Presence Of Mn3 Research Articles

Mössbauer and Magnetic Study of Lanthanum Manganite La1 – xCaxMn0.98Fe0.02O3 + δ (x = 0.05, 0.10, 0.20): Nonstoichiometric and Stoichiometric Composition

Mossbauer and magnetic study of calcium-doped lanthanum manganites La1 – xCaxMn0.98Fe0.02O3 + δ (x = 0.05, 0.10, 0.20) of nonstoichiometric (LCM–NS) and stoichiometric (LCM–S) compositions have been carried out in a wide temperature range. Phase structural separation is observed in the samples of stoichiometric composition (δ = 0). With a decrease in temperature all investigated lanthanum manganite samples exhibit superparamagnetic behavior, caused by the formation of small magnetic clusters in the structure. An expansion of the concentration range toward lower dopant concentrations in the LCM–S samples allowed us to establish the competing processes occurring at a low Ca content, including the Jahn‒Teller effects (orbital order) and the presence of Mn4+ ions (violation of orbital order), and study the dynamics of the structure and magnetic properties as functions of the Ca content.

Optical and electrical properties of manganese doped-alkali metaphosphate glasses

Phosphate glasses are of large interest for a variety of technological applications due to their several unique properties. In this work we investigate structural, optical and electrical properties of some alkali metaphosphate glasses doped with manganese oxide inside the system (50-x/2) K2O-xMnO2-(50-x/2) P2O5 with (0 ≤ x ≤ 30%mol). The glassy samples have been prepared using a melt-quench process. The obtained glasses are colored and the valence of manganese is composition dependence. The local structure of Mn2+ in the glasses is evaluated by EPR spectroscopy. The optical absorption spectra have been used to evaluate the values of the optical band gap (Eg) and Urbach energy (ΔE). The variation of these optical parameters as a function of composition is investigated. The presence of Mn3+ in the glasses is established by the optical absorption and this ion is associated with the absorption band at 520–530 nm. dc conductivity of the glasses is studied and it is found that it is thermally activated and followed an Arrhenius behavior.

Synthesis of Aurivillius Phase CaBi4Ti4O15 Doped with both La3+ and Mn3+ Cations: Crystal Structure and Dielectric Properties

Abstract The four-layer Aurivillius CaBi4Ti4O15 with introducing of La3+ on the A-site and Mn3+ on the B-site with the formula Ca1-xBi3+xLaTi4-xMnxO15 (x = 0, 0.2, 0.4, 0.6, 0.8, and 1) were synthesized by molten salt method using the mixture of sulfate salts K2SO4/Na2SO4 as the flux. XRD data confirmed the formation of single-phase Aurivillius with A21am orthorhombic structure for x = 0, 0.2, 0.4, and 0.6, whereas for x = 0.8 and 1, the impurity phases were observed. SEM analysis shows the anisotropic plate-like grains, which are a typical grain of Aurivillius phases. The cell volume decreases with increasing x, indicating a presence of mixed valences of Mn3+ and Mn4+. The dielectric constants increased with x, strongly correlated with the higher distortion of the structure, the 6s2 lone pair electrons of Bi3+ cation increase. The presence of Mn3+ unpaired electrons results in the increase of dielectric loss as increasing x.

Manganese promoted TiO2 and ZrO2 nanostructures for soot combustion with boosted efficiency

TiO2, ZrO2 and mixed-oxide (TiO2-ZrO2) materials with manganese as active promoter were synthesized. The performance of these catalysts was tested in the diesel soot oxidation reaction. The soot conversion light-off temperature was remarkably lowered by manganese in the mixed-oxide (TiO2-ZrO2) in comparison with manganese in the TiO2 and ZrO2 catalysts. On the other hand, the mixed oxide enhanced surface defects because of the promotional role played by the ZrO2 interface, which led to the formation and stabilization of defect sites. In addition, the O2/TPD characterization revealed two peaks corresponding to desorption of oxygen species and desorption of lattice oxygen between 120 and 500 °C, which was correlated with the catalytic activity. The manganese-doped-mixed-oxide (TiO2-ZrO2) catalyst displayed structural stability, higher surface area, presence of Mn3+ and Mn4+ species and soot conversion light-off temperature of 260 °C, which was preserved after three reaction cycles.

