Atomic Ratio Of Mn Research Articles

Effect of Mn substitution on superconductivity in iron selenide (Li, Fe)OHFeSe single crystals**Project supported by the National Key Research and Development Program of China (Grant Nos. 2017YFA0303003 and 2016YFA0300300), the National Natural Science Foundation of China (Grant No. 11574370), and the Strategic Priority Research Program and Key Research Program of Frontier Sciences of the Chinese Academy of Sciences (Grant Nos.

We synthesize a series of Mn substituted (Li, Fe)OHFeSe superconductor single crystals via a modified ion-exchange method, with the Mn concentration z (the atomic ratio of Mn:Se) ranging from 0 to 0.07. The distribution homogeneity of the Mn element incorporated into the lattice of (Li, Fe)OHFeSe is checked by combined measurements of high-angle-annular-dark-field (HAADF) imaging and electron energy-loss spectroscopy (EELS). Interestingly, we find that the superconducting transition temperature Tc and unit cell parameter c of the Mn-doped (Li, Fe)OHFeSe samples display similar V-shaped evolutions with the increasing dopant concentration z. We propose that, with increasing doping level, the Mn dopant first occupies the tetrahedral sites in the (Li, Fe)OH layers before starting to substitute the Fe element in the superconducting FeSe layers, which accounts for the V-shaped change in cell parameter c. The observed positive correlation between the Tc and lattice parameter c, regardless of the Mn doping level z, indicates that a larger interlayer separation, or a weaker interlayer coupling, is essential for the high-Tc superconductivity in (Li, Fe)OHFeSe. This agrees with our previous observations on powder, single crystal, and film samples of (Li, Fe)OHFeSe superconductors.

Mesoporous Mn promoted Co3O4 oxides as an efficient and stable catalyst for low temperature oxidation of CO

Mesoporous Mn-doped Co3O4 catalysts were successfully prepared via a dry soft reactive grinding method based on solid state reaction, and their catalytic performances on CO oxidation were evaluated at a high space velocity of 49,500 mL g−1 h−1. A significant promoted effect was observed once the atomic ratios of Mn/(Co+Mn) were lower than 10%, for instance, the temperature for 50% conversion decreased to about −60 °C, showing superior catalytic performance compared to the single metal oxide. Especially, the Mn-promoted Co3O4 catalyst with a Mn/(Co+Mn) molar ratio of 10% could convert 100% CO after 3000 min of time-on-steam without any deactivation at room temperature. As prepared catalysts were characterized by XRD, N2-adsorption/desorption, TEM, H2-TPR, O2-TPD and CO-titration analysis. The significant enhancement of performance for oxidation of CO over Mn-Co-O mixed oxides was associated with the high active oxygen species concentrations formed during the pretreatment in O2 atmosphere.

Li1.2Mn0.54Ni0.13Co0.13O2 hollow hierarchical microspheres with enhanced electrochemical performances as cathode material for lithium-ion battery application

Li1.2Mn0.54Ni0.13Co0.13O2 hollow hierarchical microspheres (LNCM-HS) were successfully synthesized by molten salt method used the as-prepared MnO2 microspheres as the precursor and template. The sharp and well-defined reflection peaks suggest a high crystallization degree of the samples, and no impurities were observed. Li1.2Mn0.54Ni0.13Co0.13O2 material obtained is a solid solution consisting of rhombohedral R3-m and monoclinic C2/m group symmetries, which is confirmed by XRD, Raman spectra, and HRTEM. SEM and TEM shows that the hierarchical microspheres of LNCM-HS are composed of primary nano particles with the size of about 50nm. EDS mapping demonstrates that Ni, Mn, Co, and O elements are evenly distributed without any phase separation in LNCM-HS, and the atomic ratio of Mn, Co, Ni is calculated to be 0.54: 0.13: 0.12, which is quite close to the stoichiometry of 0.5 Li2MnO3·0.5LiMn1/3Co1/3Ni1/3O2. LNCM-HS exhibits excellent rate capacity of 309.9 (0.1C), 280.1 (0.3C), 226.5 (0.75C), 178.3 (1C), 139.3 (3C), and 101.0mAhg−1 (5C), respectively, whereas LNCM-bulk cathode displays a discharge capacity of 290.1, 230.0, 163.3, 135.4, 92.7, and 60.2mAhg−1 at the same rates. The improved capacity of LNCM-HS is ascribed to the increased lithium diffusion coefficient and reduced charge transfer resistance. The enhanced electrochemical performances can be attributed to the distinctive hollow microspheres structures, the increase contacting area between electrodes and electrolyte and the buffered volume changes during Li ions intercalation/deintercalation processes.

