of rare-earth manganites.

Structural and magnetic heterogeneities, phase transitions, 55Mn NMR, and magnetoresistive properties of La0.6Sr0.3 − x Bi x Mn1.1O3

The structural, resistive, magnetic, and magnetoresistive properties of the La0.6Sr0.3 − xBixMn1.1O3 ceramics have been studied. The substitution of Bi ions for Sr ions increases the lattice parameter of the rhombohedral perovskite structure, decreases the metal-semiconductor and ferromagnet-paramagnet phase transition temperatures and the peak of the magnetoresistive effect, and increases the resistivity, approaching the system to the ferroelectric state. The 55Mn NVR study indicates on the high-frequency Mn3+ ↔ Mn4+ superexchange and heterogeneity of the valence and magnetic states of manganese due to the nonuniformity of distribution of all ions and defects. The phase diagram has been constructed, which shows a strong correlation between the structural, magnetic, and magnetoresistive properties.

Alumina-supported manganese oxide sorbent prepared by sub-critical water impregnation for hot coal gas desulfurization

Manganese oxide was loaded on the surface of γ-Al2O3 by sub-critical water impregnation using manganese acetate and manganese nitrate precursors to synthesize Mn(A) and Mn(N) sorbents for removing H2S from hot coal gas. Active component precursors present very obvious effect on the desulfurization capacity of sorbent. Mn(A, 11) sorbent with 11% Mn content in γ-Al2O3 maintains a desulfurization efficiency of close to 100% over 480min. However, it reduces to below 90% for Mn(N, 11) sorbent when the reaction lasts over 75min. The characterizing results of fresh and used sorbents from different precursors using AAS, SEM, BET, Raman, XAS and XPS techniques show that the acidity and alkalinity of active component precursor solution greatly influences the loading rate, valence state and dispersion of manganese on γ-Al2O3, which are the main properties for improving desulfurization performance of sorbents. The manganese loading rate of Mn(A) sorbent is much higher than Mn(N) sorbent. The better dispersion of manganese on γ-Al2O3 and the higher Mn2+ and Mn3+ contents on the surface of sorbent afford the high desulfurization activity of Mn(A). Moreover, Mn(A, 11) performs well in removing H2S from hot gas at 400°C after three desulfurization -regeneration cycles.

The Basic Properties of the Electronic Structure of the Oxygen-evolving Complex of Photosystem II Are Not Perturbed by Ca2+ Removal

Ca(2+) is an integral component of the Mn(4)O(5)Ca cluster of the oxygen-evolving complex in photosystem II (PS II). Its removal leads to the loss of the water oxidizing functionality. The S(2)' state of the Ca(2+)-depleted cluster from spinach is examined by X- and Q-band EPR and (55)Mn electron nuclear double resonance (ENDOR) spectroscopy. Spectral simulations demonstrate that upon Ca(2+) removal, its electronic structure remains essentially unaltered, i.e. that of a manganese tetramer. No redistribution of the manganese valence states and only minor perturbation of the exchange interactions between the manganese ions were found. Interestingly, the S(2)' state in spinach PS II is very similar to the native S(2) state of Thermosynechococcus elongatus in terms of spin state energies and insensitivity to methanol addition. These results assign the Ca(2+) a functional as opposed to a structural role in water splitting catalysis, such as (i) being essential for efficient proton-coupled electron transfer between Y(Z) and the manganese cluster and/or (ii) providing an initial binding site for substrate water. Additionally, a novel (55)Mn(2+) signal, detected by Q-band pulse EPR and ENDOR, was observed in Ca(2+)-depleted PS II. Mn(2+) titration, monitored by (55)Mn ENDOR, revealed a specific Mn(2+) binding site with a submicromolar K(D). Ca(2+) titration of Mn(2+)-loaded, Ca(2+)-depleted PS II demonstrated that the site is reversibly made accessible to Mn(2+) by Ca(2+) depletion and reconstitution. Mn(2+) is proposed to bind at one of the extrinsic subunits. This process is possibly relevant for the formation of the Mn(4)O(5)Ca cluster during photoassembly and/or D1 repair.

Electrodeposited MnOx Films from Ionic Liquid for Electrocatalytic Water Oxidation

AbstractA novel method for the electrodeposition of highly active water oxidation catalysts is described. The manganese oxide (MnOx) films are electrodeposited on fluorine tin oxide (FTO) glass substrate at high temperature (120 °C) from an ionic liquid electrolyte (ethylammonium nitrate). A range of analytical techniques, including X‐ray absorption spectroscopy (XAS), X‐ray diffraction (XRD), and energy‐dispersive X‐ray analyzer (EDX), indicate that the valence state of manganese in the deposited films can be controlled by changing the electrolyte composition. Along with the different phase compositions, a number of different morphologies including nanowires, nanoparticles, nanofibers as well as highly open and dense structures are obtained by varying the acidity of the electrolyte. The effect of morphology and chemical composition on the catalytic activity towards water oxidation is investigated. The film composed of Mn3O4 shows low catalytic activities, while the films composed of birnessite‐like manganese oxide phase and Mn2O3 exhibit high catalytic activities for water oxidation. The catalytic activities are also affected by the surface morphology, i.e., a higher surface area and more open structure shows a higher catalytic activity. High rates of oxygen production are observed from MnOx films prepared in a neutral electrolyte.