Colossal dielectric behaviour of Sr2TiMnO6-δ single crystals

Single crystals of Sr2TiMnO6-δ were grown by optical floating zone technique. The single phase nature of the grown crystal was confirmed by powder X-ray diffraction studies. The permittivity of the grown crystal was about 104 at room temperature. The presence of Mn3+ and Mn4+ state resulted in the splitting of T2g mode which is evident from Raman spectrum. The mixed valence state of Mn for charge carrier hopping was determined by X-ray photoelectron spectroscopy.

Synthesis of MgO@CeO2-MnOx core shell structural adsorbent and its application in reducing the competitive adsorption of SO2 and NOx in coal-fired flue gas

Magnesium oxide (MgO) with different morphologies was prepared by oxalic acid sol-gel method and the MgO were used to prepare three different kinds of adsorbents for simultaneous SO2 and NOx removal from coal-fired flue gas. It was found that the core-shell coated adsorption material MgO@CeO2-MnOx prepared from MgO formed by calcination of magnesium oxalate at 650 ℃ had the best performance. The MgO@CeO2-MnOx exhibited an adsorption breakthrough time up to 50 min and dynamic adsorption capacity of 0.3507 mmol/g and 0.1407 mmol/g for SO2 and NOx respectively. This is better than any other composite material. The N2 adsorption-desorption isotherms result showed that core-shell structure material possessed the largest specific surface area, which could be its basic advantage for efficient adsorption. According to different operating conditions tests, it was found that the adsorption of SO2 and NOx by the adsorbent was dominated by chemisorption. Therefore, the surface metal material (MnOx, CeO2) played an important role in the adsorption process. According to FTIR and DRIFTS analysis, it was observed that the SO2 and NO were oxidized by hydroxyl groups on the absorbent surface and the oxidation was further aggravated by the presence of Mn4+, Mn3+, Ce3+and Ce4+. Core-shell materials successfully prepared can reduce or weaken the adsorption competition between SO2 and NOx in three aspects: 1. The surface oxidation ability is strengthened and it is easy to adsorb the two substances, which makes the metal oxides on the shell surface interact fully with the adsorbents; 2. More and more effective adsorption sites are provided; 3. The adsorbent provides greater specific surface area and appropriate pore size.

Low-temperature elemental mercury removal over TiO2 nanorods-supported MnOx-FeOx-CrOx

TiO2 nanorods-supported MnOx, FeOx, CrOx, and MnOx-FeOx-CrOx catalysts have been prepared by a deposition-precipitation method, with the aim of investigating the combination of ternary metal oxides effect on elemental mercury (Hg0) removal. The TiO2 nanorods-supported MnOx-FeOx-CrOx catalyst manifested the superior Hg0 removal efficiency (∼80-83%) at low temperatures (100–200 °C) in the presence of O2. The addition of NO promoted the Hg0 removal efficiency under the same reaction conditions. Further, SEM, HRTEM, XRD, BET surface area, and XPS characterization were carried out to explore the physicochemical properties of the catalysts. It was found that the integration of three active metal oxides contributed to the enrichment of active sites and the surface adsorbed oxygen species, thereby improving the catalytic activity. Additionally, both the large surface area and high crystallization of the obtained TiO2 nanorods resulted in uniform dispersion of the manganese-iron-chromium mixed metal oxide nanoparticles and a high activity. Further, XPS data of spent MnOx-FeOx-CrOx/TiO2 catalyst indicated that the presence of Mn4+, Cr6+, and Fe3+ could promote Hg0 oxidation due to the strong synergistic interaction between the TiO2 nanorods-incorporated MnOx, FeOx, and CrOx nanoparticles.

Co-site substitution by Mn supported on biomass-derived active carbon for enhancing magnesia desulfurization.