Microelectrochemical Investigation of Atmospheric Aging Effect on Pitting Corrosion Resistance at Manganese Sulfide Inclusion in Type 304 Stainless Steel

Stainless steels are widely used in architectural applications, such as roofing and walls. In atmospheric environments, pitting causes discoloration (rust staining) on the steel surfaces, which compromises the esthetic appearance of architecture considerably. The pitting behavior of stainless steels in outdoor environments has been extensively investigated through long-term exposure tests 1. It is generally accepted that most stainless steels experience severe corrosion within the first two years in marine environments, and there is a correlation between rust staining resistance and pitting resistance 2. Even in atmospheric environments, sulfide inclusions, such as MnS, act as initiation sites for pitting. Considering these points, it is reasonable to consider the possibility that atmospheric aging improves pitting corrosion resistance at MnS inclusions in stainless steels. In our previous works 3-5, we studied the pit initiation behavior at the MnS inclusions in Type 304 stainless steels. The pit initiation mechanism was found to be as follows: 1) the dissolution of the MnS inclusions leads to the deposition of elemental sulfur on and around the inclusions; 2) the synergistic effect of the elemental sulfur and chloride ions causes the dissolution of the stainless steel side at the MnS/steel boundaries, resulting in the formation of trenches; 3) the hydrolysis reaction of Cr3+ released from the steel matrix dissolution decreases the pH in the trenches, and at the same time, the electrode potential at the bottom of the trenches decreases due to the IR-drop. Finally, the pit initiation is defined as the local transition from the passive to active state at the bottom of the trenches. Atmospheric aging is an important subject for the corrosion engineering of stainless steels, and a thorough understanding how the aging affects the described pit initiation process at the MnS inclusions is expected to help in the endeavor to create corrosion resistant surfaces for stainless steels. Micro-scale electrode areas with dimensions of approximately 300 μm×150 μm which contained a stripe-like MnS inclusion were prepared to analyze the effect of atmospheric aging on the dissolution of MnS inclusions and the pitting initiation process at the inclusions. A commercial re-sulfurized Type 304 stainless steel bar with a diameter of 70 mm containing large MnS inclusions was used in this study. This stainless steel was heat-treated at 1353 K for 0.5 h and quenched in water. The specimen surfaces parallel to the rolling direction were mirror polished, and then exposed to air at 298 K and 50% relative humidity (RH) for 1, 30, and 90 days. A SEM/EDS (scanning electron microscope/energy-dispersive X-ray spectroscopy) analysis indicated that the MnS inclusions did not dissolve during the 90-day exposure, and the atomic ratios of Mn and S of the inclusions remained almost 1:1. An AES (auger electron spectroscopy) analysis indicated no outstanding changes in the thickness of passive film on the steel matrixes after the 30 days of exposure, whereas the thickness of the oxide layer on the MnS inclusions had doubled after the 30-day exposure period. In order to investigate the correlation between the oxide layer formed on the MnS inclusions and the pit initiation at the inclusions, the anodic polarization curves of a micro-scale electrode area were measured in 3 M NaCl. It is interesting to note that the exposure for in excess of 30 days improved the resistance of the investigated stainless steel to pitting at the MnS inclusions with no stable pitting found on the specimens exposed. The extent of the dissolution of the MnS inclusions on the specimens exposed for more than 30 days measured in 0.1 M Na2SO4and 0.1 M NaCl was suppressed to less than half that of the specimens exposed for one day. In addition, the exposure for 90 days inhibited the trench formation at the MnS/steel boundaries in 3 M NaCl. The over 30 days of exposure (atmospheric aging) resulted in the suppression of the MnS dissolution by the growth of the oxide layer on the inclusions, and then inhibited the formation of the trenches at the MnS/steel boundaries as a trigger for the pit initiation at the MnS inclusions. This explains the lower activity of MnS inclusions in atmospheric environments. 1. M.J.Johnson and P.J.Pavlik, in: W.H.Ailor (Ed.), Atmospheric Corrosion, John Wiley, New York, 1982, p. 462. 2. I.Muto, E.Sato, and S.Ito, ASTM STP 1194, American Society for Testing and Materials, Philadelphia, 1994. 3. A.Chiba, I.Muto, Y.Sugawara, and N.Hara, J. Electrochem. Soc., 159, C341 (2012). 4. A.Chiba, I.Muto, Y.Sugawara, and N.Hara, J. Electrochem. Soc., 160, C511 (2013). 5. A.Chiba, I.Muto, Y.Sugawara, and N.Hara, Mater. Trans., 55, 857 (2014).

