Diffusion Of Mn Ions Research Articles

Study on the mechanism of AF nucleation induced by complex oxide inclusions after LF refining in oxide metallurgical steel

The ladle furnace refining process (before LF, add Ti, add Al, add Mg, add Ca) of oxide metallurgical steel was sampled, and the effect of complex oxide inclusions generated after LF refining on acicular ferrite (AF) nucleation were studied by SEM, TEM, TKD and EBSD. The results show that the complex oxide inclusions after LF refining are composed of MgAl2O4, CaTiO3, TiO2, TiN, and MnS. Among them, MgAl2O4, CaTiO3, TiO2 and TiN have NW orientation relationship with adjacent AF laths. There are Mn depletion zone(MDZ) with a width of about 200 nm outside MgAl2O4, CaTiO3, TiO2 and MnS. Some AF laths can be nucleated by different inclusions under the combined action of MDZ mechanism and lattice mismatch mechanism. The first principle calculations show that MgAl2O4, CaTiO3 and TiO2 all have cation vacancies, and the diffusion of Mn ions into cation vacancies has thermodynamic advantages. The formation of MDZs is the combined effect of MnS precipitation on oxidized inclusions and Mn ions occupying cation vacancies in inclusions.

Defect controlled diffusion of lithium ions in Mn doped V2O5 for potential applications as cathode material

With a motivation to unravel the effect of cation (Mn) doping-induced modifications in structure, charge transfer resistance, and Li-ion diffusion in V2O5 a systematic study using X-ray diffraction (XRD), Raman Spectroscopy and electrochemical impedance spectroscopy (EIS) has been employed using three electrodes configuration. Structural investigations using XRD suggest the selective diffusion of Mn ion towards the c-axis at a low doping percentage. Raman spectroscopy suggests the shift in 994 cm-1 modes which substantiates the uniaxial diffusion of Mn ions. Nyquist plots show that interfacial charge transfer resistance is highest for the lowest doping i.e., 1% Mn-doped V2O5 and exhibits the lowest diffusion coefficient as compared to other doped V2O5 samples. Specific capacitance calculated from cyclic voltammetry is found to be highest for the 4% Mn-doped V2O5 sample. Moreover, diffusion of Lithium ions improves with an increase in doping concentration due to higher concentration of defects as evident from Δd/d and Nelson–Riley factor (NRF) for pure V2O5 and Mn-doped V2O5.

Molecular dynamics study on the Li diffusion mechanism and delithiation process of Li2MnO3

Li2MnO3 is critical component in the well-studied Li-excess cathode materials xLi2MnO3·(1- x)LiMO2 for achieving high lithium storage capacity. In this article, the diffusion of Li ions in Li2MnO3 is studied using molecular dynamics (MD) simulation with well-behaved empirical force fields obtained by fitting against the crystal structure from experiment and phonons calculated using Density Function Theory (DFT). We have found two possible tetrahedral hopping channels, 0-TM and 1-TM(Mn4+) channel, which are differentiated by the face sharing octahedral cations. Simulation results show that the 0-TM channel is active for Li hopping, while 1-TM(Mn4+) channel is inactive. During the delithiation process, the Li ions in the transition metal (TM) layer are firstly removed, then those in the Li layer. However, the Li ions will be trapped in the tetrahedral 0-TM channels as long as the four face sharing octahedral sites are cleared. Up to x = 1.0 for Li2-xMnO3, almost all the Li ions are located at the tetrahedral sites, forming a regular array along a axis. The de-intercalation of tetrahedral Li ions requires a high voltage (>5.2 V vs. Li/Li+), limiting the practical capacities measured in lab. The diffusion of Mn ions into the Li layer is observed in a deeper delithiated structure (x = 1.2 for Li2-xMnO3), indicating an initial phase transformation to a spinel-like structure. However, the Mn ions are mainly trapped in the tetrahedral sites in the Li layer, instead of the octahedral sites in spinel-like structure. A few of Mn ions diffusing into the octahedral sites in Li layers have no face sharing tetrahedral Li ions, revealing a further Li de-intercalation is imperative for the complete phase transformation. During the delithation process, the oxygen sublattice shows a strong stability. In the deeply dilithiated structure Li0.8MnO3, the local distortion of the oxygen sublattice is observed, which may indicate the oxygen release at this high delithation stage. Our model is not stable for x ≥ 1.4 in Li2-xMnO3. Other charge compensation mechanism should be considered in this high delithiation stage, eg. oxygen release.

