Mn Substitution Research Articles

MnxFe5−xSi3 for active magnetic regenerative refrigeration at room temperature

Magnetocaloric properties of MnxFe5−xSi3 with x = 1, 1.1, 1.2, 1.3 were investigated for use in an active magnetic regenerator (AMR) for room temperature refrigeration. The Mn content was adjusted to tailor their Curie temperature and, hence, the operating range of the magnetic refrigerant. The peak magnetic entropy change and the maximum adiabatic temperature change for MnxFe5−xSi3 decreased with increasing Mn substitution. An in-house AMR testbed was built to investigate the suitability of the refrigerant in an AMR cycle. The maximum temperature span between cold and hot ends achieved by the AMR testbed using Mn1.2Fe3.8Si3 was 4.75 K at 300 K compared to 7.5 K for Gd. It was also demonstrated that the morphology of the refrigerant can have a measurable effect on the heat exchange between the refrigerant and the cooling fluid, which highlights that designing a solid magnetic refrigerant also requires appropriate technology to process the material to the desired size and shape. The magnetic refrigerant characteristics of MnxFe5−xSi3 were substantially inferior to those of Gd, but MnxFe5−xSi3 remains attractive in terms of material cost and processability.

Role of nickel doping on magnetocaloric properties of La0.7Sr0.3Mn1−xNixO3 manganites

This study reports the effect of Ni substitution for Mn on structural, magnetic, and magnetocaloric properties of La0.7Sr0.3MnO3 manganite synthesized by sol–gel technique. The structural, morphological, and magnetic properties are investigated using x-ray diffractometer (XRD), scanning electron microscope (SEM), and vibrating sample magnetometer (VSM) systems. XRD results showed that all samples crystallize in rhombohedral structure. Thermomagnetic measurements showed that TC decreases with the addition of Ni from 363 K for x = 0.00 to 324 K for x = 0.06. ΔSM determined by Maxwell’s relations and Landau theory gave compatible results in the transition temperature and region above. ΔS maxM values were determined as 4.52, 4.51, 4.41, and 3.90 J kg−1 K−1 for x = 0.00, 0.02, 0.04, and 0.06 at 5T, respectively. The Arrott plots and the scaling analysis of ΔSM, which collapsed on a single curve, showed that magnetic transitions are of second order.

Insight into the effect of manganese substitution on mesoporous hollow spinel cobalt oxides for catalytic oxidation of toluene

The cobalt oxides and manganese oxides have high-activity potential for catalytic oxidation of volatile organic compounds (VOCs), while the mesoporous hollow morphology is crucial to the mass transfer of reactant and product. Therefore, it is worth investigating the effect of manganese substitution in mesoporous hollow cobalt oxides on catalytic oxidation. Herein, a partially disordered spinel structure is formed by the Mn substitution in Co3O4 and the mesoporous hollow microsphere is improved in morphology homogeneity with the decrease of Co/Mn ratio in the range of 1.8–28.8. The 5Co1Mn (Mn-substituted Co3O4 with Co/Mn at 5.4) exhibits outstanding catalytic activity for toluene oxidation with 50% CO2 generation at 237 °C, which is 21 °C lower than Co3O4. Moreover, the 5Co1Mn displays satisfactory stability in reusability, lifetime, and water resistance. The small defective crystallite, mesoporous hollow morphology, and high specific surface area endow Mn-substituted Co3O4 with more surface chemical adsorbed oxygen, enhancing the catalytic oxidation of toluene. Theoretical calculation on (311) plane of Co3O4 reveals that Mn2+ or Mn3+ substitution increases the formation energy of oxygen vacancy and makes it difficult to adsorb gaseous oxygen on the defective surface. The interaction between Co and Mn impedes the improvement of toluene oxidation because the mobility of lattice oxygen, the surface distribution of Co3+, and the ratio of surface adsorbed oxygen to surface lattice oxygen are hindered by Mn substitution. The chemical adsorbed oxygen is more active than lattice oxygen in the oxidation of adsorbed intermediates (phenolate, benzoate species, etc.). The Langmuir-Hinshelwood mechanism dominates in the catalytic oxidation at 200–250 °C, while the catalytic oxidation follows both the Langmuir-Hinshelwood mechanism and Mars-van Krevelen mechanism above 250 °C. This work provides some enlightenment for exploring the role of surface oxygen species in VOCs oxidation and uncovering the interaction in binary spinel oxides.