Oxidation of magnesium sulfite (MgSO3) is a crucial step for reclaiming the product in wet magnesia desulfurization processes. Here, for enhancing this reaction, a bimetallic catalyst was developed by loading CoOx and MnOx species on a biomass-derived active carbon (AC) support to minimize the costs and potential environmental risks during catalyst application. The substitution effect of Mn to Co sites was investigated, and a comparison of the catalyst with plain cobalt suggested that the ratio of Co/Mn must be greater than 3. A series of catalyst characterizations was performed to reveal the synergistic effect of Co and Mn in the bimetallic catalyst. The introduction of Mn species not only improved the dispersion of CoOx-MnOx mixed oxide but also generated abundant Co3+ species and surface-adsorbed oxygen, both of which acted as the main active sites for sulfite oxidation. Notably, in the bimetallic catalyst, the presence of Mn4+ species assisted regeneration of Co2+ to Co3+ species, further accelerating sulfite oxidation. Besides, the partial substitution of Co sites by Mn also suppressed the losing of Co species during reaction, favoring to decrease the environmental risk, as well as to save the cost of catalyst.

Far- and mid-infrared emission and reflectivity of orthorhombic and cubic ErMnO3 : Polarons and bipolarons

We report on the high-temperature evolution of far- and mid- infrared reflectivity and emissivity spectra of ambient orthorhombic ErMnO3 from 12 K to sample decomposition above 1800 K. At low temperatures the number of phonons agrees with the predictions for orthorhombic space group D2h16-Pbnm (Z=4) and coexists with a paramagnon spin resonance and rare earth crystal field transitions. Increasing the temperature, a number of vibrational bands undergo profile broadening and softening approaching the orbital disordered phase where the orthorhombic O' lower temperature cooperative phase coexists with cubic-orthorhombic O. O-ErMnO3 undergoes a first order order-disorder transition into the perovskite cubic phase at Tcubic ~1329 K where the three triple degenerate phonons allowed by the space group Pm-3m(Z=1) are identified. At about 800 K, a quantitative small polaron analysis of the orthorhombic mid-infrared real part optical conductivity shows that antisymmetric and symmetric breathing modes sustain the strongest electron-phonon interactions. Above Tcubic the bipolaron fingerprint profile is the mid-infrared dominant and only feature. Its appearance correlates with the localized screening of the highest vibrational mode reststrahlen band. We propose that the longitudinal optical mode macroscopic field screening is consequence of dynamically sharing {\delta} disproportioned eg electrons hovering over the JT distorted octahedral dimer [Mn (QJT)3+{\delta} (Mn(QJT)3-{\delta}))O6/2]2. A thermal driven insulator-metal transition is detected with onset ~1600 K. We also address the occurrence of an inhomogeneity induced THz band result of heating the samples in dry air, triggering Mn3+-Mn4+ double exchange, under the presence of Mn4+ smaller ions stabilizing the orthorhombic lattice.

Local structure and magnetic properties of Mn3+–O–Fe3+ superexchange interaction in an oxygen-vacant perovskite: Experimental and theoretical study

In this work we report an experimental and theoretical study on the local structure and magnetic properties of Mn3+–O–Fe3+ superexchange interaction for an oxygen-vacant perovskite PrBaMnFeO5+δ with δ ∼ 0.5. Structural studies were performed by high resolution X-Ray diffraction technique in normal and anomalous scattering, modeled using an orthorhombic biphasic system corresponding to an oxygen-rich and oxygen-poor stoichiometries. Mössbauer spectroscopy showed the presence of two orthorhombic iron sites, one ascribed to a fully octahedral coordination and another, highly distorted, ascribed to a pyramidal coordination, in full agreement with theoretical DFT + U + SO calculations. The samples showed a spin-glass transition at ∼20 K and mainly the presence of Mn3+–O–Fe3+ type-G antiferromagnetic superexchange interactions. However, our theoretical calculations using first principles also suggested that the presence of oxygen vacancies in certain conditions could be possibly promoting local ferromagnetic interactions.

Identifying Influential Parameters of Octahedrally Coordinated Cations in Spinel ZnMnxCo2–xO4 Oxides for the Oxidation Reaction

Transition metal oxides are potential alternatives to precious metal catalysts for oxidation reactions. Among these earth abundant oxide catalysts, cobalt- or manganese-based spinel oxides have attracted consistent interest because of their superior catalytic performances. It has been found that the octahedral sites in spinels are responsible for their catalytic activities. However, little is known about the parameters of the octahedrally coordinated cations that influence their activity. Herein, a series of ZnMnxCo2–xO4 (x = 0–2.0) spinel oxides are investigated, employing CO oxidation as the model reaction, with particular attention being paid to the variation in activity caused by tuning the ratio of octahedrally occupied Mn to Co. Both Mn and Co contribute to the activity with Mn cations as the primary active species when they coexist; the intrinsic specific activity is found to be dependent on composition, and the highest activity is seen at a Mn/Co molar ratio of 0.11. The presence of Mn4+ and Mn3+ ...