Thickness dependence of microstructure in thin La0.7Sr0.3MnO3 films grown on (1 0 0) SrTiO3 substrate

This study investigates the nanostructure of perovskite thin films, and its influence on magnetic properties. Epitaxial thin films of perovskite MnO3 with thickness ranging from nm to 320 nm were deposited on SrTiO3 (1 0 0) substrates using pulsed laser deposition techniques. X-ray diffraction, along with high-resolution transmission electron microscopy (HRTEM) investigations were carried out, and showed the presence of a second, La-rich phase in thick film. Scanning electron microscopy analysis showed thinner films to have smooth surfaces, while thicker films presented large triangular shapes emerging out of the film surface. Also HRTEM images revealed epitaxial growth for thinner films. Thicker films grow with numerous misfit dislocations leading to columnar structure, where the thickest film presents branched structure with an intermediate La-rich layer. Lattice mismatch, diffusion of Mn ions into the substrate and substituting Ti ions are known as sources of strain in films near interfaces. Magnetic properties in the structure mentioned are described by double-exchange interaction, which is very sensitive to local structure. Hence, the nanostructure of films reported here has a remarkable effect on their magnetic properties.

Kinetics of stabilized cubic zirconia formation from MnO2–ZrO2 diffusion couple

Microstructure and kinetics of the cubic phase formation are studied in ZrO2–MnO2 diffusion couple. During annealing in Ar, no other compounds are detected except the zirconia solution. With diffusion of Mn ions from manganese oxide to ZrO2, the cubic zirconia are found at the phase interface. The growth kinetics of the cubic zirconia solution layer in the submicrometer scale are analyzed. The growth behavior of the cubic zirconia layer is better described by the grain boundary diffusion model, and our experiment data exhibit a t 1/4 dependence on time. The deviation from the experiment data to the theoretical value is also explained.

Facile Synthesis of Mn-Doped ZnS Nanocrystals and Determination of Critical Temperature for Lattice Diffusion Process

High-quality Mn:ZnS doped nanocrystals (d-dots) with photoluminescence (PL) quantum yield (QY) of 50-70% have been synthesized based on nucleation-doping strategy by choosing 1-dodecanethiol (DDT) as the capping ligand. Controlling the growth of small-sized MnS core nanoclusters was successfully achieved by changing the injection temperature of sulfur precursor, the growth time of MnS nuclei, and the amount of DDT. Furthermore, MnS/ZnS core/shell d-dots with a diffusion layer at the interface between the MnS core and the ZnS shell were fabricated through an overcoating of the ZnS shell layer on the presynthesized MnS core nanoclusters. The resulting monodisperse d-dots exhibited spherical shape with a zinc-blende crystal structure. The critical temperature for lattice diffusion of Mn ions in the ZnS host lattice was determined to be about 260 degrees C by annealing the presynthesized and purified Mn:ZnS d-dots.

The effect of Mn on the oxidation behavior and electrical conductivity of Fe–17Cr alloys in solid oxide fuel cell cathode atmosphere

Four Fe–17Cr alloys with various Mn contents between 0.0 and 3.0 wt.% are prepared for investigation of the effect of Mn content on the oxidation behavior and electrical conductivity of the Fe–Cr alloys for the application of metallic interconnects in solid oxide fuel cells (SOFCs). During the initial oxidation stage (within 1 min) at 750 °C in air, Cr is preferentially oxidized to form a layer of Cr 2O 3 type oxide in all the alloys, regardless the Mn content, with similar oxidation rate and oxide morphology. The subsequent oxidation of the Mn containing alloys is accelerated caused by the fast outward diffusion of Mn ions across the Cr 2O 3 type oxide layer to form Mn-rich (Mn, Cr) 3O 4 and Mn 2O 3 oxides on the top. After 700 h oxidation a multi-layered oxide scale is observed in the Mn containing alloys, which corresponds to a multi-stage oxidation kinetics in the alloys containing 0.5 and 1.0 wt.% of Mn. The oxidation rate and ASR of the oxide scale increase with the Mn content in the alloy changes from 0.0 to 3.0 wt.%. For the application of metallic interconnects in SOFCs, Mn-free Fe–17Cr alloy with conducting Cr free spinel coatings is preferred.

Improved Photoluminescence of MnS/ZnS Core/Shell Nanocrystals by Controlling Diffusion of Mn Ions into the ZnS Shell

We studied the diffusion of Mn ions in MnS/ZnS core/shell nanocrystals (NCs) from the MnS core to the ZnS shell by steady-state and time-resolved photoluminescence (PL) spectroscopy. The colloidal MnS/ZnS core/shell NCs with different thicknesses of the ZnS shell synthesized in octadecene with nucleation doping strategy were annealed at different temperatures. It was found that the PL intensity and lifetime of the MnS/ZnS NCs with a thin ZnS shell significantly decreased with increasing annealing time in the heat treatment temperature range of 220−300 °C, resulting from the diffusion of Mn ions in the MnS/ZnS core/shell NCs to the surface of the ZnS shell, while the PL intensity and lifetime of the NCs with a thick ZnS shell remained almost constant in the temperature range. Furthermore, it was noted that the MnS/ZnS NCs with a small MnS core of about 2.0 nm in diameter exhibited high PL quantum yield of greater than 40%. The experimental results indicated that highly efficient luminescent Mn-doped ZnS NC...