Mössbauer characterization of microbially mediated iron and manganese ores of variable geological ages

A combination of various techniques was applied to investigate the mineralogy of the Neoproterozoic Urucum iron and manganese deposit (Brazil) and Carboniferous and Permian manganese carbonate deposits (China). The examined deposits exhibited signs of microbial mediation from Fe and Mn bacteria and cyanobacteria. The studied samples showed diversity in their composition and particle size. Probes from Urucum deposit revealed that the rocks consist mainly of hematite, showing Mn substitution which reflects the oxidation of Mn on the active surface of Fe-rich biomat. Nanominerals occurring in significant concentration also supported the microbial contribution to the formation of these ores. Representative samples of Neoproterozoic and Permian deposits showed considerable amount of mixed carbonates with variable composition.

Evolution of structural, magnetic and magnetocaloric effect in TmFe1-xMnxO3 (x≤0.3)

The influence of Mn doping on structure, magnetic behaviors and magnetocaloric effect in TmFeO3 polycrystalline ceramics has been explored. X-ray powder diffraction proves that TmFe1-xMnxO3 (x ≤ 0.3) ceramics maintain an orthorhombic structure, and the space group is Pbnm. Compared with the original TmFeO3 sample, structural parameters change slightly and magnetic properties are effectively tuned with the gradual substitution of Mn at Fe site. The spin reorientation temperature region shifts from 90.3 to 73.2 K for TmFeO3 to 180.0–156.0 K for TmFe0.7Mn0.3O3. Besides, for TmFe1-xMnxO3 (x ≤ 0.3), the maximum magnetic entropy changes dependent on the Mn composition are 6.29 J/kg K, 6.56 J/kg K, 6.79 J/kg K and 7.22 J/kg K for 0–70 kOe, respectively. The refrigeration capacities are 159.3 J/kg, 168.9 J/kg, 176.7 J/kg and 184.4 J/kg, respectively. For a better assessing the magnetocaloric performance of TmFe1-xMnxO3 (x ≤ 0.3), we have calculated the temperature average entropy change, refrigerant capacity and normalized refrigerant capacity, and their values become larger with increasing Mn doping. Our experimental results can provide valuable references for the application and development of RFeO3 (R = rare earth) as multifunctional materials.

Structural and Dielectric Properties of La0.5Pr0.2Ba0.3Mn1−xTixO3 (x = 0.0 and 0.1) Manganite

In this work, we study the structural and dielectric properties of La0.5Pr0.3Ba0.2Mn1-xTixO3 (x = 0.0 and 0.1) samples prepared using the solid-state reaction technique. The X-ray structural analysis using Rietveld refinement method exhibits that both compounds are single phase and crystallize in the rhombohedral structure with R $${ }\overline{3}{ }$$ C space group. In addition, a scanning electron microscopy (SEM) study proved an increase in the grain size with substitution of Mn by Ti in the B site. The dielectric properties of these compounds have been studied by complex impedance spectroscopy in the frequency range from 40 Hz to 1000 kHz and temperatures from 100 K to 200 K. The DC conductivity decreases with the substitution of Ti, and the experimental data were fitted by Jonscher’s universal power law. The impedance plot exhibits semicircle arcs at different temperatures. Similarly, the variations of imaginary parts of modulus and impedance show an electrical relaxation phenomenon with non-Debye nature for both samples. The values of the activation energy are determined from the conductivity data analysis and imaginary impedance.

Understanding Co roles towards developing Co-free Ni-rich cathodes for rechargeable batteries

Current bottlenecks in cobalt (Co) supply have negatively impacted commercial battery production and inspired the development of cathode materials that are less reliant on Co. However, complete Co elimination is prevented by the lack of fundamental understanding of the impact of Co on cathode capacity and structural stability, as well as the lack of effective substitute components in practice. Here we investigate the roles of Co in purposely designed systems that include both Co-rich and Mn-substituted Co-free cathodes. Our results affirmed that Co plays an undeniable role in fast capacity and/or structural degradation, and found that Co is more destructive than Ni at high potentials, which offers unexpected but encouraging perspectives for Co reduction. Moreover, Mn substitution effectively alleviates the destructive effects of Co and enables a high potential functionality. With these fundamental discoveries, we demonstrated a series of LiNiαMnβXγO2 (X = single or multiple dopants) as a promising candidate for Co-free cathodes.