Truncated Octahedral High-Voltage Spinel LiNi0.5Mn1.5O4 Cathode Materials for Lithium Ion Batteries: Positive Influences of Ni/Mn Disordering and Oxygen Vacancies

Micron-sized truncated octahedral LiNi0.5Mn1.5O4 (LNMO) samples with different degrees of Ni/Mn disordering have been obtained by controlling the synthesis conditions, such as calcination atmosphere (O2 and air), cooling rate or additional annealing step. The influences of Ni/Mn disordering on the physical properties and electrochemical performance of the truncated octahedral LNMO samples have been systematically investigated. The analyses of thermogravimetry, X-ray photoelectron spectroscopy, X-ray diffraction, powder neutron diffraction, Raman spectroscopy and X-ray absorption spectroscopy reveal that the occurrence and degree of Ni/Mn disordering are closely related with the formation of oxygen vacancies and presence of Mn3+. Slow cooling rate and post-annealing can result in low degrees of Ni/Mn disordering and oxygen vacancies. Electrochemical measurements show that Ni/Mn disordering and oxygen vacancies have no obvious effect on the rate capability since all LNMO samples share a truncated octahedral morphology with the exposed {100} surfaces. However, they play significant roles in improving long-term cycling stability, especially at the elevated temperature of 60°C. This work suggests that the electrochemical performance of LNMO with optimized truncated morphology can be further enhanced through tuning the degrees of Ni/Mn disordering and oxygen vacancies.

Role of microstructure, electron transfer, and coordination state in the CO2 capture of calcium-based sorbent by doping (Zr-Mn)

A combination of oxygen vacancy and high Tammann temperature of the inert material in the calcium-based sorbent is crucial to capture CO2. Herein, a novel (Zr-Mn)-doped calcium-based sorbent was explored, and the role of microstructure, electron transfer, and coordination state in the process of CO2 capture was thoroughly explained. The good dispersity, favorable porosity, and optimized pore size distribution are the unique features of sorbent. The well-dispersed CaZrO3 and Ca2MnO4 crystallite phases prevent CaO crystallite growth and agglomeration. The introduction of Mn promotes the ability of donating electrons from Ca atom to Osurf that reacts with CO2. It can generate oxygen vacancy with the presence of Mn4+ and Mn3+ species. The effect of the coordination state of Mn on CO2 adsorption and electronic properties was also revealed by density functional theory (DFT) calculations. The incorporation of Mn into the surface layer of CaO is favorable to CO2 adsorption. The sorbent (Ca/Zr/Mn = 15:0.5:0.5) exhibited an excellent durability with adsorption capacity of about 0.60 g CO2/g sorbent after 65 cycles.

The crystal chemistry of oxo-mangani-leakeite and mangano-mangani-ungarettiite from the Hoskins mine and their impossible solid-solution: An XRD and FTIR study

AbstractNew chemical (EMP, SIMS) and structural data are reported for a suite of crystals of oxo-mangani-leakeite and mangano-mangani-ungarettiite from their common type locality, the Hoskins mine (New South Wales, Australia). Notwithstanding the low OH content, FTIR analysis of selected sampleshas provided considerable information on short-range order in these Mn3+-rich amphiboles, and shows that Li is associated with occupied A sites and is linked to the oxo-component at the O(3) site. Comparative analysis of all available data allows us to: (1) further improveour understanding of the crystal-chemistry of these very peculiar compositions of the oxo-amphibole group; and (2) calculate reliable site-populations. The proposed limited compositional variability has been confirmed. The two amphiboles have completely different arrangements of CR3+cations. In oxo-mangani-leakeites, those CR3+ cations related to the oxocomponent occur at the M (1) site, whereas those CR3+ cations related to the leakeite charge-arrangement occur at the M (2) site. In mangano-mangani-ungarettiite,all CR3+ cations order at the M (1) and M (3) sites, and local bond-valence requirements are satisfied by the presence of Mn3+, which assumes a strongly distorted coordination due to its degenerate eg electronic state. Therefore,the inverse patterns observed for both cation-ordering and deformation of the octahedra are incompatible with solid-solution between these two species that coexist at the Hoskins mine.

