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Manganite-based devices have shown promising resistive switching properties, the performance of which strongly depends on the electrodes used to build them. Their nature affects the physical proper...

Strain engineering of complex oxide heterostructures has provided routes to explore the influence of the local perturbations to the physical properties of the material. Due to the challenge of disentangling intrinsic and extrinsic effects at oxide interfaces, the combined effects of epitaxial strain and charge transfer mechanisms have been rarely studied. Here, we reveal the local charge distribution in manganite slabs by means of high-resolution electron microscopy and spectroscopy via investigating how the strain locally alters the electronic and magnetic properties of La0.5Sr0.5MnO3–La2CuO4 heterostructures. The charge rearrangement results in two different magnetic phases: an interfacial ferromagnetically reduced layer and an enhanced ferromagnetic metallic region away from the interfaces. Further, the magnitude of the charge redistribution can be controlled via epitaxial strain, which further influences the macroscopic physical properties in a way opposed to strain effects reported on single-phase films. Our work highlights the important role played by epitaxial strain in determining the spatial distribution of microscopic charge and spin interactions in manganites and provides a different perspective for engineering interface properties.

In view of the need to limit harmful emissions of chlorofluorocarbons into the atmosphere and sharp increase in life support areas that require cooling, the search for new magnetocaloric materials is very urgent at the present time. In this work, we suggest the ways for improving the magnetocaloric properties of the promising La0.8-xK0.2Mn1+xO3 (0 ≤ x ≤ 0.2) perovskites and compare the functional properties of nanocrystalline samples of about 40 nm with polycrystalline samples of about 1 μm. The structure, morphology, magnetic properties and magnetocaloric effect of these compounds were studied as a function of manganese doping level. The main crystalline phase of all samples is a rhombohedral R 3 ‾ c perovskite structure. The maximum doping level of excess manganese for preserving single-phase structure of the nanocrystalline La0.8-xK0.2Mn1+xO3 compounds is x = 0.10. As x increases the Curie temperature TC is increased slightly. The best composition with the highest entropy change ΔSMmax = −3.629 J/(kg⋅K) under 3 T at TC = 332 K is the La0.8-xK0.2Mn1+xO3 with x = 0.05. On the other hand, the La0.8-xK0.2Mn1+xO3 polycrystalline manganite with x = 0.10 exhibits the highest ΔSMmax = −4.176 J/(kg⋅K) under 3 T at TC = 274 K. Additionally, the effect of hydrostatic pressure P up to 1.4 GPa has been investigated for the La0.7K0.2Mn1.1O3 polycrystalline sample that leads to increasing TC to 287 K and reducing ΔSMmax to −3.145 J/(kg⋅K) under 3 T. The obtained results demonstrate the ways for controlling magnetocaloric properties of the La0.8-xK0.2Mn1+xO3 compounds under internal and external conditions.

It is recognized that different facets of minerals vary distinctively in their chemical reactivity with aqueous solutions. However, detailed molecular and atomistic understandings of these phenomena are relatively limited. This study investigated the interaction of aqueous Mn2+ and dissolved oxygen on various facets of two morphology-types of iron oxide (hematite) nanocrystals. These interactions result in the oxidation of Mn(II) and heterogeneous growth of Mn(II)/Mn(III) and Mn(III) oxides. The nanoscale morphology and atomic structure of the manganese oxide products were characterized in detail. Our results, for the first time, directly demonstrate the facet-specific oxidation of Mn(II) and nucleation of Mn(II/III) oxides, followed by their epitaxial growth on hematite. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron diffraction measurements reveal the growth of MnOx nanowires on {1 1 3} of hematite nanoplates (HNP) and {0 1 2} facets of hematite nanocubes (HNC), while the basal {0 0 1} facets on the HNP particles do not produce precipitates. The average oxidation states of the MnOx on HNP and HNC determined using electron energy-loss spectroscopy (EELS) show that both Mn(II) and Mn(III) are present. The mineral composition and growth mechanisms of MnOx catalyzed by HNP and HNC are similar. High-resolution TEM analysis reveals the presence of both hausmannite and manganite on HNP and HNC. The crystallographic relationship between the heterogeneously formed manganite with hematite, which has not been reported before, proves that hematite provides reaction sites and can function as an atomic template for the formation of MnOx nanowires. These findings advance our understanding of the redox chemistry and heterogeneous growth of minerals as controlled by the surficial structure of the substrate mineral. This has important geochemical implications as the catalytic growth of less common, highly reactive phases like MnOx are known to be consequential in complex natural and anthropogenic environments.

La0.4Pr0.25Ca0.35-xAgxMnO3 samples were elaborated using sol–gel method. X-ray diffraction study indicates that the investigated compounds exhibit an orthorhombic structure with Pbnm space-group sy...