One-pot simple synthesis and characterisation of Mn2+-doped GaN nanorods by RAPET method

In this work, we display one-step reactions under autogenic pressure at elevated temperature (RAPET) method-based synthesis of Mn-doped GaN nanorods by varying the atomic ratio of Mn:Ga as 0, 0.02, 0.04, 0.06 and 0.08, respectively. The synthesised nanorods are characterised by X-ray diffraction, high-resolution transmission electron microscopy (HRTEM) and Raman spectral methods. It is observed that there is a decrease in the lattice constant with an increase in the concentration of Mn (from 0.02 to 0.08 wt%). Moreover, the smaller covalent radius of Mn is the key for the doping process. The Mn-doped GaN nanocrystals show rod-like morphology with a length of 40–50 nm and width of 8–12 nm. This size factor mainly depends on the doping of Mn [from transmission electron microscopy (TEM) analysis] into GaN components. Well-defined lattice fringes are elucidated for the growth of crystalline hexagonal GaN (wurtzite type) nanocrystals.

Efficient low-temperature catalytic combustion of trichloroethylene over flower-like mesoporous Mn-doped CeO2 microspheres

Flower-like mesoporous Mn-doped CeO2 microspheres with three-dimensional (3D) hierarchical structures were successfully prepared by a hydrothermal method with the aid of glucose and acrylic acid and subsequent particular thermal treatment, and characterized by SEM, XRD, N2 adsorption/desorption, H2-TPR, XPS, Raman spectra and so on. The results show that the atomic ratios of Mn/(Ce+Mn) in the Ce–Mn–O samples as well as their morphologies affect obviously their catalytic performances for low-temperature catalytic combustion of trichloroethylene (TCE). These flower-like Ce–Mn–O microspheres have not only very excellent activity but also high stability, compared with pure flower-like CeO2 microspheres or bulk Ce–Mn–O samples. The flower-like sample with atomic ratio of Mn/(Ce+Mn) of 0.21 exhibits the best activity, for instance, T50 (the temperature for 50% conversion of TCE) is as low as 87°C, showing much higher catalytic activity than the sample prepared by a co-precipitation or sol–gel method. High surface area, high oxygen mobility and rich surface active oxygen species are responsible for the high catalytic performance of flower-like Mn-doped CeO2 microspheres, compared with general Ce–Mn–O mixed oxides.

Hydrothermal-Reduction Synthesis of Manganese Oxide Nanomaterials for Electrochemical Supercapacitors

In the present work, amorphous manganese oxide nanomaterials have been synthesized by a common hydrothermal method based on the redox reaction between MnO4(-) and Fe(2+) under an acidic condition. The synthesized MnO2 samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and electrochemical studies. XRD results showed that amorphous manganese oxide phase was obtained. XPS quantitative analysis revealed that the atomic ratio of Mn to Fe was 3.5 in the MnO2 samples. TEM images showed the porous structure of the samples. Electrochemical properties of the MnO2 electrodes were studied using cyclic voltammetry and galvanostatic charge-discharge cycling in 1 M Na2SO4 aqueous electrolyte, which showed excellent pseudocapacitance properties. A specific capacitance of 192 Fg(-1) at a current density of 0.5 Ag(-1) was obtained at the potential window from -0.1 to 0.9 V (vs. SCE).