Effect of Mn-substitution on the structure and magnetic properties of CoFe2O4/SiO2 nanocomposites

Mn-substituted CoFe2O4/SiO2 nanocomposites were prepared by sol–gel method using Mn-substituting for Co or Fe. The microstructural, morphological, and magnetic characterizations were carried out by X-ray diffraction, transmission electron microscope, X-ray photoelectron spectroscopy, vibrating sample magnetometer, and Mossbauer spectroscopy. It can be found that the Mn-substituted CoFe2O4 particles in obtained nanocomposites exhibit cubic spinel structure and the substitution of Co or Fe by Mn increase the lattice constant. The results of X-ray photoelectron spectroscopy, vibrating sample magnetometer and Mossbauer spectroscopy demonstrate that Mn ions exists as Mn2+ and tend to preferentially occupy octahedral A sites when it replaces Co ions as in Co0.8Mn0.2Fe2O4/SiO2 nanocomposites, which leads to the saturation magnetization Ms increasing and coercivity Hc decreasing. While Mn ions valence state is +3 as it substitutes to Fe ions as in CoFe1.8Mn0.2O4/SiO2. The presence of Mn3+ induces a decrease in Ms and Hc.

Study of DNA damage caused by dipyrone in presence of some transition metal ions

The DNA damage in the presence of dipyrone (used as its sodium salt, NaDip) and some transition metal ions in an air saturated ([O2]≈0.25mM) non-buffered solution at T=(25.0±0.5)°C was investigated by agarose gel electrophoresis. As metal ions Cu2+, Fe3+, Ni2+ and Mn3+ were selected and evaluated in the present study because of the important role they play in a biological system.pUC19 plasmid DNA damage-induced by NaDip (80–600μM) was observed in the presence of 100μM Cu2+. The damage was proportional to the NaDip concentration provided that the order of addition of reagents (pUC19 plasmid DNA+Cu2++NaDip) is obeyed. Addition in the reaction medium of ligands for Cu2+ and Cu+, respectively EDTA and neocuproine, promoted total inhibition or reduction of the pUC19 plasmid DNA damage suggesting the involvement of the Cu2+/Cu+ cycle. Besides, the decrease in the pUC19 plasmid DNA damage after addition of catalase (1.0×10−4mgμL−1) in the same reaction medium indicates that H2O2 is also involved in the damage process.In NaDip concentration range (80–600μM), and under same the experimental conditions, it was not possible to conclude whether there was pUC19 plasmid DNA damage caused by 10μM Fe3+. No damage was observed in the presence of Mn3+ or Ni2+.Although the technique used in this study is sensitive to detect the pUC19 plasmid DNA damage it was not possible to identify in which DNA base this damage occurs. Further studies with other techniques should be made to unambiguously identify the oxidative intermediates that are responsible for the DNA damage.As far as we know, this is the first study dealing with the pUC19 plasmid DNA damage-induced by NaDip in presence of copper, iron, nickel and manganese ions.

Catalytic homogeneous oxidation of monoterpenes and cyclooctene with hydrogen peroxide in the presence of sandwich-type tungstophosphates [M4(H2O)2(PW9O34)2]n−, M = CoII, MnII and FeIII

Catalytic efficiency of tetrabutylammonium salts of sandwich tungstophosphates B‐α‐[M4(H2O)2(PW9O34)2]n−, M=CoII, MnII, FeIII, was studied in the oxidation of (R)-(+)-limonene, geraniol, linalool, linalyl acetate, carveol, and cis-cyclooctene with hydrogen peroxide, in acetonitrile. Oxidation of (R)-(+)-limonene gave limonene-1,2-diol as main product. Epoxidation of linalool takes place preferentially at the more substituted 6,7-double bond, the corresponding 6,7-epoxide reacting further, yielding furano- and pyrano-oxides, via intramolecular cyclization. Oxidation of linalyl acetate occurred preferentially at the more substituted 6,7-double bond for Mn4(PW9)2, affording 6,7-epoxide at 82% selectivity. Linalyl acetate 1,2-epoxide was the major product with 51% and 77% selectivity for Co4(PW9)2 and Fe4(PW9)2, respectively. Oxidation of carveol occurred with very good conversions in the presence of Mn4(PW9)2, Co4(PW9)2 and Fe4(PW9)2, yielding carvone and carveol 1,2-epoxide in similar amounts. Oxidation of cis-cyclooctene gave only the epoxide, while oxidation of geraniol at room temperature afforded 2,3-epoxygeraniol as the major product.