We report the structural, magnetic, and magnetocaloric properties of Bismuth (Bi)-substituted manganite La0.85-xBixNa0.15MnO3 (x=0, 0.1, 0.2, 0.25, and 0.3). X-ray diffraction data implicates the rhombohedral structure with $$ R\overline{3}c $$ R 3 ¯ c space group. Bi2O3 has helped in ensuring phase pure, densified compounds even at low sintering temperature and hence avoiding the evaporation of volatile sodium. The increase in grain size and decrease in magnetic transition temperature (TC) are due to the Bi chemical activity and electronic structure. The samples have shown indirect magnetic transformation from soft ferromagnet to canted ferromagnet/antiferromagnet with Bi. Griffiths phase-like behavior in the inverse magnetic susceptibility was observed for x=0.1; with further increase in Bi, the samples are found to develop the antiferromagnetic competing phase. The phenomenological model was used to model the thermomagnetic behavior of all the samples. The sample with x=0.1 shows an increase in magnetic entropy change upon Bi substitution and the maximum of magnetic entropy change is seen at 275K emphasizing its potential in room temperature magnetic refrigeration.

The structural and magnetic properties of La 0.6 − x Y x Sr 0.4 MnO 3 (x = 0–0.3) manganite synthesized by the sol-gel method was systematically investigated. The structural properties of the samples were investigated using X-ray diffraction (XRD) patterns and confirmed by Rietveld refinement analysis. Using the energy dispersive X-ray (EDX) analysis, the atomic percentage of the elements in the samples was confirmed. To investigate the surface morphology of the specimens, a field emission scanning electron microscopy (FESEM) analysis of the specimens was performed. The effect of yttrium substitution on the magnetic properties of the samples was also investigated. The Curie constant, magnetic moment, blocking temperature, and Curie temperature (Tc) were calculated using the Curie-Weiss law and the magnetic susceptibility of the samples.

The phase formation, sintering behavior and electrical properties of Ni–Co–Zn–Mn spinel NTC thermistor ceramics of the series Ni0.5ZnzCo0.5Mn2−zO4 with 0 ≤ z ≤ 1 were studied. In contrast to NiMn2O4, which exhibits limited stability in air below 730 °C and above 970 °C, the Zn–Co-substituted nickel manganite spinels are stable at T Td > 900 °C, with Td increasing with decreasing Zn Content z. The samples were sintered at 900 °C with addition of 3 wt% Bi2O3 as sintering aid and densities of above 92% were achieved. The room temperature resistivity and thermistor B-constants are almost independent of composition at 0 ≤ z ≤ 0.6 and start to increase at higher Zn concentrations. A multilayer NTC thermistor was fabricated using green tapes of a spinel of composition z = 0.75, commercial Ag paste, and cofiring at 900 °C. The firing behavior, microstructure formation and electrical properties of the multilayer thermistor are reported.

We report the results of a detailed investigation of the role of cation substitution Co → Mn on the structural, microstructural, magnetic, and transport properties of the manganite system La2/3Ca1/3Mn1−xCoxO3 (x = 0.0, 0.1, 0.2 and 0.3). It is found that the replacement of Mn with Co does not change the crystal structure of the parent compound La2/3Ca1/3MnO3 which crystallizes in orthorhombic structure with Pbnm space group. From a systematic analysis of the magneto-transport measurements, it has been shown that the cobalt substitution leads to a decrease in the system magnetization and lowering of Curie and metal–insulator transition temperatures. The magnetoresistance percentage (MR%), which is found to change significantly by Co substitution and exceeds 100% for x = 0.3 sample at low temperatures, is also reported at 1 T applied magnetic field.

Owing to the highly activity, chemical stability and low cost, perovskite transition metal oxide has been introduced in electrocatalysis widely. However, the multiple valence of transition metal always troubles the realization of its active site as it influences the band structure and conductivity simultaneously, hampering a further effective electrocatalyst design. Here in this report we have found that the hydrogen evolution reaction activity of La0.67Sr0.33MnO3-σ is ~50% improved by the oxygen non-stoichiometry via introducing oxygen vacancy compared to La0.67Sr0.33MnO3. Although La0.67Sr0.33MnO3-σ exhibits a resistance satisfaction, the increase of active valence state Mn3+ is responsible for the overall higher catalysis activity. Our study clearly shows a trade-off strategy for an improvement of hydrogen evolution reaction based on transition metal oxide.