Doping Graphene with Substitutional Mn.

We report the incorporation of substitutional Mn atoms in high-quality, epitaxial graphene on Cu(111), using ultralow-energy ion implantation. We characterize in detail the atomic structure of substitutional Mn in a single carbon vacancy and quantify its concentration. In particular, we are able to determine the position of substitutional Mn atoms with respect to the Moiré superstructure (i.e., local graphene-Cu stacking symmetry) and to the carbon sublattice; in the out-of-plane direction, substitutional Mn atoms are found to be slightly displaced toward the Cu surface, that is, effectively underneath the graphene layer. Regarding electronic properties, we show that graphene doped with substitutional Mn to a concentration of the order of 0.04%, with negligible structural disorder (other than the Mn substitution), retains the Dirac-like band structure of pristine graphene on Cu(111), making it an ideal system in which to study the interplay between local magnetic moments and Dirac electrons. Our work also establishes that ultralow-energy ion implantation is suited for substitutional magnetic doping of graphene. Given the flexibility, reproducibility, and scalability inherent to ion implantation, our work creates numerous opportunities for research on magnetic functionalization of graphene and other two-dimensional materials.

Effect of Mn4+ ions on the structure and luminescence properties of NaY(MoO4)2: Yb3+/Er3+ phosphor

Abstract In this work, we prepare a series of phosphor of NaY(MoO4)2: Yb3+/Er3+/Mn4+ using high temperature solid state method, the results of X-ray diffraction (XRD) shows that the doped Yb3+, Er3+ and Mn4+ ions will make lattice be smaller size. The reduction of the binding energy of O-1s XPS is due to the vacancy of O2− ions in the matrix lattice which is brought by the substitution of Mn4+ and Mo6+ ions. Under the laser excitation of 980 nm, the Er3+ ions exhibit strong green up-conversion emission and weak red up-conversion emission at 532, 554 and 658 nm, corresponding to the transitions of 2H11/2/4S3/2 → 4I15/2, 4F9/2 → 4I15/2 of Er3+ ions. The reasons for the high green emission intensity are discussed in detail by analyzing the Raman spectroscopy of NaY (MoO4)2: Yb3+/Er3+/Mn4+ phosphor. It can be inferred that the emissions at 554 nm and 658 nm are a two-photon process by the relationship between pump power and up-conversion luminescence intensity, and the possible up-conversion emission mechanism has been explored. Meanwhile, the luminescence life of green and red light decreases with the increasing doping concentration of Mn4+ ions. After doping Mn4+ ions, the symmetry of the matrix lattice decreases, and the emission intensity of up-conversion will be greatly improved. The study of this work expands the research scope of traditional conversion materials, and offers reference for the exploration of up-conversion luminescent materials based on transition metals.

The structure, vacancy characteristics, and magnetic properties of GdMn1-xCrxO3 ceramics

To investigate the evolution of the structural and enhanced magnetic properties of GdMnO3 systems induced by the substitution of Mn with Cr, polycrystalline GdMn1-xCrxO3 samples were synthesized via solid-state reactions. XRD characterization shows that all GdMn1-xCrxO3 compounds with single-phase structures crystallize well and that Cr3+ ions entering the lattice sites of GdMnO3 induce structural distortion. SEM results indicate that the grain size of the synthesized samples (a few microns) decreases as the Cr substitution concentration increases. Positron annihilation lifetime spectroscopy reveals that vacancy-type defects occur in GdMn1-xCrxO3 ceramics and that the vacancy size and concentration clearly change with the Cr content. The temperature and field dependence of the magnetization curves show that Cr substitution significantly influences the magnetic ordering of the gadolinium sublattice, improving the weak ferromagnetic transition temperature and magnetization of GdMn1-xCrxO3. The enhanced magnetization of GdMn1-xCrxO3 is closely related to the vacancy defect concentration.