High electrochemical performance of high-voltage LiNi0.5Mn1.5O4 by decoupling the Ni/Mn disordering from the presence of Mn3+ ions

Electrochemical activity in high-voltage spinel LiNi0.5Mn1.5O4 (LNMO) is strongly affected by the disordering of Ni/Mn and the presence of Mn3+ ions. However, understanding the effect of the Ni/Mn disordering or the presence of Mn3+ ions on electrochemical properties is not trivial because disordering is typically coupled with the presence of Mn3+ ions. Here, we demonstrate for the first time that the doping of Li instead of Ni increases Ni/Mn disordering, which is decoupled from the presence of Mn3+ ions. The resultant material has a particle size of ~1–2 μm and can achieve 120 mAh g−1 at 10 C for 50 cycles and further deliver about 60 mAh g−1 even at a rate of ~60 C (1 min discharge). Superior electrochemical performance is achieved by increased solid-solution phase transition behavior, which is caused by increased Ni/Mn disordering during delithiation. By decoupling, we find that the electrochemical properties in LNMO strongly depend on the phase transformation behavior and that the Ni/Mn disordering, rather than Mn3+ ions, affects the phase transformation by increasing the solid-solution reaction. The fundamental understanding gained from this work could be applied to the development of other phase-separating compounds to improve their electrochemical performance. Doping LiNi0.5Mn1.5O4 (LNMO) with Li instead of Ni significantly improves its electrochemical performance, find scientists in Korea. Cathode materials with high redox potentials are needed to realize lithium-ion batteries with high energy densities. The high-voltage spinel LNMO is a promising cathode material, but its electrochemical performance is strongly affected by the disordering of Ni/Mn in the presence of Mn3+ ions. Now, Junghwa Lee, Chaeah Kim and Byoungwoo Kang at Pohang University of Science and Technology in Korea have found that doping LNMO with Li decouples Ni/Mn disordering from the presence of Mn3+ ions. This significantly improves its electrochemical performance through enhanced solid-solution phase transition. The researchers anticipate that the results of the current study can be used to improve the electrochemical performance of other phase-separating compounds. We at the first time demonstrate that the Ni/Mn disordering in LNMO spinel is decoupled from the presence of Mn3+ ions by doping Li and strongly affects phase transformation resulting in the increase of solid-solution phase transformation. The resulting material with 1–2 μm achieves superior rate capability, 120 mAh g−1 at ~38 C and 60 mAh g−1 at 60 C.

(Invited) High Electrochemical Performance of High Voltage LiNi0.5Mn1.5O4 By Decoupling the Ni/Mn Disordering from the Presence of Mn3+ ions