A set of interatomic potentials has been derived for the determination of the most favorable sites of the oxygen substituted by fluorine atoms in SrMnO3. The calculations were performed using GULP code which implements interatomic potentials calculations within the ionic shell model. Initial investigations were made on SrMnO3 perovskite material. Our results for the parent SrMnO3 are in agreement with experimental data. This substitution is favorable to full Schottky disorder and the fluorine atoms are predicted to occupy sites trans to each other in the octahedron surrounding Mn.

In this study, oxygen release/consumption behavior of calcium manganese-based oxides (CaMn1-xBxO3, where B: Cu, Fe, Mg and x = 0.1 or 0.2) used in a chemical looping oxygen uncoupling (CLOU) application was investigated. The effect of B-site dopants such as Fe, Mg, and Cu on the oxygen release behavior was also investigated with the aim to use these materials in thermal energy storage (TES). Previous literature studies about CLOU performance of doped calcium manganites were taken into consideration for dopants selection. Calcium manganite-based oxides have been used in chemical looping oxygen uncoupling (CLOU) applications owing to their oxygen release behavior to the gas phase. Studies have revealed that calcium manganite-based oxides show a promising nonstoichiometry over a range of temperatures and oxygen partial pressures, which makes them useful for thermochemical energy storage applications. However, the related literature studies have been mainly focused on their nonstoichiometric characteristics related to temperature and oxygen partial pressure and thermodynamic properties. In this work, thermal analysis and fluidized bed tests were carried out as complementary techniques. CaMn0.8Cu0.2O3 showed the highest oxygen release performance in fluidized bed tests, while CaMn0.9Mg0.1O3 had the best cyclic stability overall among the samples used in the study.

The tunable physical properties of the rare earth manganite GdMnO3 hold significant promise for different applications. Herein, we systematically investigate the modification of the structure, magnetic properties, and electrochemical performance of GdMn1−xFexO3 (x = 0, 0.1, and 0.2). The X-ray diffraction (XRD) patterns of GdMn1−xFexO3 (x = 0, 0.1, and 0.2) confirm the existence of a pure orthorhombic structure with the space group Pbnm. Rietveld refinement establishes the existence of an O′-type orthorhombic structure independent of x. With an increase in x, the lattice volume and the Jahn–Teller (J–T) distortion factor decrease. The reduction in lattice volume is attributed to the presence of Mn4+ ions accompanied by oxygen vacancies, as confirmed via XPS and XANES studies, and the decrease in the J–T distortion factor is reflected through a reduction in the intensity of the asymmetric stretching band located at 487 cm−1 in Raman spectroscopy studies. Temperature-dependent magnetization measurements reveal that the Neel temperature, TN, considerably enhances from ∼42 K at x = 0 to ∼84 K at x = 0.2, which is essentially due to improved antiferromagnetic interactions involving Mn/Fe–O–Mn/Fe. The spin dynamics of GdMn1−xFexO3, discussed using phenomenological models, such as Neel-Arrhenius, Vogel–Fulcher, and Power law models, reveal a spin-glass nature. Further, the feasibility of using GdMn1−xFexO3 for potential supercapacitor applications has been confirmed due to a 2-fold increase in the specific capacitance owing to enhanced oxidation–reduction reactions between the electrode and electrolyte. We conclude here that GdMn1−xFexO3 is a potential multifunctional material.

Manganites have attracted much attention due to the simultaneous existence of ferroelectricity and magnetism in the same phase. In this work, barium doped YMnO3 ceramic (Y0.90Ba0.10MnO3) has been synthesized by physical route solid-state reaction method and its structural and dielectric analyses have been done. The X-ray diffraction patterns of the given ceramic disclose its hexagonal crystal structure having P63cm space group symmetry. The Rietveld refinement of the material was done to obtain the lattice parameters. The variation of dielectric constant and dielectric loss as a function of frequency reveals the usual dispersion behavior. The modulus spectroscopy of the sample displays the transport phenomenon.

The effect of lattice geometric parameters of perovskite oxides on thermochemical redox CO2-splitting process is highlighted. Experimentally-derived amounts of O2 and CO evolved were found to correlate with critical radius per unit cell volume (Rc.u) and specific free volume (VF.S), respectively, in a series of phase pure A-site substituted perovskites. These findings demonstrate the possibility of designing new oxygen carrier materials based on geometric parameters while predicting their CO2-splitting activity during two-step cycles.