Enabling highly structure stability and adsorption performances of Li1.6Mn1.6O4 by Al-gradient surface doping

Manganese based ion-sieves, particularly Li1.6Mn1.6O4, can be used to recover Li+ from salt lakes due to their excellent adsorption and anti-dissolution properties. Generally, the element doping can only improve the adsorbent capacity or enhance the structural stabilities. In this work, the adsorption capacity of Li1.6Mn1.6O4 is improved from 33.4 to 40.9 mg/g (c(LiCl) = 24 mmol/L) via trace surface doping of Al (LMO-Al), likely owing to the partial substitution of Mn’s 16d sites by Al3+. Furthermore, the dissolution of Mn in Li1.6Mn1.6O4 is reduced from 5.4% (before doping) to 2.1%, which may due to stronger Al3+ and O2− chemical bond and improving the amounts of Mn4+. In addition, Al doping allowed for the reduction of the dissolution loss rate of Mn during cycling, which greatly increases the possibility in practical application.

Structural and magnetic properties of ball-milled powders of (Fe1−xMnx)75P15C10 met-glass

This paper reports on the structural and magnetic properties of a ball-milled powder sample of (Fe1−xMnx)75P15C10 (x = 0, 0.05, 0.1, 0.2, and 0.3) mixed metallic amorphous ribbons. X-ray diffraction patterns of the as-made powder samples demonstrate a structural phase transition from amorphous to the nanocrystalline structure having a tetragonal (P) type structure. Field emission scanning electron microscopic micrographs show that the particles form a nanocrystalline structure presumably due to the stress relaxation upon ball milling the amorphous ribbons. The observed phase transformation and the changed magnetic properties, e.g., significant enhancement in the coercive field leading to magnetic hardness, are attributed to the controlled milling and Mn substitution in this mixed metallic alloy system, which is the novelty of this research work.

Ca2+ effects on Fe(II) interactions with Mn-binding sites in Mn-depleted oxygen-evolving complexes of photosystem II and on Fe replacement of Mn in Mn-containing, Ca-depleted complexes.

Fe(II) cations bind with high efficiency and specificity at the high-affinity (HA), Mn-binding site (termed the "blocking effect" since Fe blocks further electron donation to the site) of the oxygen-evolving complex (OEC) in Mn-depleted, photosystem II (PSII) membrane fragments (Semin et al. in Biochemistry 41:5854, 2002). Furthermore, Fe(II) cations can substitute for 1 or 2Mn cations (pH dependent) in Ca-depleted PSII membranes (Semin et al. in Journal of Bioenergetics and Biomembranes 48:227, 2016; Semin et al. in Journal of Photochemistry and Photobiology B 178:192, 2018). In the current study, we examined the effect of Ca2+ cations on the interaction of Fe(II) ions with Mn-depleted [PSII(-Mn)] and Ca-depleted [PSII(-Ca)] photosystem II membranes. We found that Ca2+ cations (about 50mM) inhibit the light-dependent oxidation of Fe(II) (5µM) by about 25% in PSII(-Mn) membranes, whereas inhibition of the blocking process is greater at about 40%. Blocking of the HA site by Fe cations also decreases the rate of charge recombination between QA- and YZ•+ from t1/2 = 30 ms to 46ms. However, Ca2+ does not affect the rate during the blocking process. An Fe(II) cation (20µM) replaces 1Mn cation in the Mn4CaO5 catalytic cluster of PSII(-Ca) membranes at pH 5.7 but 2 Mn cations at pH 6.5. In the presence of Ca2+ (10mM) during the substitution process, Fe(II) is not able to extract Mn at pH 5.7 and extracts only 1Mn at pH 6.5 (instead of two without Ca2+). Measurements of fluorescence induction kinetics support these observations. Inhibition of Mn substitution with Fe(II) cations in the OEC only occurs with Ca2+ and Sr2+ cations, which are also able to restore oxygen evolution in PSII(-Ca) samples. Nonactive cations like La3+, Ni2+, Cd2+, and Mg2+ have no influence on the replacement of Mn with Fe. These results show that the location and/or ligand composition of one Mn cation in the Mn4CaO5 cluster is strongly affected by calcium depletion or rebinding and that bound calcium affects the redox potential of the extractable Mn4 cation in the OEC, making it resistant to reduction.