Fabrication and luminescence properties of self-assembled CdTe quantum dots embedded in an MnTe matrix

The growth of self-assembled CdTe quantum dots embedded in cubic MnTe by molecular beam epitaxy is reported. The dots are forced to form despite a small lattice mismatch of 2.3% between the dot and the barrier materials. Their properties are studied by means of time integrated and time resolved photoluminescence at various temperatures and magnetic fields. We demonstrate a considerable diffusion of Mn ions from the MnTe barrier into nominally nonmagnetic CdTe quantum dot, which is manifested as an enhancement of their magneto-optical effects, such as the Zeeman splitting of excitonic levels in the dots.

Improved photoluminescence of ZnS:Mn nanocrystals by microwave assisted growth of ZnS shell

The photoluminescence (PL) of ZnS:Mn nanocrystals was improved greatly by microwave assisted growth of ZnS shell. Under optimized conditions, the luminescence quantum yield of ZnS:Mn nanocrystals increased from 2.8% to 12.1% after the growth of the ZnS shell. Time-resolved fluorescence spectroscopic and electron paramagnetic resonance measurements indicate that the improvement of the dispersivity of the doped Mn ions is responsible for the PL enhancement. Growth of the ZnS shell not only facilitated the diffusion of Mn ions during microwave irradiation but also prohibited the segregation of Mn ions on the particle surface. As a result, more isolated Mn 2+ ions were produced after the growth of the ZnS shell, and thus the orange luminescence of ZnS:Mn nanocrystals was enhanced greatly.

Oxidation kinetics of Haynes 230 alloy in air at temperatures between 650 and 850 °C

Haynes 230 alloy was oxidized in air at temperatures between 650 and 850 °C. Thermogravimetry was used to measure the kinetics of oxidation. The formed oxides were identified by the thin film (small angle) X-ray diffraction technique. Cr 2O 3 and MnCr 2O 4 were found in the oxide scale. Multi-stage oxidation kinetics was observed, and each stage follows Wagner's parabolic law. The first slow oxidation stage corresponded to the growth of an Cr 2O 3 layer, controlled by Cr ions diffusion through the dense Cr 2O 3 scale. The faster second stage was a result of rapid diffusion of Mn ions passing through the established Cr 2O 3 scale to form MnCr 2O 4 on top of the Cr 2O 3 layer. A duplex oxide scale is expected. The third stage, with a rate close to that of the first stage, only appeared for oxidation in the intermediate temperature range, i.e., 750–800 °C, which can be explained by the interruption of the Mn flux that forms MnCr 2O 4.

Mn/MFI catalyzed reduction of NOx with alkanes

Mn/MFI catalysts were prepared by different methods and probed as catalysts for the catalytic reduction of NOx with CH4 or iso-butane in a gas flow containing excess O2. Mn/MFI with high manganese loading was obtained by solid state ion exchange (SSI). The intensity of an IR band at 957cm−1, which is due to the perturbation of zeolite lattice vibrations by Mn ions attached to cage walls is proportional to the Mn content of the catalysts. Conversely, the intensity of the 3610cm−1 band, assigned to Brønsted acid sites decreases linearly with the Mn loading. A catalyst obtained by exchanging Na/MFI with an aqueous solution of Mn acetate is found most active for NOx reduction with methane. Transport by surface diffusion of Mn ions from MnI2 to exchange positions in MFI is more efficient than their transport through the gas phase. High NO conversion over proton-free catalysts indicates that protons are not instrumental in NOx reduction over Mn/MFI.

Excimer laser induced diffusion in magnetic semiconductor quantum wells

Studies of pulsed laser annealing (PLA) of CdTe/CdMnTe quantum well structures are made in order to examine depth dependent effects in laser irradiated semiconductors. Since diffusion coefficients are strongly dependent on the temperature, depth resolution is achieved because the diffusion of Mn from the barriers into the quantum wells is depth dependent. Multiple quantum well (MQW) structures of CdTe/CdMnTe were annealed with single pulses from an XeCl laser at 308 nm. At a threshold of 90 mJ cm−2 two new emission bands are observed that are attributed to the diffusion of Mn from barrier layers to QWs. The diffusion associated with these bands, measured as the integrated product of the diffusion constant and time, is found to be 300 and 30 Å2. Calculations of the temperature, reached within the surface following PLA, using an analytical solution of the heat diffusion equation coupled with known high temperature diffusion coefficients predict the diffusion to decrease by one order of magnitude within one period at the top of the MQW stack. It is suggested that at the threshold surface melting occurs and that these emission bands arise from the QWs immediately beneath the melt front. The diffusion of Mn ions into the QWs is confirmed by magneto-optical data. A further emission band occurs at this same threshold with a Mn concentration above that of the concentration in the barrier layers of the MQW stack. This emission is attributed tentatively to the segregation of the Mn ion within the molten region following recrystallization.