A physical and chemical investigation of ceramic materials based on manganites of mixed rare earth elements – La0,8-хLnхCa0,2Mn0,94Cr0,04Ni0,02O3 – for electrochemical and catalytic applications has been carried out, and they were obtained from nitrate feedstock based on industrial-type polylanthanide concentrate, which corresponds to typical bastnaesite ore on the ratio of rare-earth elements in it. For polycrystalline samples of the obtained materials, the formation of single-phase structure or more often two-phase one has been identified after sintering in air at 1500 K, i. e., a the mixture of cubic perovskite phase based on low-cerium or A-site deficient manganite and a fluorite phase based on CeO2 with dioxide content of 54–98 %. A phase formation mechanism has been proposed, which is possible during the transition to compositions with rising cerium content at a constant sintering temperature of manganite materials. The effect of the chemical composition and structure of the materials on their conductivity and density, reached by the sintering, has been established in the paper. Investigation of electrical conductivity has shown that in the manganites the semi-conductive behavior/ charge transfer mechanism (p-type) is realized at the temperature range of (300–1270) K. The maximum conductivity within the range of (290–1270) K is achieved in this low-cerium bastnaesite-type system for a two-phase material with the composition La0,8-хLnхCa0,2Mn0,94Cr0,04Ni0,02O3 at x= 0.6 and is 39 S/cm at a density level of 50 % of the theoretical one for a ceramic sample. Manganite materials with lanthanum substitution, such as investigated polylanthanide-based ones, can provide a lower cost for fabrication of electrochemical and other devices based on them, taking into account the complex prices dynamics on the markets of rare-earth raw materials during the last decade.

Perovskite manganite (DyMnO3) films were fabricated epitaxially on SrTi0.99Nb0.01O3 single-crystal substrates by using a pulsed laser deposition technique. The films crystallized in orthorhombic structures, and the heteroepitaxial relationship between the films and the substrates was analyzed. The electrical transport properties reveal diodelike rectifying behaviors in the all-perovskite oxide structures over a wide temperature range (100 ∼ 340 K). The forward current increases exponentially with the increasing forward bias voltage, and the extracted ideality factors show distinct transport mechanisms in high- and low-positive regions. The built-in potentials were determined by using capacitance-voltage measurements at different frequencies. The results show the importance of temperature and applied bias in determining the electrical transport characteristics of heteroepitaxial oxide structures.

The effect of half substitution of diamagnetic Bi3+ with the rare earth magnetic Nd3+ ion on the magnetic and structural properties of the polycrystalline Bi0.25Nd0.25Sr0.5MnO3 and Bi0.25Nd0.25Ca0.50MnO3 was studied by X-ray and neutron diffraction complemented by magnetic measurement. We correlate the structural response of Bi0.25Nd0.25X0. 5MnO3 (X = Sr, Ca) for charging and spin ordering with a reduced amount of Bi3+, which in addition to its special contribution to itinerant eg electrons leads to a change in the average size of the A-site cations, 〈rA〉, and the mismatch between the A-site cations (size variance, σ 2). For both compounds, the corresponding charge ordering scheme and ground magnetic state of CE-type antiferromagnetic arrangement at 10 K were specified. An analysis of the data confirms that in Bi–Sr manganite a lone pair of 6s2 Bi3+ orbitals is dominant.

We report the synthesis of barium cerium manganite (BaMn0.94Ce0.06O3) single perovskite by using a conventional high-temperature solid-state reaction method. A structural phase transition occurs fr...

Significance When oxygenic photosynthesis evolved is debated with an uncertainty of approximately 1 Gy. It is generally assumed that the oxidation of manganese minerals requires biological catalysis or molecular oxygen and therefore is often used as a proxy for the presence of oxygenic photosynthetic organisms. We show that anoxic, abiotic oxidation of the mineral rhodochrosite (MnCO 3 ) by UV light forms H 2 and manganite (γ-MnOOH). Our results reveal an alternative mechanism for producing manganese oxides from rhodochrosite in the absence of molecular oxygen. These results demonstrate the potential impact of photogeochemical processes on the redox state of transition metals and hence question the interpretation of the rise of atmospheric oxygen based on the oxidation of transition metals, such as Cr isotopes.

The structural, magnetic, electrical, and thermoelectric behaviors of lanthanum silver manganite and lanthanum bismuth silver manganite were thoroughly studied in the present work. Two polycrystalline samples, viz., La0.835Ag0.165MnO3 (LAMO) and La0.67Bi0.165Ag0.165MnO3 (LBAMO) possessing almost constant ratio of Mn3+/Mn4+ were synthesized using the wet chemical method. Phase formation was identified from powder X-ray diffraction and it has been confirmed through the structural analysis of which samples crystallize into rhombohedral symmetry with R-3C space group. Apparent changes at phase transition temperature were observed in temperature-dependent resistivity, magnetization and thermoelectric power behavior for bismuth-doped samples. In addition, an enhanced magnetoresistance was observed in LBAMO samples and is attributed to the presence of both ferromagnetic and anti-ferromagnetic states. The temperature-dependent resistivity data in the temperature range (50–300 K) were analyzed using the phase separation model. Spin-dependent scattering and electron–electron interactions were considered to explain the resistivity minimum in the low temperature region (T