Tuning the large magnetoelectric coupling in Co4Nb2O9 with Mn substitution

Magnetoelectric (ME) materials have been attracting extensive attention due to their potential applications. It is important to realize strong ME effect in one single material at sufficiently high temperature, and thus substantial efforts in searching for ME materials with strong ME coupling together and a comprehensive understanding of the underlying mechanism is necessary. Herein we focus on the Mn-doped linear ME material Co4-xMnxNb2O9, in which a large electric polarization driven by magnetic field emerges below its Néel temperature TN, by presenting the detailed characterizations on the structure, magnetism, and ME effect. It is revealed that an increasing Mn substitution x allows largely enhanced TN and gradually suppressed ME coefficient αME. This ME coupling suppression is attributed to the weak spin-orbit interaction of Mn2+ with respect to Co2+. It is indicated that the Dzyaloshinskii-Moriya (DM) interaction plays an important role in the ME coupling. The measured largest αME is found in For Co0.8Mn3.2Nb2O9, reaching up to 9.9 ps/m at 10 K while the TN reaches up to 102 K, exceeding most of the linear ME materials that have been reported.

Improving the catalytic performance of LaNiO3 perovskite by manganese substitution via ultrasonic spray pyrolysis for dry reforming of methane

Dry reforming of methane is an attractive process because it uses two important greenhouse gases, CO2 for CH4, to produce valuable syngas. However, Ni-based catalysts are prone to a high carbon deposition in the dry reforming process. Mesoporous LaNi1-xMnxO3 perovskite (with x between 0 and 1) were synthesized by ultrasonic spray pyrolysis method. The substitution of Mn in the perovskite structure increased the specific surface area (from 7.2 for LaNiO3 to 22.4 for LaNi0.4Mn0.6O3), the pore size and pore volume. Temperature programmed reduction showed a lower reduction tendency of Mn-substituted samples, suggesting high structural stability. O2- temperature-programmed desorption showed significantly higher oxygen mobility as the result of partial Mn substitution. The Mn substitution improved the catalytic activity and stability, where LaNi0.6Mn0.4O3 achieved the highest conversion and remained relatively unchanged in the time on stream tests. The Mn substituted catalysts substantially decreased the carbon deposition and changed its form from whiskers to amorphous type. The XPS analysis suggests this change is due to the reversible transformation of Mn4+ and Mn3+, resulting in higher oxygen mobility. Microstructural characterization of the used catalyst revealed a lower sintering tendency for the Mn substituted catalysts than LaNiO3. Results suggest that Mn substitution significantly changed the catalytic mechanisms, where LaNiO3 removes carbon by forming La2O2CO3 intermediate, but the stable Mn substituted perovskite with high oxygen mobility and capacity removes the carbon through a cyclic redox mechanism.

Structural strain and competition between charge density wave and superconductivity in La(Fe,Mn)As(O0.89F0.11) compounds

Selected members of the $\mathrm{La}(\mathrm{Fe},\mathrm{Mn})\mathrm{As}({\mathrm{O}}_{0.89}{\mathrm{F}}_{0.11})$ system were analyzed using high-resolution synchrotron x-ray powder diffraction. The tetragonal to orthorhombic structural transition is progressively recovered in the optimally electron-doped $\mathrm{LaFeAs}({\mathrm{O}}_{0.89}{\mathrm{F}}_{0.11})$ phase by very light Mn substitution; at the same time, superconductivity is suppressed whereas magnetic ordering is restored. Distinct incommensurate satellite peaks develop within different thermal ranges and mark the occurrence of charge density waves characterized by distinct propagation wave vectors, as well as multiple incommensurate structural transitions; in particular, some of them arise in conjunction with the structural transformation process, disappearing after the completion of the dissymmetrization. The thermal evolution of satellite reflections observed at $\mathbf{Q}\ensuremath{\sim}1.93\phantom{\rule{0.16em}{0ex}}{\AA{}}^{--1}$ indicates a strong competition between the charge density waves and the superconductive state. A phase diagram of the $\mathrm{La}(\mathrm{Fe},\mathrm{Mn})\mathrm{As}({\mathrm{O}}_{0.89}{\mathrm{F}}_{0.11})$ system is drawn on the basis of the structural, magnetic, and electronic properties of the analyzed samples.