Effect of La and Ce on the Reactivity of Fe-18 mass%Cr-7 mass%W Alloy with La<SUB>0.85</SUB>Sr<SUB>0.15</SUB>MnO<SUB>3</SUB>

The reactivity of Fe-18 mass%Cr-7 mass%W-R (R = La and/or Ce) alloys with the cathode material, La 0.85 Sr 0.15 MnO 3 , of solid oxide fuel cells (SOFCs) was examined in air at 1273 and 1373 K to evaluate the performance of these alloys as separator materials for SOFCs. In every reaction couple annealed, a Cr-diffusion zone formed in the La 0.85 Sr 0.15 MnO 3 and a duplex layer consisting of a thick Cr-Mn spinel layer and a thin Cr 2 O 3 layer formed at the alloy/La 0.85 Sr 0.15 MnO 3 interface as the products of oxidation and solid-state reactions, The addition of a small amount of La or Ce strongly inhibited the growth of the Cr-Mn spinel layer. The Cr-diffusion zone and the Cr-Mn spinel layer were found to be formed by the counter diffusion of Mn ions from the La 0.85 Sr 0.15 MnO 3 side and Cr ions from the Cr 2 O 3 side. The increase in the electrical resistivity of the alloy/La 0.85 Sr 0.15 MnO 3 interface was attributed to the increasing thickness of the Cr 2 O 3 layer in the duplex product layer formed at the interface during the reaction.

Reactions at the interface La0.5Ca0.5MnO3-YSZ/Al2O3 under anodic current

The reaction at the interface of a solid electrolyte cell between air electrode (La0.5Ca0.5MnO3) and YSZ-electrolyte with different Al2O3-contents was investigated by electron microscopy (SEM) and x-ray diffraction (XRD). Formation of MnAl2O4 was detected in a 5 µm diffusion zone within the electrolyte. MnAl2O4 formation can be explained by diffusion of Mn-ions into the electrolyte and subsequent reaction with the α-Al2O3 grains during sintering. Cell performance and long-term stability in SOFC operation are not negatively affected by MnAl2O4 formation. However a rise in electrode resistance and slow delamination of perovskite oxide electrode were observed after some hours of electrolysis. This reaction is the consequence of oxygen gas pressure at the electrolyte in the MnAl2O4 diffusion zone. It is caused by local increase of electronic conductivity by MnAl2O4 formation. Long-term stability also for electrolysis conditions has been achieved by an additional intermediate YSZ-layer between air electrode and electrolyte.

Magneto-optical study of excitonic binding energies, band offsets, and the role of interface potentials in CdTe/Cd1-xMnxTe multiple quantum wells.

Magneto-optical studies on a series of CdTe/${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$Te multiple-quantum-well structures with x\ensuremath{\simeq}0.08 have identified the 1S and 2S states of both the light- and heavy-hole n=1 excitons. This has allowed changes of the exciton binding energies to be studied as a function of the depth of the confining potentials, which were tuned through the ${\mathit{sp}}^{3}$-d exchange interaction in the barrier layers by application of a magnetic field. Calculations of these binding energies by a variational technique are in general agreement with the observations. The exchange-induced splitting of the heavy-hole exciton is found to be consistent with between 0.35 and 0.45 of the band offset being in the valence band, which accounts for the absence of any evidence that the valence-band structure changes from a type-I structure to a type-II structure above a certain value of a magnetic field. However, this offset is found to be too large to account for the exchange-induced splitting of the light-hole exciton, which appears to be anomalously large. Calculations have shown that this anomaly cannot be explained in terms of the diffusion of Mn ions from the barrier regions into the wells. An alternative explanation is given in terms of field-dependent interface potentials wherein the ${\mathit{sp}}^{3}$-d exchange interaction is considered to be different in the interface regions of the multiple quantum wells to that in the barrier regions.

Electrical and Mechanical Properties of Pb(Zr, Ti)O3 Ceramics Related to Mn Ion Diffusion

The electrical and mechanical properties of Pb(Zr, Ti)O3 (PZT) ceramics with Mn ions injected by diffusion at high temperature were studied. The rise of mechanical quality factor (Qm) and the change of fracture mechanism from intergranular fracture to transgranular fracture was observed with increased diffusion temperature. These changes are related to the diffusion of Mn ions from the grain boundaries into the grains.