Electrical and magnetoresistive properties of the La0.6Sr0.2Mn1.2O3±δ (LSMO) films deposited on SrTiO3 single-crystalline and Al2O3 polycrystalline substrates by magnetron sputtering have been studied. The aim of the study is to understand the effect of substrate type on the thickness-dependent evolution of magnetotransport properties of the films of lanthanum–strontium manganites with overstoichiometric manganese content. It is shown that the decrease in the LSMO film thickness below 1000 nm causes the reduction of Curie temperature (TC) and magnetoresistance value at 300 K concomitant with the increase in electrical resistivity. At the same time, the dependence of electrical and magnetoresistance parameters on the substrate structure and type becomes stronger. It is found that TC of LSMOSTO films exceeds and resistivity is smaller than the respective parameters of LSMOAO films, and the difference grows with the decrease in the film thickness. All the results show that the behavior of the doped manganite films with overstoichiometric manganese content differs from that characteristic of stoichiometric in manganese films. These observations can be attributed to the effect of manganese excess on the film growth mechanism, making it different from the manganite films of other compositions.

Conditions (temperature, oxygen partial pressure in the gas atmosphere, and heating time) for the synthesis of polycrystalline layered manganites Ln2BaMn2O7 – δ (Ln = Pr, Nd) with an orthorhombic structure (Fmmm) and a specific oxygen non-stoichiometry were proposed for the first time. The temperature boundaries for the orthorhombic (Fmmm) to tetragonal (I4/mmm) structural phase transition were determined using high-temperature X-ray diffraction and differential scanning calorimetry. The temperature of the structural transition increases with increasing atomic number of the rare earth metal present in the manganite.

Oxygen post-annealed manganite films with low doped concentration generally exhibit drastically enhanced phase transition temperatures compared with the bulk, but the specific mechanism has not been fully understood. In this study, low-doped La0.9Sr0.1MnO3 (LSMO) films were post-annealed at a wide temperature range (Tpa) of 600–1000 °C, and oxygen post-annealing effect on the structure, magnetic and transport properties were investigated. The metal-insulator transition (MIT) and a significant enhancement of Curie temperature (TC) are observed in LSMO films (Tpa = 700–1000 °C). The analysis of Mn3+/Mn4+ ratio indicates that post-annealing induces oxygen excess state in these films, and Mn3+-Mn4+ double exchange interaction is enhanced and Jahn-Teller distortion is reduced due to the decrease of Mn3+/Mn4+ ratio. In addition, the excess oxygen increases with increasing post-annealing temperature, while a drop in phase transition temperatures TMI and TC is observed after they reach the maximum at Tpa = 800 °C, probably due to the weakened double exchange interaction induced by the dropping of Mn3+/Mn4+ ratio from the optimum value. Our study has revealed that double exchange interaction and Jahn-Teller distortion decided by Mn3+/Mn4+ ratio play crucial roles in regulating phase transition temperatures in low doped manganite films.

The contamination of water by Pb2+ ions is a problem that requires an imminent solution. Design of hydrogels based on polymers as well as inorganic phases is an innovative alternative for the generation of matrices with adapted properties. This work proposes the synthesis of a novel composite hydrogel based on collagen-polyurethane-chitosan reinforced with manganite; this inorganic phase increases the velocity of the adsorption process of the Pb2+ ions. The effect of the concentration of manganite on the properties of composite hydrogels is studied. The results indicate that the composite reinforced with manganite presents an amorphous structure, improved mechanical properties and resistance to the both acidic and proteolytic degradation. The hydrogel with 35 wt% of manganite show a removal rate of Pb2+ of 91 ± 6% at 24 h. These hydrogel composites could represent an efficient and sustainable alternative for the removal of Pb2+ ions from contaminated water.

The drift in electrical properties (e. g., the resistivity and B-value) is vital to the practical application for negative temperature coefficient (NTC) ceramics. In this work, Cu-doped nickel manganite ceramics were prepared by solid-state method, to investigate the degradation mechanism of both the resistivity and B-value. Results showed that the as-prepared ceramics exhibited typical NTC characteristics with cubic spinel phase, and that Cu doping greatly reduced the resistivity and B-value. However, the increase of Cu content in system aggravated the drift in the resistivity and B-value after the samples were aged at 300 °C for 30 h. XPS was carried out to further clarify the change in electrical properties. It was found that the decline of properties was due to the decrease of Mn4+ content in system after aging, which derived from the increase of chemical valence of Cu.