High energy density of a lithium ion battery (LIB) is an essential requirement for novel applications such as plug-in hybrid electric vehicles and electric vehicles. Increasing the redox potential of cathode materials is an effective way to achieve high energy density in the cell. For this purpose, high-voltage spinel LiNi0.5Mn1.5O4 (LNMO) is a promising cathode material for LIBs because it has a high redox potential of ~ 4.7 V, which makes its energy density (~650 W∙h/kg) 20% higher than that of conventional LiCoO2. However, the electrochemical properties of LNMO spinel depend on several factors such as its structure, the quantity of Mn3+ ions, the particle size, and the morphology of particles. Especially, the structure of the spinel has a critical influence on its electrochemical performance. LNMO structure is dictated by the ordering of Ni and Mn at two octahedral sites, which take two forms: disordered and ordered spinel. However, under typical experimental conditions, disordered spinel shows the disordering of Ni/Mn with the presence of Mn3+ ions, whereas ordered spinel shows the ordering of Ni/Mn without Mn3+ ions. As a result, electrochemical properties of the disordered spinel always depend on both the disordering of Ni/Mn and Mn3+ ions. For example, disordered spinel shows an extended solid-solution reaction during phase transformation whereas ordered spinel shows two distinct two-phases reactions. Furthermore, the presence of Mn3+ ions in the disordered spinel increases its electronic conductivity, and thereby improves its electrochemical performance. Therefore, disordered LNMO spinel can have better electrochemical performance than ordered spinel due to high electronic conductivity and facile phase transformation. The origin of the different electrochemical properties in the disordered spinel is not clear because of the coupling of the Ni/Mn disordering with Mn3+ ions. Understanding of this origin could guide improvement of LMNO’s electrochemical properties. However, experimentally understanding the effect of disordering or the effect of Mn3+ ions on the electrochemical properties is not easy because the Ni/Mn disordering is always coupled with the presence of Mn3+ ions. In this presentation, we will discuss the effect of the Ni/Mn disordering without the presence of Mn3+ on the electrochemical performance. At first, the Ni/Mn disordering was decoupled from the Mn3+ ions in this study. By using this decoupling, we will show how the Ni/Mn disordering affects electrochemical properties and the phase transformation behavior. Furthermore, we will discuss about key factors affecting superior rate capability in high voltage spinel by decoupling of the disordering from Mn3+ ions.

Insight for Formation of Oxygen Deficiency in Spinel-Type LiNi0.5Mn1.5O4-δ Using Ab Initio DFT Calculations

Spinel-type LiNi0.5Mn1.5O4 (LNMO) have attracted attention as cathode materials for lithium-ion batteries due to its high-voltage at ~ 4.7 V vs. Li+/Li. LNMO is considered to belong to two different crystal structures such that Ni/Mn ordered P4332 and disordered Fd-3m. Relationship between crystal structures and their electrochemical performances has been experimentally- and computationally- investigated, showing that disordered Fd-3m structure contains oxygen deficiency with reduction of Mn from Mn4+ to Mn3+. Although the presence of Mn3+ improve electronic conductivity, Jahn-Teller distortion and dissolution of Mn occurs. Phase transition from disordered Fd-3m to ordered P4332 occurs with diminish oxygen deficiency by annealing in oxygen atmosphere at 700 ̊C. Understanding the formation mechanism of the oxygen deficiency would be helpful to synthesis aimed crystal structure. However, computational studies with oxygen deficient model are limited so far. In this study, we evaluate the defect formation energies in oxygen deficient LNMO. The Vienna ab initio simulation package (VASP) was utilized with the generalized gradient approximation (GGA-PBEsol) + U and projector-augmented wave (PAW) methods. For the GGA + U calculations, the U values for the d-orbitals of Ni and Mn were set to 6.0 eV and 3.9 eV following relevant previous reports. An energy cutoff of 500 eV and a k-point mesh were chosen such that the product of the number of k-points and the number of atoms in the unit cell was greater than 1000. In the case of disordered Fd-3m structure, we used ‘uniform’ Ni/Mn distribution computationally reported by Lee et al., that is, the highest degree of local cation arrangements within random cation ordering. Coulombic energy was calculated for different 524 structures by Ewald method, the most stable Ni/Mn arrangement was consistent with ‘uniform’ distribution as mentioned above. The calculated lowest oxygen vacancy formation energies in P4332 and Fd-3m show 3.69 eV and 3.38 eV, respectively. Note that vacancy formation energy almost no difference in P4332 among different oxygen vacancy concentrations, whereas, in Fd-3m, vacancy formation energy decreased with increasing oxygen vacancy concentrations. This fact strongly suggests that Fd-3m structure promotes oxygen deficiency. In addition, not only oxygen vacancies type defect but also metal-excess type defect can be present as oxygen defect models. Formation energies for the system contains excess metals in P4332 and Fd-3m lattice show 2.98 eV and 2.58 eV, respectively. Formation energy for metal excess type in Fd-3m became 0.40 eV smaller than that in P4332, in agreement with experimental results that only Fd-3m contains oxygen defects. In addition, these values are lower than oxygen vacancy formation energies. These all finding indicates that metal-excess type oxygen deficiency can be more favorable than oxygen vacancy type oxygen deficiency for LNMO.