Enhanced magnetoelectric coupling characteristics of Mn2O3-modified BiFeO3-based ceramics

BiFeO3 is the most important room-temperature multiferroic material. However, the magnetoelectric coupling effect of BiFeO3 is weak, and an effective way to improve it is to suppress the spin cycloid structure. In this work, Mn ions were substituted into BiFeO3-based ceramics to enhance the magnetoelectric coupling effect. All samples were refined with the rhombohedral R3c structure. The grain size gradually decreased with increasing Mn substitution content. According to DSC analysis, the endothermic peak and exothermic peak exhibit an obvious thermal hysteresis behavior, indicating that it is the first-order ferroelectric transition. Meanwhile, a dielectric anomaly was also found at that transition temperature. The leakage current increased with increasing Mn content, which can be ascribed to the increased oxygen vacancies. The magnetic properties were enhanced for all samples, and the maximum Mr = 51.9 emu/mol was obtained for x = 0.03. In addition, the magnetoelectric properties were improved, and the value of linear magnetoelectric coefficient exhibits a maximum value αME = 0.38 mV/cm Oe at x = 0.03. Thus, the addition of Mn at Fe sites may destroy the spin cycloid structure and enhance the ME effect of BiFeO3.

Influence of Co and Mn substitution on magnetic properties of novel Y2FeSi Heusler alloy

This paper presents results of density functional theory (DFT) studies on structural, electronic, and magnetic properties of novel Y2FeSi Heusler material characterized by spin polarization at Fermi level of [Formula: see text] and magnetic moment of 1.56 [Formula: see text]. The total magnetic moment of investigated material is dominated by Iron sites, while magnetic moments coming from Yttrium sites are aligned antiparallel to the Iron. Here, we introduced Co and Mn substitutions to alter the magnetic and electronic properties of the studied material. The Heusler alloys are very sensitive to electronic structure changes induced by ionic substitutions, which allowing to specifically modulate their properties. The Co-substitution lowered the total magnetic moment to [Formula: see text][Formula: see text]1.20 [Formula: see text] and Mn caused a rise to [Formula: see text][Formula: see text]1.93 [Formula: see text]. Introduction of Mn resulted in [Formula: see text] spin polarization. We hope that this study will promote further theoretical as well as experimental interest in these types of compounds.

The decomposition of Mn-substituted siderite during coaling enhanced the transformation of NO before catalyst bed: Effect of Mn substitution

The substitution of Mn for Fe in the structure of siderite, a common mineral in coal, is universal. The effects of Mn on the transformation of siderite during coaling and the de-NO performance of the transformed products in flue gas pipelines after injecting NH3 were investigated, and a kinetic study was also performed. The results showed that the Mn-substituted siderite ((Mn, Fe)CO3) was transformed into Mn-substituted hematite ((Mn, Fe)2O3). The Fe2O3 derived from siderite displayed a positive effect on NO conversion. The substitution of Mn considerably improved the de-NO performance at reaction temperatures of 100–200 °C, especially for the 12% Mn substitution amounts (increased by 81.9–51.4%). A larger surface area, more chemisorbed oxygen and acid sites, and outstanding redox capacity are responsible for this phenomenon. Furthermore, both the Eley-Rideal and Langmuir-Hinshelwood mechanism take part in the de-NO process by selective catalytic reduction in the presence of NH3 (NH3-SCR), and the catalytic oxidization (CO) reaction occurred above 200 °C according to the in situ DRIFTS and kinetic study results, respectively. This study benefits the comprehension of NO behavior and the de-NO mechanism in flue gas pipelines after injecting NH3 during coaling.

Transition metal effect on different properties of lead-free KNN ceramics

Material series with compositional formula K0.5Na0.5AxNb1−xO3 (x is ranging from 0.00 to 0.06) were prepared where A is transition metal Mn. Pure perovskite phase with orthorhombic structure of K0.5Na0.5MnxNb1−xO3 compositions was confirmed from XRD. The lattice parameters (c, a) were found to increase with Mn content. The dielectric constant (ε) was observed to increase with substitution of Mn at room temperature. The dielectric constant increased with temperature for K0.5Na0.5MnxNb1−xO3 with x ≤ 0.04 compositions and decreased for x > 0.04. The maximum dielectric constant εmax = 4517 at Tc = 421 °C at 100 kHz frequency was achieved for x = 0.02 composition. The piezoelectric constant (d33) was found 178pC/N for 2% Mn substitution.