The spinel nickel manganite (NiMn2O4) nanoparticles (NPs) were successfully synthesized through simple co-precipitation method, and their structural, optical, morphological and photocatalytic behavior is examined in this investigation. The powder X-ray diffraction pattern confirms the face-centered cubic spinel structure of the as-prepared sample, and the average crystallite size is found to be 46.27 nm. The absorption spectrum of the material was obtained via diffuse reflectance spectroscopy (UV-DRS), and the bandgap value is calculated using Tauc’s relation as 2.41 eV. Morphological analysis was investigated by using a scanning electron microscope (SEM). From the SEM analysis, the hexagonal cake-like structure was observed from the prepared material and size was achieved around to be 50–100 nm. Furthermore, the photocatalytic behavior of NiMn2O4 (NPs) against organic dyes under direct sunlight was analyzed by using methylene blue, malachite green and Congo red and the efficiency is observed as 92%, 94% and 62%, within 120 min, 60 min and 120 min, respectively.

In this work a study of the synthesis process, crystal structure and magnetic behavior of gadolinium manganite with Fe substitutions in Mn positions of GdMn1-xFexO3(x=0, 0.1, 0.2) is reported. The samples were synthetized by the conventional solid-state reaction method. Structural characterization of final compounds was analyzed by Rietveld refinement, which revealed its crystallization in an orthorhombic symmetry belonging to the Pbnm (No. 62) space group. Results reveal that aand ccell parameters and the unit cell volume increase, while the lattice parameter band the cell volume decrease with Fe substitution. The main effect in the structure is related to oxygen positions, i.e. in the octahedral distortions and rotations. DC susceptibility measurements, in the temperature regime between 4 K and 300 K on the application of an external field of 200 Oe, show a paramagnetic feature at high temperatures for all xstudied values, with magnetic transitions associated to a magnetic ordered state at low temperatures (21.8 K < T < 25.2 K). Meanwhile, a ferrimagnetic transition is detected for x=0.1close to T=30.7 K.In order to explain the appearance of ferrimagnetism for this configuration, a model is suggested where an imbalance in the magnetic structure of GdMnO3(type-Aantiferromagnetic) generated due to the introducing a Fe3+ion in each pair consecutive unit cells is proposed. Theeffective magnetic moment obtained agrees to the reported value for the material with x=0.0, confirming the ferrimagnetic behavior for this concentration of Fe3+in the structure.

Polycrystalline samples of Bi substituted YMnO3 belonging to the series Y1-xBixMnO3 (x = 0, 0.3 and 0.5) were synthesised by employing a citrate gel method. X-ray diffraction confirmed the formatio...

In this work, we investigate YMnO3 perovskites with Sr2+ and Al3+ doping, Y1–xSrxMn1–yAlyO3, for use in thermochemical H2O or CO2 splitting for the first time. Oxygen nonstoichiometries (δ) with x ...

The current description of oxygen-vacancy behaviour in (La,Sr)MnO3 perovskite-type oxides, though widely accepted, ignores a pronounced discrepancy. Values of the activation enthalpy of oxygen-vacancy migration reported in experimental investigations (ΔHmig,v = 1.2–2.4 eV) are substantially higher than those predicted in computational work (ΔHmig,v = 0.5–1.0 eV). In this study we examine the origin of this discrepancy using molecular-dynamics simulations. Specifically we investigate the effect of various cation defects (Sr substituents, La vacancies, Mn vacancies, both types of cation antisites) on the diffusivity of oxygen vacancies (Dv) in orthorhombic LaMnO3. Our results indicate that the presence of cation vacancies can bring the computational values of ΔHmig,v into good agreement with experimental data. Applying an analytical model to our results, we predict that isothermal values of Dv in manganite perovskites containing cation vacancies will depend strongly on oxygen partial pressure (contrary to the standard assumption). The implications of our results for modelling the point-defect chemistry of, and oxygen diffusion in, manganite perovskites are discussed.

The temperature dependences of the specific heat capacities of nanosized samples of lanthanum magnesium cobaltite cuprate manganite LaMgCoCuMnO6 and lanthanum magnesium nickelite cuprate manganite LaMgNiCuMnO6 are studied via calorimetry in the temperature range of 298.15–673 K. Curve $$C_{p}^{ \circ }$$(T) shows that LaMgCoCuMnO6 and LaMgNiCuMnO6 undergo second-order phase transitions at 398 and 523 K, respectively. The standard specific heat capacities of the above compounds are calculated with independent means based on characteristic Debye temperatures determined via the Koref and Nernst–Lindemann equations. Their values agree satisfactorily with experimental data. The temperature dependences of functions S°(T), H°(T) – H°(298.15), and Фхх(T) are calculated.

The aim of this research work to synthesis the Ni(1−x)CuxMn2O4 NTC ceramics by co precipitation method sintered at 600 °C. The effect of copper on structural and physical properties of nickel manganite examined through XRD, SEM and FTIR analysis. All the diffraction patterns showed the formation of single phase cubic spinel structure with lattice constant 8.5201 A to 8.3827 A and average crystallite size (D) 24 nm to 28 nm due to copper doping. Detailed discussion of dislocation density (ρD), mechanical properties (strain), hopping length (tetrahedral LA and octahedral LB), and texture co-efficient using XRD data are reported. FTIR spectra demonstrating two significant absorption bands in between 400 cm−1 to 600 cm−1 confirms the cubic phase of the samples. Thus structural parameters of copper doped in the nickel manganite are correlated using Williamson-Hall and Size-strain analysis method.

Orthorhombic dysprosium manganite DyMnO3 with single phase is synthesized using solid-state reaction technique and the crystal structure and dielectric properties as functions of temperature and frequency are investigated. Thermally activated dielectric relaxations are shown in the temperature dependence of the complex permittivity, and the respective peaks are found to be shifted to higher temperatures as the measuring frequency increases. In Arrhenius plots, activation energies of 0.32 and 0.24 eV for the high- and low-temperature relaxations are observed, respectively. Analysis of the relationship between the real and imaginary parts of the permittivity and the frequencies allows us to explain the dielectric behavior of DyMnO3 ceramics by the universal dielectric response model. A separation of the intrinsic grain and grain boundary properties is achieved using an equivalent circuit model. The dielectric responses of this circuit are discerned by impedance spectroscopy study. The determined grain and grain boundary effects in the orthorhombic DyMnO3 ceramics are responsible for the observed high- and low-temperature relaxations in the dielectric properties.

International audience; In this paper, the degradation of three endocrine-disrupting chemicals (EDCs): bisphenol A (BPA), 17β-estradiol (E2) and 17α-ethinylestradiol (EE2) by manganite (γ-MnOOH) activated peroxymonosulfate (PMS) was investigated. Preliminary optimisation experiments showed that complete degradation of the three EDCs was achieved after 30 min of reaction using 0.1 g L−1 of γ-MnOOH and 2 mM of PMS. The degradation rate constants were determined to be 0.20, 0.22 and 0.15 min−1 for BPA, E2 and EE2, respectively. Combining radical scavenging approaches, Electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) analyses, we revealed for the first time that about 40% of EDCs degradation can be attributed to heterogeneous electron transfer reaction involving freshly generated Mn(IV), and 60% to sulfate radical degradation pathway. The influence of various inorganic ions on the γ-MnOOH/PMS system indicated that removal efficiency was slightly affected by chloride and carbonate ions, while nitrate and nitrite ions had negligible impacts. The application of γ-MnOOH/PMS system in real sewage treatment plant water (STPW) showed that degradation rate constants of EDCs decreased to 0.035–0.048 min−1 and complete degradation of the three EDCs after 45 min. This study provides new insights into the reactivity of combined γ-MnOOH and PMS, and opens new ways for the application of Mn-bearing species in wastewater treatment technologies.

Electrostatically defined perovskite oxide heterostructures, in which carriers are confined by the modulation of the A-site ion charge, offer new possibilities of tuning the magnetic properties of manganite oxides. We investigate the preferential orientation of ferromagnetic and antiferromagnetic moments in ultrathin ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_{3}$ layers embedded in antiferromagnetic $\mathrm{Sr}{\mathrm{MnO}}_{3}$ as they undergo a metal-to-insulator transition with decreasing thickness. Our results evince the role of orbital occupation, metallicity, and competition of different magnetic phases, in absence of spurious effects occurring in thin films as a result of symmetry breaking at ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_{3}$ interfaces and of incorporation of oxygen vacancies.

Nanocrystalline nickel manganite (NiMn2O4) powder with a pure cubic spinel phase structure was synthesized via sol-gel combustion and characterized with XRD, FT-IR, XPS and SEM. The powder was mixed with sodium alginate gel to form a nano-biocomposite gel, dried at room temperature to form a thick film and characterized with FT-IR and SEM. DC resistance and AC impedance of sensor test structures obtained by drop casting the nano-biocomposite gel onto test interdigitated PdAg electrodes on an alumina substrate were measured in the temperature range of 20–50 °C at a constant relative humidity (RH) of 50% and at room temperature (25 °C) in the RH range of 40–90%. The material constant obtained from the measured decrease in resistance with temperature was determined to be 4523 K, while the temperature sensitivity at room temperature (25 °C) was −5.09%/K. Analysis of the complex impedance plots showed a dominant influence of grains. The decrease in complex impedance with increase in temperature confirmed the negative temperature coefficient effect. The grain resistance and grain relaxation frequency were determined using an equivalent circuit. The activation energy for conduction was determined as 0.45 eV from the temperature dependence of the grain resistance according to the small polaron hopping model, while the activation energy for relaxation was 0.43 eV determined from the Arrhenius dependence of the grain relaxation frequency on temperature.

Asymmetric heterointerfaces that bridge two nonisostructural oxides provide valuable opportunities for novel emergent phenomena that may be unavailable for symmetric interfaces. Here we present a theoretical investigation on three different asymmetric interfaces consisting of the infinite-layer nickelate $\mathrm{LaNi}{\mathrm{O}}_{2}$ and the perovskite manganite $\mathrm{LaMn}{\mathrm{O}}_{3}$ (type A, B and C). An alternative crystal geometry, pyramid, is introduced when the planar-type $\mathrm{LaNi}{\mathrm{O}}_{2}$ and the $\mathrm{LaMn}{\mathrm{O}}_{3}$ are jointed at the interface, resulting in strong charge and orbital reconstruction. For type A interface, the magnetic moment per Mn ion has increased by 10% due to the replacement of $\mathrm{Mn}{\mathrm{O}}_{6}$ by $\mathrm{Mn}{\mathrm{O}}_{5}$. For type B interface, in contrast, the magnetic moment grew by 26% for the interfacial Ni ions due to the strong charge transfer between center nickel and apical oxygen. For type C interface, only slightly enhanced $\mathrm{Mn}{\mathrm{O}}_{6}$ distortions are observed and thus the change of charge and orbital occupancy are negligible. Our results demonstrated that an interface-selective orbital occupancy, where the Mn ${e}_{\mathrm{g}}$ orbital preferential occupation alternated from the out-of-plane ${\mathrm{d}}_{3{z}^{2}\ensuremath{-}{r}^{2}}$ state at type A interface to nearly degenerate at type C interface and then to in-plane ${\mathrm{d}}_{{x}^{2}\ensuremath{-}{y}^{2}}$ state at type B interface. The values of relative change of Mn ${e}_{\mathrm{g}}$ orbital occupancy are 15%, 2%, and \ensuremath{-}21%, respectively. The values of relative change at type A and B interface are larger than that achieved by strain $(\ensuremath{\sim}5%)$ or symmetric interface design (10%). Therefore, interface reconstructions lead to unusual electronic properties, opening space for the advancement of oxide electronics.

Nickel manganite nanocrystalline fibers were obtained by electrospinning and subsequent calcination at 400 °C. As-spun fibers were characterized by TG/DTA, Scanning Electron Microscopy and FT-IR spectroscopy analysis. X-ray diffraction and FT-IR spectroscopy analysis confirmed the formation of nickel manganite with a cubic spinel structure, while N2 physisorption at 77 K enabled determination of the BET specific surface area as 25.3 m2/g and (BJH) mesopore volume as 21.5 m2/g. The material constant (B) of the nanocrystalline nickel manganite fibers applied by drop-casting on test interdigitated electrodes on alumina substrate, dried at room temperature, was determined as 4379 K in the 20–50 °C temperature range and a temperature sensitivity of −4.95%/K at room temperature (25 °C). The change of impedance with relative humidity was monitored at 25 and 50 °C for a relative humidity (RH) change of 40 to 90% in the 42 Hzπ1 MHz frequency range. At 100 Hz and 25 °C, the sensitivity of 327.36 ± 80.12 kΩ/%RH was determined, showing that nickel manganite obtained by electrospinning has potential as a multifunctional material for combined humidity and temperature sensing.

Nickel manganite thin films were prepared by chemical solution deposition from nitrate and acetate precursors on polished alumina substrates. By variation of crystallization temperature between 650 ​°C and 900 ​°C and atmosphere during cooling of the films, the morphology, phase formation and electrical properties of the films were investigated. The electrically conductive spinel phase was formed as a main phase independent of processing conditions exhibiting NTCR characteristics. Cooling down in nitrogen atmosphere favored the decomposition of the spinel phase into nickel oxide and a spinel phase with higher manganese content, but it also reduced the resistance drift of the samples. From this finding it can be deduced that a reduced oxygen partial pressure influences defect equilibria and by that decreases cation vacancy concentration. This supports the assumption that cation redistribution by a cation vacancy diffusion mechanism is a relevant mechanism of resistance drift in such thin films.

Lithium ferrites-yttrium manganite composites were prepared by adding varying amount of yttrium manganite to lithium ferrite. The composites prepared have the general formula Li0.5Fe2.5O4+(x) YMnO3...